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Incorporating Computational Aerodynamics

INSIDE Aviation’s Grand Challenge High-speed, Electric Superbus Reviewing NASA ATP Shaping Chevy’s Volt Aerodynamics and Education Smart Test Models Bridge Cable Icing Tests China’s New Wind Tunnel

Behind the scenes at the world’s most advanced hypersonic wind tunnel


Wind Tunnel Models for powered propeller simulation

Propeller (CROR) models & test rigs Carbon composite propellers Rotating balances Telemetry systems Airbridges Mass flow control units Remote control systems For info please contact: Henri Vos, tel. +31 527 24 87 22, or

2010 Incorporating Computational Aerodynamics

No Fluke – Here’s Wind Tunnel International 2


hen we launched Wind Tunnel International in 2009, the response from you, the readers, was overwhelmingly positive. As a publication that aims to bring together, for the first time, a news medium specifically tailored to the needs and interests of professionals involved in some way in the business of wind tunnels or aerodynamics, you told us that we’d really hit a bull’s-eye. But … you also asked: “I love Wind Tunnel International … but can you really do it again?”

The answer is here and we hope that you agree that this issue is every bit as good as our first. We’ve maintained our focus on choosing articles that will inform, interest and entertain. And, in doing so, we owe a great debt of gratitude to our contributors, all of whom are readers from the industry: engineers, aerodynamicists, facility operators, suppliers of technology and scientific professionals. There once was a time when aerodynamics was something that only aviators and aircraft designers worried about. Now aerodynamics, aerodynamic technologies and wind-tunnel studies seem to touch almost every industry around and, in this issue, we’ve tried to reflect as broad a selection of stories as possible. One decision that Publisher Ian Stone and I reached early in planning this issue of Wind Tunnel International was that it should be published concurrently with the holding of the second Global Wind Tunnel Symposium (GWTS) in Pasadena on November 2&3, 2010, thereby spawning a source of stories to supplement our regular Wind Tunnel International articles. As the official media partner of the GWTS, we have included almost every presentation from the Symposium in edited form, so creating an exceptional variety of stories, dealing with multiple subjects, issues and solutions from a full spectrum of industries. All this is presented against the recent backdrop of the worst economic environment that probably any of us can remember. Such is the relevance of and interest in aerodynamics, however, that investment in new wind-tunnel facilities continues at a breathtaking pace, interestingly much (but certainly not all) of it in the automotive arena. All-new facilities are being or have been commissioned from places as far-flung as China, Denmark, Germany, Ontario and the United States, all of which you’ll find in these pages of Wind Tunnel International. At the same time, the industry is re-examining the assets still at its disposal. There are many older facilities worldwide that were created in the flurry of aviation innovation in the 1950s. Are these still valuable? Can they remain valuable if redeployed or updated? Who do these facilities serve? Are there new/different customers? Are there new areas or new industries that we can add? What do we need to do in order to serve our future customers better? Discussion of these pithy topics will dominate the sessions of the Global Wind Tunnel Symposium, just as it is a continuing theme of this issue of Wind Tunnel International. And some of the aerodynamics work is truly innovative. Like the new wind-tunnel at the Technical University of Denmark dedicated to exploring the icing effects on suspension bridge cable dynamics. And the Superbus Project from Delft University in The Netherlands. Crazy? Perhaps. Crazy like a fox? Probably. Read it and judge for yourself. For an example of aerodynamic innovation historically, you’d be hard pushed to better the SR-71 Blackbird. I am an unapologetic fan of this stunning plane, ever since 1974, when it flew the 5,645 km (3,508 mi) from New York to London in an elapsed time of 1 hour 54 minutes and 56.4 seconds. This equated to an average of 2,310.353 km/h (1,435.587 mi/h, Mach 2.68) … even when factoring in deceleration for in-flight refueling. It’s only one of the many world standards that SR-71 set 36 years before and have never been bettered. Even though it wasn’t technically an X-plane (as the United State’s experimental aircraft were called), much of the SR-71’s technology was developed from the X-plane program. One of the more interesting trends in aerodynamics is the renewed interest in hypersonics. So it’s appropriate that this issue starts with our cover story on the recent upgrades to the Arnold Engineering Development Center’s Tunnel 9, the world’s most advanced hypersonic facility, and ends with a tribute to the X-planes and the SR-71. We hope you enjoy this issue of Wind Tunnel International as much as we did pulling it together. We welcome your comments, so write to me at with your thoughts. Rex M. Greenslade, Editor Wind Tunnel International





Improving on a winning theme. Hypersonics and the SR-71


Cars, trains, choppers, MAVs … Aero brainteaser solved?




Aerodynamic performance superior to that of any other climatic wind tunnel facility


Latest developments in Pressure Sensitive Paint. Complex, full-field measurements with high resolution





World’s most advanced. Going faster to win wars. Mach 6 …And beyond 30 passengers. 240 km/h. Electric power. Crazy? No … it could just make sense


How the United States can advance its position as the world leader in aeronautics


Why aerodynamics is crucial to the success of GM’s extended range electric car


How future airliners could use less fuel, produce less emissions and make less noise. The next Grand Challenge for aviation?


How automotive design and aerodynamics are integrated at Coventry University


How students will soon be able to operate their experiments in a wind tunnel, via the Internet


World’s most advanced tilt-rotor wind tunnel model. The experts at NLR tell how it was created


UOIT in Canada is commissioning its all-new, state-of-the art climatic wind tunnel. Hydrogenpowered vehicles? No problem


20 rpm turbines feed 1000 rpm electrical generators. Torque demands are immense: think 1 million NM


New tunnel to examine vibration effects of wind, rain, ice, snow on suspension bridge cables


The phenomenal growth of China’s automotive market is demanding huge investment in vehicle development infrastructure such as the Shanghai Automotive Wind Tunnel


£20 (UK CUSTOMERS) £25/US$40 (NON UK CUSTOMERS) Contact: EDITOR Rex Greenslade, Direct: +1 248 346 6242 Wind Tunnel International – Editorial office 330 East Maple Road, Suite 170, Birmingham, MI 48009, USA PUBLISHER Ian Stone, Leading Edge Events & Media Ltd 100A High Street, Hampton, Middlesex, TW12 2ST. UK Tel: +44 (0) 208 783 2399, fax: +44 (0) 208 979 4597


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Dallara’s remarkable recent upgrades are focused on customer needs Aero-acoustic facility upgrades can be costeffective in measuring vehicle interior wind noise, says Horiba


RUAG explains how automotive safety can be improved by creating rain conditions in wind tunnels


Pratt & Miller say that the choice of aero testing method is highly dependent on the application and objective


The world’s largest flow honeycomb structure works as a wind-tunnel flow straightener. Darchem explains how it was built


Two different test sections enable Polimi to service many different fields, applications and industries


datatel’s wireless rotating telemetry systems


Different types of vertical wind tunnels and why chose one above all others for free fall simulation


Despite the economic conditions when it was created, Windshear’s wind tunnel has prospered, thanks in part to some unique technologies


When air flow measurements are on the agenda, Dantec’s instrumentation is really powerful

98 LIMITED BUDGET … NO PROBLEM How Techsburg engineered cost-effective upgrades to Virginia Tech’s wind tunnel


So many and varied are the NRC Aerospace’s facilities that a breathtaking array of possible application tests are possible.


How upcoming icing condition regulations will drive broader climatic testing conditions. And how future protection systems may help. By GKN Aerospace


Tri Models can produce all types of wind tunnel models and ground test hardware


Newly established SCE solutions can design and engineer wind-tunnel models. How the Supersonic Tunnel Association promotes operational excellence in wind tunnels


Expanding customer expectations and providing more value per test to customers is ONERA’s business focus


Flight simulation is not just for the military any longer. Bihrle describes its latest developments on commercial pilot training simulation for icing conditions


Nasa Glenn’s supersonic wind tunnel is best know for propulsion testing. But it is equally capable of more conventional aerodynamic testing


Excellent data quality is paramount. But how can a customer know that a wind tunnel is capable of doing so. NASA Langley has a major effort on date evaluation


Triumph’s latest high-capacity six-component balance system


The measurements are now in. And the BMW aerodynamic test center has proved to be every bit as accurate as predicted


The latest on the Cal Poly Cruise Efficient Short Take-off and Landing aircraft


A look back at the heritage of aerodynamics. This issue: a homage to the X-Plane program. Prepare to be amazed

MARKETING DIRECTOR Jeremy Whittingham:; tel: +44 (0) 208 783 2399 PROJECT MANAGERS David John:, tel: +44 (0) 208 783 2399 Paul Love:, tel: +44 (0) 208 783 2399 ADMINISTRATION Jini Stone:, tel: +44 (0) 208 783 2399 DESIGN AND PRODUCTION Dean Cook: The Magazine Production Company, tel: +44 (0)1273 467579 Printed in England by Warners Midlands Plc © 2010, Leading Edge Events & Media Ltd. All rights reserved. Wind Tunnel International (WTI) is a publication of Leading Edge Events & Media Ltd and has used its best efforts in collecting and preparing material for inclusion in Wind Tunnel International (WTI). Leading Edge Events & Media Ltd can not and does not warrant that the information contained in this product is complete or accurate and does not assume and hereby disclaims, liability to any person for any loss or damage caused by errors or omissions in Wind Tunnel International (WTI) whether such errors or omissions result from negligence, accident or any other cause. This publication may not be reproduced or copied in whole or in part by any means without the express permission of Leading Edge Events & Media Ltd.



Jaguar Unveils 205 mph, Active Aerodynamic Electric Car

C-X75 has opening-as-necessary front grille and brake cooling vents, deployable vertical control surfaces at rear corners and carbon-fiber rear diffuser with active airfoil

Paris, france — Jaguar’s latest concept car is a stunning range-extended electric supercar concept called C-X75 as homage to the 75 years of the company’s history. Seemingly leaving nothing on the shelf from Jaguar’s technology toy chest, the C-75 is reputedly capable of reaching 330km/h (205mph), sprinting from 0-100km/h (62mph) in just 3.4 seconds and offering mind-blowing acceleration from 80-145km/h (50-90mph) in just 2.3 seconds. Four powerful 145kW (195bhp) electric motors — one for each wheel — produce 780bhp and an astonishing total torque output of 1600Nm (1180lb ft). Two micro gas-turbines, spinning at 80,000 rpm, can generate enough electricity to extend the range to a remarkable 560 miles, yet produce just 28 grams of CO2/km from the car’s plugin charge capability. C-X75 also offers a zerotailpipe emissions range of 110km (68 miles) while running solely on battery power. Of most interest to Wind Tunnel International readers will be the C-X75’s active aerodynamics that facilitate an elegantly simple fuselage section yet remains stable at very high speed. Aerodynamics have always played a large part in Jaguar design with the late designer Malcolm Sayer elevating it into an art form in cars such as the midengined V12 XJ13, the prototype from which the C-X75 draws inspiration. In the active aerodynamic system, aerodynamic 6

efficiency is improved dramatically by opening the front grille and brake cooling vents only when necessary. At the rear corners of the car vertical control surfaces automatically engage at higher speeds to direct airflow aft of the rear wheels for increased stability and efficiency. The carbonfiber rear diffuser, a crucial element in guiding airflow under the car and creating downforce, includes an active aerofoil, which is lowered automatically as speed increases. Vanes in the exhaust ports then alter the directional flow of the gases to further increase the effectiveness of the diffuser. Shorter and lower than the current crop of supercars, the C-X75 has a simple central fuselage surrounded by prominent wheel arches. Maximum advantage of the freedom afforded by the absence of a conventional piston engine has been taken in the placement of mechanical components and the creation of an elegant engineering package. The lightweight micro gas-turbines, developed in partnership with Bladon Jets,

are, Jaguar believe, the first viable axial-flow micro-turbines and are so efficient they can be viewed as a realistic power source. Each of the micro gas-turbines weighs just 35kg and produces 70kW of power at a constant 80,000rpm. The energy created by the turbines and stored in the batteries is transmitted to the road using four independent electric motors. Also notable is the C-X75’s lightweight aluminum construction, based the technology already in production on the Jaguar XJ. Jaguar did not state when, or even whether, the C-X75 will go into production.


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Commercial Space Programs Taking Off

Xcor Lynx model in wind tunnel tests at NASA MSFC (above). Schlieren image (below)

SpaceX at liftoff

The successful launch and achievement of Earth orbit by the SpaceX Falcon 9 launch vehicle on June 4 marked a key milestone. Preliminary data indicates that Falcon 9 achieved all of its primary mission objectives, culminating in a nearly perfect insertion of the second stage and Dragon spacecraft qualification unit into the targeted 250 km (155 mi) circular orbit. “This is a major milestone not only for SpaceX, but the increasingly bright future of space flight,” said Elon Musk, CEO and CTO, SpaceX. SpaceX currently has an extensive and diverse manifest of over 30 contracted missions, including 18 missions to deliver commercial satellites to orbit. In addition, the Falcon 9 launch vehicle and Dragon spacecraft have been contracted by NASA to carry cargo to and from the ISS. Both Falcon 9 and Dragon have been designed to meet NASA’s published human rating standards for astronaut transport, allowing for a rapid transition to astronauts within three years of receiving a contract to do so. The critical path item is development and testing of the launch escape system. For less than the cost of the Ares I mobile service tower, SpaceX says, it has developed all the flight hardware for the Falcon 9 orbital rocket, Dragon spacecraft, as well as three launch sites. Meanwhile, barely over a month later on July 8

Boeing CCD capsule

VSS Enterprise and Eve in captive flight tests

15, Scaled Composites/Virgin Galactic space tourism program also passed a significant milestone as, for the first time, the team the VSS Enterprise (SpaceShip Two) flew with crew on board. As planned, the spaceship remained attached to the unconventional four-engine mothership VMS Eve (captive) for the duration of the flight. Scaled Composites plans to extend the flight test envelope suffered a setback in August, however, when VMS Eve was damaged with landing gear failure. VMS Eve flight tests resumed at Mojave, Calif., on Sept. 13 following repairs to the left vertical tail and modifications to the main landing gear. As we closed for press, Aviation Week reported that the resumption of these captive flights was imminent. Also in September, XCOR Aerospace, Inc. announced it has completed the primary supersonic wind tunnel testing of the Lynx suborbital spacecraft. Performed at NASA Marshall Space Flight Center (MSFC) using a precision scale model, the tests demonstrated the integrity of the Lynx aerodynamic shape and provided confidence that the Lynx

aerodynamic shape will have stable and controllable flight throughout the range of Mach numbers and angles of attack needed for the Lynx mission. The Lynx concept is of a two-seat, singlestage winged suborbital vehicle that lifts off from a runway powered by non-toxic, reusable rocket engines and carries a pilot and one spaceflight participant, plus engineering and scientific payloads. Lynx can be flown up to four times a day. And The Boeing Company and Space Adventures, Ltd. have established a memorandum of agreement for Space Adventures to market passenger seats on commercial flights aboard the Boeing Crew Space Transportation-100 (CST-100) spacecraft to low Earth orbit (LEO). Potential customers for excess seating capacity include private individuals, companies, nongovernmental organizations, and U.S. federal agencies other than NASA. Boeing plans to use the CST-100 to provide crew transportation to the International Space Station (ISS) and future commercial LEO platforms. The spacecraft, which can carry seven people, will be able to fly on multiple launch vehicles and is expected to be operational by 2015. Boeing and Space Adventures have not yet set a price per seat for spaceflight participants, but will do so when full-scale development is under way. Virgin Galactic is quoting $200,000 for its tickets (deposits start at $20,000) and claims to have 340 reservations already. WIND TUNNEL INTERNATIONAL | 2010


Bombardier Zefiro Very-Highspeed Train Sales Tracking Well WITh fIRM orders for 210 trains, Bombardier’s 360 km/h (224 mi/h) ZEFIRO family has become one of the most successful platforms in the global high speed rail market. Bombardier recently announced the signing of a contract with Trenitalia (Italian Railways) for the delivery of 50 very-highspeed V300 ZEFIRO trainsets. The V300 ZEFIRO is developed in partnership with AnsaldoBreda, a subsidiary of the Finmeccanica group of Italy.

The V300ZEFIRO has a capacity for 600 passengers. Its unusually high acceleration enables the train to ensure excellent travel times even in winding routes. It is fully interoperable and will provide cross-border service, taking Trenitalia’s passengers to other European countries without the need for changing trains. The first order for trains from the ZEFIRO family came from China in October 2007, with a contract to supply ZEFIRO 250 km/h trains.

Since then, Bombardier was awarded contracts to deliver 80 units of the ZEFIRO 380 model and additional 80 ZEFIRO 250 km/h trains, all ordered by the Ministry of Railways in China (MOR). The first-generation ZEFIRO 250 is already operating in China. Stephane Rambaud Measson, President, Passengers Division, Bombardier Transportation commented: “Our success in this market segment demonstrates that customers have welcomed

the innovation we have brought into making the ZEFIRO high speed family about more than just speed.” He added, “The ZEFIRO is a game changer in this industry as in addition to high speed it also offers costefficiency, coupled with high capacity capabilities, pleasing aesthetics, reliability, safety, durability and environmentally friendly transportation solutions.” One of the reasons for the ZEFIRO’s success, Bombardier claims, is its groundbreaking aerodynamic design which has been developed by leveraging the company’s distinctive transportation and aerospace expertise. The use of AeroEfficient, a tool developed in collaboration with Bombardier Aerospace, enabled Bombardier to minimize the aerodynamic resistance of the ZEFIRO train and save up to 12 percent of the energy consumed by standard-design trains. The aerodynamics also optimize crosswind stability, aerodynamic drag and pressure pulses. Advanced aerodynamics and energy-saving technologies, Bombardier say, make it the world’s most energy-efficient VHS train.

New Climatic Wind Tunnel for Scania

UK Starts Operating World’s Largest Wind Farm Construction was completed on the world’s largest offshore wind farm in September 2010 and production of electricity started soon after. There are 100 Vestas V90 wind turbines that have a total capacity of 300 MW — enough to supply more than 200,000 homes per year with clean energy. The Thanet project is located approximately 12 km off Foreness Point, the most eastern part of Kent, England. According to The Guardian newspaper, Thanet may not hold the title for very long. Two larger offshore wind farms are currently under construction (Greater Gabbard, 500 MW capacity and London Array, 1 GW). As both of these are in the UK, Great Britain will continue to be a world leader in offshore wind.


Leading truck manufacturer Scania will build a new climatic wind tunnel at its research and development centre in Södertälje, Sweden. The wind tunnel will be used for the testing of heavy duty trucks’ and buses’ comfort, road safety and environmental performance in different climates. The facility, the only one of its kind in Europe says Scania, will be completed in 2013. A wind tunnel that can simulate realistic environments, ranging from dry Arctic cold to humid tropical heat as well as various wind conditions, will make Scania’s development work more efficient and flexible, as the planning and transport of vehicles to different climates around the world will be reduced or offset “In various stages of the development phase, there are many advantages in being able to test vehicles and individual components independently of seasons and without having to transport them to another climate. Investing in a wind tunnel will strengthen our competitiveness, since it will make shorter development times and higher product quality possible,” says SvenÅke Edström, Senior Vice President Truck, Cab and Bus Chassis Development. Jacobs Engineering of Pasadena, Calif., will provide engineering, procurement and construction services to design, build and commission the wind tunnel, according to a source familiar with the project. The facility will provide a complete simulation of solar, rain, snow and soiling conditions and speeds up to 100km/h (62 mi/h).. WIND TUNNEL INTERNATIONAL | 2010


High-speed Helicopters Brace For A Showdown

it was only a couple of weeks between Sikorsky Aircraft Corp. announcing that its X2 TechnologyTM d e m o n s t rat o r h a d successfully achieved a remarkable speed of 250 knots true air speed in level flight (the program objective) and Eurocopter announcing the start of its flight test program of its high-speed helicopter demonstrator. interestingly, the Eurocopter chopper is called the X3…. The two programs take a very different approach. The Sikorsky solution combines an integrated suite of technologies intended to advance the state-of-the-art, counterrotating coaxial rotor helicopter. It is designed to demonstrate that a helicopter can cruise comfortably at 250 knots while retaining such desirable attributes as excellent low-speed handling, efficient hovering, and a seamless and simple transition to high speed. Eurocopter uses its high-speed, long-range Hybrid Helicopter (H3) concept, which has two turboshaft engines that power a five-blade main rotor system and two propellers installed on short-span fixed wings. This creates an advanced transportation system offering the speed of a turboprop-powered aircraft and the full hover flight capabilities of a helicopter. The concept is tailored, Eurocopter says, to applications where operational costs, flight duration and mission success depend directly on the maximum cruising speed.combines excellent vertical takeoff and landing capabilities with fast cruise speeds of more than 220 kts. Let the best chopper win….

Wind Tunnel Tests Show New Ford Fiesta Quieter Than Rivals

One of the reasons that the 2011 Ford Fiesta is selling unusually well in the uS market (not known for smallcar success), Ford says, is that it is significantly quieter than the competition and even as quiet as larger Ford cars. Wind tunnel tests show that the Fiesta has interior noise levels lower than the Honda Fit and the Toyota Yaris in 80 mph wind tunnel testing. Ford engineers measure noise in sones — a unit of perceived loudness inside the vehicle. In 80 mph wind tunnel testing on the highway, the inside of a Fiesta records 25.4 sones compared to 27.6 sones for the Honda Fit and 26.2 for the Toyota Yaris. The Fiesta also is quieter than the larger Toyota Corolla, which measures 30.3 sones.


Taranis Unmanned Combat Aircraft Appears The lONG-RuMOReD Taranis prototype unmanned combat aircraft of the future recently was unveiled by the UK Ministry of Defence. About the size of a BAE Systems Hawk jet and named after the Celtic god of thunder, the concept demonstrator will test the possibility of developing the first ever autonomous stealthy Unmanned Combat Air Vehicle (UCAV) that would ultimately be capable of precisely striking targets at long range, even in another continent. Should such systems enter into service, they will at all times be under the control of highly trained military crews on the ground. Speaking at the unveiling ceremony at BAE Systems in Warton, Lancashire, Minister for International Security Strategy Gerald Howarth said: “Taranis is a truly trailblazing project. The first of its kind in the UK, it reflects the best of our nation’s advanced design and technology skills and is a leading programme on the global stage.”

Taranis is an informal partnership of the UK MoD and industry talents including BAE Systems, Rolls Royce, QinetiQ and GE Aviation. Speaking on behalf of the industry team, Nigel Whitehead, Group managing director of BAE Systems’ Programmes & Support business, said: “Taranis has been three and a half years in the making and is the product of more than a million man-hours. It represents a significant step forward in this country’s fast-jet capability. This technology is key to sustaining a strong industrial base and to maintain the UK’s leading position as a centre for engineering excellence and innovation.” The Taranis prototype will provide the UK MoD with critical knowledge on the technical and manufacturing challenges and the potential capabilities of Unmanned Combat Air Systems. Initial ground-based testing commenced in 2010; the first flight is expected to take place in 2011, subject to successful conclusion of ground-based testing. 11


Look Carefully…

By now, the Boeing 787 Dreamliner is well on its way to completing flight testing (above). But we couldn’t resist printing this shot (below) from earlier in the test program. During ultimate-load testing at Boeing’s Everett, Wash., facility, the wings of the 787 Dreamliner were flexed upward by approximately 25 feet (7.6


meters). As we said, look carefully… Engineers are reviewing the detailed test results and report that initial results are promising. The test exposed the airframe to the equivalent of 150 percent of the heaviest load it is ever expected to see while in service.



Faster Than The Wind it’s a brainteaser that was first posed decades ago: can you build a wind-powered vehicle that would travel faster downwind than the wind? The answer is in and it’s yes. Thanks to Rick Cavallaro, Chief Scientist, Sportvision Inc, and his friend John Borton, who built the extraordinary Blackbird and set an official world record at 2.8X wind speed on 3 July 2010 on the El Mirage, Calif., dry lake bed. “I first posted this as a brainteaser on an R/C helicopter forum and a kite surfing forum,” said Cavallaro. “The topic became quite controversial and debate took off across dozens of forums. We soon learned that there was a student that wrote a paper describing a similar vehicle in the 40’s and that paper sparked a similar controversy. An engineer by the name of Andrew Bauer finally decided to settle it in the 60’s. He built a cart somewhat like ours and convinced his boss (A.M.O. Smith at Douglas Aircraft), but produced no reasonable documentation that would be accepted by the skeptics of the time.” Unlike Bauer, Cavallaro and Borton have kept meticulous documentation to back up their achievement. “We’ve had it above 3X wind speed going directly downwind,” said Cavallaro. “Over the winter we plan to build a turbine to replace the propeller, and next summer we plan to go directly upwind faster than the wind. In the current (i.e. downwind) configuration, the wheels turn the prop. In the upwind configuration the turbine will turn the wheels.” Interested in how it works? Or skeptical, even? Check out: (ar ti cl e by C av allaro e x p lainin g th e co n ce p t); (the official website); and (video of the vehicle running at El Mirage dry lake bed).

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The future of hypersonics is now The headlines are right. Hypersonics activity is high, led by the Arnold Engineering Development Center (AEDC), which is moving at high speed to break barriers for the warfighter. By philip Lorenz, AEDC

A Mach 10 Scramjet-powered vehicle configuration undergoes testing at the AEDC hypervelocity Wind Tunnel 9. Tunnel 9’s large scale and replication of flight physics provides the ideal environment to evaluate configurations such as this. This DARpA and uSAF sponsored test will obtain aerodynamic control data to validate models and predict flight performance. Vehicles in this class are progressing through significant ground and flight experiments and could someday power responsive access to space. (Photo by Mike S. Smith)




Aerospace Testing Alliance Outside Machinist Everett Fulmer inspects the Defense Advanced Research projects Agency’s Falcon Combined-cycle Engine Technology (FaCET) scramjet test article in the center’s Aerodynamic and propulsion Test unit test cell prior to a test. (Photo by Rick Goodfriend)


Ypersonics And scramjets are the current buzzwords on the lips of journalists, scientists, military and civilian leaders and almost anyone who follows the latest technological advancements in flight. headlines like “u.s. Air force scramjet test sees spaceships in future” and “Rise of the space planes, hypersonic weapons and spaceships in future” and “DARPA eyes sM-3 for hypersonic strike” followed the recent successful flight demonstration of a hypersonic X-51A Waverider vehicle.

Technological advancements on projects like the X-51 do grab people’s attention, acknowledged Dan Marren, site director of Hypervelocity Wind Tunnel 9 at AEDC’s remote site in Silver Spring, Md. However, he pointed out that the future of hypersonic flight is already taking shape, literally, in the unique ground test facility he manages, and at AEDC’s Aerodynamic and Propulsion Test Unit (APTU) and High-Enthalpy Arc-Heated Facilities in middle Tennessee. “AEDC’s mission is to provide high quality test and evaluation of next generation systems that will fight and win wars,” he said. “Our efforts in the 1970s and 1980s, with the National Aerospace Plane, Space Shuttle, re-entry space vehicles and others, have paved the way for the cutting-edge work this country is doing now. The fantastic success of the first X-51 flight in May was actually the realization of years of painstaking hard work by countless people behind the scenes. Programs have come and gone never to fly, but since the intellectual capital has been passed down through the decades we eventually arrive at successes like X-51. “AEDC’s hypersonic test capabilities together with other national capabilities have contributed to the recent string of successful experimental flight vehicles in significant ways. The rigorous testing in Tunnel 9, the von Kármán Gas Dynamics Facility (VKF), the Aerodynamic and Propulsion Test Unit and High-Enthalpy Arc-Heated Facilities has led to significant advancements in engine and airframe technology,” he said. “The work of engineers and those who support their efforts, through the data and analysis they provide, has resulted in high temperature 2010 | WIND TUNNEL INTERNATIONAL

Carson McAfee, ATA outside machinist and foreman, makes a control surface change to the sub-scale model of the X-51 WaveRider during a break in aerodynamic testing at AEDC’s von Karman Gas Dynamics Facility in 2006. (AEDC file photo)



Test engineers Joe Norris (left) and John Lafferty ready a hypersonic Technology Vehicle-1 model prior to a hypervelocity Wind Tunnel 9 operation. (U.S. Air Force photo)

materials, flight control algorithms and scramjet engines. “This nexus of mission, modern computing and manufacturing technologies has created the need and the ability to produce experimental flight vehicles, including the Hypersonic Test Vehicle (HTV), X-37 and X-51.” Marren said pioneering in several areas has come full circle. “AEDC’s development of new test capabilities, such as VKF’s modernization, Tunnel 9’s high altitude capability, the APTU’s Mach 8 scramjet capability and Arc Heater upgrades enabled the testing on those same experimental vehicles,” he said. “Recent successful flight experiments on the X-37 and X-51 have validated the vision, ground testing and potential of these innovative vehicles across our industry.” Marren emphasized that it is critically important to view these achievements with the bigger picture in mind. “These programs are likely to emerge as the next acquisition programs in long-range strike or space access solutions,” he explained. “Capabilities include a tactical strike capability, which translates to hundreds of miles in minutes; a global strike capability in thousands of miles in under an hour; and affordable space access on demand. “Today, in our cells, just like 20 years ago, we are working on the next generation of test capabilities and testing the next generation of vehicle technologies. “To keep pace with advancing vehicle technologies our facilities and tools need to advance as well. AEDC is advancing with cutting-edge projects on global measurement techniques in Tunnel 9, on ‘fly-themission’ varying Mach capability in APTU, on more representative environments in Arcs, and on a commitment to replicate the right physics to validate computational tools. “AEDC is also laying the foundation to validate the next generation Mach 10 scramjet, prompt global strike, flexible on demand space access, and advanced missile defense,” he said. “It is likely that 16

today’s successes in test technology and understanding of these vehicle technologies will be the seed corn for tomorrow’s vehicles just like the National Aerospace Plane (NASP) was for the X-51.” The teams at Tunnel 9, VKF, Arc Heaters and APTU work in concert on research and development testing for hypersonic flight, according to Marren. “Hypersonic testing takes multiple world-class capabilities working together to understand the physics,” he said. “Using Tunnel 9 as the ‘hub,’ the arcs test coupons for material response and then Tunnel 9 uses that response and resultant ablated shapes to test aerodynamic performance and aero thermal response in a flightrealistic environment. “We can use Tunnel 9 to address the aerodynamics of the vehicle inlet to determine in-flow to the engine. That information is critical to engine tests in APTU that will characterize the operability and durability of an engine given that known aerodynamic flow into the combustor. From that, we also learn the stability limits during engine inlet start and un-start as well as margin of thrust over drag, and then look at margin on aerodynamic stability and see if this vehicle will get to flight with that engine.” Dr. Mark Lewis, the Willis Young Professor of Aerospace Engineering at the University of Maryland, is intimately familiar with AEDC’s hypersonic ground test facilities in middle Tennessee and Tunnel 9. When asked recently whether these facilities are keeping pace with the growing demand for research and development of hypersonic flight vehicles, Dr. Lewis, the former Chief Scientist of the Air Force, said, “If you look at the [hypersonic] facilities we have today, they are really quite capable. There is always this trade [off] between how much you test on the ground and how much you test in flight. Our biggest challenge today isn’t building new things, though upgrades are important; it’s keeping the great things that we have still operating. “Tunnel 9 is a perfect example of that. In fact, very recently it went WIND TUNNEL INTERNATIONAL | 2010


through some upgrades. It’s an incredibly capable facility.” Tunnel 9 is a blow down facility capable of subjecting flight vehicles and component scale models to nitrogen gas at speeds as high as Mach 14 for up to 15 seconds. According to Dr. Lewis, the only limitation of the test facilities at Tunnel 9 is the composition of the gas it uses to simulate hypersonic speeds. “The facility can provide a Mach 14 flow for long duration under very realistic flight conditions,” he said. “There is only one main thing [missing] from Tunnel 9: oxygen. That is the nature of the facility; it runs with a nitrogen environment. You can’t run oxygen through the heater Tunnel 9 uses. So, that means you can’t do combustion work in Tunnel 9. “One obvious upgrade you might consider would be the addition of oxygen to the flow path in Tunnel 9. But the point I would make is as long as you’ve already got a facility like APTU, we can already use our facilities in concert to pretty much cover most of the conditions that we would want to simulate before we go to actual flight.” However, Dr. Lewis points out that, because of the way they are heated, propulsion test facilities often don’t exactly reproduce the chemical composition of the air. “Efforts to improve the composition of the flow in propulsion test facilities, so that it more closely matches the air an engine would see in actual flight, are definitely worthwhile,” he said. Dr. Lewis said those who question the expense or necessity for ground testing facilities need to understand the big picture, including the availability of other assets. “NASA also has some very capable facilities that the U.S. can leverage,” he said. “These were [all] expensive facilities to build and, yes, we need to keep them. “We have made a tremendous investment in these facilities,” he added. “And that investment is not only just money; it is the training and expertise that goes into running these facilities.” He described a tendency of people to migrate toward “penny wise, pound foolish” thinking when it comes to budgetary considerations for research and development on military weapons systems. “I often ask: ‘At its most basic level why do we do wind tunnel testing?’ It’s to buy down risk. You can question investing the money in the infrastructure and the testing, which can seem like a lot, until you lose a vehicle because you didn’t do enough testing. Then you realize that the initial T&E investment 2010 | WIND TUNNEL INTERNATIONAL

Carbon-carbon leading edges under test (above and below) in the 24-inch diameter nozzle in Arc heater h-2 for the hTV-3 technology program during 2007. (AEDC file photos)

would have been a very, very wise investment indeed.” So, what is the best investment to support the ground testing of hypersonic flight systems? Dr. Lewis said it depends on which vehicles will ultimately be developed. “For many of the applications of hypersonic flight, one of the key questions is transitioning from one part of the speed regime to another,” he explained. “For example, I might be able to build a hypersonic vehicle that flies well at Mach 6, but how do you get it up to Mach 6? “There are a number of ways that you might do that. One would be with an auxiliary propulsion system, a solid rocket motor for example that boosts you up to speed. Another might be within an engine that somehow changes the way it operates, that transitions its mode from one type of engine to another. “Either of those invokes the question of what happens when you change your flight Mach number,” he continued. “So, to that end, upgrades to APTU would actually be very significant. It would be a very, very important capability that you could bring to bear for testing future types of hypersonic vehicles.” CONTACT Jason Austin, Deputy Director, AEDC public Affairs Email: 17


Artist impression of the Superbus

The air-efficient Superbus Electrically powered, sustainable, 250 km/h, 30-passenger road vehicles may sound like fantasy to some. But the Delft University of Technology (DUT) in The Netherlands is building the prototype of such a vehicle, as part of a concept study called the Superbus Transport Concept. Joris Melkert of the Faculty of Aerospace Engineering at DUT describes the considerations which led to the start of the concept’s development and examines how the concept’s application of advanced aerospace technology makes high-speed transport more sustainable


he sUperbUs concept was invented by professor Wubbo Ockels and consists of a sustainable, high-speed, roaddriven vehicle for use in public transport, with dedicated high-speed infrastructure and advanced logistic support systems for its demand-driven operation.

