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LEONARDO TIMES Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’


AN EXTRAORDINARY LIFE Airport innovation Faster security? Page 10 Year 22 | N° 1 | March 2018

Formation flying Efficiency before time Page 14

Twin fuselage A renaissance of sorts Page 22

Biofuel. You won’t notice the difference, but nature will KLM has proven that aviation can be more sustainable. As a pioneer we operated the world’s first commercial flight with biofuel. However, KLM will only use biofuels with no negative effects on food production and nature. Together with partners we stimulate the development of biofuel, only when used on a large scale biofuel will make the difference -

EDITORIAL Dear reader, What a brilliant start to the year we’ve all had! We’re only a few months into 2018 and a new frontier in space flight has already been established. The launch of SpaceX’s Falcon Heavy and the successful return of its side boosters puts us in a rather prominent era, one that will see us extend human presence to another planet more successfully than ever before. I think I’m right in assuming that everyone who saw both the launch and the landing had goose bumps - and maybe even a slight feeling of jealousy at the engineers and scientists who got to work on such a remarkable project. Nothing short of a great feat worth speaking of for years to come, indeed. Now, moving past all things Elon Musk, the spotlight on global pollution shines brighter and the contributions of aviation can no longer be ignored. As air travel is expected to double over the next two decades, so will harmful emissions. A NatGeo study puts in layman terms that if aviation were a country, it’d be the world’s seventh largest carbon emitter. Major developed nations are set-

ting goals to reduce further impact on the environment. For example, The European Commission has goals to reduce carbon dioxide emissions by 75% and nitrogen oxides by 90% within the aviation industry alone by 2050. Such statistics and actions will soon push the industry into an all-electric corner. As of now, Rolls-Royce, Airbus, and Siemens have teamed up to develop a passenger aircraft powered by a hybrid-electric motor. Sure, commercializing this design will be quite a wait but you can’t deny that once it takes off, we’ll all be for the better. March is Women’s History Month, a time to celebrate the achievements of women around the world. The aviation world is no stranger to the incredible women who pushed boundaries and helped propel aviation to where it is today. Therefore, we pay homage to the extraordinary life Amelia Earhart lived, as well as delve into the mystery of her disappearance, with Amelia: A Brief History of the Pioneering Aviator (part I of the series can be found in the December 2017 Leonardo Times). This issue follows with its predecessors when it comes to diversity in content. Stef Janssen and Elise Bavelaar explores the efficiency and security of airport with the use of a novel security risk assessment methodology using agent-based modelling, further tying in the works of the pioneering project ‘Innovation Airport’ conducted at TU Delft. Luca Anselmi delves into energy generation- one of the biggest challenges we facewith the use of Diffuser Augmented Wind Turbines (DUWT), a promising concept for an urban source of energy. As we thrust past Earth’s atmosphere into space, Arjan Vermeulen tells the story of ESA’s Ariane family and its future member, the Ariane VI. Finally, a least when it comes to this editorial, we have Nicolò Nefri who investigates the environmental impact of the ever-growing aviation industry, as current pollution levels become the most severe threat to humanity.

Last edition ...

LEONARDO TIMES Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’


THE END Amelia

Drag analysis

Flying cars

An extraordinary life

Studying a cyclist

What's in our future?

Page 13

Page 16

Page 40

Year 21 | N° 4 | December 2017

If you have remarks or opinions on this issue, let us know by dropping an email at:


Likes us on Facebook /leonardotimesjournal



FRONT FEATURES 03 Editorial 07 Leonardo's Desk 08 In the News




Let's get in formation Formation flight in civil aviation is a promising concept for saving fuel. Using a Hybrid Optimal Control approach, the trajectories of aircraft performing a formation flight can be optimized.

CONTROL & OPERATIONS (C&O) 10 Safety First! 14 Let's Get in Formation

TIME FLIES 17 Amelia


INTERNSHIP 26 Internship at Deerns 30 Ma Vie dans la Ville Rose

28 Ariane VI In 2020, ESA is set to launch its new workhorse: the Ariane VI. A novel launcher in a successful family, driven by the requirements of the modern market.

SPACE DEPARTMENT 28 The Development of Ariane VI


AERODYNAMICS 32 Flow Reconstruction 36 Bobsleigh Aerodynamics

NICO'S CORNER 40 Sustainable Air Travel

AEROSPACE STRUCTURES & MATERIALS 42 Steered Fiber Panels 48 Aicraft Manufacturing Laboratory


44 Exploring Ducted Turbines

Internship at Deerns Internship at Abu Dhabi International Airport

ADVERTISMENTS 02 KLM 06 Delft Career Platform 24 DDB 51 NLR


52 GKN




The twin fuselage revival


Twin-fuselage aircraft have occupied a small place in history. How are Virgin Galactic and StratoLaunch bringing back this exceptional configuration?

Year 22, NUMBER 1, March 2018 The ‘Leonardo Times’ is issued by the Society for Aerospace Engineering students, the VSV ‘Leonardo da Vinci’ at the Delft University of Technology. The magazine is circulated four times a year with a circulation of around 5000 copies per issue.

EDITOR-IN-CHIEF: Nora Sulaikha FINAL EDITOR: Nicolas Ruitenbeek



EDITORIAL STAFF: Thijs Gritter, Katharina Ertman, Flavie Rometsch, Greeshma Boohalli Shivamallegowda, Abhishek Mittal, Nicolò Nefri, Maria Mathew, Dmitrij Mordasov, Yaren Curgul, Urh Krzic, Shashruth Reddy, Maurits Rietveld. THE FOLLOWING PEOPLE CONTRIBUTED: Vibhas Mishra, Elise Bavelaar, Stef Janssen, Martina Stavreva, Ralph van Sunten, Arjan Vermeulen, Joris Stolwijk, Luc de Ruiter, Pallav Pattnaik, Federica D’Onofrio, Luca Anselmi. DESIGN, LAYOUT: SmallDesign, Delft PRINT: Quantes Grafimedia, Rijswijk Articles sent for publishing become property of ‘Leonardo Times’. No part of this publication may be reproduced by any means without written permission of the publisher. ‘Leonardo Times’ disclaims all responsibilities to return articles and pictures. Articles endorsed by name are not necessarily endorsed editorially. By sending in an article and/or photograph, the author is assured of being the owner of the copyright. ‘Leonardo Times’ disclaims all responsibility. The ‘Leonardo Times’ is distributed among all students, alumni and employees of the Aerospace Engineering faculty. The views expressed do not necessarily represent the views of the Leonardo Times or the VsV 'Leonardo da Vinci'.

Sustainable air travel

VSV ‘Leonardo da Vinci’ Kluyverweg 1, 2629HS Delft Phone: 015-278 32 22 Email:

Between 1990 and 2006, the emission of greenhouse gases from air travel increased by approximately 90%. Is there still time to undo this trend and make air travel more environmental friendly?

ISSN (PRINT) : 2352-7021 ISSN (ONLINE): 2352- 703X Visit our website for more content. Remarks, questions and/ or suggestions can be emailed to the Editor-in-Chief at the following address:




Delft Career Platform find internships, graduation projects & jobs


Delft Career Platform is the new starting point of your career! You can find the best opportunities and events based on your preferences and academic background. powered by


A MESSAGE FROM THE BOARD Dear reader, I’m honored to write this second preface for the Leonardo Times. I hope you read this magazine with the same enthusiasm and interest as I do. I would like to compliment all the Leonardo Times editors for their dedication and eager to deliver once more such a high-quality issue. Since the aerospace industry is so broad, a wide variety of topics is included in this issue of the Leonardo Times. In this edition, we are looking back at the twin-fuselage design and we are looking forward to what this design could mean for the future. A must-read article about a safety risk analysis model for airports awaits you as well. Do not forget to let yourself be inspired by the second part of the story of Amelia Earhart. This is just a small glimpse of the articles you'll come across. I think it is marvellous how the editors managed to cover such a wide variety of branches in the industry.

Additionally, I would like to use this opportunity to inform you on the status of the society. We are halfway through the academic year as period three is beginning. As a study association, we have had the opportunity to be the bridge between industry and students in several in-house days and lunch lectures from numerous companies. With these events, we believe that students can develop themselves and learn about companies that would value their skills as engineers. Therefore, I would like to advise students that did not attend one of these events to do so in the next period, as we have a wide variety of career-related events planned. One of the biggest events that we organize in collaboration with four other study associations is “De Delftse Bedrijvendagen” or The Delft Career Fair. With over 3,000 students and more than 150 companies presenting, it is the ultimate opportunity to dive into your future possibilities. On the 6th of March, the Space Symposium took place themed: “Rescaling Limits: Ex-

ploring Spacecraft Sizing”. This symposium dove into the miniaturization trend of satellites. What are the challenges for smaller satellites? How can they cooperate with the more conventional large satellites? Coming up is: A mini symposium organised by the Women’s Department ‘Amelia’ themed: “Be the Game Changer”. By means of this symposium women at our faculty are encouraged and prepared to join the aerospace industry. These, and more, activities make that we as the 73rd board of the VSV ‘Leonardo da Vinci’ are looking very forward to the coming period. I hope you will enjoy and learn from this new issue of the Leonardo Times. With winged regards, Roger Hak President of the 73rd board of the VSV ‘Leonardo da Vinci’



QUARTERLY HIGHLIGHTS Tropomi Sentinel 5P (S5P), which was launched on October 13, last year. Sentinel 5P, is the first satellite of the atmospheric composition Sentinels, developed to reduce data gaps between the Envisat and the launch of Sentinel-5. “Having Sentinel-5P in orbit will give us daily and global views of our atmosphere with a precision we never had before,” said Josef Aschbacher, ESA’s Director of Earth Observation Programs. “Our historic data records, together with the long-term perspective of the Copernicus satellite program, opens the doors for generating datasets spanning decades – a prerequisite to understanding our ever-changing Earth” he adds.

Since the 90s, the Dutch have been designing and building atmospheric sensors for satellites, like the ones carried by the ERS and Envisat, the world's largest civilian Earth observation satellite. Building on this technological heritage, TROPOMI, the most advanced multispectral imaging spectrometer, has been developed by ESA and the Netherlands Space Office. TROPOMI, the TROPOspheric Measuring Instrument is on board the Copernicus

Soon, the geostationary Sentinel-4 and polar-orbiting Sentinel5 missions will monitor the composition of the atmosphere for Copernicus Atmosphere Services. But before that, the Sentinel-5P mission will play a key role in monitoring and tracking air pollution. TROPOMI will serve to monitor air quality and procure critical information for various services and institutions, and so aiding in important decision-making processes to improve life for European citizens. The instrument will monitor the sunlight

scattered back to space from the terrestrial surface and atmosphere, detecting unique gases in various parts of the spectrum. One of the most important features of TROPOMI is its ability to measure ultraviolet and visible (270–500nm), near-infrared (675–775nm) and shortwave infrared (2305–2385nm) spectral bands. This allows it to accurately map a multitude of trace gases such as, nitrogen dioxide, ozone, formaldehyde, sulfur dioxide, methane, carbon monoxide, and aerosols – all of which affect the air we breathe, and therefore our health, and our climate. It’s also capable of observing air pollution over individual cities, thanks to a high resolution of 7km × 3.5km.

During the Annual Fall Meeting held by the American Geophysical Union (AGU) in New Orleans, on December 16, 2017, Pepijn Veefkind presented the first results obtained by TROPOMI. Highlights from the recent "First Light" events held at DLR, and KNMI (Koninklijk Nederlands Meteorologisch Instituut) were presented. Furthermore, images of individual nitrogen dioxide plumes from the smokestacks of coal-fired power plants located on the South African "Highveld” were shown with great clarity.

Engines of the future At DLR in Cologne, tests of the ICD, Inter Compressor Duct, have started. This technology has the potential of making future aircraft engines even lighter and more fuel-efficient. The plan is to incorporate the ICD into the next generation of geared turbofan engines. In collaboration with MTU Aero Engines and GKN Aerospace Engine Systems, DLR, the German Aerospace Center, has been working together within the European research program Clean Sky 2. The main goal of Clean Sky 2 is to develop and implement technologies for an even cleaner and more efficient future in the aviation sector. Within this program DLR leads the Technology Evaluator, which consists of building and applying an integrated assessment environment that allows the benefits of the overall technology programs to be identified and evaluated in environmental, economic, transport, and competitive terms. Apart from tailoring the low-pressure compressor, ICD, and high-pressure compressor to each other to determine and utilize the potential for new engines, being more fuel-effi08


cient, is an important action on this path for the systematic measurement of flow conditions in short, sharply angled ICDs. To allow these measurements, a novel wind-tunnel test rig has been built at DLR in Cologne. Dr. Gerhard Kahl, Chief Engineer, Technology Demonstrators and Rigs at MTU, acknowledged, "with these tests, we will significantly advance our understanding of the flow in the ICD, in order to further reduce the overall length, and thus the weight of the engines, with particularly compact designs." Test operations initiated under supervision of DLR, MTU and GKN Aerospace Engine Systems. Rolf Henke, Member of the DLR Executive Board responsible for aeronautics research said, "as a national research center, DLR plays a key role in the progressive development of the entire air transport system". He added, “there have been great advances in propulsion in recent decades. Together with our partners MTU and GKN, we are very proud to introduce a further large step with this ICD rig."

For MTU, leader in the development of the system, Dr. Gerhard Ebenhoch, Director Technology Management explained, "in this collaboration, the strengths of the partners are outstandingly integrated – the skills of GKN in large, static components; the experience of DLR in the field of testing; and the compressor and system competence of MTU." Robert Lundberg, representative of GKN Aerospace Engine Systems, said, “to be able to validate our technologies at high TRL in a unique rig is really an opportunity for GKN. We have no chance to do this by ourselves in Sweden, so it really shows the importance of European collaboration.” From Clean Sky, the Project Officer of the Engine-ITD Jean-Francois Brouckaert recognized, "this new test facility allows us to perform important EU collaborative research on the next generation of engines. Congratulations to the MTU, DLR and GKN team for achieving this important milestone! It is an excellent example of complementarity between experimental and numerical work."

The Sun is no longer the only star with eight planets For the first time, researchers discovered an exoplanet around another star using artificial intelligence. In a teleconference, held on December 14, 2017, NASA and Google announced the recent discovery of an eighth planet, orbiting a distant Sun-like star called Kepler-90. The planet is 2,500 light-years from Earth and was given the name Kepler-90i. This exoplanet is characterized by a rocky landscape and a surface temperature of around 800°F (426°C) making the possibility of life highly unlikely. It orbits around its host star once every 14.4 days. For the first time, a discovery of a planet was made by means of a neural network, which has been developed by Google, to analyze archival data from the Kepler Space Telescope.

“A neural network is a machine learning algorithm that is very loosely inspired by the human brain,” said Christopher Shallue, senior software engineer at Google AI and co-author of the study. Shallue elucidated that the algorithm takes sample inputs, learns to identify patterns in the data, and after that employs those patterns for future identifications. Within four years from the launch of Kepler in 2009, the Space Telescope has produced a dataset of 35,000 planetary signals from a very small area of the sky. Back then, the datasets were mainly analyzed manually by researchers, which meant that it involved long tedious work with chances that small signals were likely to be missed. Prior to use of the neural network, researchers had to first train the algorithm to detect transiting exoplanets from Kepler’s light curves. These determine how the brightness

of a star drops off whenever an orbiting planet transits ahead of it. The neural network “learned” to correctly identify true planets employing 15,000 previously confirmed exoplanet signals as flash cards. Once the neural network comprehended which patterns it was looking for, the researchers released it on 670 of Kepler’s weaker signals. In these weak signals, the AI discovered two possible exoplanets, Kepler-90i and Kepler-80g. Paul Hertz, director of NASA’s Astrophysics Division in Washington, DC said, “just as we expected, there are exciting discoveries lurking in our archived Kepler data, waiting for the right tool or technology to unearth them.” Furthermore, he acknowledged, “this finding shows that our data will be a treasure trove available to innovative researchers for years to come.” 

UFO Unmanned aircraft are being increasingly employed and are crucial to the future of aviation, particularly in the freight transport sector. Freight aircraft could be controlled from the ground in the imminent future. "Controlling freight aircraft from the ground has several benefits," clarified Annette Temme from the DLR Institute of Flight Guidance. "For example, crews can be deployed more flexibly on the ground, as they do not need to actually travel on long-haul flights, but can operate the aircraft from a single location." This enables longer flight times and a more balanced workload division. At the moment, the DLR, German Aerospace Center, is working on a project called UFO (Unmanned Freight Operations), which focuses on examining the possibilities of the integration of unmanned freight aircraft into the conventional air transport system.

tion, all three scenarios come with different requirements. In case of transport of relief goods, one surveillance option is the division of the airspace using special corridors that resemble those used for manned relief missions. The aircraft are led to follow fixed routes, apart from the surrounding air traffic. When factory goods are being transported, certification as well as authorization for a special transport task must be considered.