World wide empirical research has shown that on average the daily travel time budget expressed in hours spent on traveling is constant. Schafer (1998) has shown that the average travel time budget is roughly one hour per day, independent of the gross domestic product per capita. (Figure 1) Other research has shown that the traffic volume (kilometers travelled per day) increases with increasing GDP. (Figure 2) Based on these two observations one may conclude that when the

GDP increases the average transport speed will go up. Victor and Schafer (1997) report that indeed there is a continuous shift towards transportation modes with higher speeds. Nowadays there is an increasing awareness that the energy consumption of the World’s population might have a detrimental influence on the climate. The energy used in transport forms a considerable part of the World’s energy consumption. It is therefore useful to consider what the effect is of the world wide trend of increasing speed in transport. Early research into this has been done by Gabrielli and Von Kármán (1950). They reported the specific resistance of vehicles as a function of their speeds. Specific resistance is expressed as the power required for propelling a vehicle divided by its weight times

Side view of the Superbus vehicle




Rolling drag is thus directly proportional to the weight of the vehicle. Reducing the weight has a direct effect on the drag and thus the energy required. The aerodynamic drag of a vehicle can be expressed with the following formula:

Daero = C w

1 ρ v2 S f 2

where: Daero = aerodynamic drag Cw = coefficient of aerodynamic drag ρ = density of the air v = speed Sf = frontal area The aerodynamic drag of a vehicle can be influenced by its designer in several ways. Speed is considered to be a given input parameter and the density is assumed to be constant for road vehicles. By making the shape of the vehicle more “aerodynamic” the coefficient of aerodynamic drag can be influenced. The better the shape the less the coefficient will become. Typical values for road based vehicles are given in Figure 5 by Hucho (1998). Another design parameter is the frontal area Sf. By reducing the frontal area the aerodynamic drag and thus the energy The Superbus full scale demonstration vehicle as designed by dr. Antonia Terzi of Tu Delft consumption can be reduced. The lessons learnt from aviation boil down to speed and their original diagram (Figure LESSONS TO BE LEARNT FROM the fact that (road) vehicles should be as light 3) shows that increasing speeds leads to AEROSpACE TEChNOLOGY as possible, have a streamlined outer shape and more-than-proportional increase in energy Aircraft are, by their nature, required to have frontal area as low as possible. maximize their fuel efficiency. The reason for consumption. Gabrielli and Von Kármán discovered a this is the compounding effect of having to ThE SupERBuS TRANSpORT CONCEpT lower limit in the specific resistance. Later take too much fuel on board. In simple words: Currently Delft University of Technology this was called the Gabrielli – Kármán line. “It takes fuel to carry fuel”. In aircraft design, (DUT) in the Netherlands is investigating At that time, no vehicle was able to have a two major areas can be distinguished where a new transport concept, called Superbus, specific resistance/speed combination below this compounding effect can be counteracted. that might be able to meet some of the this line. Only closely coupled combinations The first is the weight; the second is the challenges mentioned in the previous sections. Superbus is a sustainable highof vehicles like locomotives with a number of aerodynamic drag. In land-based vehicles, weight has an effect speed vehicle for public transport. The target carriages or a series of cars were able to show a performance below this line. Over the years on rolling friction. The rolling friction can be maximum speed is 250 km/h. The Superbus transport concept has this performance has improved, as shown by calculated using the following formula: three main aspects: (1) the vehicle, (2) Yong et al (2005, see Figure 4). Drol = µ. W the infrastructure and (3) the logistics. One can conclude that there is a trend where: The Superbus technology is based on towards a better energy performance but that Drol = rolling drag a combination of aerospace technology the development over the 55 year period µ = coefficient of rolling friction and information and communication considered is relatively small, especially in W = weight of the vehicle technology (ICT). the field of road transport.




The aerospace technology can be found in a refined aerodynamic shape and a light weight structure. Superbus will make use of its own dedicated lightweight infrastructure for high speeds but will also use existing roads where it will obey the current speed limits. The logistics will be demanddriven and highly supported by information and communications technology (ICT). The concept allows evolutionary growth. One can start simply using existing infrastructure and gradually extend the system; it is not limited by the requirement of a fully completed new infrastructure.

This is important since building the dedicated high speed infrastructure forms the most expensive part of the concept.


Figure 1: Daily travel time budget as a function of gross domestic product per capita (source: Schafer (1998))

ThE SupERBuS VEhiCLE Superbus aims to be a sustainable, road-driven, high-speed vehicle for public transport, with a typical design range of 30 to 200 km. The Superbus will be electrically driven with a seating capacity of 20 to 30 Figure 2: Motorized mobility (car, bus, rail and aircraft) as a function of GDp per capita (source: Schafer (1998)) passengers contained within an overall size that complies with current regulations for buses: no longer than 15 m; no wider than 2.50 m. The height, however, is limited to 1.65 m which reduces frontal area and, therefore, aerodynamic drag. Passengers will board the vehicle like they do in normal car via doors on the side of the vehicle. For this, the vehicle body can be raised by a height of up to 35 cm. The concept has been described in Ockels and Melkert (2004) and Melkert (2006).

Superbus logistics is being developed to enable the use as a demand-driven, point-to-point, transport system. Demand-driven transport has been applied and investigated several times. Many applications can be found in the transport of elderly and disabled people in rural areas. Evers (2005; 2006) gives an overview of applications realised. He concludes that a cost-effective operation requires some combination of demand in one vehicle. This poses practical problems for the operator. Mageean and Nelson (2003) conclude that these systems are often confronted with high costs, a lack of flexibility in route planning and an inability to handle high traffic flows but that the wide use of ICT can overcome these downsides.


Passenger transport in the future has to meet a combination of challenges: higher speed, less energy consumption, move towards sustainability and have an infrastructure iNFRASTRuCTuRE with minimal Since the Superbus environmental drives on rubber impact. The tires and meets Superbus transport current regulations concept might be with respect to sizes, able to contribute it can reach inner in meeting these cities as well as local challenges. Aerospace Figure 4: Trends in specific resistance for various transport modes (source: Yong et al (2005)) roads and highways. technologies like Superbus will use lightweight structures its dedicated highand refined aerodynamic speed infrastructure design of the outer shape when required from of the vehicle play a a safety point of view. major role in this. Delft The Superbus is a University is now building relatively lightweight a full scale experimental vehicle (axle loading demonstration vehicle. With approximately 3 this demonstration vehicle it tonnes) and the high- Figure 3: Specific resistance for various transport modes before is the intention to show the speed infrastructure 1950. (source: Yong et al (2005)) technical feasibility of the will exclusively be used by similar vehicles. That means a relatively vehicle itself. The progress of Figure 5: Typical values of aerodynamic drag coeďŹƒcients simple and lightweight infrastructure will be sufficient. Normal roads of road vehicles (source: hucho (1998)) the project can be monitored are designed to carry heavily loaded trucks. This requires them to be via the website: strong and therefore heavy. This in itself requires a lot of concrete and CONTACT asphalt. Designing dedicated infrastructure for a light weight vehicle Joris Melkert, Delft university of Technology will result in less material use and therefore significantly lower costs. E-mail: 20



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Supersonic Wind Tunnel at NASA’s Glenn Research Center, Cleveland, Ohio.


Ensuring US National Aeronautics Test Capabilities

When NASA created its Aeronautics Test Program (ATP) in 2006, it gave the program a lofty mandate: not just to make certain that the agency is able to meet its own aeronautics testing needs, but to ensure that the United States has the test capabilities required to advance its position in aeronautics leadership. Timothy J Marshall, Deputy Director, ATP, reviews how this has led to a strategic plan for ATP and how this impacts its customers


t the time of ATP’s creation, the strategic support

and financial resources for NASA’s ground test facilities were insufficient to ensure that strategically important aeronautics test capabilities in the United States were operating optimally, priced appropriately, and being positioned to meet future national aeronautics testing needs. NASA recognized that if it did not manage its unique national test resources effectively, economic and competitive processes would lead to inefficiencies and the possible loss of critical capabilities. 22

Composition of the ATP portfolio was based on research results published by the RAND Corporation in 2004 for NASA and the Office of the Secretary of Defense, titled Wind Tunnel and Propulsion Test Facilities — An Assessment of NASA’s Capabilities to Serve National Needs. In that watershed report, many

NASA ground test capabilities were categorized as strategically important to the nation and using that criterion as a basis, specific wind tunnel facilities were downselected by NASA to comprise the ground test portion of the ATP portfolio. Subsequently, flight test capabilities in ATP were selected on the basis of analysis documented by NASA in a 2006 Program Decision Memorandum and were added to the ATP portfolio in 2007. Now in its sixth year of operations, the Aeronautics Test Program continues to have its work cut out for it: its customer base has continued to shrink and facility utilization has declined by more than 50% from 2006 levels. This significant decrease is attributable to several factors, including: the overall decline in new programs and projects in the aerospace sector; the impact of computational fluid dynamics on the design, development and research process; and the reduction in research testing within a large sector of the ATP customer base — NASA’s Aeronautics Research Mission Directorate in Washington, D.C. Retirement of the Space Shuttle Program and recent perturbations of NASA’s Constellation Program will only exacerbate this downward utilization trend. Utilization is a critical factor for ATP because the program relies on customer-generated revenue to recover a substantial portion of its facility operating costs. Sustained reductions in utilization are an indicator of excess capacity and, in some cases, low-risk redundancy (i.e., several facilities with similar capability and overall low utilization that can be consolidated with little risk to the nation). However, it must be noted that low utilization may not necessarily translate to lack of strategic importance, as some facilities with low utilization are nonetheless vital in the long run. Therefore, it is crucial that



provide independent capabilities. Appropriately setting the price for user occupancy will help generate • Unitary Plan Wind Tunnel needed revenue to defray the cost of ownership for ATP’s national test infrastructure. Reducing low-risk redundancies and eliminating Glenn Research Center associated costs will enable NASA to invest in new technologies and • Icing Research Tunnel capabilities in support of U.S. aeronautics leadership in the future. • 10x10 Supersonic Unitary Wind Tunnel Establishing effective reliance agreements across NASA and the Defense • 8x6 Supersonic Wind Tunnel Department will help ATP ensure the best possible use and sharing of • 9x15 Low Speed Wind Tunnel the nation’s aeronautics test capabilities. All of this will require a new • Propulsion Systems Lab level of cooperation and a long-term view from both test customers and Dryden Flight Research Center stakeholders. It also calls for a forward-looking strategic plan that can • Western Aeronautics Test Range guide progress and assure transparency. Completed in October 2009, • Support and Test Bed Aircraft the ATP strategic plan flows from its vision and mission and is aimed • Flight Loads Laboratory at achieving program goals and objectives over the next five years. • Research Aircraft Integration Facility The ATP strategy is built around several core principles. For example, Langley Research Center the program is committed to national stewardship and ensuring healthy • National Transonic Facility and available aeronautics test capabilities - not just for NASA but • 8-foot High Temperature Tunnel also for the nation. Its capabilities must evolve to maintain relevance • Langley Aerothermodynamics Lab and meet future test requirements. The program is committed to the • 14x22 Subsonic Wind Tunnel principle of availability, not necessarily ownership. In other words, • Transonic Dynamics Tunnel NASA does not have to own and operate all needed test facilities - ATP • 4-foot Supersonic Unitary Tunnel will ensure the agency can access them through strategic partnerships • 20-foot Vertical Spin Tunnel and reliance agreements. ATP is also committed to the public good. The NASA ATp portfolio That is, NASA has a role in providing test capabilities that are not ATP periodically assess which of its test capabilities are strategically economically viable as an independent business and not available important, address the challenges associated with divestment (if elsewhere. And finally, ATP believes that its test capabilities can necessary) and determine a viable approach to both sustainment and support aeronautics research and development as well as test and improvements of the remaining infrastructure. evaluation. Strategic concerns for ATP are rooted in several areas of program Vision responsibility, including: ownership and management of capabilities; ATP’s vision is a balanced portfolio of aeronautics ground and flight understanding national aeronautics research testing needs; forecasting test capabilities that advance U.S. leadership in aeronautics in the short test capability demand; sustaining a competent workforce; strategic and long term alliances and partnerships; test facility health; test capability upgrades;

Ames Research Center

and user price stability. Given the significance of these national concerns, it becomes imperative that ATP, on behalf of both NASA and the nation, rightsize its portfolio of aeronautics test facilities and fill the capability gaps between current and future test requirements. Fiscal realities imply that low-risk redundancies must be eliminated to free up funds. User fees must be properly set to ensure adequate revenue as well attract the work that advances U.S. aeronautics. And finally, explicit reliance relationships and agreements must be established between entities that have previously operated independently: today neither NASA, nor the Department of Defense, nor the private sector can afford to

Mission • Provide guidance and recommendations to the NASA Associate Administrator, Aeronautics Research Mission Directorate and NASA Research Center Directors • Represent NASA’s and the nation’s interests related to National aeronautics ground and flight test capabilities • Provide strategic direction to test capability managers • Provide financial support by funding — a portion of expenses for testing and support facilities The ATp Vision and Mission

ATp utilization Trends




One of ATP’s most significant objectives involves the National Partnership for Aeronautics Testing (NPAT), established by a memorandum of understanding in January 2007, between the NASA Administrator and the Undersecretary of Defense for Acquisition, Technology, and Logistics. The NPAT Council is co-chaired by NASA’s Associate Administrator for aeronautics research, Dr. Jaiwon Shin, and the Defense Department’s Director of the Test Resource Management Center, Dr. John B. Foulkes. Council members include senior government officials from NASA and the U.S. Army, U.S. Navy, and U.S. Air Force. The objective of the NPAT Council is to provide a forum for the Defense Department and NASA to consult with one another and with other affected activities to facilitate the establishment of an integrated national strategy for management of aeronautical test facilities owned or operated by both parties. The NPAT Council conducts studies, addresses issues, and develops approaches and strategies for close cooperation between the parties with respect to the management and operation of aeronautical test facilities. Significant collaborative activities resulting from the NPAT include establishment of the National Force Measurement Technology Competency at NASA’s Langley Research Center in Hampton, Va., and the joint testing of a wind tunnel model in NASA and Defense Department transonic wind tunnels. The Facility Aerodynamics Validation and Operations (FAVOR) model project recently conducted cooperative wind tunnel testing that will provide engineering insight into facility processes, data reduction, flow quality and comparative data assessment for several important U.S. transonic test facilities. Comparison was made using test data obtained on the same model/balance/sting in the Air Force’s Arnold Engineering Development Center 16T, NASA’s Ames Research Center 11 foot, NASA’s Langley Research Center NTF, and NASA’s Glenn Research Center 8x6 Supersonic wind tunnels. Because U.S. leadership in aeronautics depends on ready access to technologically advanced, efficient and affordable aeronautics test capabilities, the Aeronautics Test Program has been busy ensuring, mostly through strategically directed investments, that NASA’s aeronautics test capability is available, affordable and reliable. The program has fostered healthy and highly effective working relationships involving NASA research and development programs, NASA research centers and the U.S. aerospace industry. ATP has also established a strong, high-level partnership with the Defense Department as well as working relationships with several of its field centers. However, the program continues to face challenges, some more formidable than those facing the program when it was first established. Opportunities and threats abound, particularly with respect to ATP’s aging facilities, long-range forecasting of wind tunnel test demand, workforce issues and deciding the best approach to investing in new capability across the portfolio. Its new five-year strategic plan will help ATP continue progress in these and other vital areas and focus its energies and resources on the capabilities and opportunities that prove to be the most strategically important for both NASA and the nation. For more information on ATP, including a comprehensive description of its capabilities, please see index.html. CONTACT Timothy J. Marshall, NASA Aeronautics Test program E-mail: 24

propulsion Systems Lab at Glenn Research Centre, Cleveland, Ohio. The National Transonic Facility at NASA’s Langley Research Center, hampton, Va.


The icing Research Tunnel, at Glenn Research Centre, Cleveland, Ohio. © NASA

inter-agency and multi-center comparison test program sponsored by the Aeronautics Test program (ATp), Facility Aerodynamic Validation and Operational Research (FAVOR) Check Standard Model which was tested in the NASA Glenn 8x6 Supersonic Wind Tunnel (SWT) in late May 2010.



How The Chevy Volt Got In Shape

Many view the Chevrolet Volt as the next step in the evolution of the automobile. The Volt is an extended range electric vehicle: it can reach an initial 40 miles solely on battery power, from which point, the backup engine powers the electric generator for hundreds of additional miles. Able to re-charge the battery from a standard wall outlet, many drivers will never use a drop of gasoline in their daily commutes, yet the extended range is there whenever needed., Maximizing battery life and energy efficiency were fundamental goals to meet these mileage requirements of this unique vehicle, and aerodynamics played a crucial role in that quest. Nina Tortosa and Ken Karbon of General Motors Aerodynamics Staff report


hiLe the Vo l t ’s propu lsion system doesn’t directly affect its shape efficiency, it does make aerodynamics much more important than in traditional vehicles. Aerodynamic performance is the second largest contributor to electric range, behind vehicle mass. Therefore, it was critical to reduce aerodynamic drag as much as possible while maintaining the key styling cues from the original concept car shown to critical acclaim in January 2007. This presented a number of challenges during the development, such as evaluating drag due to underbody features, balancing aerodynamics with wind noise and cooling flow, and interfacing with other engineering requirements. These issues were resolved by spending hundreds of hours in the wind tunnel and running numerous computational fluid Dynamics (cfD) analyses.


The Chevrolet Volt is currently the lowest drag vehicle in General Motor’s lineup

Reduced scale (1:3) testing developed most of the Volt’s aerodynamic shape. Stereo lithography parts enhanced the clay model fidelity

WiND TuNNEL TESTiNG Since physical testing still provides the most accurate measurement of coefficient of drag (CD), the wind tunnel was the primary tool for development of the Volt exterior surface. Another significant advantage to wind tunnel testing is the quick turnaround in design changes. On average, fifteen design iterations were evaluated in a single eighthour shift. This provided rapid feedback to modifications in specific vehicle features. Wind tunnel testing started with a 1/3-scale clay model of the concept car’s design, proportioned to fit on to GM’s small car platform. 25

GENERAL MOTORS CFD led the development of the Volt’s front end airflow. (bottom) An exploded view shows the velocity profile on the five heat exchanger cooling package

Over 500 hours of testing were spent to improve the basic shape of the vehicle. Reduced scale testing was ideal for early shape development of the Volt because less clay needed to be sculpted for a given geometry change. Particular attention was paid to the front end curvature and rear trailing edges

The GMAL fan unit is 43 feet in diameter with six blades made from laminated Sitka spruce

GM’s Wind Tunnel Facility

On August 1st 2010, the General Motors Aerodynamics Laboratory (GMAL) celebrated its 30th year of operation. Designed in the early 1970’s, the wind tunnel’s construction was interrupted by the mid-seventies oil crisis. The requirements for improved Corporate Average Fuel Economy (CAFE) resulted in a restart of construction in 1978. The final commissioning of the lab occurred in July of 1980, followed shortly thereafter by the first wind tunnel test, on a pontiac Fiero. The GM Aero Lab is a closed-jet, closed loop wind tunnel. After 30 years, GMAL remains the largest closed-jet wind tunnel dedicated to automotive vehicle aerodynamics development. In 2003, the test section and airpath were treated with sound-absorbing materials to reduce the ambient noise. This enabled more accurate aeroacoustic measurements. Since GMAL started operation three decades ago, it has seen thousands of vehicles installed in its test section, including the EV1, Chevrolet Corvette, Chevrolet Tahoe Hybrid and, most recently, the Chevrolet Volt.


Over 500 hours of testing were spent to improve the basic shape of the vehicle. Reduced scale testing was ideal for early shape development of the Volt because less clay needed to be sculpted for a given geometry change. Particular attention was paid to the front end curvature and rear trailing edges. It was also this early 1/3-scale testing that showed the pedestal door-mounted mirror design had lower drag than the more traditional patch-mounted design. GM’s approach to vehicle aerodynamics development mandates simulation of the airflow through the engine compartment and underbody to account for any interaction with the exterior surface flow. This methodology is applied even in reduced scale, where grilles, radiators, and chassis components are represented while evaluating the styling surface drag. Early testing of the Volt also showed that both underbody panels and an airdam would be needed to achieve aggressive CD targets. Once the aerodynamic drag of the 1/3-scale model was significantly reduced, development moved into the full-scale testing phase. With the full scale clay model, it was possible to fine tune the exterior surface and component details, including A-pillars, mirrors, underbody panels, and the airdam. One of the biggest challenges in developing the Volt was the outside rear-view mirror. The styled mirror had to meet global market vision requirements, aero performance, and wind noise performance, all within the design theme of the car. The swept, door-mounted design initially had a low CD increment, but its aero-acoustics performance was not acceptable. Significant wind-tunnel development resulted in a silent mirror that maintains a low drag contribution. Testing of engineering prototypes and pre-production vehicles facilitated final adjustments to components and the validation of the CD established with the clay models. In the case of the Volt, excellent correlation was achieved between the final full scale clay and sheet metal vehicles, indicating that all key aerodynamic features were captured throughout the entire development process. The final and official drag coefficient will be obtained from a saleable production vehicle tested according to the requirements in the new SAE Recommended Best Practice J2881, “Measurement of Aerodynamic Performance for Mass-Produced Cars and Light-Duty Trucks.” WIND TUNNEL INTERNATIONAL | 2010


Flow visualization connected data to design. When comparing different vehicle themes, iso-surfaces of total pressure identify the unique wake structures

COMpuTATiONAL FLuiD DYNAMiCS While wind tunnel testing has it strength in CD accuracy and quick turnaround of exterior changes in clay, Computational Fluid Dynamics (CFD) can provide much more in-depth and non-intrusive airflow analysis. The flexible nature of the virtual computer model was critical to designing the underhood and underbody layout of the Volt. The grille openings, heat exchanger orientation and sealing system were developed in detail with simulation and deliver the necessary cooling airflow to meet high temperature driving conditions. CFD testing optimized the amount and direction of airflow to minimize the parasitic cooling drag through the engine bay. The high-definition CFD model helped design the underbody splash panels and wheel liners. Pressure and velocity results from the computations showed the airflow interaction under the hood, how the panels contribute to aerodynamic drag and the areas where improvement could be effected. Further simulation focused on a venting strategy to reduce the drag while still allowing the splash panels to provide water protection to the Volt’s electrical components. Throughout the aerodynamic process, visualization and analysis from CFD explained complex airflow behavior and complemented the hardware development in General Motors Aerodynamics Laboratory

(GMAL). Engineers applied flow simulation to rank early studio themes and to compare the aero performance of the Volt’s styling features to those of its competitors. The review of simulation results during wind tunnel tests was a great communication tool to help designers understand why modifications to the clay surfaces led to changes in drag coefficient. CFD evaluation was also used when physical parts could not be obtained or fabricated in the clay models. When the Volt hits the showroom in late 2010, it will be one of the most aerodynamic vehicles on the road and GM’s lowest drag vehicle currently on the market. Designers and engineers worked hand-in-hand to deliver the necessary styling and aero performance to set the Volt apart from conventional cars. Hundreds of wind tunnel hours and thousands of computer CPU-hours were used in the development process. From the front grille openings to the rear trailing edge, all components exposed to airflow were studied. From start to finish, the Volt CD was reduced by 30%, providing an additional 7 miles of electric range.

Aerodynamic improvements added 7 miles of electric range to the Chevy Volt


high definition virtual models helped guide low-drag, vented splash panels. pressure contours are shown


Nina Tortosa, GM Aerodynamics Staff Email: Ken Karbon, GM Aerodynamics Staff Email: 27


Aviation’s Grand Challenge Worldwide societal demands are increasing for a step-change reduction in the negative impacts of aircraft fuel burn, emissions, and noise compared to the more gradual reductions achieved by modern aviation over the last few decades. NASA’s Environmentally Responsible Aviation Project has set out aggressive goals to enable these step changes. In this exclusive article for Wind Tunnel International, Fayette Collier, Project Manager, Environmentally Responsible Aviation for National Aeronautics and Space Administration (NASA) describes the innovative work that has contributed to substantial progress in meeting these lofty targets


AsA’s enVironMentALLY Responsible Aviation (eRA) Project goals include a fuel burn reduction goal of 50 percent relative to a current technology aircraft, a reduction of the oxides of nitrogen 75 percent below the current standard, and aircraft noise that is 42 dB below the fAA’s stage 4 certification level. These goals have a timeframe of the year 2020 for technical readiness of key technologies.

Identifying, assessing, and developing new technologies and aircraft configurations that are also promising enough to produce these step changes is a complex process requiring higher fidelity prediction, design, and testing methods including extensive wind tunnel and other ground test campaigns. 28

The Hybrid Wing Body (HWB) aircraft configuration has emerged as one aircraft concept that fundamentally has the potential to improve aerodynamic performance and to reduce noise. Developing the enabling technologies for the HWB has been one focus of an extensive effort by NASA and its partners in recent years. The enabling technologies for a viable HWB have been flight dynamics and a lightweight structural concept for the non-cylindrical pressure vessel. Technologies and specific configuration changes that develop the low noise potential of the HWB also will have performance impacts and will require a highly integrated solution in order to simultaneously achieve noise and fuel burn reduction goals. This article will briefly address these points and highlight some of the key ground test campaigns that are contributing to the progress to date. WIND TUNNEL INTERNATIONAL | 2010


BWB rotary balance test

TheX-48B at NASA’s Dryden Flight Research Center

Free-spin test of 1.1% dynamically-scaled BWB model in the VST

FLiGhT DYNAMiCS Addressing the HWB flight dynamics challenge involved a methodical series of wind tunnel tests followed by a set of flight tests, all on the same Boeing Blended-Wing-Body (BWB) configuration that is representative of the more general HWB class. The objectives of these tests were to: • Explore the stability & control characteristics of a HWB class vehicle. - Assess stability and controllability about each axis at a range of flight conditions. - Characterize departure onset. - Characterize post-departure and out-of-control modes of motion. 2010 | WIND TUNNEL INTERNATIONAL

- Assess dynamic interaction of control surfaces. - Assess asymmetric-thrust control requirements. • Develop and evaluate fl ight control algorithms designed to provide desired flight characteristics. - Assess control surface allocation and blending. - Assess edge of envelope protection schemes. - Advance the state-of-the-art in control theory. • Evaluate prediction and test methods for HWB class vehicles. - Correlate flight measurements with ground-based predictions and measurements. The first of the wind tunnel tests on this BWB configuration was a free spin-and-tumble test with a 1.1 percent dynamically scaled model in the Langley 20-Foot Vertical Spin Tunnel (VST). The objective of this test was to identify potential post-departure spin or tumble modes and explore recovery control combinations. The test was also used to develop an emergency parachute recovery system required for the planned higher-risk experimental flight testing outside the normal operating envelope. Following the spin and tumble test a rotary balance test was conducted on a 2-percent scale model in the VST. The objective of this test was to measure forces and moments under steady rotation for a large range of angle of attack, sideslip, and rotation rate. Data from rotary balance tests are used for analyzing subsonic rate damping characteristics, predicting spins, and for implementation of spin modeling in highfidelity 6-DOF (degree-of-freedom) simulations. The bulk of the BWB low-speed aerodynamic database was developed from a series of tests with a 3 percent scale multi-purpose model in the Langley 14- by 22-Foot Subsonic Tunnel. The basic static aerodynamic data were collected with the model on a post mount system. The test conditions covered the normal operating envelope. The test included individual and combined control effectiveness as well as the high lift slat geometry effects. With 18 control surfaces and the leading-edge slat the test matrix was extensive, requiring about 650 hours of tunnel time. Testing was also conducted with this same model at flight conditions beyond the normal operating envelope. A large angle test was conducted to evaluate the low-speed static stability and control characteristics of the configuration over the full range of angle of attack (±180°) and sideslip (±90°). These data were collected for use in simulation studies of the edge-of-the-envelope and potential out-ofcontrol flight characteristics. The model was mounted on a bent sting in four different positions (upright and inverted facing both forward and aft) to provide the full angle-of-attack range. The third in the series of tests with the 3-percent model in the Langley 14- by 22-Foot Low-Speed Wind Tunnel was a forced oscillation test. The model was mounted to a sinusoidal forced motion rig through 29


BWB 3% scale model in NASA 14- by 22-foot low-speed tunnel

BWB 3% scale model large angle test

a six-component strain gauge balance. The rig produces constant frequency and amplitude sinusoidal motion about the pitch, roll or yaw axes. The desired amplitude and frequency are set prior to each run. A limited set of combined control deflections were tested in both the slatextended and slat-retracted configurations. The data from this test was used to develop the dynamic derivatives for the simulation model. A follow-on ground effects test was conducted in the Swift Engineering 8- by 9-Foot Wind Tunnel. This tunnel has a rolling road ground belt with a top mount telescoping blade strut that allowed the angle of attack and height above the ground belt to vary. Testing was conducted in both take-off and landing configurations. A series of transonic tests were conducted in the NASA National Transonic Facility (NTF) and the Air Force Arnold Engineering Development Center (AEDC) 16-foot Transonic tunnel (16T). These high-speed tests were used to validate predicted cruise performance at near-flight Reynolds numbers, explore Mach effects on stability and control surface effectiveness and assess Mach tuck and buffet boundaries. The tests were conducted on a 2-percent scale model in both facilities. A free-flight test was conducted in the Langley FullScale Tunnel with a 5-percent scale model. The freeflight test technique uses a remotely controlled model flown unconstrained (except for the slack umbilical cable which houses the safety and electrical cables and the 30

pneumatic hose for the jet ejectors) in the tunnel test section. This technique, with a dynamically scaled model, provides a sixdegree-of-freedom, 1g flight environment for early evaluation of an aircraft configuration’s stability, controllability and flying qualities. It is particularly useful in flight regimes that are highly dynamic or difficult to model such as 1g departures, asymmetric thrust conditions or configuration transitions. The technique has also been used to evaluate flying qualities in dynamic environments such as formation flight or wake encounters. The free-flight model control laws were developed from the aerodynamic data provided from the previous 3-percent model tests. The control laws were designed to allow the model to be manually flown within the operating wind tunnel test section in all six degrees-of-freedom at a variety of speeds and angles of attack. The objectives of the freeflight test were to characterize the BWB 1g departure characteristics including the asymmetric thrust minimum control speed and evaluate the effectiveness of center engine lateral thrust vectoring. The free-flight test explored the minimum control speed at forward and aft center of gravity locations, with and without slats, and with symmetric and asymmetric thrust. The last of the low-speed wind tunnel tests conducted on this BWB configuration was in the Langley Full-Scale Tunnel on the X-48B. This test provided a rare opportunity to collect wind tunnel data on a flight test vehicle. In addition to the static aerodynamic data, the test was used to calibrate the airdata system and measure the control surface hinge moments. The low-speed wind tunnel tests culminated in the flight testing of the X-48B. The flight test vehicle recently completed its 80th flight. These flights combined with the vast wind tunnel data have fully addressed the all low-speed flight dynamic research objectives.

ADVANCED NON-CiRCuLAR STRuCTuRAL CONCEpT The goal of the structural concept development in ERA is to create a lightweight, manufacturable airframe that will withstand all flight and ground loads and satisfy all acoustic requirements for a HWB vehicle at an acceptable cost. In order to meet this goal, a new structural concept is being explored which will lead to a structurally efficient, light-weight airframe while meeting all FAA requirements for a transport aircraft. The outer surface shape of a HWB vehicle poses structural challenges that have to be addressed. In a traditional aircraft, the tubular fuselage is the pressure cabin. Cylinders carry pressure loads uniformly and the bending loads induced in flight cause welldefined structural requirements, which can easily be met using current state-of-the-art metal structure. The non-circular pressure cabin inherent in the center section of the HWB results in structural requirements not found in a traditional fuselage. First, pressurizing this region causes out-of-plane loads in the near-flat surfaces of the shell. One way to address that increased loading is to add more material; but that approach leads to a heavier structure. Second, the bidirectional loading in a HWB center section is not typical of the loading in a traditional cylindrical fuselage because there are similar stiffness requirements in both in-plane directions. Third, the HWB airframe will benefit from fabrication of larger components than the typical barrel section used today to produce a minimum number of joints and fasteners, thereby reducing the weight of the airframe, the number of parts to be assembled and the assembly time. NASA, the Air Force Research Laboratory (AFRL) and The Boeing Company have worked to develop new low-cost, lightweight composite structures for aircraft.



A new design and manufacturing approach called the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept has been developed which offers advantages over traditional metallic structure and is well suited to a HWB application.

STRuCTuRAL AND MANuFACTuRiNG ADVANTAGES In this concept a stitched carbon-epoxy material system is used. By stitching through the thickness of a dry carbon fabric, the labor associated with panel fabrication and assembly can be significantly reduced. When stitching through the thickness of pre-stacked skin, stiffeners, clips and other elements, the need for mechanical fasteners is almost eliminated. Because parts count is reduced, so too is structural cost. In addition, stitching reduces delamination and improves damage tolerance, allowing for a lighter structure with more gradual failures than traditional composites without throughthe-thickness reinforcement. The PRSEUS concept consists of carbon-epoxy panels fabricated from dry components and then infused using high temperature (but only vacuum pressure) so no autoclave is required. Skins, flanges and webs are composed of layers of graphite material forms that are pre-kitted in multi-ply stacks. Several stacks of the prekitted material are used to build up the desired thickness and configuration. Specimens are stitched together using Vectran fibers. Stiffener flanges are stitched to the skin and no mechanical fasteners are used for joining. To maintain the panel geometry during fabrication, first stiffeners and then the skin are placed in a stitching tool for assembly prior to moving to a curing tool for consolidation in the oven. Stiffeners running in the axial direction consist of webs with a bulb of unidirectional carbon fiber rods at the top of the web. Carbon fiber overwraps surround the bulb. The stiffeners in the lateral direction are foam-filled hats. (See sketch of the intersection of axial and lateral PRSEUS stiffeners and a PRSEUS panel.) PRSEUS provides a solution to problems associated with using either metals or traditional composites in a HWB center section. With the near-flat surfaces on the upper and lower cover panels subjected to cyclic pressure loading, the structure is loaded in fatigue in a manner not typical of circular fuselage sections. Long-term use of metals would result in fatigue-induced failure at the critical locations while, in a traditional, laminated composite, the large pulloff loads would lead to interlaminar failures such as delamination. To avoid out-of-plane problems, PRSEUS provides thickness reinforcement through the stitches. Often a bidirectional loading implies that a sandwich design should be considered, but thin sandwich skins are very susceptible to damage that may require repair, and would at least open a load path for moisture to penetrate the core of the sandwich. Any aircraft structure must be able to sustain low levels of damage in service. Minimum-gauge PRSEUS structures can withstand at least 45 ft-lb of impact energy at the critical flange-skin region without a reduction in load-carrying ability. Although this level of damage to a PRSEUS structure would be considered barely visible, the damage to a sandwich structure would be severe enough to require repair. In addition, sandwich structures require complicated pad-ups at most penetrations. For these reasons, PRSEUS is an excellent choice for a HWB and, in fact, is the only concept which meets all of the requirements for the structure today, which makes it an enabling HWB-vehicle technology. In addition, trade studies indicate that PRSEUS would be 10-percent lighter than its sandwich counterpart, plus the out-of-autoclave processing and simplified internal tooling makes PRSEUS an economical choice. 2010 | WIND TUNNEL INTERNATIONAL

Above (all images): Forced-Oscillation setup of 3% scale BWB model.



Ground effects test of 3% scale model in Swift Engineering tunnel BWB free-flight test in Langley Full-Scale Tunnel (images above and below)

Transonic BWB model mounted in the NASA NTF tunnel

Transonic BWB model mounted in the AEDC 16T tunnel

COMpONENTS TESTiNG AND EVALuATiON NASA and Boeing are employing the building-block approach to obtain the information required to apply PRSEUS to future aircraft. In so doing, smaller test articles are evaluated while larger, more complicated ones are designed, so lessons learned from these less expensive specimens can be applied to larger ones. In addition, the complexity of the loading conditions goes from unidirectional in-plane loading to complex combined loads. Currently, PRSEUS panels have been loaded in uniaxial tensile and compressive loading to verify the accuracy of analytical predictions of deformations, failure loads and crack arrestment. Additional unidirectional panel tests are to be conducted soon and tests to evaluate joints and repairs will follow. A cube is being designed with PRESUS panels on all sides to explore joint design and response under pressure loading. In addition, repair concepts are being studied to find practical and economical ways to address in-service damage and micromechanics models are being developed to better understand the behavior of adhesive bonds within the structure. The influence 32

of both discrete-source impact damage and of impacts like tool-drops is being evaluated. The structural evaluation of a 30-foot long multi-bay box representative of the center section of a HWB vehicle will follow the building block tests. This multi-bay box will be subjected to a series of loads to verify that it behaves as expected and withstands all required flight loads. Loading will include both pressure and mechanical tests where the pristine test article will be subjected to a combination of loads, and then it will be damaged at one or more critical locations through impact and/or discrete source damage, with the loading repeated. The displacements and strains will be monitored during each test and the results compared to analytical predictions. The design of test-article covers, bulkheads, interior elements and joints is now underway at Boeing. In addition, the tooling arrangement must be developed to support the manufacturing of the composite parts and the load introduction interfaces are being designed. The multi-bay box test article will be delivered to NASA Langley Research Center in less than two years and tested in the Combined Loads Test WIND TUNNEL INTERNATIONAL | 2010


The 21-foot span X-48B undergoing static balance test in the Langley Full-Scale Tunnel

System (COLTS) facility (see preliminary model of the multibay box test article). This structural development from coupons to elements to large-scale components will result in experimental evidence that a PRSEUS center-section will sustain the required loads for a flight vehicle. The current PRSEUS development is a continuation of work began under the NASA Advanced Composite Technology Program that focused on stitching development and lightweight structure for traditional aircraft. This work was continued by the AFRL and Boeing to develop the PRSEUS concept of the rod with the more unitized structure. Today the SFW and ERA projects are taking that development one step further by designing and testing more complex structures and subjecting them to more complicated, realistic loading conditions.

ACOuSTiCS To pursue ERA’s aggressive noise goal, the HWB configuration represents an unconventional aircraft concept that introduces fundamental changes that have the potential for the required significant step change. In 2010, an HWB with twin turbofan engines was modeled and a system noise assessment was performed. For the important and difficult-to-predict aft radiated noise sources, a key contribution to the system noise assessment was the use of experimental data from a large-scale integrated propulsion airframe aeroacoustic interaction experiment that was performed by NASA and Boeing in the Boeing Low Speed Aeroacoustics Facility. With this information, the baseline HWB aircraft with existing 2010 | WIND TUNNEL INTERNATIONAL

Sketch of pRSEuS panel assembly.

technology turbofan engines assessed at a level of 22.0 dB cumulative below the Stage 4 level. Cumulative noise level is the sum of the noise at the three certification points of takeoff (also called sideline), flyover, and approach. A configuration that included several near term technologies was developed in the experiment and assessed at 40.0 dB cumulative below Stage 4. This configuration consisted of engines placed two fan nozzle diameters upstream of the trailing edge for shielding. It included chevron nozzles and a pylon oriented in the crown position to reduce jet source noise and relocate jet noise sources upstream for more effective shielding. Also, on the crown pylon was an acoustic liner for additional fan exit noise attenuation. For the bypass ratio seven engine of this HWB configuration, the 33


Structural test component buildup

bypass ratio engines (approaching BPR 10) that are currently being introduced, this next configuration should be able to exceed the 42 dB goal by a considerable margin. It is now clear that a new configuration like the HWB does introduce a new paradigm for noise reduction. Even with its inherent potential, a low noise HWB must be designed from inception with noise as a goal in order to maximize the noise reduction especially including the propulsion airframe aeroacoustic technology developed simultaneously for source reduction and increased shielding effectiveness.


Centerbody pressurized multibay test article

jet noise remains the dominant component at both cutback and takeoff conditions and is a particular challenge because of the distributed sources. The total installation of the jet and combining of the pylon orientation at the crown with the aggressive chevron design was very effective at reducing the jet source level and increasing shielding effectiveness. Chevron technology has advanced rapidly in recent years for jet source noise reduction. The fact that chevrons can be effective at the combined objective of source reduction and relocating sources upstream, making the shielding more effective, opens a new design space for integrated pylon and chevron technology. The benefit of the crown pylon is especially valuable for its simultaneous impact on jet source relocation and fan exit noise attenuation. This study has also identified the importance of reducing landing gear noise at the source. An additional configuration projecting further noise reduction from the near-term technologies of quiet technology landing gear and from more advanced PAA chevron and pylon technology assessed at 42.4 dB cumulative below Stage 4, meeting the ERA project’s noise goal. The impact of this technology can be seen in the accompanying illustration, in terms of a ground contour of Sound Exposure Level from a single event landing and takeoff. The area within a noise level is calculated to be 66 percent less than that for a state-of-the-art (SOA) commercial large twin aircraft. Even more reduction could be obtained with a few more logical configuration changes. The location of the vertical surfaces can be moved outboard and the use of deflected elevons for additional shielding can be included. Since jet and landing gear noise would still be the dominant noise components, the technologies relevant to reducing these sources and enhancing jet shielding should be advanced further. And finally, considering a configuration that would include higher 34

Simultaneously meeting a fuelburn and noise-reduction target is extremely challenging because many of the key technologies are not synergistic, i.e., noise reduction technology can actually increase fuel burn and vice versa. For example, acoustic liners add weight thus increasing fuel burn while reducing noise. Or, open rotor propulsion technology can significantly reduce fuel burn, but at the cost of increased noise. Predicting these complex interactions is also a challenge, but is necessary to enable informed technology investment decisions, and to track progress towards meeting fuel-burn and noisereduction goals. In order to analyze these interactions, the first step is to create a technology database. The database attempts to capture all relevant technologies with appropriate Technology Readiness Level (TRL). A technology compatibility matrix is then populated to identify both synergistic and conflicting interactions among all of the potential technologies. Based on the compatibility matrix, a large set of technology packages are defined, containing synergistic sets of technologies. Next, several advanced concepts are identified, such as advanced tube-and-wing, and hybrid-wing-body concepts.



hybrid Wing Body propulsion airframe aeroacoustics experiment in the Boeing Low Speed Aeroacoustics Facility (LSAF). (Boeing photo)

These advanced concepts, called “technology collectors�, are utilized as analytical test beds on which all possible combinations of the technology packages are installed and assessed. An integrated set of analysis tools is utilized to perform this assessment. These tools include propulsion cycle and flowpath modeling, aerodynamics, structures, aircraft performance and noise prediction. Utilizing this integrated toolset in an automated process, a large design space is then created mapping out the performance potential of these advanced concepts. This design space illustrates the trade-offs between noise and fuel-burn reduction. By examining the design space, the optimum technology collector and associated set of technology packages can be

In the near future will be the structural evaluation of a 30-foot long multi-bay box representative of the center section of a HWB vehicle. This multi-bay box will be subjected to a series of loads to verify that it behaves as expected and withstands all required flight loads. And finally, a technical path for a low noise HWB has been developed and validated

The key technology hurdles for the HWB have been addressed including the flight dynamics and a light weight structural concept. All low-speed flight dynamic research objectives have been accomplished through an extensive set of wind tunnel SuMMARY and flight tests. A low cost, light weight Achieving simultaneously the fuel structure for the HWB concept is being burn, emissions, and noise reduction goals enabled by a new design and manufacturing of the ERA project represents a grand approach called the PRSEUS concept. To challenge for aviation. NASA and its partners date, PRSEUS panels have been loaded in have advanced the HWB aircraft concept uniaxial tensile and compressive loading to together with integrated technologies verify the accuracy of analytical predictions and p r o p u l s i o n of deformations, failure loads and crack technologies as arrestment. Additional panel tests to evaluate a p r o m i s i n g joints and repair concepts are being studied to approach that find practical and economical ways to address could achieve the in-service damage issues. step change In the near future will be the structural represented by evaluation of a 30-foot long multi-bay box the goals. representative of the center section of a HWB vehicle. This multi-bay box will be subjected to a series of loads to verify that it behaves as expected and withstands Above: hybrid Wing Body (hWB) Technology Collector all required flight loads. And finally, a Calculated sound exposure technical path for a low noise HWB has been levels (SEL) for a simulated landing and takeoff for a state- developed and validated. of-the-art (SOA) twin engine In sum, the key technology paths are in commercial transport and for a low noise hWB aircraft concept development showing progress of the HWB concept and integrated technologies to meet the ERA goals simultaneously. Dan Vicroy, Russell Thomas, Craig Nickol, Dawn Jegley also contributed to this article. The authors retain copyright to all materials, and give Wind Tunnel International permission to publish/distribute this article.

identified. The results of this analysis can be used for technology investment planning and for tracking progress towards meeting the fuel-burn and noise reduction targets simultaneously.




The Art in Aerodynamics How the convergence of aerodynamics and automotive styling/design is handled at Coventry University’s School of Art and Design. Study of Wind Tunnel International’s first edition was required reading. By Dr. Geoff Le Good, part-time lecturer at Coventry University and past aerodynamics specialist for Aston Martin, Bentley and Rover


n the world of automotive aerodynamics it remains t r ue t hat wh ilst t he cont r ibut ion of nonstyled surfaces, such as underfloors, is important, it is the exterior style which sets the main characteristics of aerodynamic performance.

This immediately emphasises the inextricable link between Design and Aerodynamics and, without wishing to debate aesthetics and the concept of “form follows function”, it is possible for styling and aerodynamics to be complementary - as witnessed by the streamlined designs of the 1930s and 1950s and 36



Design, Build, Test:  2nd Year Coventry university Transport Design Students 2009-10 try a variety of creative approaches to meet the brief of their Aerodynamics group project

perhaps less obviously so by some modern cars. Within automobile manufacturers, aerodynamicists are responsible for test and development but it is the designer who has control of the exterior geometry which delivers that aerodynamic performance. Thus an understanding of how changes in shape and form influence these key attributes has become essential for designers and this is also the aim of the Aerodynamics module contained within the second year of the internationally renowned Transport Design course offered by the Industrial Design group within the Coventry University School of Art and Design. The course, which began in 1972, continues to evolve with the introduction of new technologies but the basics of sound design remain the foundation, supported by significant ergonomics and engineering content to help students ensure that their design concepts are innovative and feasible. The Aerodynamics module comprises a series of lectures and wind tunnel demonstrations together with an assessed group-project. The lectures include the basics of fluid mechanics, flow around bluff bodies, vehicle aerodynamic characteristics, the influence 2010 | WIND TUNNEL INTERNATIONAL



of aerodynamics on vehicle economy, emissions and handling as well as test techniques using wind tunnels and computational fluid dynamics (CFD). Hucho’s “Aerodynamics of Road Vehicles”, Barnard’s “Road Vehicle Aerodynamic Design” and “Streamlined – A Metaphor for Progress” edited by Lichenstein and Engler are suggested as principal texts. Students are also encouraged to read about the most up-to-date technologies and applications of aerodynamics in other fields. In this respect the timing of the publication of the first edition of Wind Tunnel International magazine was perfect to support the 2009-10 module and was added to the required reading list. The feature on the new BMW Wind Tunnels was of great interest and discussed in both the first and final lectures. The highlight of the module remains the group-project which includes the opportunity for students to build models of their own design and conduct force and moment tests using the University’s Low-Speed Wind Tunnel. The tunnel is of the closed-test-section (0.759m2), closed-return type design and for automotive testing a ground-board is inserted into the working section which contains a 6-component strain-gauge balance turntable. Test speeds are up to 50ms-1. The physical characteristics of the tunnel limit students to approximately 1/10th scale models but these have the advantage of being easy to build, relatively inexpensive and enable shape-changes to be made very quickly by the use of interchangeable parts or by sculpting surfaces in foam, modelling-wax or clay. Flow visualisation is conducted using a dedicated smoke tunnel. Despite this being small in section and with a low wind speed, a multi-probe smoke-rake provides a good opportunity for students to assimilate their measured data with observed flow regimes. The theme for the group-project changes each year. For 2009-10 students were given a rudimentary set of package requirements, a common floor-pan and wheel design, some restrictions on overall dimensions and then challenged with morphing a rectangular block of foam, which was the set baseline style, to yield an optimised body-shape with the minimum sum of weighted coefficient data for drag, lift, lift-balance and yawing moment. 38

Examples of model build and testing during the Spring of 2010 are illustrated. In each year of the group-projects, students have requested more wind tunnel time, which is indicative of their enthusiasm for, and perception of, the importance of aerodynamics. They often remark that it is when they see the results of their own shape-changes in the measured data and smoke tests that they begin to fully understand the principles shown during the lectures. Perhaps their appreciation of three-dimensional form gives them an advantage but many of these young designers rapidly pick-up a “feel” for flow around vehicles in a way that perhaps fewer engineers manage despite their technical background. Undoubtedly there is art in aerodynamic design and this is based on an innate feel for shape and flow as well as technical knowledge. Thus at Coventry University it is entirely appropriate that future designers from the School of Art and Design have the opportunity to blend the principles of aerodynamics with their early design training. CONTACT Geoff Le Good, Coventry university School of Art and Design E-mail: WIND TUNNEL INTERNATIONAL | 2010


Space-Age Education by Space-Age Means

Jack Gilbert with Flotek 1440 wind tunnel

While teaching at an Aviation High School, Jack Gilbert found that the study of aerodynamic principles fascinated his students. Many of his students could grasp math and science concepts if there was a real world connection to the formulas. Surprisingly, many aerodynamic formulas only require simple algebra. But how many schools can afford a wind tunnel? None needs to now, as Gilbert and his company MechNet have developed an educational initiative where students design and operate their own wind tunnel experiments using remote Internet control of MechNet’s tunnels. By Jack Gilbert, MechNet Inc.


echnet inc., of Mentor, Ohio, is starting a new and innovative service to allow schools and universities to operate research grade wind tunnels via the internet to support sTeM (science, Technology, engineering and Math) education.

Using a wind tunnel may not seem like an obvious tool to teach basic math formulas but surprisingly many of the formulas only require simple algebra: for instance, the continuity equation used with a venturi is as simple as V1 x A1 = V2 x A2. This gains the students interest and gives them the confidence to continue with more and more complex math. Some of the more advanced lessons are calculus-based. The important thing is that now the math becomes a tool to solve a problem. True engineering involves first asking the question, “What do I want to achieve?” - followed quickly by the question, “What do I need to learn before I can answer the first question?” At this point many students may see a true need for learning how to do a particular math formula even though they are not currently achieving at a high level in math class – as a first step to understanding why the math is important. In order to be successful, an engineer must not only have the knowledge of many separate concepts, but also the ability to integrate 2010 | WIND TUNNEL INTERNATIONAL

these concepts into a practical understanding. Considering and applying these concepts provides students with an understanding of science and engineering so they can make an informed choice about the suitability of a career in that field. This type of instruction also makes engineering fun, making it more likely they would consider a career in science and engineering. To provide data with the degree of accuracy required to conduct math formulas requires that the wind tunnel and data acquisition system are of research quality. The wind tunnel must produce a laminar, low turbulence air flow and all of the instrumentation must be extremely accurate. Unfortunately the cost and difficulty to operate these systems makes the operation of a wind tunnel on site infeasible for many schools. Operating the wind tunnels remotely solves this issue since the schools will only pay a low hourly fee for the time they are actually operating the wind tunnel. Plus the wind tunnel will be completely configured for the test they have requested. The schools will not be required to change models and reconnect all of the complex instrumentation tubing required. Multiple FLOTEK wind tunnels by GDJ Inc. will be equipped with a wide range of models such as wind turbine blades, different NACA profile airfoils, venturis, golf balls, and so on. An instructor will be able the show the difference in lift data between a NACA 4415, NACA 39


Flotek 1440 with NACA 4415 airfoil - Labview computer screen is displaying real time data from test in progress

NACA 4415 with Tuffs showing rear section of airfoil in stall condition while the leading edge is still in laminar flow


2415 and NACA0015 airfoil by just logging into a different IP address. They actually could operate two wind tunnels at once and show the data difference on two monitors simultaneously. The wind tunnels will interface to a state-ofthe-art system based on National Instruments hardware and LabVIEW, which will control the wind tunnel and display performance data. The application was developed by Viewpoint Systems. With this system the experience of operating the wind tunnel remotely, will be the same for the students as if they where in the same room as the wind tunnel. Interactivity will include adjustable test section velocity and airfoil angle attack giving the student complete control of the experiment. By adding audio and video the students will be able to actually see the effects of stall on airfoil as the angle of attack is increased. A side benefit of this process is that the ability to remotely control a device located in another distant location may well be more exciting to the student than a device that is immediately in front of them. Wind tunnels will also be made available for students to send models to Mech-Net for testing. Students will make their own wind turbine blades, 1/10th scale car bodies and other experiments. Once the experiment is mounted they will log in and conduct the experiment in real time on their own model. WIND TUNNEL INTERNATIONAL | 2010


DATA ACQuiSiTiON AND CONTROL SYSTEM The National Instruments platform selected for data acquisition and control was the CompactRIO. This platform was perfectly suited since it offered the requisite size, channel count, signal conditioning, and realtime control capabilities. The NI CompactRIO programmable automation controller (PAC) is a low-cost reconfigurable control and acquisition system designed for applications that require high performance and reliability. The system combines an open embedded architecture with small size, extreme ruggedness, and hotswappable industrial I/O modules. CompactRIO is powered by reconfigurable I/O (RIO) fieldprogrammable gate array (FPGA) technology.


NACA 4415 with Tuffs illustrating laminar flow

WiND TuNNEL DESiGN The tunnel hardware was designed in conjunction with NASA Glenn Research Center in Cleveland, Ohio to provide ultra-low turbulence, straight-line (laminar) air flow, permitting true aerodynamic engineering, data acquisition and analysis. FLOTEK wind tunnels bring advanced aeronautic design principles to the high school and college laboratory. The standard models are the FLOTEK 1440 wind tunnel with 12’ x 12” x 36” test section where air flow velocity can reach up to 185 mph and the Flotek 360, with a 6” x 6” x 18” test section.. The tunnel is fitted with a 20-tube manometer for enhanced visual reference with a two-component balance-beam for measurement of drag and side force. Larger custom wind tunnels will be used for student based model testing. A wind tunnel with a round test section is being developed for wind turbine blade testing.

National instruments Labview Screen developed by Viewpoint Systems used to remotely control the wind tunnel while retrieving real time data


The software was written in LabVIEW Realtime and LabVIEW FPGA by Viewpoint Systems, of Rochester, New York, a Select Partner of the National Instruments Alliance program ( We had looked at some other solutions for remote lab control, but they didn’t provide the tight closed loop control needed for other applications we provide, such as engine dynamometers. The application allows real-time display of up to 16 readings of pressure and velocity over the test model while controlling the angle of attack and fan RPM. An airfoil stepper motor controller allows for computer control of the airfoil angle of attack from a slide bar on the Remote Panel and an additional stepper motor will be used to raise and lower a yarn streamer for visual enhancement. All sensors and control actuators are calibrated for accuracy. Operating the wind tunnels over the Internet allows access to expensive research grade equipment at a very affordable cost. Schools will not have to maintain the equipment or change models. By combining the powerful feature-set of the CompactRIO and FPGA technology and the NI Remote Panel capability, the system is able to meet the needs of STEMbased education. Educators and students from all over the world can now log-on and deliver classroom instruction with real-time data and presentation of a model wind tunnel operating without the hassle of owning and maintaining one. This system also provides an excellent opportunity for a business to provide an outreach program for their local school. A business can provide cutting edge technology to their local school with little or no actual time investment on their part. CONTACT Jack Gilbert, MechNet inc. Email: Website: 41


pilot approaching Malpensa airport in a Tiltrotor simulator at NLR, controlled by the ATC simulator operated by Sicta in Naples (photo: NLR)

The Model with The Most Smarts

The European rotorcraft industry and its partners are currently working on various research aspects of ERICA (Enhanced Rotorcraft Innovative Concept Achievement), a hybrid tiltwing/tiltrotor concept. The level of complexity of this research model in the field of remotely controlled systems, powered rotor simulation and embedded sensors is far beyond wind tunnel models developed so far. Joost F. hakkaart of The Netherland’s National Aerospace Laboratory (NLR) explains


his ericA research is partially

f unded by the european commission in the sixth framework program: NIceTRIP (Novel Innovative competitive effective Tiltrotor Integrated Project) and the design is intended to overcome many of the operating and performance limitations associated with traditional tiltrotor designs. The planned 10-tons transport aircraft will have small-diameter prop rotors to allow running take-offs, outer wing sections that will tilt independently of the nacelles to reduce rotor downwash, and a continuous tubular structural connection between the prop rotors. 42

Calculated instantaneous pressure distribution on the ERiCA rotor and wing (illustration: NLR / Agusta)



Recently, successful first pilot-inthe-loop simulation studies were conducted by NICETRIP partners to evaluate the introduction of tiltrotors in the European Air Traffic Management system. The NLR Helicopter Pilot Station (HPS), in cooperation with the Sphere EUROCOPTER Simulator, the HeliFlight University of Liverpool Simulator and the SICTA control tower simulator, was involved in an integrated scenario to evaluate specific non-interfering tiltrotor ATM concepts and procedures. To reduce future risks on the critical technologies, like the tiltrotor aerodynamic interaction and rotor performance, a complex large scale research model has been developed on scale 1:5 by NLR for future wind tunnel testing in strategic European wind tunnels.

Based on the validated CFD results, further simulations have been performed to provide aerodynamic data and insight into the aerodynamic behavior of the complete aircraft in terms of drag and interference characteristics for the configurations to be tested in the wind tunnels. These simulations have been performed by the aforementioned research institutes as well as POLIMI (Italy). The applied wind tunnel model scale, in combination with the other requirements, did not allow representing a gimbaled rotor. The model rotor with collective and cyclic setting is stiff in plane. Therefore, flight mechanics models are adapted to include the hub configuration of the experimental rotor system and are used to predict the trim parameters for the wind tunnel test conditions.



instrumentation of the NiCETRip model rotor at NLR. Remote control units for flap and flaperon are shown on the foreground. (photo: NLR)

In order to prepare the wind tunnel testing, aerodynamic simulation Within the NICETRIP project a NLR-designed full-span large scale of the tiltrotor aircraft has been conducted to mitigate the risk of the powered wind tunnel model has been manufactured to prove the wind tunnel test campaign. The simulations help to define critical ERICA concept liability with respect to low speed interaction and high flow configurations. speed performances so that, in turn, the general architecture, flight In order to consolidate and validate the simulation codes for flight control system and laws and operational performance can be “frozen�. mechanics, aerodynamics, aeroacoustics and performance, hover The research model has a central gearbox with two out-going drive to forward flight conversion conditions are simulated with several shafts which are each connected to a gearbox in the relevant nacelle. advanced CFD methods. CFD calculations have been performed by the Two stiff rotors are mounted on these gearboxes via rotor balances participating European research institutes CIRA (Italy), DLR (Germany), (supplied by Onera). The rotors are equipped with swash plates NLR (Netherlands) and Onera (France) and were analyzed by the enabling remotely controlled setting of both collective (with a total Industries AgustaWestand (Italy) and Eurocopter (France). range of 80 degrees) and cyclic blade pitch. Both outer wing and nacelle The CFD method of NLR is capable of representing the combination can be tilted independently, consistent with the ERICA configuration. of the rotating propeller and the fixed wing, by applying the sliding To enable efficient tunnel operation, without the need to stop the grid approach. In this approach, wind tunnel for model configuration changes, all control two grid systems are used, being surfaces (two flaps, two flaperons, rudder and aileron) are a rotating system about the rotor remotely controlled by advanced compact units developed and a fixed system about the wing, at NLR. The hinge moments of these control surfaces are with a non-overlapping interface. measured separately. The loads on the T-Tail are measured Flow states are interpolated on with a dedicated six component balance mounted in the aft the interface. The computations fuselage. Several of the external model contour parts have are compared with the results of been manufactured by TsAGI (Russia) and were integrated previously available wind tunnel at NLR. The model is furthermore equipped with a large experiments, which have been number of static pressure ports (672). The distribution of executed for the wing/nacelle/ the ports is determined such that it will allow integration of rotor configuration in flight the pressures to calculate the loads on outer and inner wing conditions ranging from hover, Function testing and calibration under simulated aerodynamic separately. Furthermore 54 dynamic pressure transducers loads of the elevator remote control with hinge moment balance. through conversion, to cruise (photo: NLR) are included to study unsteady flow behavior. mode. The calculated blade pressures for this validation case agree well with the experimental blade pressures, whereas the wing pressure comparisons are satisfactory. Deviations between simulated blade pressures and experimental blade pressures are attributed to the inviscid flow model assumption of the simulation and known uncertainties in the experimental results. Through the successful simulation of the tiltrotor/wing configuration during conversion it has been demonstrated that the sliding grid approach is capable of vortex convection through the interface. NiCETRip model assembly and functional demonstration during delivery at DLR-Braunschweig (photo: DLR) 2010 | WIND TUNNEL INTERNATIONAL



For safety-of-flight monitoring, the rotor blades are instrumented with strain gauges for measuring the blade bending and torsion. Likewise, temperature sensors are used to monitor the gearbox operating conditions. The model is equipped with three compact 48-channel amplifiers (developed by DLR) to supply independent sensors and to boost their output signals to be transmitted over the long cables towards the data acquisition unit. The level of complexity of this research model in the field of remotely controlled systems, powered rotor simulation and embedded sensors is far beyond wind tunnel models developed so far. During the 2.5 year development period, approximately 50 NLR employees spent over 20,000 man hours producing 171 CATIA drawings, 23 wiring diagrams, and installing 2.5 kilometers of pressure tubing, 70 pneumatic connectors, 5 kilometers of electrical wires and about 300 electrical connectors. To limit the amount of wires and tubes to be fed through the wind-tunnel sting, onboard acquisition systems are applied and wiring and tubing is combined as much as possible. Furthermore, the integrated EPOS2 remote control drive units are combined in two Can busses: three actuators of both rotors are connected to the pilots HMI via the first Can bus; while the surface control system, which connects the ten remaining actuators to the control PC, are grouped to the second Can bus. Having completed the wind tunnel model integration and sensor system wiring, function tests and calibrations were performed. During this phase the proper functioning of the remote controls was validated by applying the expected aerodynamic load.

Wind tunnel test and the preparation phase After delivery of the research model by NLR to the project coordinator AgustaWestland, DLR is now performing extensive pre-test at their rotor test stand in Braunschweig (Germany). Besides preparing and testing the control software, instrumentation calibrations are validated after integration in the DLR data acquisition system. Before spinning the rotor the first time up to full rpm, ground vibration tests (GVT) were performed by DLR for the Identification of the structural behavior (Eigen frequencies, mode shapes, etc.). During these tests, 107 acceleration sensors were installed to completely observe the structure in the frequency range up to 200 Hz with special focus on nacelle and outer wing movement. Although about 55 modes in the frequency range from 0 to 200 Hz were detected, no un-damped modes are found. After completion of the preparatory activities at DLR, model installation in one of the preparation halls of the DNW large low speed wind tunnel (DNW-LLF) will start. In this phase, the model will be mounted on an internal balance equipped with an airline bridge for powering the air motors driving the central gearbox. During this final preparation phase, the model will be tested with high thrust and GVT tests will be repeated on the final sting configuration. Wind tunnel testing will start early 2011, after model acceptance by the coordinator of the NICETRIP project. The first test phase will be performed in the DNW-LLF (tiltrotor 44

NICETRIP powered wind tunnel model mounted for pre-testing by DLR. (Photo: DLR)

How To Get Smart NLR (The Netherlands’ National Aerospace Laboratory) has made the development of “smart” wind tunnel models a specialty. Jan van Twisk, Department Manager, Engineering & Technical Services at NLR, reviews their latest and future developments in smart models Typical examples of smart models are those with rotating systems like propellers/ fans or rotor systems, models with remotely controlled parts like flight controls, models with special instrumentation like balances or dynamic pressure sensors, and cryogenic models. Of these areas, those dealing with powered propeller simulation systems, both for single-propeller and counter-rotating open-rotor testing, is still of particular interest, and was covered in Wind Tunnel International’s 2009 issue. In this article, we’ll cover NLR’s developments of remote control (RC) systems for wind tunnel models. Wind tunnel test campaigns that require many (flight control) configuration changes, like high-lift systems testing or stability and control testing, can be very inefficient due to the many non-productive down-times needed for mechanical model configuration changes. Depending on the hourly cost of the wind tunnel and the accessibility of the tunnel, the resulting costs of these type of test campaigns can be very high. For quite some years, NLR has continued the development of a number of standard concepts for remote control (RC) systems to drive the control surfaces and highlift devices of wind tunnel models, as well as mechatronic technologies for various applications to support these remote control systems. These concepts allow configuration changes in seconds rather than minutes or, in some cases, hours and, depending on the type of wind tunnel, can be a very effective means for reducing the overall wind tunnel test cost. Every RC system consists of a drive unit, a kinematic mechanism, a position sensor and a control system. NLR prefers self-braking RC systems, which are able to take the full (aerodynamic) load without giving (some) way. In cases of extreme loads, however, a separate brake may still need to be added as an integral part of the complete RC system. At NLR, the selected drive unit (motor) is usually of a commercially available electromechanical type. A kinematic mechanism is required to convert the mechanical output of the motor into the (rotational) movement of the model part, and is of specific NLR design, being very dependant on the model requirements. Position sensor and RC control system are either selected from commercially available products or specifically designed by NLR. The total integration as a complete RC system in the model is again of specific NLR design, depending on the model requirements and available model space. For low speed models, where loads are relatively low and available space relatively large, NLR can supply virtually all required RC systems for rotating or hinged model parts. WIND TUNNEL INTERNATIONAL | 2010


helicopter mode and conversion corridor at low speed, incl. ground effect). Three different sting configurations will be used, including a vertical mounting of the model for interference free hover testing and studying autorotation and vortex ring state conditions. The second phase of the test will be performed in the Onera Modane S1 wind tunnel (aircraft mode at high speed up to M=0.6). Including so many sensors, equipment and technologies in one model as well as the thorough pre-test phase, results in the smartest and most complex wind tunnel model ever developed. CONTACT Ir. J.F. (Joost) Hakkaart, National Aerospace Laboratory - NLR Email:

Ground Vibration Tests performed by DLR with the NiCETRip model (photo: NLR)

high speed model of air refuelling boom with remotely controlled wing

Remotely controlled rotor head for tilt rotor model

Wind tunnel model tail section with remote control systems for elevator and rudder for low speed pressurized wind tunnel

Remote control unit with four independently controlled canards for high speed missile model

Aileron remote control system for low speed wind tunnel

Usually, sufficient space for RC systems is available in the fuselage of the model, but this may interfere too much locally with other space requirements. To avoid this interference, NLR has developed a complete range of elevator, rudder and aileron remote control systems that can be integrated in the (usually) relatively thin horizontal stabilizer, vertical fin and wings of the model. These various RC systems are all based on the same common design concept. They have been developed through thorough prototyping and testing to assure absolute reliability before being cleared for industrial applications. These type of RC systems have already been applied successfully in various models, the recent Nicetrip tiltrotor model being one of them. This model features 17 RC systems in total for driving the various control surfaces and both rotor heads (see main article). Also, specific RC systems have been developed for high- and lowmounted horizontal stabilizers, for canards, for missile steering fins and for other unique applications. Although these systems also rely on standard design principles, their applications are very much tailored to the specific models due to their specific integration requirements. In principle, this common low speed concept is also available for transonic and higher speed models but, in these applications where loads are usually higher and available space smaller, applications are more critical and unique. The most critical RC systems are those for pressurized and cryogenic wind tunnel models. The loads are high, space is limited and the large cryogenic temperature range (115 - 300째K) through which they have to operate reliably makes the design even more challenging. 2010 | WIND TUNNEL INTERNATIONAL

Family of remote control systems for aileron, elevator and rudder

Demonstrator of hydraulic remote control system for cryogenic applications

Rudder remote control system on calibration rig

Remote control system in cryogenic test box

At the same time, addressing the challenge is well worth while since pressurized and, even more so, cryogenic wind tunnels are very inaccessible, causing model configuration change times of many minutes or even hours. Thus, it is obvious that cryogenic RC systems have an enormous cost saving potential. Few cryogenic applications have been achieved, so more development in this area is required and a cooperation agreement was signed on the 27th of February 2009 between NLR and ETW, the European Cryogenic wind tunnel in Cologne, Germany, for the joint development of remote control systems for smart cryogenic wind tunnel models. Since then, a concept has been designed for a RC mechanism that will drive a control surface like an elevator/rudder/aileron using the available space in the stabilizer/wing. A demonstrator will be built and tested this summer. If successful, this concept will also be usable for transonic applications at ambient atmospheric conditions. Traditionally, the motors of RC systems have been of the electromechanical type, but also systems based on hydraulic and piezo-electric motorization have been examined and will be studied further. Also studies will be continued on RC system applications for non-rotating parts, like sliding or translating flaps and slats. Just like for low speed models, also for high speed models standard reliable concepts will be developed in the coming years for the various requested research and industrial applications. CONTACT J. (Jan) van Twisk, National Aerospace Laboratory - NLR Email:



insulated walls being installed in test section


Return leg of circuit from Corner 2 to Corner 3

New Benchmark Under Construction The University of Ontario Institute of Technology (UOIT) recently completed the construction of the new Automotive Centre of Excellence (ACE) on its Oshawa, Ontario campus. This is the first commercial research, development and innovation centre of its kind in Canada and, in many respects, the world. The facility is owned and operated by the university and is specifically focused on fostering collaboration between entrepreneurs, engineers, researchers and students. Gary M Elfstrom and John A Komar of UOIT give a deep insight into the facility and its capabilities as startup and commissioning are under way.


ce is a multi-level centre with an area of approximately 16,300 square metres and was developed in partnership with uOIT, General Motors of canada ltd. (GMcl), the Partners for the Advancement of collaborative engineering education (PAce), the Government of Ontario and the Government of canada. The total cost of the facility to date is $99 million (cdn).