When unmanned aircraft approach an airport, they are integrated into the arrival and departure sequence, while considering their individual requirements. It is crucial that at busy airports, unmanned freight aircraft do not obstruct conventional air traffic. To avoid this, researchers enhanced and tested the air traffic control support systems in order for air traffic controllers to be able to identify the features of unmanned aircraft.

Furthermore, integration into the air transport system needs to be considered. While longhaul freight transport can solely be integrated into conventional air transport system. In this circumstance sector-less guidance would be feasible, by means of air traffic controller that monitors unmanned aircraft over an extended length of the route. Expressly instructed traffic controllers could administer the unmanned aircraft. They would be in contact with a pilot on the ground, who carries out the instructions of the controllers.

Temme proudly announced, "the project has shown that unmanned long-haul freight transport is generally possible in technical and organizational terms." Despite this, many issues remain open regarding the actual implementation of unmanned freight flights, such as defining responsibilities for tasks that pilots have so far performed on site or making the security of the communication data link clearer. Once these issues are solved, the use of unmanned freight aircraft is certainly conceivable.

Several solutions for the airspace managed by air traffic control have been created, resulting in three different scenarios. These include freight transport between two manufacturing sites, long-haul freight transport and the transport of relief goods. About the selection, Temme expressed, "the chosen scenarios cover a wide range of different airspace integration issues." For each scenario, researchers developed and validated new support systems, procedures, and technologies for air traffic controllers and pilots. In terms of airspace integraLEONARDO TIMES N°1 2018


SAFETY FIRST! Agent-based simulations for safer airports C&O

Stef Janssen, PhD Candidate, TU Delft & Elise Bavelaar, Project Lead Innovation Airport, TU Delft

Part I of this article describes a novel security risk assessment methodology that uses agent-based modelling to analyze the efficiency & security of airports. This project originated from “Innovation Airport”, one of the pioneering innovation initiatives of the Faculty of Aerospace Engineering, which is briefly described in Part II.

I. AGENT-BASED SECURITY RISK ASSESSMENT Security Risk Assessment is used to qualitatively or quantitatively find security risks in a domain. Security experts commonly use the so-called Threat, Vulnerability & Consequence (TVC) methodology (ASME, 2009). Four important steps of this methodology are: Threat Identification, Threat Likelihood Assessment, Vulnerability Assessment and Consequence Assessment. Threat Identification is the first step, in which experts aim to identify a set of possible threat scenarios. These threat scenarios are a potential cause 10


of an unwanted incident, which may result in harm to the domain. For each identified threat scenario, a Consequence Assessment is executed. In this step, one aims to quantify losses in case the identified threat scenario were to happen. In the next step, Threat Likelihood Assessment, the probability that the threat scenario will happen in some time period is estimated. Then, Vulnerability Assessment is performed to quantify the likelihood that the attackers executing the scenario are successful. In other words, this means that all defence measures in the threat scenario fail. Risk with respect to a specific threat scenario

is then the product of Threat Likelihood, Vulnerability and Consequence. Threat Likelihood, Vulnerability and Consequence are often quantified using analytic tools used by security experts. These tools include event trees (Ezell et al., 2010), historical data analysis, intelligence data, and the experience of security experts (ASME, 2009 & ICAO, 2011). It is often observed that these methods do not properly take the inherent dynamic and intelligent nature of adversaries and defenders into account (Cox, 2008). Furthermore, these methods often struggle with the realistic modelling of underlying socio-technical processes often present in domains like airports. To model the inherent dynamic and intelligent nature, researchers focussed on using


Figure 1 - The airport layout of the case study, with indicators for different areas. A, B and C are facility areas. D is the check-in area and E are queuing areas. F is the security checkpoint area and G is the gate area. on security experts and leads to more consistent quantitative results.


game theory to represent a threat scenario (Brown et al., 2016). While these so-called security games allow for the modelling of intelligent and dynamic adversaries, they still require the input of security experts to determine pay-off values. These pay-off values still have to be defined by relying on the above discussed methods to quantify Vulnerability and Consequence. To overcome the above-mentioned limitations, we propose an Agent-based modelling and simulation method, that can be used to assess both Vulnerability and Consequence. Agents (like attackers and defenders) can be defined to be intelligent and adaptive. Furthermore, using agent-based modelling, more realistic modelling of the underlying socio-technical processes can be created. It further reduces dependency

An agent-based simulation model mi is defined to replicate some identified threat scenario si. The model contains a set of defender agents, adversary agents and other agents. The set of defender agents is responsible for the defence in si. The set of adversary agents execute the subversive actions in threat scenario si. The remaining set is the set of other agents present in si. This can, for instance, be a set of pedestrians or airport passengers. Vulnerability and Consequence are estimated using a Fail function and a Consequence function respectively. A Boolean Fail function F(mi,j) is defined, that determines the success of the adversaries (and therefore the failure of the defence) for simulation run j, denoted mi,j. The function is equal to 1 if the defenders failed and 0 otherwise. Furthermore, a (real-valued) Consequence function C(mi,j) determinwa the Consequence of the simulated threat scenario. This Consequence function incorporates estimates of direct losses and indirect losses. Direct losses for instance, include fatalities of an attack and are estimated from mi,j. Indirect losses, like business disruptions, are based on the historical data and estimated direct losses. Monte Carlo simulations are performed to

estimate Consequence and Vulnerability values. This is done by performing N simulations and calculating the averages of the outcomes of the Consequence function and Fail function respectively. This approach can easily be extended to multiple threat scenarios of a domain by replacing the set of adversary agents with a new set that executes different actions.

AN IMPROVISED EXPLOSIVE DEVICE ATTACK IN THE AIRPORT TERMINAL We apply the above defined agent-based security risk assessment methodology to a case study at an airport terminal. In this case study, a single threat scenario in which an attacker aims to detonate an Improvised Explosive Device (IED) in the open areas of the airport is investigated. In the corresponding agent-based model, operations like check-in, facility visits, security checkpoint operations, queuing, gate processes and the movement of passengers between these processes are represented. A visualization of the airport terminal used in this case study is shown in Figure 1. The model contains three types of agents, namely passengers, employees and an attacker. Passengers randomly arrive at the airport, perform different activities, like checking in, going through the security checkpoint, LEONARDO TIMES N°1 2018


for a short period of time. Opening more security checkpoint lanes or reducing the number of passengers present, then does not influence this anymore. Comparing Figure 3(a) and (b) show lower conditional risks if the BDE is present. The differences are due to the lower vulnerabilities if the BDE is present at the airport. While it is beneficial from a risk reduction point of view to hire a BDE, airports have to invest in their training and salary. Furthermore, it can be seen that opening a maximum number of security checkpoint lanes at all times beneficial from a risk reduction point of view as well. However, opening more security checkpoint lanes costs the airport more money. Airport managers regularly have to make decisions that influence both security risks and costs, and the presented methodology can aid them to make better informed decisions. For more information about this project, please contact Stef Janssen, s.a.m.janssen@


Figure 2 - The security checkpoint area with queuing passengers. shopping, etc., and finally leave the airport when their flight leaves. If passengers cannot perform their desired activity, they wait in a queue. Figure 2 shows an illustration of a group of passengers waiting to go through the security checkpoint. Two employees are distinguished in the model: the standard employee and the Behaviour Detection Employee (BDE). The standard employee interacts with passengers when they check-in or go through the security checkpoint. The BDE walks around the airport terminal and tries to observe abnormal behaviour in other agents to distinguish between passengers and attackers. If abnormal behaviour was observed, the BDE tries to arrest the passenger or attacker. Finally, the attacker brings an IED to the airport terminal. The attacker aims to cause as many fatalities as possible, by detonating the IED at the location with most people. If the attacker is not observed and arrested by a BDE, it moves towards the chosen target. It finally detonates the IED when it arrived at the target area. To assess the Consequence and Vulnerability of the threat scenario, both a Fail function and Consequence function have to be defined. The Fail function is simple: if the bomb was detonated by the attacker, the function returns 0 and 1 otherwise. The Consequence function assess the number of fatalities of the attack. It is based on the work of Pope (Pope, 2011), who designed a prediction tool that is able to quickly assess the human injury after a terrorist attack. The 12


assessment is based on a physics model that estimates pressure differences and trajectories of fragments.