ACE is a one-stop-shop with a full range of testing facilities, research labs and offices under one roof. The flagship chamber is the climatic wind tunnel (CWT). It has a mandate to provide automotive manufacturers (OEMs), Tier 1 suppliers and university researchers with an independent test capability, to validate prototype car, truck and bus thermal operation under a full range of climatic conditions. This is a model which has precedence with Tongji University in China, University of Stuttgart in Germany and RMIT in Australia. Aiolos Engineering Corporation, an international supplier of design, construction, and commissioning services of climatic and other facilities for global customers, has worked collaboratively with UOIT on all aspects of facility realization, from test definition to design, construction, and subsequent commissioning. 46

There is a dearth of facilities with a large enough nozzle size for bus and large truck thermal testing in North America. Until ACE, there was none within Canada. Furthermore, none of the existing facilities was truly independent of OEM and Tier 1 suppliers. The capital and operating cost of running a CWT large enough to accommodate bus testing at relatively low wind speed while also accommodating car testing at high wind speed would be prohibitive, and so an extensive trade-off study was made to examine cost-effectiveness of various alternative configurations. The end result of the trade-off studies was: • Full thermal testing, static and dynamic, of cars and SUV’s would be accommodated in a CWT facility with a nominal nozzle size of 9.3m2 • Full thermal testing of large trucks and buses would be accommodated using a larger nozzle size with a reduced wind speed • Static thermal testing of large trucks and buses would be accommodated in two static test chambers. Related thermal and acoustic chambers would accommodate Noise, Vibration and Harshness (NVH) testing. An extensive facility development phase was then conducted to arrive at a CWT which would be unique and have provision for growth. The key aspects of the CWT final design include: • Temperature range -40°C to +60°C; humidity range 5% to 95% relative humidity (RH) • Wide speed range (-16 to 240kph) for automobile full climatic testing using a variable nozzle (7.0m2 to 9.3m2) • Maximum variable nozzle size (up to 14.5m2) at reduced wind speeds and long test section (14.8m) to enable climatic testing of trucks and buses • Flow conditioning and variable nozzle aerodynamic design to provide exceptionally high flow quality for WIND TUNNEL INTERNATIONAL | 2010


Wind tunnel circuit

advanced thermodynamic testing, with provision for improved flow quality commensurate with aerodynamic testing • Circuit acoustic treatment suffi cient to provide low background noise level (71dBA at 50kph) to permit detection of vehicle drive away anomalies, such as misfires, transmission hesitation, etc. • Boundary layer management scheme including a 5.25m-wide scoop-type primary removal system at the nozzle exit and provision for a distributed suction secondary system • Unique 11.7m-diameter turntable incorporating a chassis dynamometer with four independently powered rolls, to provide climatic testing at yaw and to enable long wheelbase tandem axle Class 8 truck testing.

Test section showing adjustable nozzle at 7m2

pERFORMANCE SuMMARY Accompanying figures show the wind speed versus air temperature requirements and the humidity capabilities for various temperatures that the CWT has been designed to meet.

Test section showing adjustable nozzle at 13m2 setting with yaw.

FLOW AND ThERMAL uNiFORMiTY SuMMARY The expected flow, temperature and humidity uniformity in the core region exclusive of the shear layer region are as follows (1 sigma): • Wind speed: 1% of set point • Flow angularity: 0.5° • Temperature: 0.3°C • Humidity: 0.5°C (dew point) The targets for wind speed, temperature and humidity stability are given as follows: • Wind speed: ±0.5kph • Temperature: ±0.2°C at velocity > 48kph • Humidity: ±0.5°C (dew point)

Test section with adjustable nozzle at 5m width and nozzle ceiling raised.

WiND TuNNEL CiRCuiT The airline for the CWT was kept as compact as feasible, keeping in mind the following key goals: • Test section length should be suffi cient to allow limited thermal testing of long vehicles and to minimize the influence of axial static pressure gradient for aerodynamic testing • Test section height and width suffi cient to accommodate by-pass flow during idle/city testing and to accommodate a large solar simulation system • Inclusion of suitable acoustic treatment to reduce the background noise level at low wind speeds The test section configuration was chosen as follows: • Overall dimensions: L20.1m x W13.5m x H7.5m • Front wheel dynamometer axle located 3m from the nozzle exit plane • Turntable centerline: 6.1m from nozzle exit plane • Support provisions to add anechoic treatment to insulation panels • Mounting provision to incorporate an adjustable collector 2010 | WIND TUNNEL INTERNATIONAL

• Structural support rail provisions for gantry (probe) in test chamber floor The settling chamber has the following aerodynamic features: • Main heat exchanger is located at the downstream end of a wide-angle diffuser • Aerodynamic flow quality in the largest nozzle test section will be achieved by having a moderate contraction ratio (5.54), two flow conditioning screens and provision for a deep-cell honeycomb flow straightener • Idle-city testing is accommodated using a by-pass fl ap in the contraction together with re-injection into the test section at the upstream wall. The main fan, 4.85m diameter, has a rated power of 47


Wind speed vs temperature

inside variable nozzle

There are two configurations of snow simulation possible: frontal and overhead. In both cases, snow guns are used to create the snow.


humidity vs temperature

2500kW continuous, with excursions to 2900kW on a limited duty cycle basis to accommodate the wide range of operating conditions. A wide range of vehicle types and sizes can be accommodated by the turntable and variable nozzle, as shown by the artist’s renderings.


The CWT is designed to accommodate hydrogen-powered vehicle testing: • Hydrogen is plumbed into the CWT from a trailer located outside directly to the test vehicle’s engine or fuel cell, thereby bypassing the onboard fuel tank • Safety: appropriate electrical class codes are followed, including a separate purge system for the ceiling area • Fire fighting: Supersonic water misting system in the test section, and vehicle on-board fire extinguishers, to supplement conventional water sprinklers Additionally, high-power outlets are available for plug-in hybrid and electric vehicles. The CWT has the many ancillary systems included in the design, such as: • Purge systems (2) to accommodate lighter-than-air fuels, such as hydrogen and conventional fuels such as gasoline • Exhaust extraction system • Make-up air system • Vehicle starting power • Radiator pressure fi ll A test automation system has integrated test facility device control, test parameter control and test technique synchronization, in fully automatic and manual modes.

The chassis dynamometer is floated on air bearings during a change in yaw position, synchronously driven by the turntable, which in turn is supported on roller bearings in the steel floor. A summary of the key performance features of the chassis dynamometer is as follows: • Confi guration: two-wheel drive (2WD) and four-wheel drive (4WD) • 200kW motoring power on front and rear rolls • Fixed front roll set, rear set moveable 4.24m The chassis dynamometer includes an automatic floor track and side roll cover system with a moveable central inspection port carrying WhERE ThE FuTuRE LiES, a remotely controlled thermal imaging camera. A central inspection DEFiNED BY ACE The Automotive Centre of Excellence opens up a world of possibilities. walkway is accessible via stairs from below. Located in the heart of the UOIT campus, ACE will attract academic, SiMuLATiON SYSTEMS government and industry researchers, the best students and scientists, A solar simulation system exhibits full diurnal function with azimuth and industry leaders to collaborate, create, test and validate paradigmand altitude automatically controlled by a combination of articulated shifting innovations. lamp positioning and intensity control. It has a full spectrum capability More specifically, the UOIT CWT is about to establish a new with vertical and bi-axial movement to accommodate different vehicle benchmark in climatic test capability and will serve the present and sizes and solar incidence requirements. A summary of the capabilities emerging thermal test demands of conventional automobiles, trucks is as follows: and buses. Provisions for improved aerodynamic and acoustic features • Target area: L6.5m x W2.5m will permit continual improvement to keep pace with these demands. • Intensity 600-1200kW/m2 Construction is complete, and start-up and integrated testing underway, • Incidence: 0 to 52.5° with commissioning expected to be complete early in 2011. A frontal rain simulation system located at the nozzle exit consists CONTACT of an array of up to 12 nozzles of various sizes as needed to provide Gary M. Elfstrom, Director, Business Development, adequate coverage of a given vehicle. The system is designed for 150kph university of Ontario institute of Technology at 20°C but will operate as low as -5°C to perform freezing rain tests. Email: 48



Meadow Lake wind farm in indiana

Transmitting One Million Newton Meters

In mid-summer 2010, the sustainable energy industry was surprised by leading automotive supplier ZF Friedrichshafen’s announcement of a substantial investment in its Gainesville, Ga., plant to supply gearboxes to wind turbine manufacturing giant Vestas of Denmark. The agreement represents not only a fascinating cooperation between two leaders in their fields but also a meeting of seemingly quite different industries. Elizabeth umberson, Division President, Commercial Vehicle and Special Driveline Technology, ZF Group North American Operations provided the background to this development to Wind Tunnel International’s Rex Greenslade


HIS TECHNICAL tie-up between Vestas and ZF is interesting because it brings together two giants and technology leaders of apparently quite different industries. When was the arrangement first discussed? We have been working intensively together on the new gearbox for more than one year.

Who approached whom? ZF approached Vestas about our capabilities, and we eventually both concluded that ZF could contribute positively to the design and manufacture of a new gearbox. Why is this arrangement attractive? Vestas needed a reliable and cost effective gearbox, to support their growth, especially in North America. ZF wanted to diversify its product portfolio and our years of design experience and automotive reliability methods bring significant added value to the wind industry. Vestas has been a wind industry heavyweight for years and, after bringing 41,000 wind turbines to the grid in 65 countries, Vestas can even claim the title of world heavyweight champion in this emerging energy sector. Entering this business with the market leader – Vestas – was attractive for ZF: we can also follow Vestas’ growth around the world. 2010 | WIND TUNNEL INTERNATIONAL



Schematic of the inside of a wind-turbine nacelle. No gearbox, no electricity. The slow turn of the rotor blades has to be converted into 1000 rpm before the generator can begin to create electricity

What sales are you expecting from this initiative? We are putting our experience to use in developing and producing high-quality driveline technology so that we can enter this market of renewable energies, which is showing particularly high growth rates. In the medium term, we expect to generate EUR 200 million sales per year with this new business. By way of comparison, ZF’s total U.S. sales currently total approx. EUR 1 billion. When will ZF production start? The plant in Gainesville is destined to start up production In early 2012. The annual production rate is slated for up to 1,500 wind-turbine gearboxes for turbines with a capacity of two megawatts. The first six meter (19.7 ft) prototypes are entering the testing phase. What technical needs does Vestas have that ZF can supply? The biggest factor that we address is reliability, which starts with the design but also must be carried out in the manufacturing, assembly, and test processes. ZF has used our knowledge about materials, 50

bearings, finite element analysis, and testing in order to fulfill these demanding reliability requirements. Are there commonalities between the design of an automotive or marine transmission and a wind turbine gearbox? From a technical standpoint, there are few points of comparison between the extremely heavy wind turbine gearboxes and the gearboxes of machinery, commercial vehicles – or even cars. For a start, the turbine’s rotor blades rotate slowly – maybe 12 to 18 times per minute – so the gearbox needs to bring the speed up to 1500 to 2000 rpm. So the gearbox of a wind turbine operates in the converse sense of an automotive gearbox which reduces input speed to a level required for the wheel or axle speed. In doing so, a wind turbine gearbox must cope with torque ratings well over one million Newton meters. That is the equivalent of the maximum torque output of more than 2400 BMW 535i cars.

Despite these fundamental differences, however, ZF brings important advantages to the table which help provide a technical edge. Such as? ZF’s automotive background has helped us extensively in the design and testing phase — we utilize our central research and development experts for gear design and calculations, bearing design , material specifications, lubrication, and load testing. Our automotive background also contributes significantly to our knowledge of quality, especially developing repeatable processes, and in our supplier development activities. Finally, our experiences with large gearboxes in the marine field helped us significantly in our prototyping and material handling for large gearboxes. What is the most pressing requirement for a wind turbine gearbox? Complex repairs, with enormous cranes lifting out gearboxes weighing several tons, can eat up the profits of renewable energy production rapidly. In the past there were even entire batches which failed during operation. ZF’s wind turbine gearboxes of the future are to have a service life of 20 years and be particularly easy to service. If we succeed with this, we can export, also to Asia or to Europe. What unique technical requirements or challenges to the gearbox do wind turbines present? One of the key technical challenges is to identify, simulate, and test the load profile in order to achieve the desired reliability. There is a large variability in the speed and force of the wind. Vestas has a huge amount of experience from which they define the duty cycle that we need to design and develop to. But, still, attempting to identify the variations in a typical 20-year lifetime and the effect they have on the components within the gearbox, and the gearbox as part of the wind turbine system, is quite challenging. To do so, ZF uses special software to apply statistical modeling and thereby predict how the gearbox will react over time and under specific load conditions. ZF also utilizes finite element analysis in order to design components within the gearbox that weigh less, but still have the durability needed. Finally, ZF also uses dynamic simulation models to understand how the gearbox will react in operation. ZF Services also collects valuable field and warranty information from repairing wind turbine gearboxes, which is incorporated into our design experience. As well as using our existing test facilities, ZF designed and built a new functional test bench for wind turbine gearboxes. In addition, wind turbines operate in particularly arduous environmental conditions, almost by definition: that’s where WIND TUNNEL INTERNATIONAL | 2010


Great expectations: the growth in capacity in the 10 leading wind power nations in megawatts

the wind blows most reliably. So wind turbine gearboxes must be particularly robust and durable. They are often sited at high altitudes and in air that can be wet and salty (at sea, for instance) and the temperature ranges we need to design for vary from -40C to 60C. While the turbine is designed not to operate in extreme wind speeds (it is shut down to prevent overloading), normal operation should occur for wind speeds up to 25 m/sec (90 km/h or 55.9 mi/h). In the area of product validation, ZF is even planning new standards for wind turbine gearboxes. This is necessary because conventional product testing has its limits when dealing with products that must run nonstop for 175,000 operating hours. The ‘dedicated process management’ is another one of ZF’s strong points. We can offer the wind industry decades of process management experience gained in the automotive sector, as well as the quality assurance know-how that we have collected building industrial, marine, and rail gearboxes. Please describe the testing process. Who does it? Where is it done? What criteria are measured or evaluated? In the development 2010 | WIND TUNNEL INTERNATIONAL

phase, we conduct functional tests with and without load applied, lubrication tests, and system integration tests. Finally the gearboxes are also installed up in a tower for field testing. We are conducting the tests together with Vestas at our facilities, and at their test facility in Denmark. Are there any new technologies in the new design? The gearbox that ZF has developed for wind turbines is a new design. Our material specifications are different and we believe our design will allow for more maintenance while the gearbox is still installed in the nacelle. There are different types of gearboxes, depending on the needs of the customer. The most common design is a planetary stage combined with two spur gear stages. Will this arrangement produce cheaper electricity, more reliable electricity or both? Reliability is definitely linked to cost, so we believe both will be affected. CONTACT Bryan Johnson, ZF Group North American Operations Email: 51


Bridge Cables – and Wind, Rain, Ice and Snow

A collaboration between the Technical University of Denmark (DTU) and the Danish company FORCE Technology, funded by the Danish bridge owners/operators Femern Bælt A/S and Storebælt A/S, has resulted in a special climatic wind tunnel facility specifically designed to examine ways of reducing the risk of cable vibrations on cable-supported bridges. By Holger H. Koss, DTU, Christos T. Georgakis, DTU and Søren V. Larsen, FORCE Technology


he decision for developing this new wind tunnel facility is closely related to the challenges engineers meet in the structural design of modern large cablesupported bridges. Presently the world’s largest suspension bridges in terms of main span are the Akashi Kaikyo Bridge (Japan, 1998) with 1,991m, Xihoumen Bridge (China, 2009) with 1,650m and the Great Belt Bridge (Denmark, 1998) main span is 1,624m long. The largest cablestayed bridges are the Sutong Bridge (China, 2008) with 1,088m, the Stonecutters Bridge (Hong Kong, 2009) with 1,018 and the Tatara Bridge (Japan, 1999) has a main span of 890m. The 2006 proposal for the Messina Bridge considered a single-span suspension bridge with a central span of 3,300m. Bridge cables are subjected to static and dynamic loading. The static loading mainly originates from by the weight of the bridge 52

deck, the traffic load, time averaged wind loading and from the dead weight of the cable itself. For inclined cables, the additional effect from pre-stressing to counteract the cable sag has to be considered as well. The dynamic loading on the other hand derives either from motion of the bridge structure due to traffic and wind action on the bridge deck and pylon or, more significantly, due to direct aerodynamic excitation of the cable. In recent years, particular focus was directed towards windinduced vibrations of bridge cables under certain climatic conditions leading to large amplitude vibrations. Beside visual annoyance the observed vibrations cause serious fatigue

problems on the anchoring, connectors and in the cable strands. With the materials and design philosophies currently applied, architectural visions and dimensions have reached their limit yet with still many problems unsolved.

Cable Vibration The known phenomena for cable vibration are related in different degrees to certain climatic boundary conditions. The accurate simulation of these conditions is a core aspect in the design of the test facility. Wind-induced vibrations of cables are predominately due to buffeting, vortex shedding, galloping, wake galloping or some




FiGuRE 1a (above) - Reynolds number regions for a circular cylinder [2], 1b (below) - Drag coefficients of a cylinder for varying surface roughness and flow turbulence [3].

form of rain-wind interaction. Cables can vibrate under all meteorological conditions, particularly due to their large exposure and their low inherent damping. However, the largest amplitudes of vibration are usually attributable to rain, ice or sleet. A review of the known vibration mechanisms and the available mitigation measures was provided by Kumarasena et al in 2007. Experimental research on the wind-induced vibrations of cables has been hampered by the lack of suitable facilities that can simulate true meteorological conditions. Furthermore, wind-tunnel testing of cables needs to be undertaken at appropriate Reynolds numbers and preferably at full scale, as 2010 | WIND TUNNEL INTERNATIONAL

certain forms of wind-induced vibration are highly dependant on this number and on the correct formation of rain or ice. Smaller low-speed wind-tunnels are often unable to achieve the necessary Reynolds numbers without significant levels of blockage. Apart from wind-tunnel blockage, the physics of ice accumulation including thermodynamic effects and rivulet establishment for rain conditions are significantly biased at reduced scale. As several of the most dominant windinduced vibrations occur within the subcritical and critical Reynolds number regions (Fig. 1a), it is desirable that a wind-tunnel test facility should be able to test up to at least the supercritical range. The supercritical range for circular cylinders (cable sheathing) can be assumed to start at approximately 3×105 for smooth flow (Fig. 1b).

The general Reynolds number Re for a circular cylinder of diameter D is Re = V·D/ν, where the kinematic viscosity of air is approximately ν = 1.5 x 10-5 m2/sec at 20°C and V is the mean velocity of the approaching wind. Neglecting suspension bridge main cables, the largest structural cables in use are suspension bridge hangers and the stay cables on cable-stayed bridges. The Great East Belt suspension bridge (second longest span in the world) has a largest hanger diameter of D = 115mm, whilst the longest and second longest span cable-stayed bridges (Sutong and Stonecutters, respectively) have largest cable diameters of 158mm and 169mm, respectively. The largest known cable diameters used to date are in the order of 250mm (e.g. Øresund Bridge, Denmark-Sweden). The new test facility should be able to test cables with a diameter of up to approximately 200mm. Based on the Reynolds number the required airspeed V in the test section to reach the supercritical range at Re = 3×105 for smooth flow will be 22.5m/s. The maximum allowable blockage in a windtunnel, before result correction leads to doubt in test accuracy, is approximately 10% of the total test section. According to Simiu and Scanlan, this will result in a necessary correction in force coefficients of about 15%. Based on the above considerations, the test section cross-sectional area is set to 2.0m × 2.0m. Most structural cables are subject to both smooth and turbulent wind. Large terrain roughness or a heavily built-up environment can produce wind turbulence intensities of up to 20 percent. In nature, turbulent flow in the atmospheric boundary layer is characterised by a composition of vortices of different sizes. For

Øresund Bridge, Denmark-Sweden



FiGuRE 2 – Overview sketch of the Climatic Wind Tunnel (CWT) geometry and main features for flow conditioning.

this reason the generation of the turbulence is envisaged as a combination of bar grids, dynamically controlled flaps and fan revolution control. Detailed design will be subject of future research. For the simulation of rain and ice two different systems are used: rain will be simulated by some kind of sprinkler system whereas for ice accretion a water atomising system is installed. The latter shall create climatic conditions as known from ground-near supercooled clouds. Here, the maximum required liquid water content (LWC) is about 0.4 gr/m3, as water contents above this level would not result in any further water or ice accumulation on the surface of

a cable. The air temperature shall be variable at least down to -5°C. Temperatures below this level would not allow for the adequate transfer of precipitation to a cable surface. Finally, a suitable wind-tunnel test facility will be able to test cables for varying wind angles-of-attack. An examination of the existing cable-stayed bridges reveals that bridge cables with angles of inclination of less than 22.5° would start to become structurally inefficient. Consequently, a test section of 2m height would result in a section length of approximately 5m (length = 2m/sin22.5°). This leads to the following basic specifications for a climatic wind-tunnel testing facility: 1. Minimum wind velocity............................................................................................................25 m/sec2 test section cross-sectional area.......................................................................................2.0 m ×2.0 m turbulence intensity ........................................................................................................................1 - 20% temperature range ....................................................................................................................-5°c - 40°c Lwc (in-cloud condition).............................................................................................................0.4 g/m3 test section length ..................................................................................................................................5 m


FiGuRE 3a (above) – Test section steel frame structure to carry different panel modules to suit various test setup requirements, 3b (below) – First setup for measuring aerodynamics forces on a vertical cable (looking upstream).


With respect to the requirement generating air temperatures at least as low as -5°C and controlling the temperature level accurately the concept of a closed circulation was chosen for the CWT. The thermal insulation of the wind tunnel reduces the effort to cool the air and fulfils at the same time environmental requirements regarding noise emission. The technical layout and orientation of the CWT is a workable compromise between the requirements from aerodynamic design and the available space. The inner maximum dimensions of the wind tunnel are about 20.5 m in length, 4 m wide at the settling chamber and 7.3 m high. The required fan performance was calculated from the overall pressure drop in the circulation at design airspeed of 25 m/s with cable and turbulence generating equipment installed. The calculation was based on available literature for lowspeed wind tunnel testing and design. With the above described aerodynamic layout, a fan with a shaft power of 210 kW has been installed to meet the test requirements. The cooling unit has a capacity of 250 kW to compensate for heat due to air friction and motor waste heat and to heat transmission from ambience. The design of the CWT spray bars and peripheral equipment is based on the Altitude Icing Wind-Tunnel at the National Research Council (NRC) in Canada. The CWT spraying system consists of five spray bars with nozzles, directly behind the wire mesh at the honeycomb. To allow for a large variety of experimental setups the test section with its steel frame structure is designed for modular combination of wall, floor and ceiling elements (door panel element shown). WIND TUNNEL INTERNATIONAL | 2010


Is available to view online 2010

nal Aerodynamics Incorporating Computatio

FiGuRE 4a (above) – Distribution of normalised mean airspeed, 4b (below) – Distribution of longitudinal turbulence intensity iu [%].


Incorpora ting Comp utational Aerodyna mics

INSIDE Aviation’s Grand Challenge High-speed, Electric Superbus Reviewing NASA ATP Shaping Chevy’s Volt Aerodynamics and Education INSIDE Smart Test Models Aviation’s Grand Challenge Bridge Cable Icing Tests High-speed, China’s New Wind Tunnel Electric Superbus OF WIND TUNNE LS Rev WINDO W TO THE WORLD iewingL NAS THE INDUST RY GLOBA A ATP Shaping Chevy’s Vol t Aerodynamics and Education Smart Test Models Bridge Cable Icin g Tests China’s New Wind Tunnel

Behind the scenes at the world’s most advanced hypersonic wind tunnel 04/10/2010 11:56

WTI Issue 2 2010.indd 1


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Behind the scenes at the world’s m advanced hypersonost ic wind tunnel


OF WIN D TU NN ELS 04/10/2010


CWT ChARACTERiSATiON – FiRST RESuLTS Put into operation in June 2010, the first measurements have been made to characterise the basic flow conditions in the new CWT. Flow properties have been measured in a grid of 49 points at three different positions of the test section, as well as the distribution of the mean airspeed Umean and longitudinal turbulence intensity Iu at the centre of the test section (grid position II). The airspeeds are normalised with the velocity at Prandtl-tube. The flow was measured at the design mean airspeed of 25 m/s without the three mesh screens in the contraction of the settling chamber and without spray bars. The results show a quite uniform flow distribution over the test chamber cross-section at low turbulence intensity (practically below 1 percent in the core flow). The basic flow fulfils in this respect already the desired specification. The design contingencies in the wind tunnel allow for this basic configuration mean airspeeds above 30 m/s. Currently, the work in the CWT focuses on flow improvements, generation of in-cloud droplets and rain impact and aerodynamic loading.

The online Window to the World of Wind tunnels

CONTACT holger h. Koss, Department of Civil Engineering, DTu E-mail: 2010 | WIND TUNNEL INTERNATIONAL



Aero In The East The automotive market in China is now the world’s largest. It underwent phenomenal growth in the last two decades, growth which highlighted the need for world-class vehicle development infrastructure within China, including a dedicated automotive wind tunnel facility. In this exclusive article for Wind Tunnel International, Dr. Zhigang Yang, Director of the Shanghai Automotive Wind Tunnel Center (SAWTC) and Changjiang Chair Professor, School of Automotive Studies, Tongji University describes the SAWTC and how it came into being


he pAst twenty years have witnessed the emergence and the rapid growth of the automotive market in china, paralleling the country’s economic growth over the same period. In 1992, the sales of vehicles (passenger and commercial vehicles combined) in china reached one million units. By 2009, the chinese auto market had reached 13.6M units, making it the largest auto market in the world. It is worth noting that the market still grows at a rapid rate, with a growth rate of 10 percent or higher expected for 2010. Both global automakers and Chinese domestic automakers serve the Chinese auto market, with the joint ventures of the global automakers having about ¾ of the market at the end of 2009. Because of the importance of the Chinese auto market, it has become worthwhile for the global automakers to pay particular attention to the needs of the Chinese consumers, including meeting the aesthetic taste of the Chinese vehicle buyers (and, in turn, unique styling designs for the Chinese market) as well as meeting the demand for compact and sub-compact vehicles, the fastest growing market segment; the fuel economy is much more important for these vehicles, because consumers of these vehicles are price sensitive and fuel cost is a larger portion of the total cost over the product’s life cycle. Both consumer needs lead to an important role for aerodynamics in vehicle development for the Chinese market. This importance, and the consequent need of a dedicated wind tunnel for automobile testing, was recognized in 2004, by Professor Gang Wan, then President of Tongji University and currently the Minister of Science and Technology. As the total market passed 5 million units, 56

SAWTC floor plan



Aerial view of AAWT test section

CWT test section

AAWT test section

Wheel rotation unit

The project was approved and kicked off in December 2004. The project team spent the next one and half years on design and research. During this phase, on the design side, the final specifications for the wind tunnels were decided, the overall layout determined, the wind tunnel airlines designed, and the major equipment with long lead time ordered; on the research side, attention was paid to the control of buffeting of open jet wind tunnel and the control of the boundary layer. The construction phase of the project started at the summer of 2006. During the next three years, the civil engineering work for the wind tunnels was done, the major equipment installed and their performances tested, the wind tunnel control system developed with an in-house team and the wind tunnel commissioned. By July 1, 2009, the wind tunnels were put into service on a trial-run basis. Both the full scale aerodynamic and aero-acoustic wind tunnel (AAWT) and the full scale climatic wind tunnel (CWT) are of the open jet type and have a horizontal layout. These two wind tunnels are connected to an common office space, supporting workshops, and storage areas (OSS). The OSS has four client rooms that respect the confidentiality requirement of the client on the one hand, and allow multiple clients to be present at the wind tunnel center simultaneously.

Professor Wan made a proposal to construct a dedicated automotive wind KEY pARAMETERS FOR ThE AAWT tunnel facility â&#x20AC;&#x201C; the Shanghai Automotive Wind Tunnel Center Project. Nozzle Dimensions 6.5m x 4.25m The scope of the project contains one full-scale aerodynamic and Nozzle Area 27m2 15m aero-acoustic wind tunnel and one full-scale climatic wind tunnel. The Nozzle Jet Length: project is budgeted at 490M RMB, with f unding from the Shanghai Test Section Dimensions: 22m x 17m x 12m 250Kph Municipal government (with half of the total investment), the Reform Top Speed and Development Commission of the Central Government, the Ministry Static Pressure Gradient 0.001/m of Finance, and the Ministry of Education. The auto industry had Background Noise < 61 Db(A), At 160Kph provided 20 percent of the funding for the project, in the form of the The road simulation is provided by a five-belt moving road system, with a center belt that is 7m in length and 950mm/1100mm in width pre-payment of fees for testing services. 2010 | WIND TUNNEL INTERNATIONAL



and four mini-belts to drive the wheel rotation. Both the center belt and the mini-belts have a top speed of 250kph and can move in synchrony with the wind. The five-belt system together with a scoop and the distribution suction for the areas before the moving belts provide a near-realistic representation for the relative motion between the vehicle and the ground. The aerodynamic forces are measured by a sixcomponent balance that has a resolution of 0.005% and 0.007% for drag and lift, respectively.