RESULTS Experiments are performed with the model to determine the influence of the number of security checkpoint lanes open (2, 3, 4), the interarrival time of passengers (15s, 20s, 25s, 30s), and the presence of a BDE (true, false) on the conditional risks with regard to the IED attack. Conditional risk is defined to be the multiplication of Vulnerability and Consequence. The interarrival time is the expected time between two arrivals of passengers at the airport. Figure 3(a) shows the results for the conditional risks in the case that no BDE is present, and Figure 3(b) shows results for the conditional risks in the case that a BDE is present. Results are presented in the form of a heatmap. It should be noted that higher interarrival times lead to lower conditional risks. This makes sense, as higher interarrival times leads to fewer passengers, resulting in fewer expected casualties. Furthermore, a higher number of security checkpoint lanes leads to fewer casualties as well. As passengers are processed faster in these cases, queues are shorter and therefore, lower conditional risks are observed. An exception to these observations is the top right portion of the heatmaps (high inter-arrival times and high number of security checkpoint lanes open). Here, the conditional risks remain mostly similar, as passengers only wait in a queue

The above project originated from the Innovation Airport Initiative, one of the pioneering projects of the Faculty of Aerospace Engineering. The Innovation Airport started in 2016 as the shared ambition of the Aerospace faculty and DIMI (Delft Delta’s Infrastructure and Mobility Initiative). The project’s purpose is to combine and leverage the knowledge and expertise of all TU Delft faculties in the field of airports in a larger program than could be achieved individually. Since all faculties already significantly contribute to airport research, there is a sizable opportunity for the TU Delft to play a key role in changing the future of airports. Table 1 shows an overview of airport related expertise areas in the TU Delft. Considering the challenges airports and aviation in general are facing, this change is a necessity. For example, the coming years expect a continuous growth in air travel demand. The annual number of passengers is expected to increase from 3.8 billion in 2016 to 7.2 billion in 2035 (IATA, 2017). This growth presents various challenges, such as congestion and capacity issues, and an increase in noise and emissions. To overcome these hurdles, and to achieve the aviation goals set forth by the European Union (European Commission, 2011; ACARE, 2017), changes to the current way of travelling are required and new concepts and innovations need to be embraced. The focus should be on radical futuristic research and developments at a ‘system level’, rather than a more slowly, step-by-step approach, as this would probably not suffice. Innovation Airport therefore aims to: • Conduct research around the subject of airport development using a ‘sys-

Figure 3 - Conditional risks for different interarrival times and security checkpoint lanes open. a) No BDE present (Left). b) BDE present (right).

Airport Performance Optimization Resilience & capacity Maintenance Safe & Secure Airports Landside & airside Cyber security Green Airports Noise & emissions Energy efficiency Circular economy Comprehensive engineering Responsible innovation Value design Policy making

Smart Airports Digitization Automation New technologies Seamless door-to-door journeys Passenger experience Future of baggage Cargo Intermodality & connectivity Aerotropolis Airport cities Better airport regions Airport networks

Table 1 - Examples of airport expertise areas in TU Delft

tem approach’, including the broadest range of insights and disciplines (e.g. landside, terminal, airside) relevant for future airports. Facilitate co-operation and networking between scientific entities and the industry, focusing on innovation in airports, such as ‘Living Lab’ initiatives.

LIVING LAB To stimulate multi-disciplinary research, innovations and collaboration between different stakeholders, Innovation Airport aims to establish an Airport Living Lab: an (airport) environment where real-life tests and pilot projects can be carried out within the actual processes and systems of the airport. The first steps towards an Airport Living Lab have already been taken by Rotterdam The Hague Airport (RTHA), who signed a Statement of Interest with the TU Delft. In addition, over 30 partners have showed interest in the Innovation Airport initiative. As a result of this, multiple projects have been initiated and some of them have (potential) links to the living lab.

Some examples are: • A research/innovation cluster (2PhD’s, 7MSc’s, 1 Assistant-Professor) focussing on modelling and analysis of Terminal Processes. Within this project an agent-based simulation tool is developed capable of analysing and improving efficiency, security, and resilience of airport terminal operations, and to better understand relations and trade-offs between them. The project mentioned in this article is part of this research cluster. • RTHA-EcoWall Project. The main goal of this project is to design a multi-functional & sustainable structure able to reduce noise & particulate matter and serve as a connector to the airport region (e.g. by adding public functions). • Project for the TUD-Minor “Communication Design for Innovation”. Focus is on developing a communication strategy for the living lab and an effective way of working between involved researchers, businesses, government organisations, the airport and other relevant stakeholders.

The TUD-RTHA living lab will be further developed in 2018. For more information about the Innovation Airport Initiative, please contact Elise Bavelaar, References [1] ASME Washington. All-Hazards risk and resilience: prioritizing critical infrastructures using the RAMCAP Plus SM approach. ASME, 2009. [2] Barry Charles Ezell, Steven P Bennett, Detlof Von Winterfeldt, John Sokolowski, and Andrew J Collins. Probabilistic risk analysis and terrorism risk. Risk Analysis, 30(4):575589, 2010. [3] ICAO. Aviation security manual (doc 8973 restricted). [On-line; accessed 29-November-2017]. [4] Louis Anthony Tony Cox Jr. Some limitations of risk= threat x vulnerability x consequence for risk analysis of terrorist attacks. Risk Analysis, 28(6):1749-1761, 2008. [5] Matthew Brown, Arunesh Sinha, Aaron Schlenker, and Milind Tambe. One size does not fit all: A game-theoretic approach for dynamically and effectively screening for threats. In AAAI conference on Articial Intelligence (AAAI), 2016. [6] Daniel J Pope. The development of a quick-running prediction tool for the assessment of human injury owing to terrorist attack within crowded metropolitan environments. Philosophical Transactions of the Royal Society of London B: Biological Sciences 366, 127–143, 2011. [7] International Air Transport Association (IATA). 2017. IATA 20-Year Air Passenger Forecast. ). [On-line; accessed 29-November-2017]. [8] European Commission. 2011. Flightpath 2050: Europe’s Vision for Aviation. [9] Advisory Council for Aviation Research and Innovation in Europe (ACARE). 2017. Strategic Research & Innovation Agenda (SRIA) Volume 1. LEONARDO TIMES N°1 2018


LET'S GET IN FORMATION Implementation of a Hybrid Optimal Control Approach AIRBUS


G. (Joris) Stolwijk, MSc Graduate Aerospace Engineering, TU Delft

Formation flight is a promising operational concept for reducing the fuel burn of civil aviation flights, which in turn results in a lower emission footprint and operational costs for the airlines. However, making an optimal planning for the trajectories of flights to join in formation is a challenging task.


ith an expected 50% rise in air traffic in Europe, new paradigms such as Trajectory-Based Operations (TBO) are in development for air traffic control to enable more efficient aircraft trajectories. With the implementation of TBO, the concept of civil aviation formation flying to reduce fuel burn becomes more feasible. Because of this expected development, a great interest is currently being shown in methods to determine the best trajectory for an aircraft to fly in formation, given a certain optimization goal.

CONCEPT OF FORMATION FLIGHT Based on the phenomenon of the V-for14


mation in which birds tend to fly, formation flight, as a concept for civil aviation in order to reduce fuel consumption, is a field of research where significant knowledge has been obtained by various researchers in the last two decades. Lissaman et al. found that birds, when flying in large formations together, are able to achieve a range increase of as much as 70% compared to flying solo. Similarly, for civil aviation, the idea is that by letting civil aircraft share a long enough section of their flight path to fly in a formation together, the trailing aircraft will save fuel through aerodynamic benefits. A significant reduction in induced drag is achieved by ‘surfing’ the upwash of wingtip

vortices generated by the leading aircraft. This in turn leads to a significant reduction in fuel burn for the trailing aircraft, making formation flight an economical and environmentally friendly flying strategy. Wingtip vortices persist for a long time, so an aircraft can still experience the drag benefit when the streamwise separation from the leading aircraft is 40 wingspans and hence mitigate safety risks.

OPTIMIZATION PROBLEM Since it is of interest to achieve the highest possible fuel saving benefit from an executed formation flight, a multi-aircraft trajectory planning problem arises regarding how the candidate aircraft should fly before, during, and after the formation flight in order to have lowest possible total fuel consumption. Such problems are often dealt with using

also called the phase structure, constitutes the discrete combinatorial element of the optimization problem. Additionally, the timing of these formation phase switches is also to be optimized for.