Balance for AAWT

KEY pARAMETERS FOR CWT Nozzle Dimensions 3.06m x 2.29m/ 3.06m x 4.58m Nozzle Area 7m2/14m2 Nozzle Jet Length: 15m Test Section Dimensions: 20m x 13m x 8m Top Speed 200Kph/100Kph Test Temperature Rang -20°C ~55°C Relative Humidity 5~95%,

Solar simulation systems for CWT


Furthermore, the CWT is equipped with a chassis dynamometer with movable and drivable rollers for both axles. A solar simulation is installed that has a solar radiation intensity up to 1200W/m2 and has a radiation spectrum representing that from the sunlight. To extend the temperature range, a cold-start chamber is built in the wind tunnel center that can reach a temperature of -40°C. It is noted that the cold-start chamber, the test section and the chassis dynamometer of the CWT were all selected in such a way that both commercial vehicles and passenger vehicles can be tested. Since the wind tunnel was put into operation in the summer of 2009, it has been warmly received by the automakers serving the Chinese market. Up to now, more than 10 companies have used our wind tunnels for their product development. Currently, the AAWT is close to fully booked on a one-shift basis and the CWT, which came into trial operation a few months later, is booked about half of the time. In addition to providing test services to the automakers, the Shanghai Automotive Wind Tunnel Center has been asked to be a key test facility for China’s high-speed train program. In addition to the test facilities, Shanghai Automotive Wind Tunnel Center has a research group focusing on the assessment of the applications of commercial CFD tools for vehicle development. It is believed that these activities, leveraging on the access to the test data on the one side and the research resources of the university on the other, would facilitate the complementarities of the wind tunnel test and the CFD approach to vehicle aerodynamic development. Operating within a university, Shanghai Automotive Wind Tunnel Center has a multi-component mission. While providing test services for our clients in the auto industry is our main task, doing basic research (in vehicle aerodynamics, vehicle aero-acoustics, vehicle thermal management, and CFD) and education are also part of our mission. Fan for CWT

Fan for AAWT

CONTACT Doctor Zhigang Yang, Shanghai Automotive Wind Tunnel Center Email: WIND TUNNEL INTERNATIONAL | 2010

your low-speed testing Never used a high-speed wind tunnel for low-speed results? You’re missing out. Operating at Mach 0.2 at Reynolds numbers greater than 8.5 million per foot, the Trisonic Wind Tunnel at the National Research Council Canada (NRC) combines high productivity with high-quality results to give you a clear advantage in aircraft development. Put us to the test. Use our proven low-speed capability to improve your take-off and landing performance at the Mach number you need and the Reynolds number you want.

Tel: +1 613 990 0765 Vous trouverez ces mêmes renseignements en français sur le site Web indiqué.


Closer to Reality Than Any Other CWT fan

BMW’s Energy & Environment Test Centre (EVZ) in Munich, Germany, is a state-of-the-art test complex that gives BMW the ability to test at practically all environmental conditions experienced by its vehicles worldwide, including wind, temperature, altitude, humidity, solar, rain and snow. Commissioning tests have demonstrated that it provides an aerodynamic performance superior to that of any other climatic wind tunnel facility. Michael Doiron, VP Business Development of Aiolos provides the background


he eVZ comprises of three large climatic wind tunnels (cWTs), two smaller specialized test chambers, nine soak rooms and all support infrastructure. While the three wind tunnels have been designed for differing test capabilities and are varied, they share a common air circuit design (airline), which has been optimised for energy consumption and is very compact for its large, 8.4 m2 nozzle crosssection. The wind-tunnel test section was designed to meet demanding aerodynamic specifications, such as axial static pressure distribution, low-frequency static pressure fluctuations and overall flow uniformity. The aerodynamic performance of the BMW cWTs rivals that of the latest-built fully aerodynamic facilities. The demanding aerodynamic design was achieved, in-part, by use of computational fluid dynamics and a purpose-built model wind tunnel. 60

View of CWT test section from collector



Concept work began as early as 2003, with Aiolos starting to look at a response to BMWâ&#x20AC;&#x2122;s requirements that would, in time, become the EVZ project. By 2005, the test facility configuration had developed to the current three climatic wind tunnels and two climate chambers and associated soak rooms. In 2006, BMW began a study phase for the schematic design of the EVZ. The design brief was to fit the three CWTs, a climatic chamber, an altitude climate chamber, preconditioning rooms and various work areas into a defined building envelope. The product of this study was a preliminary design and budgetary cost for the new test facility. A consortium of three partners, Aiolos, MCE Stahl & Maschinenbau and Imtech Deutschland, was formed to design and built the competitively bid project, awarded in December 2006. Aiolos had the role of technology leader, with responsibility for aerodynamic, process and mechanical design, equipment specifications, controls definition and schematic design, technical support during fabrication and construction, coordination of start-up, and performance testing.

CWT air circuit

Altitude Chamber (EK) air circuit

Engineered Solutions Aerodynamic & Aeroacoustic Wind Tunnels Climatic Wind Tunnels Environmental Chambers Extreme Weather Simulation Facilities Emissions Test Facilities Reverberant Acoustic Test Chambers Boundary Layer Wind Tunnels Ground Runup Enclosures Freefall Facilities Altitude Chambers Specialized R&D Facilities Specialized Dynamic Process Systems

Design & Engineering Project Management Design/Build Constructio Support Services

Aiolos Engineering Corporation 2150 Islington Avenue, Suite 100 Toronto, Ontario M9P 3V4 Canada Tel: +1-416-674-3017 Fax: +1-416-674-7055 Email: Web:


3D pictorial of EVZ configuration

Typical CFD plot for EK

Typical CFD plot for CWT

STuDY ChALLENGES The focus of the initial study and concept design was to address a number of demanding simultaneous requirements: • Building Layout — limited space was available to house all wind tunnels, chambers, soak rooms and work areas • Wind Tunnel Design — stringent fl ow quality requirements (jet length, pressure fluctuations, axial static pressure gradient), and • Efficiency – fan power was to be minimized while meeting all other performance specifications.

pROJECT ChALLENGES Once the concept had been finalized, design development challenges included the management of the final aerodynamic design and the mechanical design of the wind tunnels to achieve the following objectives: • Aerodynamic design – fi nalize the design of high fl ow quality CWTs within the allocated space • Validation of the design – extensive model wind tunnel tests • Aerodynamic design of the altitude wind tunnel (EK) circuit – effi cient return circuit within the limited space • Wind tunnel foundations — designed in time to support building planning leading to excavation in month 8 of the project, and • Delivery and installation of major steel parts — design of the contraction, settling chamber and corners 3 and 4 of the climatic wind tunnels in time to support installation in month 12 of the project.

CWT AiRLiNE DEVELOpMENT The approach to the development of the CWT airline was, first, to achieve the flow quality specifications while optimizing the shell costs versus the operating costs (the more efficient the wind tunnel; the greater the shell surface area and length), second to ensure all diffusers operate without flow separations, and third to fit the airlines within the available building envelope. 62

The final airline has the following features: • High contraction ratio • Jet length sized to meet the fan power limit • Effi cient diffusion within the return circuit, including the use of expanding corners • Flexible elements for trimming the axial static pressure distribution and pressure pulsations Beyond traditional wind tunnel design methods, a Model Wind Tunnel (MWT) program and Computational Fluid Dynamic (CFD) were effectively utilized. Aiolos has found very good correlation on past projects between model and full-scale wind tunnel results for the axial static pressure gradient and pressure fluctuation requirements. The MWT tests were used to further develop the following design aspects: • Optimization of the collector size and angle • Optimization of the collector gap • Determination of the sensitivity of the various trim devices • Determination of the infl uence of devices external to the jet, such as solar simulation and rain rig. CFD was used to optimize the diffusion devices within the return circuit and as a general validation of all other air circuit design features.

AERODYNAMiC DESiGN OF ThE EK The EK is an altitude capable chamber with a small (2 m2) nozzle cross-section. Even with the smaller nozzle size, the configuration of the EK is similar to an overhead return climatic wind tunnel but with the heat exchanger in the return leg to save space and achieve the heat exchanger face area needed for the large heat loads. Extensive CFD simulation was required to configure the airline to provide good flow uniformity into the heat exchanger with a very compact circuit.

CONCLuSiONS The commissioning programme of the full scale facility in 2009 confirmed that the following design and performance goals were met: • The three climatic wind tunnels exhibit exceptional flow quality that is closer to a purely aerodynamic facility than any other world class climatic wind tunnel facility in existence today. • The solution to minimize the static pressure fluctuations was very effective. • The axial static pressure gradients were within the tight specification and are unmatched by any other climatic wind tunnel facility. CONTACT Michael Doiron, Aiolos Email: WIND TUNNEL INTERNATIONAL | 2010


No Touching Surface pressure measurements are of fundamental importance for all aerodynamic testing. The Aircraft Research Association Ltd (ARA) has developed and fully proven a Pressure Sensitive Paint (PSP) capability that can provide non-contact, full-field measurements on complex aerodynamic surfaces with high spatial resolution. By Robert Bosher, Chief Operating Officer, ARA


he AircrAFt Research Association ltd (ARA), of Bedford, uK, has developed and fully proven a highly productive Pressure sensitive Paint (PsP) capability for its 9ft x 8ft Transonic Wind Tunnel (TWT) over the full Mach Number range of the tunnel (M = 0.2 to M = 1.4). The lifetime PsP technology used by ARA has been developed by Innovative scientific solutions Inc (IssI) of Dayton, Ohio, usA. ARA selected lifetime PSP to enable nearto-real-time 2D images to be processed during testing; this facilitates quality control of the data acquired by ARA and provides instant pressure field visualisation to our customers during test campaigns. ARA and ISSI continue to work very closely to continually improve and enhance this PSP process and related technologies to provide a fully integrated PSP test service. PSP provides the same fidelity of surface pressure measurement data as Computational Fluid Dynamic (CFD) tools. Compared 2010 | WIND TUNNEL INTERNATIONAL

to conventional pressure measurement techniques PSP can provide non-contact, fullfield measurements on complex aerodynamic surfaces with high spatial resolution. Surface pressure measurements are of fundamental importance for all aerodynamic testing including the integration of pressures to provide load analysis as well as information on specific flow phenomena. Such data can also be used to validate CFD code outputs. Providing experimental data comparable to CFD data in near-to-real time during a Wind Tunnel Test Campaign, early in the project life cycle, is extremely desirable and valuable to our customers. ARA’s production PSP capability is described in detail by Vardaki et al., in “Pressure Sensitive Paint Measurements at the ARA Transonic Wind Tunnel” (AIAA 2010-4796), presented at the 27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference in Chicago, USA. ARA has developed techniques to overcome the known uncertainties inherent in the 63


M = 0.8, a=2º Oil flow photos and PSP pressure data for the upper surface of the port and starboard wing of the ARA Reference Model at M = 0.8, α = 2°.

PSP measurements and has now completed several commercial PSP tests for a variety of customers. Extensive studies have been conducted on applying the PSP technique to high-speed flows. ARA has focussed on and achieved delivery of a cost-effective, production PSP capability for the ARA TWT. For instance, a comparison of the outputs from conventional oil flows and ARA PSP data shows a high degree of conformance in depicting flow phenomena and pressure flow contours across the aerodynamic surfaces. The high-quality PSP data measured at ARA is achieved via an excellent understanding of the equipment and technique, structured pre-test preparation, data acquisition and post processing with increasing automation, overall process definition and control. A key necessity, of course, is ensuring the customer’s requirements are fully understood, which is achieved through close liaison between the customer and the highly 64

motivated and competent ARA team. All of the above is essential for a successful delivery of quality data. To date, ARA has conducted tests on fullspan civil and military aircraft models, using up to 12 cameras to capture data across all model surfaces. A significant investment has been committed to the development of its PSP capability in data acquisition computers, multiple cameras and lamps and model preparation facilities such as the model spray booth and curing oven. Data quality is of prime importance to ARA, highlighted by the fact that the average deviation of the PSP data is 700Pa or better when compared with conventional pressuretap data for the complete aerodynamic surface being tested. Careful development of the test technique has allowed us to prove that any flow features developing on the model under test have not been changed by the presence of the paint, providing evidence of the non-intrusive characteristics of the

paint used. For example, the aerodynamic loads recorded by the internal strain gauge balance have shown a difference of no more than 5 drag counts when compared with the loads from an unpainted model. Valid PSP data has been acquired covering the entire model geometry, including deflected surfaces such as spoilers, ailerons, elevators, flaps, rudders and at the model buffet onset across the full Mach number range (M = 0.2 - 1.4). This was achieved using the recently established cost effective data acquisition techniques and has provided to the ARA customer a significantly enhanced and unique PSP capability. In keeping with its ethic of continuous improvement, ARA, in partnership with ISSI, has detailed plans to develop and productionise the following PSP and related techniques over the next few months. • Low speed PSP using the ISSI binary paint for the automotive and aerospace industry low speed wind tunnels. WIND TUNNEL INTERNATIONAL | 2010


â&#x20AC;˘ PSP on rotating propellers for both steady and unsteady flows. â&#x20AC;˘ Ongoing improvement of the ARA/ISSI PSP lifetime system in the ARA TWT. ARA is the sole agent in Europe for the ISSI complete range of products for academia and commercial use in low and high speed testing facilities. ARA provides the full range of complimentary services of Computational Fluid Dynamics (CFD), Wind Tunnel Model Design and Manufacture and Experimental Testing. Its highly regarded CFD capability is used for the aerospace, motorsport and renewable energy markets, using the state of the art software tools developed by ARA. Indeed, the expertise of the Computational Aerodynamics department in optimising computer processes has been important in the development of the PSP data processing, from CAD geometry manipulation to data reduction and analysis. This combination of skills including the PSP capability offers unparalleled data sources to support design and development programmes in these market sectors.

Data acquisition equipment, LED lamp and pSp camera in the TWT and the ARA Reference Model in the spray booth/curing oven.


CONTACT Nigel Corby, Development Executive, ARA E-mail: ncorby, Website:



Dallaraâ&#x20AC;&#x2122;s recently upgraded 40-percent wind-tunnel facility

Investing in the Futureâ&#x20AC;Ś with an eye on the customer Despite the recent economic crisis, Dallara Automobili, world leaders in the design and production of racing and high end production cars, has implemented some incredible upgrades in recent years, Andrea Vecchi, Wind Tunnel Manager explains 66




Wind-tunnel testing and CFD are at the heart of all Dallara cars

estLed AwAY between Italy’s

“These facilities complete the resources existing in Dallara and are food valley and the Apennine second in quality only to that of the dedicated people working here” Mountains, Dallara Automobili said Andrea Pontremoli, Dallara CEO. In its nearly 40 years of history, has a unique location and a continuous investments have proven successful in obtaining the results unique perspective. faced that have made Dallara one of the major racing car constructors in with the worst financial crisis since the the world. end of the second World War and a greatly Led by an award-winning engineer Dialma Zinelli, the aerodynamic changed world market for wind tunnels department has always been at the heart of Dallara: in 1982, through and aerodynamic consultancies, Dallara company founder Gianpaolo Dallara’s vision, Dallara built the first continued to adhere to its values – the moving-belt wind tunnel in Italy and use of this facility by the highestpursuit of excellence and belief level customers that regularly use Dallara’s in continuously investing in services continues today. It is generally its facilities and extending the appreciated that preliminary aerodynamic breadth of client services. Dallara is now better positioned to face the arrival of studies give advantages not only to cars at Dallara is now better positioned the level of Formula One Grand Prix (F1) but serious competition due to worldwide overcapacity to face the arrival of serious also to road cars in general. This has made it and the availability of new facilities and evercompetition due to worldwide even more challenging for engineering firms increasing pressures on efficiency, quality and cost overcapacity and the availability like Dallara to efficiently and cost effectively of service. of new facilities and evercover all of the automotive spectrum from high increasing pressures on efficiency, quality end road cars to F1 or Le Mans projects. and cost of service. Such has been the reputation of Dallara’s expertise that many of the Dallara’s facility investments started in most prestigious automotive manufacturers have beaten a path to 2008 with the creation of a new wind tunnel Dallara’s door to have some of the Italian design ‘magic’ introduced to facility, continued last year with both a new their most exciting road cars. Collaborations and consultancies have supercomputer for the computational fluid ranged from Honda F1 to the Maserati MC12 to road cars such as the dynamics (CFD) and finite element analysis Bugatti Veyron supercar, Alfa A8C and the KTM X-Bow. (FEA) departments and a radical upgrade of Because of the anticipated increase in demand for Dallara’s the existing 40-percent scale wind tunnel aerodynamic services, the new wind tunnel was built next to the and will finally culminate this year with the main factory complex. This new 60-percent scale wind tunnel upcoming inauguration of its state-of-the-art facility includes 1000 m2 of design offices, private meeting rooms, driving simulator. four separate model shops, a machine shop and a rapid prototyping 2010 | WIND TUNNEL INTERNATIONAL


VENDOR AUTOMOBILI DALLARA always-improving service makes Dallara theideal partner with which to develop a vast range of automotive projects

The new ‘state- of-the-art’ 60-percent scale wind tunnel complex


department, all secured by radiofrequency identification (RFID) entrances to all areas. Even since the recent 2008 debut, an extensive software and hardware update has been performed aimed at offering customised solutions to Dallara’s clients, thus guaranteeing the service necessary to be at the leading edge of competition. This has not stopped Dallara from upgrading its smaller 40-percent scale wind tunnel in order to offer highly competitive services for smaller budget projects. A new, redesigned, fully automated, internal model motion control system and a new belt tracking system allow Dallara to perform the whole motion envelope of any car without having to neglect any real car positions. Applying this to smaller scale models without losing in stiffness has been a challenge but has been proven successful. This has resulted not only in more detailed results but has improved the testing time, thus optimising the wind tunnel usage of clients even further. It is widely recognized that both wind tunnel testing and CFD alone may not be enough to reach the



the machines, but also an optimised design of all model components, which in turn reduces the model shop fitting time and wind-off time in the tunnel. The final result is an overall reduced time-to-test (the time need to go from the design office to the end of the wind tunnel test) and a more efficient (and therefore cheaper) use of clients’ wind tunnel time. In 2009 the two wind tunnels ran on both two and three-shift formats, the rapid prototyping machines performed with a laser productivity of 78 percent (based on 24 hours a day) and the company averaged two CFD cases per day. This is a testament to the efficiency that Dallara offers to its clients. The combination of all the above and the never ending pursuit towards offering an always-improving service makes Dallara the ideal partner with which to develop a vast range of automotive projects. CONTACT Andrea Vecchi, Wind Tunnel Manager, Dallara Automobili Email:

desired results. This is true not only on projects where performance is paramount but also in projects such as high performance road cars. Acoustic, thermal and comfort analyses through the use of state-of-the-art CFD and post-processing software are examples of the integration Dallara regularly performs between experimental and numerical aerodynamic areas. This is an added advantage that allows Dallara’s clients to receive a complete qualitative and quantitative analysis. Using CFD in preliminary stages of aerodynamic development has also proven to be a cost-effective method of preparing for a more thorough wind tunnel development program: a more optimised series of components tested in the wind tunnel, a higher quality of test results and a reduction in the time necessary to reach the desired project targets results in a more efficient use of the client’s aerodynamic budget,. Finally, Dallara also offers an integration with its structural analysis department in performing fluid-structure interaction analyses of critical car components. Having such a variety of clients Dallara also needs a great selection and modularity in the tools it offers its clients. In the wind tunnel we have the capacity of customising the hardware on the models with features such as active suspensions, steering systems, load cells, pressure tapings and flow meters (to mention just a few). In the CFD department, we have a full-time research and development area dedicated to the optimisation of software and hardware tools to be put at the disposal of Dallara’s CFD engineers. In order to offer the best possible service the quality, efficiency and modularity that rapid prototyping can offer in wind tunnel testing cannot be forgotten. Recently Dallara has added a third SLA 700 machine to its stereo lithography department. Dallara now has the capacity of producing around 9000 wind tunnel model components per year. This requires not only a very efficient use of





ooperation between HORIBA

Automotive Test Sy s t e m s (AT S ) a nd a G er ma n car manufacturer led to the development of a tailor-made balance platform module designed to confront these challenges. The development of t he HOR IBA ba la nce platform module for the acoustic wind tunnel gives automobile manufacturers new opportunities for solving aeroacoustic problems. The wide range of vehicles available and the fact that motorcycles are tested in addition to 4-wheeled motor vehicles means that an extremely flexible system is necessary.

The modular structure of the balance platform module allows it to meet all the requirements. The new wind tunnel balance concept permits high-precision force measurements to be carried out on the vehicle when it is subjected to a constant airflow. The overall concept also permits the use of various new measurement techniques allowing the wind flow and the acoustics in the underbody region of the vehicle to be analyzed.

The concept behind the balance platform module

Together with a German OEM HORIBA developed a tailor-made balance platform module for aero-acoustic and aerodynamic

The Sound of Silence

Interior noise comfort in vehicles is strongly affected by wind noise. To confront the problem of wind noise in the design phase of vehicle development, it is necessary to use new testing and simulation techniques. In order to conduct these series of tests as cost-effectively as possible, it is reasonable to retrofit existing wind tunnel systems with additional technologies which expand the range of possible aero-acoustic measurements. This approach minimizes the cost of operating the wind tunnel systems while avoiding costly down times. By Dieter Weiss, General Manager Productline Brake Dynamometers and Windtunnel Balances, HORIBA Automotive Test Systems. 70

The balance platform module is the combination of several highprecision individual systems from HORIBA based on the wind tunnel balance. This, in turn, consists of four individual fullyfledged six-component balances, one of which is also designed to serve as a wind-tunnel balance for model measurements. Further retrofitting of this model balance system allows vehicle models to be measured aerodynamically while still in the pre-series phase. The balance cell signals of the individual balances are digitalized



The wind tunnel balance consists of four individual fully-fledged six-component balances and forms the basis of the entire balance platform module

and combined using precision amplifiers from HBM. An electromechanical test weight is incorporated into each individual balance in order to prevent measuring errors from occurring. This reference weight allows the individual balances to be checked for correct functioning at all times while revealing measuring errors at an early stage, thus avoiding costly repeat measurements. The data acquired are used to calculate the forces required and to determine the four single-wheel lift forces, the overall resistance of the vehicle and the lateral forces at the front and rear axles. All four individual balances can be adjusted electromechanically in such a way that measurements of the entire range of motor vehicles can be accommodated. Wheelbase and track direction can be adjusted


A cover system is mechanically coupled to the individual balances, guaranteeing the synchronized adjustment of individual balance and cover system

individually to suit the model in question. The aerodynamics of motorcycles can also be investigated using the wind tunnel balance by positioning two of the individual balances in the X-axis of the wind tunnel balance. The wheelbase can be adjusted flexibly in the same way as it can with other vehicle types. The turntable topping the balance platform module is mechanically coupled to the wind tunnel balance, has an overall diameter of 6.490 mm and is part of the test section floor. Wind tunnel balance and turntable can be rotated clockwise and anticlockwise by 180° with a positioning accuracy of +/- 0.05°. The various test modules belonging to the wind tunnel balance allow different measurement techniques to be used in each case. The module required in each case is integrated into the turntable. A track system incorporated into the turntable and the measuring section floor allows the test modules to be replaced and moved with little effort.

AERODYNAMiC FORCE MEASuREMENTS FOR MOTOR VEhiCLES AND MOTORCYCLES The innovative cover modules which HORIBA has developed for the four adjustable individual balances can also be adjusted flexibly. In addition, the cover plate is able to withstand a specified wheel load of 10 kN; careful design of the cover system ensures that it does not affect the test results in either aero-acoustic or aerodynamic measurements. The cover system is mechanically coupled to the individual balances, guaranteeing the synchronized adjustment of individual balance and cover system. HORIBA was also able to develop the entire system in a way which makes it virtually maintenance-free. When the modules are replaced, the test modules with a weight of approx. 10,000 kg are moved on the track system in the turntable by electric motors specially installed for this purpose. This can be achieved quickly as no mechanical

work is necessary in order to decouple the individual balance and the cover system. Modifications in the underbody region of the vehicles are possible at all times without removing the vehicle from the test section. For this purpose, specially designed vehicle lift platforms are installed on the individual balances. These lift platforms can lift the vehicles by up to 600 mm, so the underbody region can be accessed very easily without the necessity of laboriously repositioning the vehicle on the module balance. To prevent the introduction of errors into the test result by a change in the downward displacement of the vehicle, the individual lift platforms are synchronized with the movement of the vehicle’s suspension.

GLASS MODuLE FOR LASER-OpTiC MEASuREMENT TEChNiQuES It is necessary to use laser-optic measurement techniques to perform vibration analysis of parts of the vehicle’s underbody as well as measurements of the flow field. A test module made of special glass allows these measurements to be made on the balance platform module. Here it was important to find a material that does not affect the results on the one hand - while allowing the necessary load bearing capacity of 10 kN on the other. As laser-optic measurements do not require force measurements to be carried out via the individual balances but do require a good view of the vehicle’s underbody, the individual balances are removed from the test zone. The balance platform module is equipped with a modern laser system which can be continuously repositioned in the underbody region of the vehicle with a precision of 1/10 mm. A total of eight transparent glass plates allow inspection of the underbody. Four of the plates can be replaced by optional hydraulic lifts if modifications are to be made to the underbody.

MODiFiED SOFTWARE In order to operate the extensive range of functions and the new measurement technology used in the balance platform module, the host computer software had to be modified and expanded. The adjusted software allows measurement cycles and automatic program execution loops to be preset and stored for future reproduction. In addition, all functions of the balance platform module which are not relevant for safety are controlled from the host computer whereas the safetyrelated functions are operated on location via a portable system. To replace the modules easily, hORiBA has developed a foldaway rack system in which unused test modules are stored


CONTACT Andy Keay, hORiBA Automotive Test Systems E-mail: WIND TUNNEL INTERNATIONAL | 2010


Rainmakers from Emmen How today’s engineers use wind tunnels to improve safety in rainy driving conditions. By Andreas hauser,, Head Aerodynamic Engineering, RUAG Aviation.


AinY roAd conditions are annoying to every driver; at high traveling speeds, or if the environment changes very suddenly, they can even be dangerous. Next to the more obvious aquaplaning phenomena, safety is also influenced by maintaining adequate forward, side- and rearward visibility even during the most adverse weather and road conditions. Next to drag, lift and cooling flow optimization, the engineering field of “soiling” represents another important but often overlooked area of aerodynamic car design. Water accumulations and flows have to be such as to provide sufficient viewing conditions at all times: for example, windshield wipers need to cleanly remove the water from the windshields at all driving speeds.

But it’s not only car manufacturers, with their overall design responsibility, that are interested in providing for example a perfectly designed wiper system ideally matched to the wind shield curvature. Automotive component suppliers are deeply involved too. In the RUAG Large Wind Tunnel in Emmen Switzerland (LWTE), all relevant rain conditions can be simulated for full-sized cars under the repeatable laboratory conditions of a wind tunnel at wind speeds up to 240 km/h or 150 mph. A spray rig upstream of the car seeds the air flow with water droplets of Fluid flow against wind speed for different rain conditions the required size and quantity. At the same time, it generates additional controlled and homogenously distributed spray across the vehicle’s turbulence so that the flow conditions are more representative of what is frontal section. Its intensity is adjustable between 0.25 millimeter of encountered on the road. An array of spray nozzles creates an accurately water per hour corresponding to a light drizzle and up to an extreme 2010 | WIND TUNNEL INTERNATIONAL



downpour with 40 mm/h. To achieve exactly the right intensity, the fluid flow from the reservoir needs to be accurately matched to the current wind speed. Not only is the intensity relevant for a realistic environmental simulation, but also the droplet sizes have to be representative of those encountered on the road. Small droplets in the range of 0.1 millimeter – as in a drizzle – or larger than 1.5 millimeter for a summer downpour will generate significantly different soiling patterns on the wetted automobile. To enhance the visibility of the soiling flow on the car’s surface, a fluorescent dye is mixed into the spray water before being ejected into the test section. With multiple UV lamps mounted flush in the test section walls, the car is optimally illuminated from all angles. Downstream of the test section the waterdye mixture is collected after its use and removed from the wind tunnel. The test findings are recorded with a number of remotely controlled video and still

Windshield, wiper and pillar design effects on forward visibility (good & improvable)

Side window and mirror housing effects on splash pattern (good & improvable)




cameras which are operated from the control room. Data is overlaid over the video information and the result is stored and made available for online processing and documentation. This data is the basis for qualitative and quantitative evaluation and comparison of the soiling performance of the test object in its different configurations. One main focus for car manufacturers and component suppliers lies in the windshield and A-pillar area. By juggling with different sets of wiper and rubber shapes, arm systems, contact pressures, windshield flatness, pillar-seals and numerous other aspects the wind tunnel becomes an interesting and appropriate playground for the engineer where experience makes the difference and has a vital influence on the final safety margin of the car. The second main design focus is the rear-view mirror housing. The shape of the mirror housing strongly influences the flow pattern and its soiling effects

propeller abrasion due to rain (wood & composite propeller blades)

on the mirror pane and the driver side window. The aerodynamicist’s freedom in finding a solution that offers optimal safety for all rain and speed conditions is constrained not only by car styling guidelines – an important branding item and thus selling argument – but also by national and international road traffic regulations which define the minimal size, area and positioning of the mirror. Rain simulation is also of interest for the aviation industry although their primary goal is not only an optimal view on the panoramic surroundings for the pilot but also the rain droplets hitting the fast rotating propellers which can be a serious concern. The impact of water droplets on the propeller’s leading edge may cause abrasion and delamination after only a few minutes of flying time. Thus the propellers are optimized in design to better withstand these forces without imposing a negative effect on the aircraft thrust performance. By simulating environmental conditions in a laboratory surrounding, their influence on the test object can be systematically created and repeated over an arbitrary timeframe. This provides engineers – from the automotive or from the aviation industry – with consistent and verifiable development results at a massively reduced time and cost budget compared to tests on the track or in flight. CONTACT Andreas hauser, head Aerodynamic Engineering, RuAG Aviation E-mail:

Efficiency, accuracy, competence, flexibility: This is what you can expect at RUAG Aviation’s premium aerodynamic testing facility. We provide competent and highly skilled personnel, advanced instrumentation, high precision strain gauge balances and modern data acquisition software. This guarantees not only most accurate data but also a high efficiency during preparation and performance of the test – getting you the most out of your wind tunnel time. Whatever your low-speed wind tunnel testing needs are, RUAG Aviation can offer the solution. Why don’t you put us to the test and experience the difference?

Too much drag? RUAG wind tunnel testing helps you do better. RUAG Aviation Aerodynamics Center · P.O. Box 301 · 6032 Emmen · Switzerland Legal domicile: RUAG Switzerland Ltd · Seetalstrasse 175 · P.O. Box 301 · 6032 Emmen · Switzerland Tel. +41 41 268 38 01 · Fax +41 41 268 38 97 · ·




CFD Flow Viz – Streamlines & Cp

Horses for Courses Pratt & Miller Engineering (PME) has designed and engineered racing cars that have won the 24 Hours of Le Mans and the Daytona 24 Hours numerous times as well as other motorsport events and championships. PME’s skill in producing exceptional aerodynamic performance has been key to that success and is a major factor in PME’s increasing customer base beyond the motorsport industry. PME’s Doug Louth, Director of Engineering, reviews the various aerodynamic engineering methods, assesses their strengths and weaknesses, and shows how Pratt & Miller engineering leverages each tool to best solve the problems at hand


o redUce product development time and cost, the appropriate selection and implementation of available development methods is critical. for vehicle aerodynamics, the range of possible development methods has expanded over the last five to 10 years. full-scale rolling-road tunnels and increasingly effective computational fluid dynamics (cfD) resources have joined scale rolling-road tunnels, full-scale fixed-floor tunnels, and vehicle track testing as viable development tools. Pratt & Miller Engineering (PME) provides clean-sheet and turn-key vehicle and systems solutions including conceptual and digital domain development, prototyping and testing, and manufacturing support including lowrate production. Historically a motorsportfocused entity, PME now has customers in OE automotive, defense, and alternative-energy markets. A key component of many programs is aerodynamic development and, similar to other vehicle and system solutions, PME brings 76

high-level development tools and processes to the effort. Full- and partial-scale wind-tunnel testing, on-track aero measurements, and CFD are all components in PME’s comprehensive aero tool kit and are leveraged according to utility in meeting program performance objectives, budget, and timing. Corvid Technologies Inc, a wholly owned subsidiary of PME, is the state-of-the-art computational resource that provides CFD analysis for PME programs. Corvid’s in-house flow solver, RavenCFD™, is the core of one of the most capable and time/cost efficient CFD operations in the world. Complementing the software tools is an in-house high-performance computer cluster with more than 2500 CPUs, which is ranked in the top 100 largest private systems in the world. Corvid personnel are integrated in all PME programs that include a CFD component, and participate in overall development planning and direction in addition to performing the surfacing, grid generation, computations, and the analysis that is CFD.

TYpiCAL MOTORSpORT AERO DEVELOpMENT pROGRAM Accurate characterization of aero forces and moments is critical for racing vehicle programs in both the development and operational stages. Aerodynamic targets defined via full vehicle track simulations to ensure competitive race performance must be met early in the design and development phase due to time requirements for body tooling and manufacturing. Once the race car gets to the track for competition, an aero force-moment model is a required component for vehicle simulation and for the analysis tools used to tune and optimize laptime performance. CFD is typically the first aero development tool employed in the conceptual and early design phase of a PME vehicle program. Fundamental drag and downforce prediction and flow field analysis are used to evaluate conceptual alternatives through virtual development iterations. In a fully funded program, scale wind tunnel testing is brought on-line in parallel to the CFD analysis. Validation between methods is performed, WIND TUNNEL INTERNATIONAL | 2010


CFD Flow Viz â&#x20AC;&#x201C; Streamlines

CFD iso-Vortical Surfaces from above and below

and ongoing development is divided between CFD and tunnel testing based on relative efficiencies. Once a full-scale vehicle is complete, ontrack testing is performed and, if budgeted, full-scale wind-tunnel testing is performed. Again, correlation between methods is checked and ongoing development distributed among the various test plans. When the final production configuration is decided, a full battery of aero computations and testing is executed to build aero models for engineering support of the deployed vehicles. Pitch-heave, yaw, and roll mapping is completed and the test data is regressed into equations and/ or tables used in vehicle simulation. Mapping of adjustable aero settings is also performed. With the resulting comprehensive aero models integrated into vehicle simulation and analysis 2010 | WIND TUNNEL INTERNATIONAL

tools, race engineers have maximum ability to understand interactions and trade-offs between aerodynamics and other vehicle and chassis settings and to optimize the overall vehicle performance for any race track and environmental conditions. The results of this process have been demonstrated repeatedly when new PME vehicles meet and exceed performance targets the first time they hit the track and go on to compete successfully in their respective racing categories. Further, translating motorsportbased methodologies to non-motorsport development environments has proven successful for PME with aerodynamics being a prime example. Processes and tools developed for the competitive short-cycle-time motorsport arena can meet the challenges faced by OE automotive and defense programs.