Figure 1 - Example of a branch-and-bound discrete solution tree. trajectory optimization methods. Studies in the research field of aircraft trajectory optimization are generally based on optimal control theory, in which the problem is described using continuous variables. However, for formation flight, trajectories also have a discrete element: The dynamic behavior of the modelled aircraft changes with each switch in formation setup en-route. Therefore, Hybrid Optimal Control (HOC) theory is applicable, which aims to deal with systems

that are both discrete time and continuous time from a mathematical perspective. The formation flight optimization problem can then be approached as a hybrid optimal control problem. Much of the complexity of a hybrid optimal control problem depends on how much is known a priori about the switching structure between discrete states. In the case of formation flying with three or more aircraft, determining the sequence in which aircraft join and leave the formation,

For the M.Sc. thesis, an optimization tool is developed which can solve the introduced formation flight hybrid optimal control problem for cases where a maximum formation size of four aircraft is considered. This is done by extending existing optimization software, based on optimal control theory, having functionality to deal with the discrete aspects of the optimization. An efficient algorithm for the evaluation of the discrete solution space of the HOC problem, essentially all possible phase structures, is developed through implementation of a branchand-bound method. In this approach, the discrete solution space is categorized in a tree structure where each tree level represents an additional discrete variable (e.g. formation flight phase) as shown in Figure 2. The algorithm then only evaluates ‘branches’ which show promising characteristics, while ‘chopping’ the other branches. This way, a significant computation time reduction is achieved since a major part of the discrete solution space can be discarded.This

Figure 2 - Horizontal trajectories of Case 1: solo (dotted lines) vs. formation (solid lines). LEONARDO TIMES N°1 2018


Figure 3 - Horizontal trajectories of Case 2: solo (dotted lines) vs. formation (solid lines). evaluation is performed at every tree depth level until the last remaining tree depth level is reached. A branch node is considered promising if the obtained result yields a significant fuel reduction when compared to its parent node (i.e. if the added formation phase makes sense). In the developed trajectory optimization model, the aircraft dynamics are evaluated as a reduced-order point mass model, with the formation flight phases using a single point, multiple mass model to accommodate the presence of multiple aircraft. The physical separation between aircraft is thus not modelled. The induced drag benefit for trailing aircraft is incorporated in the aircraft dynamics by implementing a static reduction factor [3], for each trailing aircraft in the relevant formation phases: The first trailing aircraft receives a 25% induced drag discount, whilst any additional trailing aircraft receive a 50% discount. All phases are connected appropriately using linkage constraints for the state vectors of the linked phases. The used aircraft model characteristics are based on the Boeing 747-400 aircraft.

CASE STUDIES In several case studies, multi-aircraft transatlantic formation flight scenarios are evaluated using the developed HOC tool. The results obtained from this optimization tool are formatted as a 4D flight trajectory for each aircraft. Case 1 considers four transatlantic flights from Europe to North America, with unconstrained departure and arrival times. The modelled flights are: 1. 2. 3. 4.

London (LHR) – Atlanta (ATL) Madrid (MAD) – New York (JFK) Amsterdam (AMS) – Boston (BOS) Rome (FCO) – Toronto (YYZ)



The optimal horizontal trajectories are presented in Figure 3, with the original solo trajectories indicated with dotted lines. This case yields an overall 26kg reduction (-8.90%) in fuel burn for all the flights together. However, it is observed that the leading aircraft actually uses 3.3kg more fuel (+4,00%) to accommodate the formation. Hence, the distribution of the benefits is not equal among the participating aircraft. Also, a flight time increase is observed for all flights, with a total additional flight time of 02:02:21 (+6.90%). This flight time increase is mainly explained by the detours which the participating aircraft fly to join the formation.

be even more optimal if KL641 is allowed to depart later.

Case 2 is more focused on a real-world scenario by using existing flight schedules for the selection of candidate flights. Here, three flights are chosen which in the current schedules are already promising candidates for formation flight as they have similar departure times: KL641, AF6 and VS45, all to New York (JFK) from Amsterdam (AMS), Paris (CDG) and London (LHR) respectively. Because KLM and Air France are already operating together and also recently bought a 31% share in Virgin Atlantic, a high feasibility is expected from a cooperation standpoint. In this case, the departure times are fixed.

To conclude, the usefulness of a HOC approach is very high for the chosen application of trajectory optimization for multi-aircraft formation flying, since a promising and significant fuel saving potential is identified. Recommendations for future research include a further development of the HOC approach, the evaluation of formations with multiple different aircraft models and the inclusion of atmospheric effects and wind in the model. Given the number of flights that are performed every day, the impact of saving fuel just by optimizing their trajectories using formation flying can be very high on a global scale, both environmentally and economically.

The optimal horizontal trajectories of Case 2 are presented in Figure 4. Case 2 yields a 20.4 kg fuel burn saving (-11.47%), a higher percentage saving compared to Case 1 even though only three flights are considered. The flight paths in this case are very well aligned since all flights go to the same destination. Therefore, no significant detours have to be flown and the formation flight phases can be extended. However, KL641, which has a ‘headstart’, does make a detour to allow the other two flights to catch up for the formation. The results could thus

It is found that the developed tool is efficient and functional at evaluating the hybrid optimal control problem of multi-aircraft formation flight trajectory optimization. Even for four-aircraft experiments, computation time remains within practical limits at 5 hours, due to the effectiveness of the branch-andbound algorithm. The convergence behavior of the optimization tool is identified to be heavily influenced by the accuracy of the adapted initial guess. However, the robustness of the developed HOC tool leaves room for improvement.

References [1] SESAR Consortium, “European ATM Master Plan Executive View,” 2015. [2] P.B.S. Lissaman and P. Shollenberger, “Formation Flight of Birds,” Science, vol. 168, pp. 1003–1005, 1970. [3] S. A. Ning, “Aircraft Drag Reduction through Extended Formation Flight,” 2011. [4] “Virgin Atlantic Sells Stake To Air France-KLM, Strengthens Alliance With Delta Air Lines,” Forbes. [Online]. [Accessed: 11-Oct-2017].




A brief history of the pioneering aviator

Katharina Ertman, Editor Leonardo Times




"We are in a line position of 157- 337. Will report on 6210 kilocycles. Wait, listen on 6210 kilocycles. We are running North and South." Amelia Earhart and Fred Noonan did not arrive on Howland Island. An hour after the last transmission was received, USCGC Itasca initiated a search around the island for signs of the missing plane, with the little information it knew from the plane’s general location. A few days later, US President Franklin D. Roosevelt declared a formal search for the pair, involving both the US Navy and US Coast Guard. The two-week search was unprecedented, with upwards of $4 million ($68 million today, adjusted for inflation) put towards the effort, making it the most expensive search-and-rescue operation completed by the United States up to that point. Seven ships and 65 aircrafts were involved in the effort, and together they covered around 700,000 and 400,000 square kilometers of ocean, respectively. The extensive search turned up with nothing, and on 19 July 1937, Amelia Earhart and Fred Noonan were declared lost at sea and the search was called off. This did not stop Amelia’s husband, George Putnam, from continuing the search until October 1937 on his own dime. He hired independent help to search nearby islands which were not searched in the original rescue mission. However, still no trace of the plane or its crew were ever found. On 5 January 1939, Amelia Earhart was declared dead in absentia by a court in Los Angeles, CA.



ioneering aviator, international icon, glass ceiling breaker.

tude as 7,000ft, flying at 150kts. 1,300km into the flight, the Lockheed Electra reported out its last position.

And it all came crashing down. 2 July 1937. Departing from Lae, Papua New Guinea, in the early hours of the day, Amelia Earhart and Fred Noonan set off for Howland Island. But as the story goes, they did not make it. Faulty equipment, water ditching, Japanese capture, Japanese cooperation, missed communications, navigational errors. The rumors began to swirl and have not stopped since.

2 JULY 1937 Amelia Earhart and Fred Noonan left Lae at 10am, loaded up with 1,110 gallons of fuel, more than enough to make the 4,113km journey to Howland Island. The weather was less than perfect, with the crew reporting clouds and rain early on in the flight. Five hours into the flight, Amelia reported they were descending from 10,000ft because of the high cloud cover. Two hours later, she reported their alti18


The US Coast Guard cutter Itasca was tapped to assist in communications for the flight, as the stretch from Lae to Howland Island was scheduled to be the longest segment completed over water. The ship was stationed near Howland Island and was receiving transmissions from the Electra in the final stages of the flight. Since Howland Island is quite small, only 2,000m long and 500m wide, Itasca was employed to provide a presence to ensure Amelia and Noonan would navigate correctly to the island and land safely. At 19:30 GMT, 5:30am local time, a message was received: "KHAQQ calling Itasca. We must be on you but cannot see you...gas is running low...". An hour later, the last transmission from the Electra was the following:

We may not know exactly what happened on that fated day, but to say that it was a freak accident would be to ignore the circumstances surrounding the accident. Most of the discussion regarding the cause surrounds the radio equipment used on both the Electra and USCGC Itasca. The purpose of having Itasca stationed nearby Howland Island was to facilitate a smooth landing. This necessitated two-way communication between the plane and the ship in the final stages of the flight. However, when it came time to establish communications, it was reported that Itasca received communications from the Electra, but the Electra was apparently unable to hear radio transmissions from Itasca. The radio transmissions were intended to serve two purposes: to provide a method of audio communication between Itasca and the Electra, as well as to provide directional information, to aid in pinpointing the exact location of each vessel. The locationality function was critical to the success of the flight, since Howland Island is essentially a landing strip in the middle of the ocean. However, neither directionality nor two-way communications could be established.

Fred Noonan himself had his doubts about the ability of the radio equipment to conduct accurate navigational communications. For previous segments of the flight, a radio direction finder (RDF) was installed, but was deemed too heavy for the Lae-Howland Island flight. Already heavy, the aircraft was instead equipped at the last minute with a mechanism that allowed a loop antenna to be connected to the existing receiver. The loop antenna, theoretically, would be sufficient for navigational use. Compounding the issue, Itasca was transmitting from its loop antenna at 7500kHz. One theory persists that most RDF equipment in the 30s were unable to detect signals coming in at frequencies higher than 2000kHz. Above that frequency, the directionality of the RDF is lost. This means that Amelia should theoretically have been able to hear Itasca, but would not have had the ability to determine exactly where the ship was. Popular speculation also points to the installation of a new system just before takeoff as a compounding factor in the disappearance. A Bendix coupler replaced the bulky RDF unit previously installed in the Electra. The Western Electric 20B receiver was not purposely-built for use in navigation. The Bendix coupler was, therefore, put in place to allow the receiver to read in signals from the loop antenna, and thus provide some form of radio directionality.


There is a good deal of speculation as to why two-way communications were not established between Itasca and the Electra. Some point to possible failures of the radio communication equipment, others focus on a possible mismatch in equipment between Itasca and the Electra.

Figure 1 - A recently unearthed photo, which some claim to show Amelia Earhart and Fred Noonan on a dock in the Jaluit Atoll. circumstances.


A BOTCHED RECOVERY Once the command of Itasca had reason to believe that Amelia and Fred Noonan were not going to land at Howland Island, a search mission was begun almost immediately. This, upon later analysis, was based on potentially faulty information and may have impacted efforts to search for the presumably-downed Electra.

In the 1930s, the processes surrounding search and rescue missions were in a fledgling state. There were generally no formal procedures for evidence-gathering and, by today’s standards, search and investigation techniques were fairly rudimentary. There was an additional layer of water-muddying, with officials becoming increasingly concerned about how the press would report their efforts in searching for an international icon.

• • • •

• •

• Amelia was trained on the operation of the device, including how to read out incoming signals, only just prior to the flight. The operation of such a device is more complex than the use of the original RDF unit, which has fueled speculation that Amelia was not able to operate the unit correctly. Independent investigations into Amelia’s disappearance revealed that the coupler-receiver system was particularly complex, involving a number of operations such as tuning, changing bands, and physically cranking a device. Some hypothesize that this could have contributed to difficulties in flight. Numerous investigations into the exact equipment and their capabilities have revealed some information that may be of use. A leading opinion, that of The International Group for Historic Aircraft Recovery (TIGHAR), states that the radio equipment that was installed on the Electra was suitable for a cross-country flight, and was sufficient for the flight segments already completed. However, when it came to an entirely cross-oceanic flight, it may have contributed to the Electra’s unfortunate

The first mistake made in the initial search mission was that it was almost entirely based on erroneous information. Later analysis completed by TIGHAR indicated a key phrase in the final set of transmissions, “1/2 hour gas left”, may have been a misunderstanding. Nevertheless, Itasca commander Walter K. Thompson began the search mission, taking this statement as fact. Prior to the flight, he believed the Electra was loaded with sufficient fuel to make the trip, with some to spare. This strong belief quickly eroded in the face of peril. The search was initiated on the assumption that the Electra must have crashed into the ocean somewhere near Howland Island. However, analysis completed later revealed that even an hour after the supposed “1/2 hour” remark was made, Amelia was still transmitting and in the air, ruling out the possibility of low fuel at that point in the flight. Regardless, in Thompson’s mind, given that half an hour of fuel would not have been sufficient to reach any nearby islands, the initial search was conducted exclusively by air and sea. This information was included the

1922: Woman's world altitude record: 14,000ft 1928: First woman to fly across the Atlantic Ocean 1930: Speed records for 100km (empty and with 500kg cargo) 1931: First woman to fly an autogyro, autogyro altitude record: 18,415ft 1932: First woman to fly the Atlantic solo 1932: First woman to receive the Distinguished Flying Cross 1932: First woman to fly nonstop, coastto-coast across the U.S. 1933: Women's speed transcontinental record (1933) 1935: First person to fly solo between Honolulu, Hawaii and Oakland, California 1935: First person to fly solo from Los Angeles, California to Mexico City, Mexico  1935: First person to fly solo nonstop from Mexico City, Mexico to Newark, New Jersey 1937: Speed record for east-to-west flight from Oakland, California to Honolulu, Hawaii

“Known Facts” document provided during the rescue mission. This assumption dictated the search efforts for the next several days. The bias exhibited in the early stages is both credited with why the search was not successful, and concurrently played into the conspiracies surrounding the incident. The search covered several thousand square kilometers of ocean, mainly focused on the North-South heading given by Amelia in the final transmission. Land near Howland Island was also surveyed from above. This presents problem two of the investigation: what and where. Based on the assumption that Amelia crashed at sea, crews were directed to search by air and sea. The driving motivation that was any LEONARDO TIMES N°1 2018



Amelia Earhart and Fred Noonan’s circumnavigational flight route evidence of Amelia and Noonan would manifest itself as flotsam on the ocean surface. All ships and aircraft involved in the search turned up with nothing after the search efforts. Interestingly though, aircraft deployed from the USS Colorado reported “signs of recent habitation” on Gardner Island. According to reports, they circled the island looking for people in distress. However, they gave up their efforts when they did not find anyone. This action is believed to possibly have been motivated by the pilots’ incorrect assumption that all islands in the vicinity were inhabited. On the contrary, Gardner Island had been uninhabited since the late 1890s. Even after the initial search, George Putnam continued to fund search efforts by his own means. He chartered expeditions to some of the islands near Howland Island, in hopes that some trace of his beloved Amelia would be found.


earlier. The mood was sour between the two countries, and led to a plethora of conspiracy theories when Amelia went down. A persistent claim over the years has pinned Amelia as a spy, either for the Americans or the Japanese. In 1943, a film titled Flight for Freedom was released, starring Rosalind Russell, Fred McMurray, and Herbert Marshall. The story followed a celebrity female pilot embarking on a round-the-world flight (sound familiar?). She is approached to use her flight as a means to spy for the US government and gain information about Japanese-held islands in the Pacific. Her final flight was to be flown to Gull Island, a small strip of land in the middle of the Pacific, but instead she vanishes and is never to be seen again. The film kept alive the rumors that Amelia was approached by the US government to serve as a spy. The explanation given for why Amelia was never found was that the government

did not want to give up information that Amelia was a spy, because she had been captured by the Japanese forces. This was never confirmed. Another theory that has perennially emerged in conjunction with the American Spy conspiracy theory, is that Amelia was indeed captured by Japanese forces, but was returned to the United States in 1945 and subsequently lived out the rest of her life under the name Irene Bolam. The idea was heavily publicized in 1970 by the book Amelia Earhart Lives by Joe Klaas. However, he later retracted the book when the real Irene Bolam sued the book’s publishers, providing evidence that she was not Amelia Earhart. Subsequent investigation revealed major flaws in Klaas’s premise, and photographic evidence of both women supported the conclusion that Amelia was, indeed, not Irene Bolam. The media was particularly keen to pick up on the Japanese interference claim early on in the search. Most conspiracy theories revolved around the capture of Amelia and Fred Noonan with no speculation as to their fate, but one in particular pinned Amelia as a member of the Tokyo Rose, the name given to a group of women broadcasting Japanese propaganda in English. Reports were given that claimed people recognized Amelia’s voice on one of the broadcasts, adding fuel to the still-smoldering rumors surrounding the plane crash. George Putnam was said to have investigated these rumors, trying to grasp any information he could get. But like all of the other rumors, theories, and hearsay, nothing came of the stories.