AERO METhODS DETAiL: The various aero methods available for PME programs have different levels of utility depending on the scope and phase of the program and the topic being investigated. Depending on program content, timing, and budget, PME aero development is planned with a mix of methods to best achieve overall program objectives. Thoughtful integration and correlation of the different methods builds confidence in both absolute and relativetrend accuracy and in resulting development decisions. PME has extensive experience with correlation of surface pressures, forces/ moments, and ride height sensitivity between CFD, Wind Tunnel, and On-Track testing. Understanding the similarities and differences between methods is the first step in maximizing the outcome of a given aero program. 77


Table-1 (right) provides a generalized ranking of the different aero methods versus development objectives. The development objectives included in this table are the typical high priority aero performance characteristics for a motorsport program. Rankings for the accuracy and precision of results and a metric representing cost and time associated with the alternative methods are presented simply as best, mid, and poor. While the rankings are simplistic, and the development objectives are motorsport-specific, this general approach for ranking and selecting alternatives applies to any development program, aero or otherwise. Basic cfD analysis is performed at Corvid Technologies in Mooresville N.C. A combination of COTS hardware and Corvid proprietary software are used to build and analyze CFD models. Grid generation is performed using ICEMCFD™, which is augmented by grid refinement and pre-process tools developed at Corvid. Solutions are developed using Corvid’s proprietary flow solver, RavenCFD, which solver that provides super-linear scalability performed on an in-house computational is an unstructured, arbitrary polyhedral in a parallel environment. Calculations are resource consisting of over 2500 CPUs and 5TB of memory. Post processing and flow visualization is performed using Intelligent Light’s Filedview™ visualization tool. Core analysis for each solution is performed using Corvid’s proprietary post-processing tools that allow the analyst to drill down into the results at the component level, in addition to providing overall force and moment results. Using these post-processing tools, the analyst can determine cause and effect relations between design alternatives, which help drive the design process. Basic CFD development for symmetric vehicles is performed with halfcar models containing 40-60 million elements. Grid resolution is determined by successive automated global refinement until the solution stabilizes. After nearly 10 years of application and methods development, CFD is a trusted development tool used to drive development not only in the early design stages, but through the life of a program. Advanced cfD methods, including rigid body motion, overset and immersed boundary methods as well as time-accurate computations, are possible with RavenCFD™, and are useful for various development topics. For a significant number of problems, the advanced CFD methods meet or exceed the accuracy of alternate methods and expand the scope of the design space by removing restrictions imposed by static analysis. For example, rigid body motion is used to examine yaw performance, either static or dynamic, in a single solution. Overset grids allow development of parts independently and CAD Layout – Corvette GT2 car allow the analyst to investigate a larger number 78



of design alternatives in a reduced cycle time. Immersed boundary methods are analogous to rapid prototyping tools in that they allow the analyst to quickly perform relative comparisons of component performance in the initial design phase. Time-accurate computations efficiently provide force-moment results through yaw sweeps and can also be used to give first-order dynamic response of aero forces and moments. A key feature of RavenCFDâ&#x201E;˘ is the ability to mirror a half-car model in the solver which represents a major reduction in surfacing and grid generation time for the full-car cases required for much of the advanced analysis. scale Wind Tunnel Testing is a proven development method for motorsport vehicles. Tunnel facilities such as ARC in Indianapolis, Ind., and Swift in San Clemente, Calif. have been used by PME on programs funded for this option. With advanced model motion systems, these facilities provide the most efficient method of mapping aerodynamics through a full domain of heave, pitch, roll and yaw. In addition to comprehensive maps to support vehicle modeling, mini-maps with a reduced number of conditions can be run for successive development iteration to expand analysis potential. In terms of cost and timing, designing and building a scale model can rival the challenge of the Full-scale wind tunnel test of actual Team Corvette GT2 race car actual vehicle build, but using and reusing standardized spines and instrumentation offer economies. A typical data quality concern is the accuracy of the scale model relative to the actual full scale vehicle and requires critical attention from designers, model makers, and test engineers. Test cases at extreme low ground-clearance conditions can also be challenging due to structural vibrations induced by highly non-linear and dynamic ground-effect forces. Model vibration reduces measurement quality and, in the worst case, causes model contact with expensive ground belt and can quickly reduce the feasible pitch/ heave test map relative to the on-track domain. On-track Aero Testing is the lowest-cost option once a vehicle exists and has been a fundamental method used for most PME motorsport vehicle programs. On-track testing has inherent accuracy advantages relative to other methods as the test subject is most often the actual race car, but the measurement quality is highly dependent on advanced instrumentation methods and test procedures. The primary challenge of on-track testing is to achieve test repeatability in a less-than-laboratory quality environment. The ability to achieve accurate and repeatable results is dependent on atmospheric and track conditions and on the signal-to-noise characteristics of the measurements being performed. Low stable wind speed and a flat daily temperature profile improve data quality. Downforce measurements are more repeatable on a light vehicle with higher levels of downforce, while testing heavier vehicles with lift near zero is not always feasible. On-track testing is typically limited to pitch and heave mapping. While roll-mapping is possible but challenging, yaw mapping has not been successfully accomplished by PME on track. full-scale Wind Tunnel Testing methods and focus depend on program budget and scope. PME has tested at various fixed floor fullscale tunnel facilities including Lockheed, GM Aero Lab, Chrysler AeroAcoustic, and AeroDyn. Each of these tunnels has varying accuracy with respect to on-road performance depending on the type of vehicle and the topics for development. With many vehicle types, upper body and internal flow development is not only repeatable, but accurate 2010 | WIND TUNNEL INTERNATIONAL

both directionally and in terms of absolute magnitude. For vehicles with low ground clearance, the fixed floor and boundary layer control effects on underbody pressures must be understood and accounted for as possible. Full-Scale Rolling-Road Tunnels are scarce and relatively expensive, but are a valuable option as they provide much of the same utility as the scale tunnels with an accuracy improvement resulting from use of the actual car. PME has tested at the Windshear Inc. tunnel in Concord, N.C. with excellent results. Large detailed maps are completed with relative efficiency and ground effects are clearly more representative of the real world than the fixed-floor tunnels. Data quality remains critically dependent on the accuracy of vehicle/tunnel setup and instrumentation. Similar to scale-model testing, pitch/heave oscillations can reduce measurement quality and cause contact with the belt. Due to the extreme cost of a full-scale rolling road belt, contact sensors are typically required on the bottom of the model and trigger an automatic shut-down. In this case, the system shut down can add significant and expensive time to reset the tunnel test systems, adjust the pitch/heave map, and possibly repair ground-contact sensors. As a last note on test/ development options, for all of the methods discussed here, software is often a key enabler to improve the accuracy, speed of execution, and overall development utility. Test command file generation, data I/O and regression, and real-time analysis are critical in realizing the maximum potential of a given test. Having the ability to analyze results in real time allows the test engineer to adjust procedures to improve the test measurements and to navigate through a dynamic test plan which can significantly increase the value of a given test session. PMEâ&#x20AC;&#x2122;s Tools and Methods department working in conjunction with PME development engineers and test facility operators have not only improved PME testing efforts, but at times have help operators improve their capabilities.

CONCLuSiONS: Aerodynamics development can be performed via an increasing number of methods, each having inherent advantages and challenges relative to results quality, cost, and timing. For the aero development leader, it is critical to understand the various methods and chose wisely to best achieve development objectives. While the methods discussion provided here is more aligned with the automotive motorsport environment, the general approach to assess and leverage available methods should prove valuable in any development undertaking. This approach can also help development leaders ease institutional biases and achieve a more comprehensive, integrated, and effective development process. It is the PME authorsâ&#x20AC;&#x2122; hope to offer case studies to expand this topic in future issues of WTI. CONTACT Doug Louth, pratt & Miller Engineering Email: 79


14m x 14m x 1m – Largest Honeycomb in the World Flow straighteners have been used in wind tunnels since such facilities were first built, beginning with wonderfully carpentered wooden constructions, through readily available bonded aluminium honeycomb, to present-day top-end flow straighteners constructed of stainless-steel honeycomb. Greater manufacturing precision is possible with the laser-welded stainless-steel honeycomb and it is more robust/durable in operation. Michael Field, Darchem Engineering Ltd., describes the creation of the flow straightener – at 14M x 14M x 1M, the world’s largest honeycomb structure – fitted to Boeing’s Philadelphia wind tunnel


ncreAsinG sophisticAtion in all aspects of technological development pressurises all modern-day engineering – not least aircraft designers and aerodynamicists. It will be no surprise, therefore, to learn that Boeing demanded the highest standards for the new flow straightener in their awardwinning centre-of-excellence low-speed wind tunnel at Philadelphia.

were in terms of the aspect ratio and whether to eliminate the frames normally used in assembling such structures. As is generally known (eg “Flow Quality issues for large Wind Tunnels’ – Reshotko, Saric and Najib .American Institute of Aerospace and Aerostructures January 1997), flow straightening is improved with an aspect ratio (depth of honeycomb diameter by cell size) With this straightener, the principal of 15 to 20. But there is a view that there are aerodynamic considerations to be addressed further flow quality benefits if an aspect ratio 80

of 40 or more can be achieved. With frames, there are occasions when the “shadow” of the frames can be detected in the test section. The relative benefits can be debated by aerodynamicists but Boeing took the straightforward approach that if there were no “dis-benefits”, then logically a longer flow path was better and not having frames was better. In consequence, they decided that they wanted a homogeneous flow straightener with an aspect ratio of 40. As the flow straightener is 14 metres high by 14 metres wide it will be appreciated that this then produced its own engineering challenge. Fortunately, Darchem had had previous experience with both NASA and Boeing on smaller flow straighteners and, when consulted, was confident that the Philadelphia requirements could be achieved. The engineering challenge neatly split into two. First, to design the flow straightener and, second, to join blocks of honeycomb together on site in the wind tunnel and thereby construct the flow straightener in its entirety. Would it be possible to build such a single immense block of honeycomb without the bottom row of cells collapsing from the weight of 14 metres of stainless steel above them, while maintaining ligaments thin enough to meet the aerodynamic criteria ? From previous work, the stress engineers had formulated a methodology WIND TUNNEL INTERNATIONAL | 2010


for performing a finite-element analysis without overwhelming the computer memory capacity and, using this analytical process, they were able to determine that this was feasible â&#x20AC;&#x201C; providing that certain precision was achieved in the honeycomb manufacture. Clearly, any such structural systemic weaknesses would be catastrophic. The criteria imposed by the combination of the Boeing specification concerning honeycomb cell angularity with the results of the stress analysis created a need for closer tolerancing and greater control in the manufacture of the honeycomb itself than had been achieved before. But using prior experience with similar but smaller structures, Darchem found that it could use, with some equipment modifications, the same fundamental process that had been successfully applied previously. Installation itself presented several additional challenges. The flow straightener needed to be constructed from a number of blocks of honeycomb, so the obvious first step was to determine the maximum block size that could be manufactured: larger blocks meant fewer joints to be made on site. Movement of the blocks needed to be taken into consideration: shipping, transport of the blocks within the wind tunnel and manipulating the blocks into position. Eventually, it was concluded that the


optimum block size was 3.5 metres long by 1 metre wide and with the agreed cell size of 25mm then the depth of the honeycomb block was 1 metre also. In consequence there were 42 blocks to be made from 0.55 mm stainless steel foil, each block weighing about 1 tonne. The next stage for the installation was how to assemble these blocks on site and join them together. Swinging 1 tonne blocks around in a wind tunnel is a skill in itself so it was decided that the best way forward was to use an attached framework, which was attached to each block on the laser welding work bed immediately on completion of manufacture. This framework served as the means of lifting thereafter. The frameworks were also provided with a mechanism to enable them to be supported from each other as the blocks were assembled in the wind tunnel. This was essential as otherwise any uneven loading of the blocks on each other would cause unstoppable and irreversible failure of the blocks. Key to achieving the flow quality was precise assembly of the blocks and careful joining of the honeycomb sections to their neighbours. Adjustment in the framework support assembly mechanism enabled each block to be precisely positioned to achieve the best possible cell angularity.

The next step was to join the honeycomb sections. For vertical joints a special methodology was derived to ensure that it was almost impossible to see the joint as all the honeycomb cells had to be the same. The horizontal joints were less demanding, but all joints had to be achieved in a cell of only 25mm depth. Specially designed welding equipment was used to ensure that the integrity of the honeycomb joints was as good as the rest of the factory-made honeycomb. This required great care and was painstakingly achieved. Having completed all of this welding in situ in the Philadelphia wind tunnel, the team â&#x20AC;&#x201C; with no little trepidation â&#x20AC;&#x201C; then had to remove the supporting frameworks to allow the single 14-metre-by-14-metre structure to bear its own weight. Ever-greater and more terrifying creaking and groaning accompanied the removal of each framework as the whole structure settled into place. But ongoing and subsequent measurements showed the deflections to be as forecast and the aerodynamicists were satisfied that the required cell angularity was achieved. CONTACT Michael Field, Darchem Engineering Ltd. Email:



Overview of the politecnico di Milano Wind Tunnel

Bridges and Boats and Planes… And So Much More The Politecnico di Milano Wind Tunnel is unusual in that it has two different test sections in the closedcircuit loop. This arrangement provides the ability to test in many different fields, applications and industries. prof. Giorgio Diana, of Politecnico di Milano describes the facility


he poLitecnico di Milano Wind Tunnel (GVPM)

has been operating since 2001 and is located on the academic campus of the Politecnico di Milano university. Thus the GVPM has a dual aim, being both a purely research tool and, secondly, a modern instrument for high-technology industrial applications, offering advantageous reciprocal synergies. A peculiar characteristic of the facility is the closed circuit arrangement with two different test sections in the loop. The Boundary Layer Test Section (section 14 m x 4 m, length 35 m, maximum wind velocity of 16 m/s and turbulence index <2 percent) enables the setting up of upstream active or passive turbulence generators to simulate the atmospheric boundary layer (turbulence index higher than 25 percent). The high-speed low-turbulence test section (4 m wide, 3.84 m high, and 6 m long) facilitates tests in a closed test section and in an open jet. The maximum wind velocity is 55 m/s and the turbulence level is less than 0.1 percent. Thanks to these capabilities the facility can operate in a wide range of research fields in aerodynamics, including: suspension bridges, buildings, sailing boats (America’s Cup class), high-speed trains, vehicles, aircrafts, helicopters, sport aerodynamics and wind energy. 82

LONG SpAN BRiDGES AERODYNAMiCS Bridges are subjected to static and dynamic loads due to the incoming wind. A bridge with a main span longer than 500 m is generally defined a long bridge. If over 1000-1500 m it is considered a very long span bridge. Very long span bridges are generally, up to now, suspension bridges while smaller ones (500-1000 m) are generally cable stayed and those below 500 m bridges can be of any type including steel lattice structures. With regard to long span bridges, wind effects are a major problem to be considered for the stability of the structure. Politecnico di Milano’s Research Centre for Wind Engineering (CIRIVE) gained experience in bridges aerodynamic because of the studies carried out on the project of the Messina Strait Bridge that, with its length of 3300 m, when completed, will stand undisputed as the world’s longest single span bridge. For this purpose state of the art test rigs were designed in order to perform tests on both full bridge aeroelastic models and sectional ones. Considering the aerodynamic of the bridge, the deck is most sensitive part to the wind action: sectional models permit complete experimental aerodynamic characterization of the deck section. Steady state coefficients, flutter derivatives and aerodynamic admittance functions WIND TUNNEL INTERNATIONAL | 2010


Test rig for the active turbulence generation

…this methodology allows the setting up of numerical simulations of the bridge wind response including non-linearity effects.

The Messina Strait Bridge. 1:300 scaled full bridge aeroelastic model

Messina Strait Bridge deck sectional model with the test rig for forced motion tests

are fundamental information for the design. Wind load measurements are performed by means of internal and external force balances and pressure scanners. Equipment incorporating oleodynamic actuators allows forced motion tests. Tests on elastically suspended “taut string” sectional models make it possible to analyze the deck sensitivity to vortex-induced vibrations and its response to wind turbulence. Scales up to 1/45 and wind velocities up to 55 m/s give benefits in terms of Reynolds Number. A specific test rig for the active turbulence generation has been designed for harmonic wind simulation. Unlike the usually adopted passive turbulence generation methods, the proposed method can give every spectral turbulence component at a time; this enables the effect of parameters like the reduced velocity and the gust wavelength to be separated and investigated in detail. Moreover, 2010 | WIND TUNNEL INTERNATIONAL

this methodology allows the setting up of numerical simulations of the bridge wind response including non-linearity effects. Experimental tests on aeroelastic models of the full bridge itself (up to a length of 13.5 m) and of the towers (up to a height of 3m) are performed in smooth flow and atmospheric boundary layer conditions for the direct evaluation of the bridge wind response.

SpORT AERODYNAMiCS Politecnico di Milano, CIRIVE, also works in the field of sport aerodynamics, a topic that is constantly increasing in importance so as to achieve best results in many sports. In the last few years, Wind Tunnel tests have become an essential design tool for improving performance of sailing yachts taking part in top-level competitions, such as the America’s Cup, Volvo Ocean Race, and all the Olympic classes. Tests are useful for sail plan, sail

design, rig tuning, keel and rudder shape optimization. The Politecnico di Milano Wind Tunnel facility excellence in this field as well in general aerodynamics is recognised worldwide. The very high standards of flow quality in the two test sections, the relevant height and the very large total area of the boundary layer test section, combine to make the most suitable wind tunnel for sailing yacht applications. In the boundary layer test section, the onset flow can be made to match the desired vertical wind profile in terms of both absolute value and direction, using a devoted twisted flow device. The wide dimensions of this test section make it possible to test largescale models, typically scale of 1:10, or two models at the same time, to investigate blanketing effects for tactical purposes. A sixcomponent dynamometer balance measures the aerodynamic forces, and a sail flying shape detection system simultaneously produces a 3D geometry of the flying sail’s shape that can be used for CFD analysis. In the high-speed section, yacht appendages can be tested at full scale Reynolds numbers. The large size of the low speed test section enables yacht models of quite large size to be used, with significant operational advantages, including: the sails are large enough to be made using normal sail making techniques; the model can be rigged using standard model yacht fittings and small dinghy fittings without the work becoming too small to handle; commercially available model yacht sheet winches can be used; and, most importantly, the deck layout can be reproduced around the sheet winch, allowing all the sails to be trimmed as in real life. The forces are shown in real time on the virtual panel designed on the computer screen, so that the sail trim can be optimised: the effects of trimming the sails on the driving and heeling forces can be directly visualised. 83


high speed train ETR500 wind tunnel tests for wind barriers effects evaluation

The biker Magnus Backstedt on the special test rig with both turning wheels.

America’s Cup Class yacht tests for sails performance study (Luna Rossa)

Recently a new sailing yacht testing technique has been developed with the aim of improving the simulation of sail modelling in the wind tunnel. In particular, a hardwarein-the-loop (HIL) system based on a real-time Velocity Prediction Program (VPP) and a servomechanism enabling the model yacht to heel dynamically in respose to the aerodynamic forces in the wind tunnel has been developed. The real-time VPP is based on a 4 degrees of freedom model of the yacht neglecting the pitching moment and forces up the mast equilibriums, while yaw equilibrium has been taken into account because for depowering and heeling studies rudder angle affects the boat speed significantly. The yacht model is fitted, as for standard testing procedure, with remotely controlled winches to allow for instantaneous sail trimming. The measured forces from the six-component-force balance (placed inside the model hull) are converted in high rise-buildings wind study showing the results of surface pressure measurements (Milano, CityLife project)

force coefficients and entered into the real time VPP. The real time VPP has been designed as an “open system” in such a way it is possible to enter hydrostatic and hydrodynamic data for any hull form including proprietary towing tank data regression curves if available. The converged solution is displayed on the screen panel allowing adjustment of the sail trim for maximum yacht speed. The resulting heeling angle is then transmitted to the heel servomechanism and the model is heeled to the desired angle. Different wind speeds are used in the real time VPP, generally starting with a low wind speed where the sails are fully powered and as the wind speed is increased, the sails are progressively depowered to maximise boat speed by limiting the heel angle and rudder angle. Wind tunnel tests are useful also to test athletes of various disciplines with their race equipments. The athletes inside the wind tunnel are subjected to the same aerodynamics loads as in the races. Thus they can look for the best equipment and position in order to optimize their aerodynamic efficiency. A special testing equipment allows to measure aerodynamic forces and moments on various kind of sport equipments (both with and without the athlete) changing also the yaw angle if necessary. This platform can accommodate various test equipments fitted to correctly simulate the particular boundary conditions of the sport to be tested. A special bike support allows the athlete to simulate the correct thrust on pedals by the means of an adjustable resistance to the back wheel rotation. Both the wheels are rotating. To test luge and bobsleigh the track geometry is reproduced using movable panels simulating track borders. CONTACT prof. Giorgio Diana, politecnico di Milano, CiRiVE Email:, Website:




Smaller, faster … and wireless

Leading provider of wireless data transmission datatel supplies rotating telemetry for test instrumentation in a very wide range of applications covering aero engines (including flight testing), helicopter rotors and transmissions and propellers. Michael Diefenthaeler of datatel describes applications relevant to Wind Tunnel International readers, including counter-rotating, open-rotor propulsion models for wind tunnel testing


hese AppLicAtions have very can be built up into systems with 600+ demanding requirements both channels of simultaneous data transmission. in installation space constraints For dynamic signals (e.g. blade vibration, and in performance, involving dynamic pressure) these transmitters can high-ba ndw idt h dy na m ic provide bandwidths up to 96kHz per channel pressure and strain measurement, signal with all channels operating simultaneously phasing accuracy between rotors and although 30-50kHz is adequate for most true simultaneous data transmission. measurements. Note that this refers to true Measurement of forces in rotating load signal bandwidth, or frequency response, not balances is also often needed. “sampling rate”. Datatel telemetry was used on the original datatel has a static transmitter with single-rotor wind-tunnel propulsion model several innovative features. In addition for the Airbus A400M. Full size testing is also to having simultaneous channels which relevant and datatel telemetry is employed are fully interchangeable for use with on the A400M propellers for flight testing. static strain gauges, pressure transducers, A new generation of datatel digital telemetry thermocouples or RTD’s in any combination is available for such applications which offers with a bandwidth of DC to 19kHz, constant significant advances in channel count and the current is used for strain gage excitation. In ability to provide a mixture of sensor types in contrast to the more usual constant-voltage the same compact transmitter. Multi-channel, excitation, this automatically eliminates the multi-sensor transmitter modules from datatel effects of lead wire resistance variation due to 2010 | WIND TUNNEL INTERNATIONAL

temperature, with a consequent improvement in accuracy. A major feature of the new systems is the provision of diagnostic functions to permit continuous monitoring of parameters throughout the measurement chain to check data integrity. These include sensor excitation current on/off, selection of excitation current level, dynamic S/G shunt calibration, detection of open or shorted sensors, resetting of sensor measuring range, monitoring of transmitter on-board temperature and power supply, etc. These functions are controlled remotely at the system receivers via, for example, Ethernet connection. Digital telemetry systems can offer either traditional analog data outputs or a digital interface for direct readout to external data acquisition, display and analysis, via for example a high-speed Ethernet link. Besides providing data in the formats required for 85


Rotor 1 and 2 Telemetry systems for counter-rotating, open-rotor propulsion model testing

modern digital recording systems the digital interface offers both improved accuracy and a more compact, and hence lower cost, receiver. The Ethernet link to the receivers can be used to connect with a graphical user interface (GUI) provided with datatel systems. In this way a PC can be used to configure the complete telemetry installation. This configuration, which is unique to that test installation, can then be stored on the PC for reuse or modification as required. If the test is taking place at a remote site a central laboratory can monitor the system performance continuously via the Ethernet link checking diagnostic parameters for system integrity. However, even more importantly, if problems are observed or data is questioned, the laboratory can take over control of the telemetry remotely, check any individual channels, make adjustments to settings as required, reconfigure the system and return control to the test operator. This is a powerful support capability. With compact multi-channel transmitters and their arrays of closely spaced connections, sensor lead wire hookup becomes increasingly difficult, particularly since, in most applications, access is restricted. For systems with several hundred channels, this becomes a major issue and a technique for dealing with this has been developed. In this approach printed circuit boards are used as connectors with pins or tabs on one side to which wires from sensors, RF antenna terminals and power supply terminals can be attached. This is usually done by soldering but crimp connection is also possible. On the other side of the boards are pins which plug directly into 86

sockets in the transmitters and their associated power supply modules. In some cases, the board can make direct connection with a mating half of a proprietary multipin connector which brings the sensor leads to the interface. The board tracks provide all the required interconnections. Standard pcb industry gold plated pins and sockets are used to ensure safe and reliable contacts. In this way not only is hookup easier and quicker but possible damage to the transmitters by direct soldering is avoided. Also this technique gives greater flexibility in the direction of sensor wiring to the interface since connector boards can be arranged to suit preferred routing and clipping. This technique has become an integral part of datatelâ&#x20AC;&#x2122;s application engineering and has been used on many telemetry installations from the very small to the very large. All telemetry transmitters require a low voltage DC supply and this can be supplied directly

from batteries but, in almost all cases in the aerospace context, inductive power supply is used. This requires stationary and rotating coils, usually arranged as concentric windings, acting as a rotary transformer and AC power is supplied to the rotating element. Since inductive transfer by its nature requires small gaps between rotor and stator, it is usual to arrange the transmitting and receiving RF antennae with the power coils to give the best coupling. Coil/antenna assemblies are often integrated with the transmitter carrier but they can be quite separate if the installation requires it. It will be clear from the above that in the development testing arena the creation of a rotating telemetry system for a particular application is not a simple matter of selecting a set of â&#x20AC;&#x153;off-the-shelfâ&#x20AC;? components and wiring these together. Although the electronic units are fully modular and can be assembled into an architecture to meet the broad measurement



A400M propulsion model equipped with telemetry

requirement, each physical installation is a distinct application engineering task. Having chosen numbers and types of transmitters to provide the required channel counts of various sensors, a carrier must be designed to support them at the speed involved. If the sensor hookup technique described above is used, the circuit board connectors and their mounting arrangements must be designed. Space constraints always make integration into the engine or machine difficult and parts will need modification to accommodate the telemetry. So the design process becomes an exercise in close cooperation between the telemetry supplier and the customer, each supplying relevant skills and knowledge to ensure that the installation is fully integrated into the machine


Advanced digital multi-channels telemetry transmitter modules

and gives satisfactory performance with prolonged and reliable operation. datatel has developed particular expertise in this type of application engineering and has all the experience, skills and resources needed to provide complete turnkey telemetry installations. CONTACT Michael Diefenthaeler, datatel Telemetry Email:



Free fall Simulation

Three different types of Vertical Wind Tunnels for Free Fall Simulation are offered by WTtech.CZ in the Czech Republic, as John Rosen describes


ontActs in 1989 with a group of parachutists triggered

The Conventional Closed Circuit Wind Tunnel

The Double Return Leg Tunnel

The Axis Symmetric Multi Fan Free Fall Simulator


the interest in developing wind tunnels with a purpose of improving the conditions for free fall simulation. In early facilities, open or half-open test sections had a very peaky velocity distribution and in open-circuit tunnels the external weather conditions heavily influenced the bad flow quality of these tunnels.

After training in USA and Europe, a group of parachutists from Gothenburg, Sweden described a number of faults in most of these foreign facilities, faults that easily could be cured or improved by applying modern wind tunnel technology. The first design proposals addressing these shortcomings were published in 1992 in a paper presented during a Swedish Civil Aviation Group (SCAG) exposition and meeting in Budapest. In this proposal, it was demonstrated how a four-fan system enables building height to be reduced compared to conventional layouts. Another multi-fan, compact layout was subsequently improved by means of computational fluid dynamics (CFD) studies. One further advantage of this axis-symmetric design with ten fans was that an amphitheater could be installed on top of the tunnel where spectators can observe the individuals which are subject to free fall in the “diving” chamber. After further redesigns carried out in the middle of the first decade of a new century, WTtech.CZ, originally launched by Czech skydivers, offers primarily three different types of Vertical Wind Tunnels – Free Fall Simulators (VWT-FFS).

The Vertical Wind Tunnel - Free Fall Simulator VWT-FFS-4372 erection in prague (flying chamber diameter 4.3m, nominal max. airspeed 72 m/s)



ThE CONVENTiONAL CLOSED CiRCuiT WiND TuNNEL Modern wind tunnels generally have closed test sections because that part of the test section with good velocity distribution can be longer than in Göttingen-type tunnels where the induction of external air will cause a typical peaky velocity distribution. On top of that closed-circuit tunnels require less power to run. The drawback, however, is that conventional single fan/ diffuser tunnels are too long especially if length has to be replaced by height (as is the case in a vertical wind tunnel). As a result, multi-fan systems are more competitive: the length of fan plus diffuser is reduced dramatically.

Intend to buy or upgrade your Wind Tunnel?

ThE DOuBLE RETuRN LEG TuNNEL To reduce the building height of a free fall simulation facility further, it is possible to arrange a bifurcation of the air at the top of the tunnel. In this way the height of the horizontal ducting will be half the height of the single return leg type. The same space saving can be applied to the ducting at the bottom of the tunnel. For a facility with a flying chamber of 4.32m diameter, the total height of the building can be reduced to 22.5m.

ThE AXiS SYMMETRiC MuLTi FAN FREE FALL SiMuLATOR In this facility, ten or twelve fans are arranged in a circular formation around a circular or deka or dodecagon type of duct section and bring air downwards in order to turn the flow into a common contraction unit. From here, the flow is introduced into the high “diving” section, where free flight can be simulated; constant air speed is established both across and along the stream. At the top, a common radial diffuser has been designed, that will terminate in ten (or twelve) individual ducts leading to corner vanes, which are connected to a corresponding number of vertical fans with diffusers. Some wind tunnel designers have made model tests to convince financing people of the sanity of their products, but that is not possible to get a realistic picture from a laminar flow type of model when it later on is scaled up 25 or 50 times. Therefore a CFD study of this concept was made. In this way the correct Reynolds number could be chosen and a realistic picture of the separation risks could be determined. After several modifications a final geometry was accepted. It also resulted in a 15% reduction of the installed power. Another advantage with ten to twelve fans is that it may be feasible to keep one extra fan as a spare in order to improve the redundancy to protect a continuous operation of the facility. Two VWT-FFS facilities designed by WTtech.CZ are under construction now; more detailed technical parameters are planned to be published in the next issue of Wind Tunnel International. CONTACT John Rosen, Vojtech Mraz E-mail: 2010 | WIND TUNNEL INTERNATIONAL

Development, design and delivery of testing as well as research and educational facilities in experimental aerodynamics and fluid mechanics. Development of control, measurement and data processing Wind Tunnel software.  VWT-FFS

Vertical Wind Tunnels – Free Fall Simulators - Closed-circuit WTs for Free Fall simulation


Low-Speed Wind Tunnels - Low-Speed WTs of open or closed circuit configurations


High-Speed Wind Tunnels - Supersonic Variable Mach Number WTs - Trisonic Variable Mach Number WTs - Transonic WTs - Axis symmetric Slotted Wall Variable Mach number WTs


Boundary Layer Wind Tunnels - WTs with simulated Atmospheric Boundary Layer

 FVCWT Flow Visualization and Cavitation Water Tunnels  Wind

Tunnel Fan-Drive Systems

 Multi-component

Aerodynamics Balances - internal, external, dynamic

 Calibration

Rigs for calibration of multi-component balances

 Model

positioning systems

 Traverse


 Accessories  Special

(probes, jigs) and models

measurement and test rigs

 Schlieren


WTtech.CZ | 89


The Windshear inc wind tunnel in Concord, NC is conveniently located just 25 miles from the Charlotte (NC) international Airport and within a one day drive of most of the uS motorsport and automotive industry

Advantage ... Born Out Of Adversity Early 2008. An American auto industry under increasingly unbearable stress. An economic crisis heading towards a possible global meltdown. Yet in Concord, N. C., a small group of professionals, pulled together from various industrial and technical backgrounds, began fervently working to create the worldâ&#x20AC;&#x2122;s first full-scale wide-belt rolling-road wind tunnel, primarily aimed at the motorsport market. The solutions they developed to assure its commercial success in the face of such challenges were so innovative they define what the team there calls The Windshear Advantage. Jeff Bordner of Windshear explains 90



NASCAR Sprint Cup car installed in the Windshear rolling road wind tunnel. highlighted is the versatile Windshear Universal Restraint System.