80 YEARS LATER The world continues to turn, and people forget the past and look towards the future, but some remain who are committed to finding the reasons behind Amelia Earhart’s disappearance.

With nothing to grasp onto, the public was sent into a decades-long frenzy trying to answer the question, “What happened to Amelia Earhart?” Theories that popped up over the ensuing years ranged from plausible to absurd. The most reasonable theories that have persisted over the years are the crash-and-sink theory and the alternate-island theory. Both of these theories rely on investigations completed long after the flight occurred, which found that a combination of non-functioning navigational equipment, combined with possibly outdated maps, were possible sources of confusion for the fated crew. However, tensions in the Eastern hemisphere were brewing in 1937. Though the Pacific Theater would not become entangled in World War II until 1941, the United States was already beginning to cut ties with Japan years 20


Figure 2 - Commemorative stamps issued by the Marshall Islands, depicting a possible crash landing by the Electra.

In 2017, two reports that may provide possible clues to Amelia’s fate came to light. In July, The History Channel reported on what was believed to be a bombshell discovery. An undated photograph at the United States National Archives was discovered by Les Kinney, who is involved into the continued efforts to investigate Amelia’s disappearance. Said photo, shown in Figure 1, shows a harbor scene on Jaluit Atoll, part of the then-Japanese-controlled Marshall Islands. Normally, such a photo would not raise suspicions, but Kinney claims both Amelia and Noonan are in the photo, with Noonan standing facing the camera on the far end of the dock, and Amelia sitting on the edge of the pier with her back to the camera. Kinney also alleges that a boat in the background is carrying a plane, similar in profile to the Electra. Though the photo is undated, Kinney believes there is evidence that the photo is, at the very least, from around the same time Amelia flew. He argues that “the photo must have been taken before 1943 as U.S. air forces conducted more than thirty bombing runs on Jaluit in 1943-44.” The territory was already held by Japanese forces, possibly providing evidence that Amelia and Noonan were captured by Japanese forces. The photo was revealed as part of a special, which also examined other pieces of evidence that may hold clues about Amelia’s disappearance. Earhart researchers found commemorative stamps from the Marshall Islands depicting the Electra’s final flight and subsequent recovery from the Mili Atoll on 2 July 1937. One of the stamps, shown in Figure 2, shows the Japanese ship Koshu, which witnesses claimed to have picked up the Electra and brought it to the Marshall Islands. Some believe that Koshu appears in the newly-uncovered photograph. However, like with many of the accounts and evidence that have appeared over the last eighty years, there will always be detractors. Soon after the unveiling of the Jaluit photo, some were quick to discredit the findings. According to a Tokyo-based blogger, Kota Yamano, a copy of the photo was found at Japan’s national library, but with a very different story. He claims the image was published as part of a travelogue in 1935, two years prior to Amelia’s disappearance. So the plot thickens. Like any good mystery, the evidence is muddled, with seemingly credible information coming from all sides. Potentially corroborating the Japanese capture story are eyewitness accounts, both old and new, that place Amelia and Noonan in Japanese-controlled territory, and their execution a few days later.

In the years following the infamous disappearance, a number of eyewitnesses came forward claiming two tall Caucasian people, a man and a woman, were seen on Saipan, which was then-controlled by Japanese forces. Their accounts fueled speculation that Amelia and Noonan were captured by the Japanese, and possibly killed. One witness, who shared her story to the San Mateo Times (California) in 1960, claimed to have seen the two taken away by Japanese soldiers and subsequently heard shots ring out. Others repeated stories from parents, grandparents, or friends who claim to have been on the island around the time of Amelia’s disappearance. Many of these stories have a common thread that a Western-looking woman was seen, but generally no one knew what she was doing there or who she was exactly. Some say she was killed, some recall she was ill. Even as recently as November, people have come forward with their stories. After the emergence of the Jaluit Atoll photo, a man from the Mariana Islands claimed his uncle worked in a prison where Amelia and Noonan were held. His claim extends so far as to speculate whether the United States government was aware of Amelia’s capture and kept it under wraps. The other contending theory on the Electra’s disappearance is that of TIGHAR. They are testing the hypothesis that the Electra, due to a number of factors, veered off-course somewhere between Lai and Howland Island. Because of this, they were not able to navigate to and communicate with Itasca and had to make an emergency landing on Gardner Island (now called Nikumaroro). There, they sent distress signals, which went unheeded, while the Electra was consumed by rising tides. In recent years, the organization has sent search expeditions to Nikumaroro and surrounding Kiribati Islands in search of any clues about Amelia’s fate. A photo was taken of a piece of metal sticking out from a reef nearby Nikumaroro, which TIGHAR says is consistent with a strut and wheel of a Lockheed Electra plane. Other evidence gathered on the expeditions includes a riveted aluminum panel, a pair of shoes that look similar to those seen in photographs of Amelia during her round-the-world trip, and a piece of Plexiglass. Though these are not conclusive evidence that Amelia did indeed land on Nikumaroro, it does provide some anchor for future investigatory work, and possibly coming closer to finding an answer.

LOST BUT NOT FORGOTTEN Even though Amelia Earhart’s story may never come to a definitive conclusion, her legacy will live on. During her lifetime, she dedicated her life to pushing the boundaries of aviation and soci-

ety. She was a woman ahead of her time, who rejected the traditional confines of femininity and what it meant to be a woman at the turn of the century. From romping around in bloomers, collecting bugs and sliding off a shed roof, to openly declaring her desired an equal partnership in marriage and insisting on being referred to as Ms. Earhart, Amelia was never keen to be forced into a box. Her aviation accomplishments, of course, speak for themselves. Over the course of her lifetime, Amelia set a number of records and was the first person or woman to complete a number of flights, both in an airplane and an autogyro. Her historic flights captivated the world and gave her the support to continue doing what she loved. Her work inspired several generations of aviators. The Ninety-Nines, the organization she helped to found in 1929, continues to honor her legacy and promote women in aviation. Her story inspired hundreds of female pilots during World War II, who were part of the Women’s Airforce Service Pilots group. Several memorial flights have been completed in Amelia’s honor, including two circumnavigational flights mimicking the original flight path, including one completed last June for the 80th anniversary of Amelia’s attempt. Her story fascinated even those outside of the aviation world. Hundreds of books, articles, and documentaries have sought to understand, publicize, and memorialize Amelia’s life and contributions to aviation. And dozens more foundations, scholarships, awards, and even a corona on Venus, have been dedicated in honor of the aviatrix. Her passion continues to spark minds, young and old, and to this day is a source of inspiration for women around the world. Though we may never know what happened on 2 July 1937, Amelia’s legacy will forever live on. References



THE TWIN FUSELAGE REVIVAL Will StratoLaunch and Virgin Galactic revive the twin-fuselage aircraft? STRATOLAUNCH


Maurits Rietveld, Editor Leonardo Times

Today’s aircrafts generally contain only one fuselage, wouldn’t it be interesting to have two? Despite the short-lived attempts at twin-fuselage aircrafts in the past, there are new developments, which show the high potential of this design. THE BEGINNING Various twin-fuselage designs have already been used in the past. It all started during the Second World War. Small propeller planes were equipped with weapons to take out enemy aircraft or carried bombs to drop on strategic points. The war demanded rapid development on these planes, with all parties wanting faster aircraft that pushed the boundaries of flight. This meant more power was needed. However, there was not much time for an extensive design process. Hence, two existing planes were often combined to double the engine power, thereby greatly increasing the range and velocity. The result led to the twin-fuselage aircraft.



A nice example is the P-51 Mustang, which the United States designed in 1940. The plane was used as a fighter aircraft to destroy enemy aircraft and to escort bombers to Germany. Escorting the bombers meant flying long distances, which the P-51 was well capable of. However, it soon became apparent that planes with even longer ranges were necessary, as the United States would need planes that could fly from the Philippines to Tokyo during the war against Japan. The Twin-Mustang was the solution, extending the range of the original Mustang greatly. However, the war against Japan quickly ended after the deployment of the atomic bombs, making the Twin-Mustang unusable. After only a few flights, the aircrafts were grounded.