Speeds of 180mi/h (290km/h) are made possible by the 22ft (6.7m) diameter fan powered by a 5300hp (3952Kw) electric motor


t wAs clear that, in order to survive the cyclical economic downturns and unpredictability of the motorsport industry and hence be a commercial success, the Windshear wind tunnel needed to not only stand out technically, but also have the flexibility to provide test services for the widest possible variety of customers. Portfolio diversification is nothing new - economists have for decades extolled its virtues – and the Windshear operation could even look “inward” to see the proof. The Windshear operation is staffed entirely by a team from Jacobs Technology and diversification of customer base and a wide breadth of technical talent have sustained Jacobs Technology - even, in some cases, allowed it to thrive - through other trying economic times. It was clear that diversification would allow them to maintain a technical edge and keep the operation completely independent of affiliation with any one racing team. 2010 | WIND TUNNEL INTERNATIONAL

As a consequence, the Windshear team had to engineer solutions to a number of operational issues, always focusing on the key factors of adaptability, efficiency, and precision. Drawing on the experience and talent of the hand-picked operations team, as well as reaching back to the skills and knowledge base of the entire Jacobs Technology organization, Windshear has been able to invent a number of key technologies that enable customers to have the most accurate aerodynamic test experience available – an experience that we have named “The Windshear Advantage.” The most visible example of the innovations at Windshear is probably the vehicle restraint system. Restraining the vehicle in the test section using the cables provided with the rolling road machine appeared to be an easy solution to implement. However, with the wide variety of potential customers, and considering the range of ride height travel that many potential customer vehicles might move through, those cables quickly became a less-than-desirable solution. Cables attached to a vehicle chassis that moves up and down as much as five inches would require on-the-fly measurement of the restraint angle changes to allow for accurate resolution of the drag and side force measurements. Add to that the induced uncertainty of changes in the pretension of the cables as the vehicle moves, and you have an unimaginably complex system, that must be removed and reinstalled, with consistency, on a daily basis. Clearly, this was not an operationally friendly 91


Delta Wing prototype racer at Windshear. The Windshear Universal Restraint System has been adapted to the full range of customer applications.

concept in this application. Instead, the Windshear team designed an operationally simple solution of cylindrical struts attached to proprietary restraint hubs, which are easily adapted to a multitude of vehicle designs. The Windshear Universal Restraint System has now been successfully adapted to vehicles from nearly every major motorsport series, including NASCAR Sprint Cup, Nationwide, and Camping World Truck, Indy Car, Formula One, ALMS and Grand Am prototypes and GT cars. And, most recently, the system was adapted, in a more simplified form, for use on production cars. The outboard end of the restraint is attached to a biaxial load cell that measures and resolves the restraint forces into the longitudinal and lateral components. This load cell is set at a level that matches the height of the mounting point on the test vehicle to eliminate the need for geometric corrections. The mounting point on the test vehicle varies but, in most cases, is a custom hub-and-bearing assembly, which is mounted at the wheel centerline and allows the wheel to rotate freely, while holding the vehicle in position on the rolling road belt. The clevis and mono-ball union is designed to allow for up to 13 degrees of angle change to the camber of the wheel during ride height moves without binding. The restraint bars themselves are constructed of a high strength steel alloy to 92

maximize strength and minimize deformation. The cross-section of the bars has been intentionally left as a cylinder, rather than an airfoil section. This ensures that whatever the drag or side force contribution of the bars is, it is (for the most part) consistent – no matter what the local flow angle is. Typical installations use two or three bars, depending on the application and the magnitude of the anticipated aero forces. Another of the key innovations at Windshear is the onboard Automated Ride Height Actuator System. This system, coupled with the Jacobs’ Test SLATE facility control system, allows for the Windshear team to build a customized test sequence for each customer (and often several sequences for each customer), which includes a vehicle rideheight matrix, wind speed, road speed, yaw angles, and other set points. Once programmed, this sequence is ported to the wind tunnel and becomes the automated test plan for every run, with the automation providing a superior (efficient) customer experience.

Close-up view of the new Windshear Force Measurement Wheels, with the restraint hub attached.

And still another innovation developed early on at Windshear is an improved temperature compensation strategy for the “thru-the-belt” down-force (lift) measurements. Perhaps the most challenging problem that the Windshear team has had to overcome in the first two years of operation has been the accurate measurement of aerodynamic side force. Because the four vehicle tires are resting on the rolling road belt, which is essentially non-metric, the forces exerted at the tire contact patches must be isolated from the measurement. Further complicating this condition is the fact that tire mechanical WIND TUNNEL INTERNATIONAL | 2010


forces (ply-steer, camber thrust, Windshear Force Measurement Wheels measure the tire contact patch lateral force which is then use to isolate aerodynamic side force. conicity, stagger, etc) are all proportional to normal load, so in the case of a race vehicle with high aerodynamic down-force, the tire forces cannot be removed through a standard wind-off tare process. To solve this problem, the team looked at a number of possible solutions, including elaborate systems for measuring the force within the huge rolling-road machine or a mechanical device to impose simulated down-force loads on the vehicle after the data run to complete a post-run tare of the tire forces. However, in the end, these systems presented wheel. Version 1.0 of the Windshear Force Measurement Wheels themselves to be complex operationally, very costly to design and has been rolled out to customers and is being successfully used to implement, and largely unproven technology. isolate the aerodynamic side force. The team is also working on The concept chosen was that of a wheel force transducer to measure future enhancements to the technology which will allow for real the loads from the tire contact patch in real time and mathematically time measurement of rolling resistance and camber corrections. remove them from the total load measurement, yielding the desired This innovation was designed exclusively for Windshear by Jacobs aerodynamic side force value. To do this effectively meant designing Technology and First Sensors Ltd, UK. a custom wheel force transducer, which allowed for the hub mounted It is through this continuous engineering innovation process that restraint system and did not carry with it the aerodynamic interference Windshear Inc. keeps itself at the leading edge of technology for wind of the current off-the-shelf wheel force products. The result is the tunnel testing, and continues to provide to its customers with The recently launched Windshear Force Measurement Wheels (patent Windshear Advantage. pending). These wheels have been designed to have virtually CONTACT no impact on the aerodynamic flow field surrounding the wheel Jeffrey S. Bordner, Windshear inc. environment, as compared directly to a standard NASCAR race Email:

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The flow field in front of a car measured by particle image Velocimetry in Visteon’s climatic wind tunnel (Photo: Visteon Deutschland GmbH-

All you need for air flow measurements Although CFD has developed dramatically with ever-more powerful computers, experimental data from wind tunnels is still very much in demand. Modern air flow measurement techniques are so powerful that they are sometimes the most efficient way to optimize the design of the experiment. Dantec Dynamics’ palle Gjelstrup explains


ith the diminishing fossil fuels resources and the legislative measures to reduce the carbon footprint of transport and power generation, wind tunnel experiments play an increasingly important role in optimizing the aerodynamics of vehicles, airplanes and wind turbines. Very often, computational fluid dynamics (cfD) studies go hand in hand with wind tunnel experiments in the development process and, while cfD has developed dramatically with improving computer power, experimental wind tunnel data is still very much in demand. Modern air flow measurement techniques are so powerful that they can be the most efficient way to optimize the design of the experiment.

• Wake fl ows • Commissioning of wind tunnels • Validation of CFD models • Cooling/heat management • Spreading of pollutants in urban areas. We have extensive product lines within: • Constant Temperature Anemometry (CTA, hot-wire anemometry, thermal anemometry) • Laser Doppler Anemometry (LDA, Laser Doppler Velocimetry, LDV) • Particle Image Velocimetry (PIV) • Particle generation (Seeding) systems for the optical measurement techniques Dantec Dynamics has a long and proven track record in supplying • Traversing systems for the above. advanced instrumentation for airflow measurements in wind tunnels. In addition to standard products, we provide customized solutions Our equipment is used in a wide range of applications, such as: such as integrated, streamline-shaped optical probes to be placed in • Instantaneous velocity fi elds the wind tunnel, and endoscopic camera and light sheet probes for • Turbulence spectra measurements in regions with limited optical access. 94



We offer our customers extensive in-house expertise for assistance with complex research applications. With thousands of systems installed worldwide in major universities, government research facilities and in the automotive and aerospace industry, Dantec Dynamics is the largest company in terms of market share and number of employees that is dedicated exclusively to fluid mechanics research instrumentation for wind tunnels. Our current and future customers enjoy a very strong industrial partner with a stable financial performance and our total commitment to overall customer satisfaction.

WhiCh TEChNiQuE, WhEN? For a full description of the principles of the measurement t e c h n i q u e s w e s u p p l y, please see our website www. Below is an outline of the Strengths and lille-vers5.qxd 23-06-2010 A custom 14:20 Side 1 built LDA probe for use in an automotive full-scale wind tunnel Weaknesses of these techniques.

AIRFLOW MEASUREMENTS • Particle Image Velocimetry • Laser Doppler Anemometry • Hot-Wire Anemometry

• Aerodynamics • Wind Engineering • Contract measurements 2010 | WIND TUNNEL INTERNATIONAL



Measurement of air-flow near the helipad of a ship using a hot-wire probe array



Measures one, two or all three velocity components in a point, using very small probes with one or more electrically heated wires. This technique is capable of measuring velocity fluctuations with bandwidths to more than 100 kHz. Multipoint systems are available. sTReNGThs • Turbulence spectra and fi ne scale turbulence due to its ability to follow very fast velocity fluctuations • Boundary layers due to its high spatial resolution (small sensor) • Price is lower than any of the laser based techniques WeAKNesses • Requires velocity calibration – but automatic calibrators are available • Fragile probes – but easy to replace • Intrusive – the probe must be inserted into the fl ow • Cannot measure reversing fl ow • Sensitive to temperature variations – which can be compensated for

Measures the two components of the velocity of seeding particles in the flow, using a laser light sheet and double camera exposures to detect the movement of the particles. With two cameras, all three velocity components can be measured. sTReNGThs • Non intrusive technique • Measure velocity fi elds rather than one point at a time • Intuitive results (vector plots) • Ideal for identifying spatial fl ow structures WeAKNesses • Spatial resolution • Require optical access from two sides • Measurements near solid surfaces are diffi cult piV measurement in pininfarina’s wind tunnel of the flow field behind the side mirror of a car

LASER DOppLER ANEMOMETRY Measures one, two or all three components of the velocity of tracer particles (seeding) in the flow, based on the Doppler shift of laser light scattered from the seeding. sTReNGThs • Non-intrusive, optical technique • High spatial resolution (small measurement volume) • Can measure zero velocity and positive or negative fl ow direction • Insensitive to temperature or pressure variations • Can be placed outside the wind tunnel and measure through windows ThE iNNOVATiON CONTiNuES WeAKNesses Through our more than 50 years in the market, we have • Requires seeding particles in the fl ow had many breakthroughs and significant industry ‘firsts’ including: • First commercial hot-wire anemometer • First commercial laser Doppler anemometer (LDA) • First fi ber optic LDA system • First real-time PIV • First Time-Resolved PIV We are continuing our innovation and have recently introduced Volumetric Velocimetry systems capable of measuring all three velocity components in a volume, and Dynamic Mode Decomposition (DMD), an advanced method for the analysis of flow instabilities and spatial modes, based purely on experimental data. Three-component LDA study of the flow field around an airfol (courtesy of Computational Fluid Mechanics Laboratory, university of new South Wales, Austalia)


CONTACT palle Gjelstrup, Dantec Dynamics E-mail: WIND TUNNEL INTERNATIONAL | 2010

Is available to view online 2010

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Incorporat ing Compu tational A erodynam ics

INSIDE Aviation’s Grand Challenge High-speed, Electric Superbus Reviewing NASA ATP Shaping Chevy’s Volt Aerodynamics and Education Smart Test Models Bridge Cable Icing Tests China’s New Wind Tunnel

INSIDE Aviation’s Grand Challenge High-speed, Electric Superbus Reviewing NASA ATP Shaping Chevy’s Vo lt Aerodynamics and Education Smart Test Mode ls Bridge Cable Icing Tests ELS China s NeTHE WOR LD OF WIND TUNN w Wind AL WIND OW ’TO Tunnel THE INDU STRY GLOB

Behind the scenes at the world’s most advanced hypersonic Behind the scenes wind tunnel at the world’s m advanced hypersoost nic wind tunnel 04/10/2010 11:56

WTI Issue 2 2010.indd 1

TH E IN DU ST RY WTI Issue 2 2010.

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The online Window to the World of Wind tunnels


Cross-section schematic of Virginia Tech Stability Wind Tunnel anechoic test configuration. Flow is out of page, Kevlar test section side panels not shown.

Limited budgets can drive innovation

It is often said that “Necessity is the mother of invention”. Replace “Necessity” with “Limited Budget”, and one has an accurate picture of many aerospace product development programs. In today’s wind tunnel testing market, managing overall program cost is certainly necessary to allow the inventing to occur. Engineers at Techsburg and AVEC have worked closely with faculty at Virginia Tech to add new test capabilities to the university’s primary low-speed research wind tunnel, while maintaining the same low cost to customers. By Jon Fleming, Techsburg, Inc. and patricio Ravetta, AVEC


he stAbiLitY Wind Tunnel was originally built at NAsA langley in 1940 and, 20 years later, was moved to the campus of Virginia Tech in Blacksburg, Va. for the last 50 years, it has provided university research programs as well as commercial customers w it h high-qualit y test capabilities. Its 1.83m x 1.83m test section and maximum speed of 80 m/s is well suited to meet a variety of test requirements, and its low cost makes it a particularly good match for smaller-scale programs, such as unmanned aircraft projects.

Landing gear test model installed in Virginia Tech Stability Tunnel anechoic test section. inset: Noise map of landing gear


Approximately six years ago, a new test section was designed and fabricated for the Stability Wind Tunnel to allow aeroacoustic testing. Drs. William Devenport (VT Tunnel Director), Ricardo Burdisso (VT/AVEC, Inc.), and Wing Ng (VT/Techsburg, Inc.) collaborated to create the Virginia Tech Anechoic Wind Tunnel, an innovative approach based on using “acoustically transparent” Kevlar fabric wall panels for a new test section. Acoustically treated sections line the floor and ceiling, while larger anechoic chambers are placed on each side of the test section for placement of microphone arrays or other instrumentation. The major components were manufactured at Techsburg and moved to Virginia Tech in

2005. Since then, many successful aeroacoustic research projects have been conducted using the new test section hardware. With additional treatment of the wind tunnel circuit, the background noise is sufficiently low to collect acoustic data for smooth airfoils, in addition to shapes and devices that generate considerably more turbulence. One of the first projects to use the new test section was a NASA-sponsored noise identification and reduction study for the main landing gear of a Boeing 777. The anechoic test configuration has also been used for noise studies of powered aircraft models. More recently, a customer had a need for very-low speed testing of an unmanned VTOL aircraft design. Simulation of descending flight was one of the key test requirements. In order to perform this test, engineers at Techsburg collected flow survey data in the 5.5m x 5.5m plenum of the VT Stability Tunnel, just downstream of the tunnel’s seven antiturbulence screens. By testing in the plenum section, as opposed to the standard test section, the tunnel mass flow was sufficiently large enough to generate very steady flow no matter the model’s orientation or power setting, and wall interference effects were minimized as well. After the plenum velocity survey results verified the test flow uniformity and overall WIND TUNNEL INTERNATIONAL | 2010

TECHSBURG VTOL wind tunnel model mount stand assembled in 5.5m x 5.5m plenum of Virginia Tech Stability Tunnel

quality, a special turntable and support stand were built to hold the model in the center of the plenum. Tests were run at speeds from 1 m/s to 7.3 m/s and over a 360째 range of pitch angles. Customer feedback indicated improved flying characteristics after integration of this data into the vehicle flight control system. These are two examples of innovative approaches for wind tunnel testing that usually requires a large budget. Providing high-quality test results that enable real performance breakthroughs, while also maintaining low costs is a primary objective for the team of Techsburg and AVEC. Airfoil test model in Virginia Tech Stability Tunnel anechoic test section


CONTACT Jon Fleming, Techsburg, inc., Email: patricio Ravetta, AVEC, inc., Email:



A full-size tractor trailer undergoes testing in NRC Aerospace’s 9m x 9m low-speed wind tunnel

Your Choice …High-speed, low-speed, large, small, fixed-wing, rotary-wing, no wings at all – with or without ice The National Research Council Canada Institute for Aerospace Research (NRC Aerospace) in Ottawa, Canada, is uncommon in the world for the diversity of the wind tunnels it maintains and the services it offers, explains Dr. Steve Zan, the Director of NRC Aerospace’s Aerodynamics Laboratory. NRC has eight wind tunnels that range from high-speed to low-speed and large to small and that can accommodate fixed-wing and rotary-wing aircraft and bluff bodies to meet just about any client’s needs. 100



Spray bars and fan located upstream of the test section in NRC’s propulsion and icing Wind Tunnel.


A tail rotor in NRC’s propulsion and icing Wind Tunnel in preparation for tests to determine its ice shedding characteristics

or ideAs to take off—on the runway or the highway—they full-vehicle flow simulations. When combined with high-quality wind have to be engineered from innovative thinking to feasible tunnel data and a breadth of research experience, these approaches design, and then they have to be proven aerodynamically provide cost-effective support for research and product development in a wind tunnel. That’s where the National Research for a broad clientele. council canada Institute for Aerospace Research (NRc These diverse facilities, tools and expertise lead to an atmosphere Aerospace) in Ottawa, canada, comes in for an increasing number that encourages continual improvement and cross-pollination between of clients in an increasing number of areas. disciplines. In fact, NRC Aerospace researchers regularly wonder “what NRC Aerospace supports eight wind tunnels of varying size and would happen if…,”drawing on different areas of their discipline to speed (see sidebar). Using these facilities, the organization engages spur new approaches to aerodynamics. in research and technology development, and provides services to The success of this approach is particularly evident in the clients in a broad range of areas, including fixed-wing and rotary-wing developments NRC Aerospace has done for the automotive industry, aerodynamics, icing, and in the aerodynamics of bluff bodies such as refining surface vehicle aerodynamics for all classes of vehicle, from surface vehicles, ground-based structures and, even, Olympic athletes. cars and light trucks to buses and tractor-trailers. One case in point: NRC Aerospace also employs sophisticated computational fluid NRC Aerospace researchers had a hand in developing many efficiencydynamics (CFD) tools to develop new and innovative approaches to boosting measures for tractor-trailers that save fuel by improving leading-edge research in areas ranging from turbulence modeling to aerodynamics. Examples include roof-mounted deflectors, “skirts” 2010 | WIND TUNNEL INTERNATIONAL



NRC Aerospace recently added a 5.6-metre “rolling road” in its 9-metre by 9-metre (30 ft x 30 ft) wind tunnel

A Bell 429 model undergoes testing in NRC Aerospace’s 2m x 3m wind tunnel

NRC Aerospace worked with Bombardier Aerospace to test the aerodynamics for the Global Express, the Challenger 300 business jets, the C-Series, the Dash8, and the CRJ regional jet family (one which is pictured here)

NRC AEROSPACE’S DIVERSE WIND TUNNEL FACILITIES No matter what the testing requirement, the National Research Council Canada Institute for Aerospace Research (NRC Aerospace) has a wind tunnel to suit. The organizations’ eight wind tunnel facilities support industrial, government and university clients, as well as in-house research projects. Projects are normally of a customized nature and extensive efforts are applied to derive innovative approaches in instrumentation, software and operations to meet client needs.

hERE’S A SAMpLiNG OF WhAT’S ON OFFER 9 m x 9 m Low-Speed Wind Tunnel: a horizontal closed circuit atmospheric facility with a large test section (9.1 m wide x 9.1 m high x 22.9 m long (30 ft x 30 ft x 75 ft)). The facility is powered by an air-cooled 6.7 MW (9000 hp) DC motor whose speed may be varied and set at any value from 0 to 230 rpm and maintained within ±0.1 rpm. Its maximum wind speed is about 55 m/s (180 ft/s). In addition, the facility now includes a 5.6-metre “rolling road” to simulate conditions underneath a car that are similar to real-life conditions when a car is in motion. 1.5 m x 1.5 m Trisonic Blowdown Wind Tunnel: a pressurized, wind tunnel capable of running in the subsonic, transonic and supersonic flow regimes. The speed range is from Mach 0.1 to 4.0+. The basic test section is 1.5 m square with solid walls for measurements in supersonic flow. For subsonic and transonic flow regimes, a separate test section with perforated walls is contained within a pressure-tight plenum chamber and minimizes the impact of shock reflections and blockage. A test-section insert (0.38 m wide and 1.5


on the side of truck trailers, and narrower gaps between the cab and the trailer. To ensure the development of more of these innovations, NRC Aerospace added a 5.6-metre “rolling road” in its 9-metre by 9-metre (30 ft x 30 ft) wind tunnel last year, one of only two full-scale facilities of its kind in North America. Designed to simulate the movement of the road relative to the car up to 160 kilometres per hour (100 mph), this new ground-effects simulation system can generate conditions underneath a car that are similar to real-life conditions when a car is in motion. Because it is installed in NRC Aerospace’s largest wind tunnel, the rolling road can take full advantage of the test chamber’s size and the road’s long length. These features allow NRC to test large commercial vehicles and SUVs, and perform drafting studies (one car over the belt and another in front) to measure slipstream effects. NRC Aerospace is also now responding to client demands for full-scale particle

m high) is available to produce aerodynamic data on 2-D aerofoil sections. Chord Reynolds numbers approaching full-scale values on transport aircraft up to Mach 0.9 can be achieved. 2 m x 3 m Wind Tunnel: a world-class secure facility for subsonic aeronautical and industrial testing. The facility is used extensively by commercial organizations, universities, and government for research and development in the areas of steady and unsteady aircraft aerodynamics, aeroacoustics, surface vehicle aerodynamics, marine hydrodynamics, wind engineering, and wind energy generation. 3 m x 6 m Open-Circuit Propulsion and Icing Wind Tunnel: a facility that bridges the gap between a conventional wind tunnel and an engine test cell with several unique features that allow a variety of applications. A connection to the NRC Aerospace compressor/exhauster facility allows the simulation of jet effluxes, the driving of turbine-powered fans, and the simulation of intake characteristics. The open-circuit layout, with fan at entry, permits contaminants associated with the test articles (such as heat, combustion products, wakes, jets, lost lubricants etc.) to discharge without recirculating or contacting the fan. A high solidity fan attenuates unsteadiness due to atmospheric wind. This layout also allows icing research in a naturally cold test section during the winter. 0.57 m x 0.57 m Altitude Icing Wind Tunnel: a facility used to simulate in-flight atmospheric icing conditions. The tunnel’s comparatively small test section, combined with its relatively high-speed capabilities (up to Mach 0.5 with insert), make it particularly suitable and efficient for the testing of instrumentation and the viewing of the microphysical processes of ice accretion. This wind tunnel can simulate flight at altitudes as high as 23,000 feet. WIND TUNNEL INTERNATIONAL | 2010


in 2008, NRC Aerospace researchers completed a series of tests on a 4.8 per cent model of the proposed Boeing C-17B transport aircraft

image velocimetry (PIV) measurements on the rolling road. But the results of NRC Aerospace research and testing aren’t limited to the highway. Within the past few years, NRC Aerospace researchers worked with Sikorsky Aircraft to complete icing tests on its S-76C++ and D helicopter series in NRC’s Open-Circuit Propulsion and Icing Wind Tunnel, turning it into a state-of-the-art facility for icing certification tests on engines and their surrounding nacelles. This winter, NRC researchers will use the tunnel in a project investigating helicopter rotor ice accretion and shedding. In addition, NRC Aerospace researchers worked with Bombardier Aerospace to test the high-lift aerodynamics of its prototype Learjet 85 aircraft in NRC’s 1.5 m trisonic blowdown wind tunnel. Using a half-model of the aircraft, this work built on NRC’s previous work with Bombardier to develop the aerodynamics for the Global Express and Challenger 300 business jets, and the C-Series, the Dash8, and the CRJ regional jet family. In 2008, NRC Aerospace researchers also completed a series of tests to evaluate the aerodynamics of different wing flap configurations on the proposed Boeing C-17B transport aircraft. Working with a 4.8 per cent model, the researchers verified that Boeing’s proposed wing flap changes would reduce the runway length required for the large aircraft. Last year, NRC Aerospace researchers completed a collaborative research project for the US Federal Aviation Administration (FAA) and Transport Canada in NRC’s open-circuit icing wind tunnel to support regulatory decisions for safe departures in mixed precipitation conditions involving ice pellets. “These are just a fraction of the projects we’ve carried out over the past few years, with the variety of work carried out being a testament to the quality of our work, the diversity of our facilities and the depth of our expertise,” says Dr. Steve Zan, Director of NRC Aerospace’s Aerodynamics Laboratory. “By offering a broad range of services and expertise, we make full use of the facilities we have, ensuring continual 2010 | WIND TUNNEL INTERNATIONAL

For the Vancouver 2010 Olympics, NRC Aerospace researchers used mannequins (pictured here) to help select the Canadian Long-Track Speedskating Team’s suit

challenges for ourselves, which we like, and delivering innovative client solutions, which we like even better.” The Aerodynamics Laboratory has an ISO9001 accreditation and regularly conducts projects in compliance with International Traffic in Arms Regulations (ITAR). CONTACT Jeff Mackwood, Marketing Manager, NRC Aerospace Email: Website: 103

GKN AEROSPACE Engine intake test under way at GKN Aerospace’s icing wind tunnel

Intelligent Aviation Ice Protection Airborne icing is a climatic condition that large modern passenger aircraft are well equipped to deal with routinely when ascending, descending or following holding patterns. However, a continuous drive to enhance the aviation industry’s impressive safety record is being made through developments in regulation and technology which will allow us to make more efficient use of aircraft onboard power, fuel and air space. The questions posed are how will a broader climatic icing design envelope be simulated for aircraft certification and what are the future ice protection technologies to deliver enhanced safety and efficiency? By paul Nicklin of GKN Aerospace


ircrAFt icinG regulation change is being driven by the aviation industries desire to improve the overall efficiency of the worldwide aviation network. The ability of aircraft to continue unhindered in more extreme icing conditions and posses the ability to sustain holding patterns for longer periods provides an ideal situation for making the most efficient use of modern airspace.

Introducing more extreme environmental certification however takes a great deal of industry preparation: from enhancing the capability of the icing wind tunnels simulating the climatic conditions for testing, through to developing more capable ice protection technologies. The newly proposed Federal Aviation Regulations (FAR), released to industry in 2010 for discussion, include a condition known as Super Large Drops [SLD] which is encountered infrequently, yet would usually cause an aircraft diversion. Also included in the proposed rules, FAR 25 Part C Appendix X, are lower temperature extremes. These two main requirement changes have a significant impact on icing wind tunnel designs and, for some facilities, changes may run into many millions of dollars. The most significant effect of atmospheric icing encounters is on 104

forward-facing surfaces during flight which, when exposed to air flow containing ‘super-cooled’ water droplets and ice crystals, start to build ice layers. The location and rate of ice deposit depends principally upon flight speed, temperature, cloud density and water-drop size. In extreme icing conditions and in the absence of protection, ice collects rapidly, rendering the handling of most aircraft significantly degraded within a matter of minutes. Needless to say, aviation rules prohibit aircraft without ice-protection systems from flying into known icing conditions. Aircraft wings, engines, cockpit windows and flight sensors are particularly sensitive to in-flight icing. For aircraft certified for flight into known icing conditions, there is a multitude of systems available today to ensure that flights into normal conditions are made safely. Systems range from ‘hot engine bleed gas’, most commonly used on large passenger aircraft, through to ‘pneumatic boots’ and ‘de-icing fluids’ bled onto wing surfaces, more typically found in general aviation. An emerging generation of large fuel-efficient passenger aircraft, however, is calling for ‘more-electrical’ systems employing electrical heaters or mechanical actuators, built into the icing prone surfaces. WIND TUNNEL INTERNATIONAL | 2010


The trend for ‘more-electrical’ aircraft architecture has been born not only out of the recent financial shocks from aviation-fuel price fluctuations, but also from international pressure on the industry to reduce emissions and, of course, fierce competition. More-efficient passenger aircraft are the next logical evolutionary step; however, designing aircraft for continuous flight in all possible icing conditions, as proposed by the new rules, would potentially demand far higher energy use and redundant weight. This is particularly true when considering the trend towards more efficient wing aerodynamics which can only be provided when the wing surfaces are kept clean, ice included. There will therefore be a greater challenge for the first aircraft certificated under the new rules and a more significant performance demand for the very latest technologies. In order to meet more stringent regulations whilst reducing the energy required there is a strong argument for investigating the feasibility of alternative ice protection system philosophies. Such a need may be realised with an ice detection system offering ‘real-time reporting’ of icing conditions, which, in conjunction with other aircraft systems, could advise pilots of the safest course of extreme weather avoidance, particularly in cases where conditions are beyond the capability of the ice protection system. To gain industry acceptance of an ice protection system philosophy as proposed would rely upon the development and certification of an ice detection system, which not only detects the presence of icing conditions but, most significantly, accurately measures the severity of the climatic conditions. Aircraft with such systems could be operated confidently in the majority of recognised icing conditions; potentially, without any need to take evasive action and burn excess fuel, whilst extreme icing encounters would be announced to the pilot allowing a change of course to exit into safer conditions. An intelligent ice-protection system such as this, capable of accurately determining icing severity, would be particularly useful to aeroplane manufacturers needing to make the best use of available power on the aircraft. Aircraft safety could then be assured without compromising efficiency. The immediate questions for the icing systems suppliers are therefore: Are there adequately qualified icing test facilities for system certification? What are the technology solutions, at no extra cost to the operator? And how does industry convince the regulators that a new system solution is safe? GKN Aerospace uses its own icing tunnel to develop ice protection products and therefore in preparation for the new Appendix X icing rules, GKN has been working to expand the operating envelope of its tunnel facility in the UK. In 2010 an upgrade provided a low temperature capability at -55degC for water drop and ice particle conditions. The capability has already been used for GKN R&D activity and customer testing. A more extensive upgrade plan is now under consideration; the desire being to provide the GKN Aerospace icing tunnel with the capability to simulate Super Large Drops [SLD]; these are challenging conditions to achieve uniformly across any icing tunnel working section, as larger drops tend to ‘fall out’ from a horizontal air-stream. GKN will carry out a series of CFD analyses to optimise an SLD spraying system. The SLD conditions have been achieved in a limited portion of the current tunnel working section for research purposes; however the upgrade will aim to provide the conditions more uniformly across the entire tunnel working section. CONTACT paul Nicklin, GKN Aerospace Services Limited Email:, Website: 2010 | WIND TUNNEL INTERNATIONAL

Airflow turning vanes at corner of icing tunnel circuit

icing tunnel heat exchanger array

These spray bars and nozzles create the simulated supercooled water-drop cloud in the tunnel air flow



A Model of Precision Tri Models is a leader in the field of Wind Tunnel Model and Ground Test hardware for the global aerospace market. in business since 1972, TMi has been involved in the development of many of today’s vehicles including the Space Shuttle, Boeing 787 and 747-8, Airbus A380, Joint Strike Fighter, Embraer E-Jets and phenom, Bombardier C-Series, Learjet 85 and many more. Our reputation is built on a strong commitment to providing our customers with a high-quality model, on schedule and at a reasonable cost. Many of our customers rely on our expertise in joining their test requirements with the capabilities of the wind tunnel. Our customers include the ‘seasoned’ wind tunnel groups as well as the firsttime novice, who requires our assistance with such basics as model-to-tunnel integration, balance selection, tunnel positioning and model sizing. We provide a full range of services including model design, strength analysis, N/C programming, fabrication, inspection and welding.


Lockheed Martin/pratt& Whitney FaCET Freejet Engine Test Model in the AEDC ApTu Facility Photo courtesy of AEDC

We remain a privately owned, small business that specializes in precision machining and precision models. The core of our business is wind tunnel models and our commitment to the customer results in repeat business. Located in Sunny in Southern California we have access to a large pool of qualified suppliers for specialty processing. Coupled with our vast machinery resources and expert staff, Tri Models has the ability to meet

most any challenge. Tri Models has a vast wealth of experience in all types of wind tunnel models and ground test hardware. Please contact us to discuss how we can support your next project. CONTACT Chris Athaide, Director of New Business, Tri Models inc. Email:



Your technical partner for Wind-Tunnel Model Design & Engineering SCE solutions is a newly created design & engineering consultancy dedicated to wind-tunnel model design & manufacture. We propose a complete project management solution including design, mechanical and mechatronical engineering, prototype production, model instrumentation and calibration, model manufacture and preparation, wind-tunnel testing support. Our long wind-tunnel model design & engineering experience coupled with our worldwide network of suppliers allows us to deliver our clients with the most effective solutions tailored to their individual needs. Do you want us to design and manufacture a complete new wind tunnel model for you or do you want to adapt an existing model in a specific facility ? We can do both. Our project management includes model specification, supplier selection, site installation supervision and functional checks. Are you looking for some design support for a specific project? Our CAD service is available as either a standalone service or as part of a complete wind tunnel model package. Efficiency, flexibility and quality are some of the characteristics appreciated by our customers. Our goal is to be your technical partner, working alongside you to achieve your targets. Feel free to contact us at any time if you have any questions or require further information about our services.


CONTACT StĂŠphane Chosse, SCE solutions Tel : +49 151 291 48 661 E-mail :



More Value Per Test

Continuously mindful of the global competition its testing services face, ONERA is always looking for ways to offer more value per test to its customers, and has a major initiative on expanding customer expectations, as Stephen Wolf of ONERA describes


nerA (the french Aerospace lab) has operated a suite of world-class wind tunnels for over 55 years, within its GMT division. GMT is responsible for providing customers with comprehensive testing services (both model and test). Our first priority is to satisfy the primary objectives of a client, in the most cost-effective way. furthermore, we are mindful of the global competition we face, so we are forever looking for ways to offer more value per test to our customers. One approach is the focus of our presentation at the Global Wind Tunnel symposium, which will be about expanding customer expectations. Our service is much more than just the wind tunnel capabilities.

a powerful tool for reducing risk in the design phase, and promoting innovation. We are committed to helping our customers develop technology, at minimum cost. We understand customers want to prove the worth of a new technology (commercial advantage), in the preliminary design phase. Investment in testing services encourages this to happen sooner. This can be shown graphically using a “clarity line” (see accompanying illustration). Here, we show how investment in testing services improves the “clarity” a customer possesses, at any given time, to make a commitment for the project’s full development. Wind tunnels testing has changed significantly over the last 50 years. We are no longer just providing forces, moments, and pressures. Test campaign optimization is the “norm” today, meaning our customers A new flying vehicle today requires complex optimization of more focus their testing on critical areas of the flight envelope, which disciplines and requirements than before. We see the wind tunnel as Computational Fluid Dynamics (CFD) cannot model adequately. GMT’s 108



Low-speed pSp measurements commercially available in the pressurized F1 wind tunnel

Low-Speed pSp: Acquisition time is in the order of 1 minute. Repeatability/deviation from pressure tap data is +/- 0.05 in Cp at landing or take-off speeds (Mach0.2), and high Reynolds numbers (17 x 10E6 per m).

continual quest for improved test techniques and measurements, are key to expanding customer expectations for these focused test campaigns. Sustained effort in specific topics has been made with a clear desire to overcome current limitations, in both the model design and test. Examples of these topics are Model Deformation Measurements (MDM); Particle Imaging Velocimetry (PIV) flow measurements; Pressure Sensitive Paint (PSP) global measurement techniques (both steady and unsteady), improved data corrections of wind tunnel sting and wall effects, aero-acoustics, and model automation. One topic of customer expectations that we are expanding is the commercialization of global measurement techniques, such as PIV and low-speed PSP. These techniques will provide extensive pressure distributions, local loading, flow mapping around the model, propulsion integration effects, and so on. For 2010 | WIND TUNNEL INTERNATIONAL

Why should a customer invest in WT simulations during the preliminary design phase of a project ?

low-speed use of PSP, we have overcome issues of the pressurized environment, high temperature sensitivity, small pressure differences to measure, and long optical paths. After several years of effort, this measurement technique is now being offered to customers. The marriage between wind tunnels and CFD is well established, and the limitations to CFD are now better realized. Wind tunnel testing will remain a significant factor in reducing project risk. Continually expanding the expectations of our customers is, we believe, the best way to promote utilization of wind tunnels in the future and, as a result, remain competitive in a world market. CONTACT Stephen Wolf, Business Development Manager, ONERA Wind Tunnel Division Email: 109


icing Contamination Effects Flight Training Device (iCEFTD)

Better training, better pilots

Wind tunnel testing of aircraft at unusual attitudes, stalls, and spins and the accurate modeling of these effects in flight simulation can better prepare pilots for in-flight conditions. Traditionally used for military aircraft pilot training, such simulations are increasingly being used for commercial aircraft. Edward Dickes of Bihrle Applied Research Inc. describes how the development of unique Icing Contamination Effects Flight Training Device (ICEFTD) has led to successful hands-on pilot training courses


pset conditions are typically described as an unintentional pitch attitude greater than 25° nose up, pitch angle of 10° nose down, bank angle greater than 45°, or “inappropriate” airspeeds within the above parameters. such conditions may be caused by environmental conditions, system anomalies, and/or pilot inputs.

database in the angle-of-attack – angle-of-sideslip space, including regions where data are interpolated, extrapolated or held and a comparison with a representative FAA/JAR acceptance region shows that the normal flight envelope, to stall, is well covered. But overlaying of data gathered from accident investigations clearly shows the lack of coverage of modeling these The typical coverage of a commercial aerodynamics extreme events.




Rotary-Balance Testing

Typical Commercial Trainer Aerodynamics Model Coverage

Rolling Moment Characteristics due to Body-Axis Roll Rate

post-Stall Characteristics at Large Sideslip

STALL/pOST-STALL MODEL DEVELOpMENT The practice of simplifying the data set to its basic derivative form in simulations has left important aerodynamic functionality unrepresented. Wind-tunnel testing in the stall/post-stall regime has shown the aerodynamic characteristics to be much more complex and these functional dependencies are crucial to properly model the Consequence of Linearization aircraftâ&#x20AC;&#x2122;s behavior. Capturing effects beyond the typical ranges is extremely important. While the yawing moment exhibits a slope (see diagram) that can be effectively represented as a derivative at low sideslip, directional stability is significantly reduced at higher sideslip. Rotary-balance testing, initially developed to analyze spin characteristics, defines damping characteristics about the velocity vector as a function of rate. Such data typically reveal linear behavior at low angles of attack and exhibit significant non-linear variation as stall is approached. The measurement of body-axis damping as the model oscillates at photos of Twin Otter Model and Full-Scale Aircraft a particular rate, known as the Specific Point Method, has also been Data from static and dynamic wind-tunnel tests were incorporated devised. These data illustrate similar characteristics to the rotary data, with non-linear damping exhibited as stall is approached, with into an aerodynamics model, validated against flight, and implemented into the ICEFTD that has been successfully utilized extrapolation leading to incorrect roll-damping increments. in hands-on short courses conducted by the University of Tennessee AppLiCATiON TO CiViL SiMuLATiONS Space Institute to train pilots. In support of NASAâ&#x20AC;&#x2122;s Aviation Safety Program, a training simulation CONTACT was developed by Bihrle Applied Research to model the effects of Edward Dickes, Bihrle Applied Research, inc. E-mail: in-flight icing for the DH-6 Twin Otter aircraft. 2010 | WIND TUNNEL INTERNATIONAL


NASA GLENN Typical test article installed in the 10x10 SWT test section. This is a forebody-inlet model for a Rocket-Based Combined Cycle powered vehicle.

Well Known But Not Fully Understood NASA’s 10-by-10-Foot Supersonic Wind Tunnel (10x10 SWT) was originally designed for propulsion testing. But it is lesser known, however, for its capability to support other types of tests, including aerodynamic force and moment testing. Allen Arrington describes the facility and makes the case for wider customer consideration


he 10X10 sWT at the NAsA Glenn Research center is flow quality. Over the past 20 years, several flow quality tests were NAsA’s only high speed (Mach > 2.0) wind tunnel with conducted that document the facility has excellent flow characteristics propulsion test capability and is the largest supersonic and can support aerodynamic testing. wind tunnel within the agency. While designed to These tests include: provide testing of propulsion systems, the 10x10 sWT • Transition Cone testing in the late 1980s. These showed the is also fully capable of supporting other test types, including 10x10 SWT has the lowest disturbances in the test section flow aerodynamic force and moment testing. The aerodynamic field compared to the other supersonic wind tunnels surveyed. testing capabilities of the 10x10 sWT are often overlooked or • A comparison test was conducted in 2002, using a high-speed even discounted due to the belief that the facility is solely capable research model configuration. The data were compared with of propulsion testing. Misconceptions about the flow quality are testing using the same model in the NASA Langley Unitary Plan most often stated as the reason for not doing aerodynamic testing Wind Tunnel. The data collected from the 10x10 SWT and the in the 10x10 sWT, but staff experience and test techniques are also UPWT compared very closely, providing additional verification incorrectly listed as shortcomings. of the aerodynamic test capabilities. The 10x10 SWT is a very capable facility, with a Mach number • Particle Imaging Velocimetry (PIV) measurements made in range of 2.0 to 3.5 and Reynolds number up to 3.5 million/ft, and 2009. While the PIV measurements were made to support the gets its name from the test-section cross-sectional dimensions of 10 Mars Science Laboratory (MSL) test, the data documented low feet high by 10 feet wide; that section is also 40 feet long, so that large turbulence and flow angularly levels in the test section. Airspeed test articles can be accommodated. It can be operated in either a variations in the lateral and vertical planes were less than 10 ft/ closed-loop (aerodynamic) cycle or in an open-loop configuration to sec (±3 m/s). The turbulence levels were on the order of 0.5%. allow for exhausting the products of combustion from propulsion or • Wind tunnel calibration and flow quality data collected full-scale engine testing. The facility was originally built in the 1950s periodically. This information is used for the development and started operation in 1955 and, in the intervening period, testing of the calibration relationships to accurately set test section has supported a variety of supersonic test programs for atmospheric conditions, but also provides a detailed mapping of the test flight, launch vehicles and, more recently, extraterrestrial exploration. section flow quality at several planes. The data set provides a Relative to concerns over the ability of the 10x10 SWT to perform precise representation of the flow field through the volume of aerodynamic testing, the issue most often raised is the test section the test section. Pressure, Mach number, temperature and flow 112


NASA GLENN Layout of the 10x10 SWT showing the primary facility components and listing the operating range of the tunnel.

angularity data are collected as part of the calibration testing. The data collected from the testing listed above show that the test section flow quality is more than adequate to support aerodynamic testing in the supersonic regime. Other concerns that have been raised by the wind tunnel community focus on the test support systems and equipment and the experience of the 10x10 SWT test personnel in aerodynamic testing. Again, the incorrect assumption is that the 10x10 SWT and the support staff are only versed in propulsion testing. Much of the concern is focused on an assumed lack of experience with internal strain gage balances that are integral for force and moment testing. The fact is that the test engineering staff supporting the wind tunnels at NASA Glenn is well versed in the use and calibration of balances and has successfully used balances in many test programs. Also, if needed, the NASA Glenn engineers can easily call upon expertise and equipment from elsewhere in the agency: NASA Glenn has successfully leveraged the experience in aerodynamic testing and test techniques of NASA Langley and NASA Ames in the support of specific test requirements. Also, since NASA Glenn does not maintain a stable of strain-gage balances, we typically work with NASA Langley and borrow the needed equipment from their inventory. Training is also a key. At present, there are several junior engineers supporting wind tunnel testing across all of the Glenn facilities. These engineers are quickly gaining the needed expertise through on-the-job training, mentoring relationships with the senior engineers and training classes. Another vital training activity is the cooperative test program between Ames, Glenn, Langley and the Arnold Engineering Development Center (AEDC). A modified F-111 model has been tested in the transonic wind tunnels at each center and the test 2010 | WIND TUNNEL INTERNATIONAL

installation photo of the high-Speed Research model that was used to compare aerodynamic loads test results between the 10x10 SWT and the Langley unitary Wind Tunnel.

engineering staff from each center has been part of the overall team for testing at each location. This test program has allowed for the sharing of best practices between the centers. The program has also proven extremely beneficial for training of Glenn personnel, as junior test engineers were assigned to conduct the project, under supervision from senior personnel. This project was funded, in large part, through the NASA Aeronautics Test Program (ATP). NASA Glenn continues to invest in enhancing the capabilities of the test facilities. These enhancements include upgrades to data acquisition systems or control systems as well as development of new test support systems and test techniques, maintaining the facility calibration, and training the test engineers and technicians. The facility staff is also looking at upgrades to further expand facility capabilities or to improve data quality. Examples of recent projects are: • Schlieren system upgrade: The original 1950-vintage mirrors have been refurbished and the light sources have been upgraded to LED. New optics and controls will allow customer selection of 5 different measurement techniques to

highlight different flow features. • Phase I of the video recording upgrade project (completed in 2009): The project included installation of new video cameras, monitors, recorders, etc. The new system will provide improved monitoring of research test hardware and video data acquisition. • Buildup of a new model translation system (completed in 2009): The translation system mounts to the floor strut and is capable of translating a model 8 feet along the sting axis. This system could be used for sonic boom or store separation testing. • Automated rotating sting: A new capability for remote rotation (roll) of small test articles is being developed. • Particle Imaging Velocimetry (PIV): In 2007, a PIV system (including seeder system) was successfully used for the Mars Science Laboratory test program. While the system was used for a specific test, the staff are in the process of making this a permanent capability. • Test section optical access: The optical access to the test section was improved in 2007 with the addition of six new windows. These additional windows are used for PIV, photogrammetry, or simply additional lighting and cameras. • Expanded low-pressure range: By using the Glenn Central Air Exhaust System, lower total pressure conditions were achieved in the 10x10 SWT. This capability simulated the Martian atmospheric pressure condition in support of aerodynamic decelerator systems for Mars landers. • Expanded Mach number range: The facility staff is reviewing the feasibility of expanding the maximum Mach number capability to 4.0. Modifications to the facility second throat system are being investigated to provide the required margin in pressure. A CFD analysis has been completed and a detailed flow quality mapping of the second throat is planned to confirm the CFD. A detailed discussion of the aerodynamic testing capabilities of the 10x10 SWT will be provided in an AIAA paper to be presented at the January 2011 Aerospace Sciences Meeting in Orlando, FL. This paper will provide additional information on the 10x10 SWT test section flow quality as well as other initiatives to enhance all testing capabilities. CONTACT E. Allen Arrington, Sierra Lobo, inc., NASA Glenn Research Center at Lewis Field Email: 113

NASA LANGLEY Figure 1. Check standard model for the National Transonic Facility

Evaluation and Control of Wind Tunnel Measurement Processes At the top of the priority list for all customers of wind tunnel facilities is excellent data quality. But how is a customer to know that a wind tunnel is capable of delivering the data quality desired, especially during her test? For that matter, how is the facility itself to know what level of data quality it can deliver and whether it can actually control that data quality? By Michael J. hemsch and Eric L. Walker, NASA Langley Research Center


n 1997-2000, the Wind Tunnel enterprise (WTe) at NAsAâ&#x20AC;&#x2122;s langley Research center in hampton, Va. began a series of intensive process improvements designed to enhance customer satisfaction, reduce costs, and improve operational efficiency, maintenance, and data quality. At that time, eight tunnels and one jet test facility were included in the WTe. As part of the data quality effort, the WTe adopted a new framework for statistical evaluation and control of its wind tunnel measurement processes over time. The methodology used in the new framework was originally developed by Walter A. shewhart in 1924 for quality control of the manufacture of telephones, then probably the highest tech gadget in ubiquitous use. The methodology was (and still is) a great success and was eventually noticed by churchill eisenhart, chief of the statistical Division of the National Bureau of standards (NBs). Around 1960, eisenhart and his staff adapted the methodology for quality control in precision calibration laboratories in the united states. 114

The NBS data quality control methodology is based on the notions of statistical quality control (SQC), now very familiar from precision manufacturing, together with check standard testing. Unlike national standards or transfer standards which exist to provide true values, check standards exist to provide an unchanging work load for the target measurement system in situ. The true values of measurements made on check standards are not particularly important. What is important is that they remain unchanged and that they be reasonable surrogates for customer testing. Each tunnelâ&#x20AC;&#x2122;s check standards typically consist of a suitable wind tunnel model and a calibration probe, among others. Examples of WTE check standards are given in Figures 1-5. In Figure 1 (NTF), the green tape strips on the floor are used to protect the wall interference pressure orifices during model installation. Also, the chordwise rows of white dots on the starboard wing are used to measure wing deformation. Hence, the NTF check standard model provides the ability to control a number of measurement processes. In Figure 5, the check standard probe for the 14-Foot by 22-Foot Subsonic Tunnel (14x22) can be seen at the center top of the picture. The boundarylayer rakes on the test section floor to the left and right of the probe mounting system are removed during check standard testing. The results over time of the check standard repeat-run sets, called groups in the literature, are analyzed using statistical control charts familiar to the SQC community. Using control charts, the output from the check standards is monitored for back-to-back repeatability, within-test repeatability and across-test repeatability. Our experience suggests that back-to-back repeatability, i.e. withingroup, is essentially a function of the instrument(s) chosen and the test section used. However, the between-group variation, i.e. withinWIND TUNNEL INTERNATIONAL | 2010

NASA LANGLEY Figure 2. Check standard model for the Transonic Dynamics Facility

Figure 3. Check standard model for the unitary plan Wind Tunnel. The airframe is a generic fighter.

Figure 4. Check standard model for the 14-Foot by 22-Foot Subsonic Tunnel in the closed test section configuration.

test and across-test, can include significant effects of test personnel decisions and facility activities, making it important to monitor such variations. For example, see Figure 6 which shows time-ordered repeat lift-coefficient measurements on the check standard airfoil in the Low-Turbulence Pressure Tunnel for a normal run condition. The data were acquired in six groups of ten back-to-back measurements over several months. It has been clear since the dawn of precision measurement that one must expect between-group measurements (e.g. day-to-day) to show greater scatter than would be seen within-group (e.g. back-to-back) and that is obvious in Figure 6. What is of interest is to determine if the within-group scatter and the between-group scatter, as quantified by the standard deviations, remain constant over time. And, of course, the mean should not drift either. The check standard control charts are simple to prepare in concept. For each group in Figure 6, compute the range and plot the results in time order together with the average of the range. Standard SQC textbooks then give appropriate limits for the ranges. Once a reasonable number of groups have been obtained, the average and limits are frozen and new data are placed on the plot as check standard tests are run. The usual back-to-back variation itself, evidenced by the average range, is a function of the measurement system and its environment and should not change unless the system or environment is changed. If new data are outside the limits or show significant non-random runs, then action should be taken immediately by the tunnel staff to find the cause and eliminate it before a customer test is run. A similar approach can be taken for the between-group variation by plotting the group averages in time order. This approach can also highlight any change of state due to improved measurement processes which can then lead to new limits. 2010 | WIND TUNNEL INTERNATIONAL

Figure 5. Check standard probe for the 14-Foot by 22-Foot Subsonic Tunnel in the open test section configuration.

Figure 6. Time-ordered lift coeďŹ&#x192;cient data obtained on the check standard airfoil in the LowTurbulence pressure Tunnel.



Figure 7. Chart of calibration parameter within-group ranges obtained with the 14-Foot by 22-Foot Subsonic Tunnel check standard probe over nine years

Control charts for the check standard probe for the 14x22 for a normal test condition are shown in Figures 7 and 8. Because the 14x22 can be run in six different modes (open, closed, boundary-layer removal system on/ off, etc), it is important to make sure that the calibrations for each mode are controlled. Figure 7 shows the group ranges for the calibration parameter over time obtained in groups of three back-to-back data points. The lack of evidence of non-random behavior and no points outside the limits for nine years of testing show that the short-term variation of the calibration is stable with the variationto-be-reported to the customer given by the average range. Figure 8 shows the group averages for the data of Figure 7. The group average that would be used for the calibration is given by the solid black line. The dashed red lines show the SQC limits that would be given by the back-to-back repeatability. Clearly, the between-group variation is significantly larger as would be expected. The dashed black lines represent appropriate SQC limits for the between-group variation. Note that for this chart, within-test and betweentest variation are combined together. Both Figures 7 and 8 are the kind of charts that the tunnel staff likes to see — boring and no evidence of significant change. Similar charts for measurement of the normal-force coefficient on the 14x22 check standard model and measurement of the axial-force coefficient on the NTF check standard model are given in Figures 9 and 10, respectively. The computation and interpretation of the results are identical to that of Figures 7 and 8. The WTE has applied SQC methods to the evaluation and control of various other measurement processes as well. Those processes include test section flow angularity measurements, instrument calibration, measurements of wing twist and bending using videogrammetry, tracking of balance and pressure gage zeros during a test, repeatability of wall interference estimates, 116

Figure 8. Chart of calibration parameter group averages obtained with the 14-Foot by 22-Foot Subsonic Tunnel check standard probe over nine years

Figure 9. Chart of normal-force coefficient group ranges and averages obtained with the 14-Foot by 22-Foot Subsonic Tunnel check standard model over nine years

Figure 10. Chart of axial-force coefficient group ranges and averages for NTF check standard model

installation and measurement of trip dot heights, and model buffet measurements. How does all this impact the customer? First, she will know that the measurement process has historically been stable at the reported level of variation (measurement process traceability). Second, by making repeat measurements during her own test, she can check against the tunnel’s check standard results for verification that the measurement processes continue to be stable during her test. She can also report the measurement variation as part of her reporting process, including uncertainty quantification. CONTACT Michael J, hemsch, NASA Langley Research Center E-mail: Eric L. Walker, hampton, NASA Langley Research Center E-mail: WIND TUNNEL INTERNATIONAL | 2010


Balance of Power The latest innovation in force balance design from Triumph’s Aerospace System group is the Six Component High Capacity Force (Hi-Cap) Balance. The Hi-Cap Balance measures forces in the normal and side planes, rolling moment and axial force. Pitch and yaw are resolved from the outputs of the normal and side elements. Dennis Booth gives the background to this development The successful features of its predecessor, internal flexure design and axial element, were incorporated into the Hi-Cap design with only minor user interface changes to the outer geometry. The internal workings of the balance were redesigned to allow for a dramatic increase in load capacity while reducing the deflection and maintaining the diameter. A redesign in gauge layout creates greater accuracy and closer matched output for all components, drastically reducing output tradeoffs in the design phase. Utilizing the Automatic Balance Calibration System, the Hi-Cap Balance excels in both the 3 Force 3 Moment Format and when defined in a 5 Force 1 Moment Format. Although overall load capacity is increased, it has not adversely affected the performance at the low-end range of the operating envelope. Hi-Cap balance The Automatic Balance Calibration System (ABCS) is calibrations include multiple calibrations able to apply any single component or combination across the load envelope with a tailored of loads to fully characterize six component balances smaller-load envelope calibration to riUMph’s Force Measurement systems group (fMs) increase low-end resolution performance for alternative testing embodies a legacy of decades of experience forged into applications. The ability to redefine the allowable loads based on test cutting-edge measurement devices. force-type balance requirements enable a single balance, rather than the usual multiple designs have continued to evolve to meet the complex balances, to fill the requirements of the test. needs of the aerospace industry. The Hi-Cap’s rugged precision was utilized in both continuous-flow Previous force type balances design, dating back and blow-down facilities including government, 50 years, suffered load limitations. These commercial, foreign and domestic. Many have limitations occurred as a result of all applied commented on its “stellar performance” from loads acting on the load sensing elements tests on the next generation of aircraft. and the deflection of the internal workings. Having reached design maturity in a The Hi Cap Balance reduces the few short years, the Hi-Cap The MC-44h-1.750 Balance is a compact version of the hi-Cap series. The short length and high loads are suited for testing launch vehicles magnitude of the stress from loads Balance is a proven and reliable in all directions industry tool. It is the except the primary ideal balance load direction. The for meeting deflections of this the demanding type of balance are wind tunnel test The MC-60h-2.50 hi-Cap Balance has a larger frame for testing models with increased load ranges of low when compared requirements of today and the Normal and Roll. The load range is also adjustable to meet test requirements. with conventional single piece future. Anticipating the needs of and other force type balances the future aerospace industry at the same load capacity and has led the FMS team to diameter. examine new systems, The new-generation Hi sensors, and other leadingThe MC-60h-2.00 hi-Cap Balance is well suited for testing a wide variety of aero models. The load Cap design offered challenges edge approaches to balance range is adjustable to meet changing test requirements to successfully incorporate technology. these changes without sacrificing the state-of-the-art high level of CONTACT performance of the existing design (the Flexured Force Balance), Contact Dennis Booth, Triumph Aerospace Systems while maintaining the ability to fabricate and instrument the balance. E-mail:





View from above within the BMW AEROLAB, clearly showing the mounting of a 50% scale model on the huge rolling belt

BMW’s New Wonder

New information is emerging from BMW’s Aerodynamic Test Center (ATC), which was featured prominently in last year’s Wind Tunnel International. Final commissioning of the newly built facility was completed in November 2008, so BMW is now approaching two years of successful product research and development testing in their ATC. Rex Greenslade reports


o the passer-by traveling through the heart of Munich, the ATc provokes a dramatic impression – a mix of beauty, technology, and excitement reminiscent of that conjured by BMW automobiles. In keeping with BMW’s technology and design ethos, significant function is integrated within the form. As can be seen from close inspection of the photograph, the ATc actually includes two wind tunnels. The outer, horizontal loop that appears to float above the ground is the BMW Windkanal, an aero-acoustic wind tunnel dedicated to fullscale testing. The enclosed vertical circuit is the BMW AEROLAB, dedicated to both 50%-scale and full-scale testing. The hallmark of both is leading technology. 118

Also included within the facility is a 32,000m2 support building with spaces for design, vehicle and model preparation, and engineering. The wind tunnels and support building are, in truth, one, the architectural strategy having focused on spurring collaboration between the various functions included within the facility. Hence, the nested wind tunnels provide close proximity of test sections, control rooms and related support spaces. BMW has recently published significant new information about the technical capabilities of their ATC. To realize how important aerodynamic technology is to BMW, one need look no further than the fact that between 1995 and 2008, BMW reduced the fuel consumption of vehicles sold in Europe by 25 percent, bettering by far the self WIND TUNNEL INTERNATIONAL | 2010


Technicians at work on a scale model in the AEROLAB (above). Smoke trail demonstration with wheels removed to illustrate wheelarch aerodynamics (below). Aerial view of the ATC exterior clearly showing the two wind tunnel circuits and the snugness within the surrounding neighborhood (bottom)

(Photo: BMW)

committed target of the ACEA (European Association of Automobile Manufacturers). The primary statistics for the Windkanal are quite impressive. The facility features an automatically adjustable nozzle that morphs between 25m2 and 18m2 with a top wind speed of 300 km/h. Optimizing the axial static pressure gradient within the test section was a key BMW objective in developing the facility; this because the adverse gradient normally encountered in open jet test sections has a strong influence on measured vehicle forces and moments. Analytical correction methods have been developed for the resulting horizontal buoyancy and wake distortion effects, but these are not ideal given inherent nonlinearities and an inability to correct localized flow effects. Since BMW optimizes countless design details in developing a new model, a flat pressure gradient was a top priority. Detailed measurements have now been presented, including details of the novel flow collector deployed in the rear of the test section to stabilize the jet flow and avoid adverse gradients. The results show a gradient of essentially zero, within Âą0.001/m over a length of 8m or more. This same level of performance was also achieved in the AEROLAB. The constant pressure region is sufficient to capture the length of 2010 | WIND TUNNEL INTERNATIONAL

a vehicle and its near wake, eliminating one of the major hurdles vehicle developers must overcome during wind-tunnel testing. Published data confirm top performance in other key performance areas. Pressure fluctuation levels (Cp,rms = prms /q) are in the range of 0.6% to 1.6%. These numerical levels are similar to data published for other leading aero-acoustic wind tunnels, but it must be noted that these levels are measured within the flow while other facilities have focused on out-of-flow measurements. BMW focused on in-flow fluctuation levels because these are most relevant to 119


The BMW Windkanal with full-scale test car (3-Series Convertible). Note the novel flow collector (above and below right) that produces exceptional longitudinal pressure gradient performance

vehicle testing (the test vehicle is of course located within the flow), and the authors highlight the differing physical mechanisms that lead to variances between in-flow and out-of-flow measurements. A key element of success in achieving low fluctuations was the use of novel Helmholtz resonator technology to suppress unsteadiness at natural frequencies of the wind tunnel. The passive technology was developed in an intensive program encompassing both CFD and scale-model testing, and the full-scale version was proven to provide dramatic suppression of fluctuation energy at dominant frequencies. The available performance data are extensive and the performance results quite uniform for both wind tunnels. Turbulence levels at the nozzle exit are 0.05%. Planar nonuniformity of total and static pressure (�P/q) within the jet was measured to be 0.20%. Temperature nonuniformity levels (�T/T) are within 0.2°C. Flow angularity levels of approximately 0.1° were measured for both pitch and yaw. Airspeed stability is within ± 0.03 m/s. The tunnels maintain air temperature at 20°C, stable within ±0.1°C independent of ambient conditions. These performance levels match or redefine the state-of-the-art in all cases, providing a stable environment with excellent flow quality for vehicle testing. The special systems integrated into the ATC test sections provide 120

test capabilities not available in other wind tunnels. One features a single belt rolling road while the other features a five belt system (long center belt plus four smaller belts located under the spinning vehicle tires) with integrated underfloor force and moment balance. For both, customized boundary layer control systems remove the floor boundary layer just upstream of the moving ground system. Both test sections are equipped with overhead traverse systems to enable probe measurements around the perimeter of the test vehicle or the application of advanced diagnostic techniques. The AEROLAB actually contains two overhead traverse systems, one with embedded systems for simulating complex model motions. The availability of two systems also provides the capability to simulate drafting and overtaking maneuvers with tandem test models. Even before construction was complete, it was clear for all to see that the BMW ATC would make a striking architectural statement. Now that the facility is engrossed in vehicle development activities and technical details have become available, we can confirm that its function is commensurate with its form. For the traditional measures of wind tunnel quality, the ATC wind tunnels redefine state-of-the-art. Taken together with the closely-integrated design, engineering, and test support functions housed within the facility, the ATC represents an automotive wind tunnel capability without rival anywhere in the world. WIND TUNNEL INTERNATIONAL | 2010


Future Perfect?

California Polytechnic State University (Cal Poly), San Luis Obispo, Calif. is currently in its third year of work on a NASA Research Announcement (NRA), collaborating with Georgia Tech Research Institute (GTRI) to develop and validate predictive capabilities of the design and performance of a next generation (N+2) Cruise Efficient, Short Take-Off and Landing (CESTOL) subsonic aircraft. Eric paciano of Cal Poly describes the latest work.

computational fluid dynamics (CFD) validation, the resulting data will include many measurements that go undocumented in traditional wind tunnel tests. Some of the more impactful of these measurements include acoustic signature and global skin friction. Each of these measurements contributed their Cal poly’s N+2 CESTOL airliner during fuel efficient cruise, with slots retracted own requirements, restrictions, and demands h e co n c e p t UA L a i r c ra f t, to the testing procedure and facility. In order developed by David hall at for the required acoustic measurements to Dhc engineering and refined be made, a 70-element stationary phased by cal Poly, was designed array, eight surface mounted as a 100-passenger, regional unsteady pressure airliner with a hybrid blended wing- Kulites, and a 30° body, circulation control flap system, and m i c r o p h o n e over-the-wing engine configuration. The were necessary design focused on N+2 goals of 25 percent additions to reduction in fuel consumption and progress t h e t e s t i n g Sting-mounted model with acoustic towards -52 dB cumulative lower noise instrumentation. instrumentation levels than current-generation aircrafts. Furthermore, in the NFAC tunnel. Mach contours Based on NRA requirements and available acoustic testing shown with circulation control wind tunnel sizes, the wind tunnel model was r e q u i r e d t h e jet streamlines overlaid in yellow sized to 1/11th of the full scale airliner, or 10 tunnel test section feet in span. The model, called the Advanced be lined with noiseModel for Extreme Lift and Improved absorbing acoustic Aeroacoustics or AMELIA, will be tested treatment. in the summer of 2011 in the National FullOne of the more unique quantities utilized scale Aerodynamics for CFD validation is Complex (NFAC) 40 global skin friction, x 80 ft wind tunnel which will be obtained at the NASA Ames using the FringeResearch Center. In Imaging Skin Friction the months after the (FISF) technique. The test, experimental process requires that data will be postimages be taken at a processed, used to close proximity to the validate the developed model surface within prediction tools, and minutes of testing. compiled to a publicly As a result, tunnel available, extensive transient time, test database to support section lighting, and next-generation model accessibility aerodynamic and were significant acoustic modeling considerations for the efforts as a validation wind tunnel design of dataset. experiments. As a wind tunnel Any difficulties Fringes on the reflective surface of a test article during the test intended for application of the Fringe-imaging Skin Friction technique faced in the data



An example of CFD solution showing skin friction on the model surface, and contours and streamlines of Mach number

Advanced meshing techniques like this fully structured mesh are constantly being explored

acquisition process were easily trumped by the challenge of incorporating circulation control flow technology. Circulation control consists of blowing high speed air tangentially from slots to the wing’s upper surface at the leading and trailing edges of the wing. The addition of circulation control necessitated the use of the valves, plenums, and bellows that comprise the low pressure air control system housed within the model. The high speed jets needed for circulation control also create the issue of large amounts of downwash, in some test conditions preliminary CFD showed downwash exceeding 10 feet below the model. In order to eliminate the possibility of jet flow impingement on the tunnel floor, the large NFAC test section was required. CONTACT Dr. David D. Marshall, California polytechnic State university E-mail: 121


X Stands For Extraordinary


Or experimental… Or exceptional… Or exciting he X-1 became the world’s

of advanced aerodynamics and astronautics. The accomplishments of the X-Plane Program are almost too many to list, but include: the first aircraft to break the sound barrier; the first aircraft to use a variable-sweep-wing in flight; the first to fly at altitudes in excess of 30,000, 60,000, and 90,000 m (100,000, 200,000 and 300,000Üft); the first to use exotic alloy metals for primary structure; the first to test gimbaled jet and rocket engines; the first The program included: a range of vertical to use jet-thrust for launch and landing; the takeoff and horizontal landing vehicles; first to fly three, four, five, and six times the smaller, propeller-driven reconnaissance speed of sound; the first to test boundary-layervehicles; and a series of unmanned missile airflow control theories over an entire wing testbeds of both single and multistage designs. at transonic speeds; the first to successfully Although the program grew to include complete a 180-degree turn using a post-stall conventional propeller-driven aircraft, a maneuver; and the first missile to reach an common theme of all designs was the research intercontinental flight range.

Historical purists may argue with our choice of X-Plane examples. Why include the XB-70 that’s not on any X-Plane list … because it was originally a US Air Force project? But it became the prototype research plane for the United States’ Supersonic Transport (SST) project and did the research that banned overland supersonic flight and, some would say, killed the Concorde. It also happens to be breathtakingly beautiful. And beautiful is also an adjective we’d use in describing (and justifying the inclusion of the SR-71 Blackbird). It wasn’t an X-Plane because it went into (limited) production but can be argued as the epitome of the X-Plane spirit as it incorporated so much of the X-Plane research and technology in its design.

best-known experimental aircraft after it became the first airplane to break the sound barrier (October 14, 1947). That was only the start of the X-Plane Program which eventually encompassed over 30 different major research designs, both rocket-powered (as the X-1 was) and nonrocket-powered, that were built and tested.

XS-1: the world’s first supsersonic airplane

X-2: swept-wing configuration. Mach Mach 2.44; maximum altitude of 90,440 ft

X-5: successful variable sweepwind design

X-3: titanium construction, self takeoff and landing, led to understanding of inertia coupling

X-29A: forward-swept wing, advanced composites

X-4 was designed to test a semi-tailless wing configuration at transonic speeds

XB-70: Mach 3/high altitude bomber prototype that evolved into SST (supersonic transport) prototype; supersonic boom research

X-15: hypersonic (Mach 6.33); high altitude (354,200 ft.)


A collection of NASA’s research aircraft on the ramp at the Dryden Flight Research Center in July 1997: X-31, F-15 ACTiVE, SR-71, F-106, F-16XL Ship #2, X-38, and X-36


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Wind Tunnel International 2010