The combination of two fuselages often resulted in a cockpit that was placed in the middle of the wing. This allowed pilots to have a better view from the cockpit, which is vital in combat. Soon after all these developments, the disadvantages of two fuselages in one aircraft started to surface. The planes didn’t roll very fast due to a higher mass moment of inertia, making turning difficult. In addition, the towering cockpit experienced high accelerations when turning, making the pilot not able to withstand high load factors during turning. This, all while maintaining maneuverability, is key in air battles. A significant increase in drag was also observed, which is due to the larger frontal surface area. Soon, jet engines were developed; increasing the range and speeds of fighter aircraft drastically and by doing so, became a better option than combining fuselages. This meant twin fuselages didn’t play a part in aviation for a long time.


extend. Landing on one fuselage without gear has the risk of the wingtips striking the ground and spiraling out. The same is applicable for a water landing. Another scenario is that one of the engines stops working, creating a moment that needs to be counteracted by the rudder. Two fuselages contain two rudders; meaning less yaw deflection is needed to keep the aircraft stable, allowing for a smaller rudder and decreased weight.

thus somewhat less fuel needed to make the flight. More importantly, launching rockets becomes less difficult logistically. Using a strategically-placed launchpad, being dependent on the weather and closing air traffic in surrounding area is no longer a burden. Instead, existing runways can be used, launches can take place any time during the day and all air travel can simply continue.

For launchers in the space industry, the most prominent advantage turned out to be the space between the fuselages, which is excellent for transporting payloads to high altitudes, making it functional as a launcher for spacecraft. Currently, two major twin fuselage projects are going on in the space industry, namely originating from StratoLaunch and Virgin Galactic.

Virgin Galactic, on the other hand, is mostly concerned with a different area in the space industry: space tourism [3]. Instead of $20 million per passenger asked for by some space agencies to launch them into space, Virgin Galactic wants to make spaceflight happen for only $200,000. Its twin fuselage aircraft, WhiteKnightTwo, developed by Scaled Composites, carries Virgin Galactic’s SpaceShipTwo. This spaceplane contains a hybrid rocket engine and can carry 6 passengers and two crewmembers to space. WhiteKnightTwo, with a wingspan of 43m, is first able to fly SpaceShipTwo to an altitude of 15km, after which the hybrid rocket engine of the space plane brings itself to transport passengers to 110,000km into space. Flight tests are already taking place, and Virgin Galactic expects to conduct flight tests into space this year. First commercial flights are anticipated to be in 2019.


STRATOLAUNCH Launching a missile is a complicated task. Not only do the engines need to be powerful enough to bring the missile to high speeds, weather and launch location are important variables as well. StratoLaunch developed a new way of launching which can potentially reduce these problems greatly by building a twin-fuselage aircraft, called StratoLaunch.

THE PRESENT In recent years, however, the two-fuselage configuration has resurfaced. Some of the original advantages are driving this change, but also several new benefits. The first and main quality is a structural one. For a conventional aircraft, the highest bending loads are experienced at the root of the wing. By spreading this moment over two fuselages, this bending moment is greatly reduced [1]. This reduction in bending moments leads to less structural stress and thus more payload capacity, and more engines. This also allows the wing to have a higher span and aspect ratio. This is highly favorable from an aerodynamic point of view, as the vortices at the wingtips are reduced, decreasing induced drag significantly. Furthermore, two fuselages are advantageous from a safety perspective. Consider the case in which the landing gear fails to

This enormous aircraft with a span greater than a soccer field, was presented in 2011 with the purpose of sending rockets into space [2]. The plane allows for a missile to be hung in the middle and to be brought to a cruising altitude of 9.1km. From here, the missile can continue its journey. With the missile already brought to 9.1km, it will continue on its own and propel itself into a low earth orbit (LEO) of about 2000km. This makes it excellent for cheap launches for small satellites. With the first plane already built, testing is already in progress. This past December, StratoLaunch started its taxi tests on a runway, with the next step of tests with increasing taxi speeds. In 2019, the airplane is planned to fly for the first time, with the goal of beginning commercial launches in 2020. The main reasons to build such an aircraft are abundant. First, flying the rocket in a higher part of the atmosphere has the natural advantage of less dense air, less drag, and

So can we expect this version of the twin fuselage aircraft to remain functional for a longer period compared to their historical counterparts? While we can’t peek into the future, the purpose of the twin fuselage configuration is vastly different from when they were first conceived. With this, there is more certainty that they won’t suffer the same fate this time around. References [1] Gao, X., Hou, Z., Guo, Z., Chen, X. “Design and performance test of a twinfuselage UAV” *College of Aerospace Science and Engineering, National University of Defense Technology, ChangSha City, HuNan Province, P. R. China [2] StratoLaunch website www.stratolaunch. com, 2018 [3] Virgin Galactic website, 2018




INTERNSHIP AT DEERNS Designing and Constructing in Abu Dhabi INTERNSHIP

Luc de Ruiter, MSc Student Aerospace Engineering, TU Delft

Deerns together with Naco, a company of Royal HaskoningDHV, are design teams at the construction site of the new airport in Abu Dhabi focusing on the design of apron systems, MEP engineering, and data networks. I flew to Abu Dhabi to work on the location of the $4.5 billion mega-airport project for three months.


irports are continuously adapting their facilities. Commercial airplanes are increasing in size and becoming more technologically advanced. Extra design space in airports, and high-tech engineering systems are required for aprons. On one hand, engineers must take into account the interests of stakeholders around the airports, as well as the increasingly strict rules and regulations regarding safety, security, and sustainability. On the other hand, costs must be minimized. One of my main reasons to choose Deerns for an internship was that I wanted to get real world practical experience within a project team and learn about 26


the management of a large project, as well as acquire professional skills other than those taught during my technical studies in Delft. Today’s large engineering projects are not only of a technical nature, but also require strong communication between different cultures and good management keeping a close eye on costs and planning. Besides my technical duties , during my internship I found it very valuable to gain insight into the project management of a large airport.

PROJECT WORK My internship took place from the end of August until halfway through December.

The first two weeks started in the head office in Rijswijk where I got acquainted with the company, its projects, and its software, as well as the people from Deerns. I was an integral part of the team on-site, which means that I assisted the team in preparing variations to the design and holding several meetings. However, most of my day was spent working with AutoCAD. The work consisted of supporting all the specialists. My largest assignments were on the development of the IT infrastructure within the Midfield Terminal Building, the placement of airfield ground lightning and Signage-Stopbar; and the placement of delayed egress doors and security cameras. This meant that the setup of all the sector files drawings was my responsibility. These sector files are the main files that contain the plans and all the information necessary to send an Issued for Construction (IFC). For example, a chal-

lenging task was to coordinate and deal with the Security department and the Fire and Life Safety department, as they have differing views on the airport operations system. The security would like to have everyone in a certain area for as long as possible in case of an unexpected situation or to keep track on potential terrorists. They require having as many doors locked as possible and preferably with a delay time, and want to prevent the passenger flow going from airside to landside and vice versa. In contrast, the Fire and Life Safety department wanted to have the doors be opened as quick and easy as possible in case of a fire or emergency when people need to flee. Safety is most important here. Multiple CAD drawings had been made during the internship in order to automate the process. Since the documentation for the Midfield Terminal was huge, a document controller AECOM was needed to lead the quality and acceptability of documents. The architect may issue sketches or written clarifications known as RFI's to ask for clarifications of the IFC drawings. Another task was to issue site instructions and documentation necessary to facilitate the construction process. If the contractor sent his shop drawings (SDS) to the design teams, it was checked if the design intentions were met, and if it will be a workable solution on site. It was also required that the contractors sent the document "as built" conditions that had to be reviewed. In this document, all changes are reflected from the specifications and working drawings during the construction process, and show the exact dimensions, geometry, and location of all elements of the work completed under the contract. A big challenge in designing airports in the desert climate is the adequate cooling of airplanes at the gate, which can reach temperatures of up to sixty degrees Celsius in summer time. Airplanes should be cooled at the gate to strict maximum temperatures, but the International Civil Aviation Authority (ICAO) puts limitations on the maximum airflow that can pumped in the airplane. After consulting with multiple parties and several months of research, Deerns came up with a solution. They managed to go from conventional Auxiliary Power Units, which are small

turbine engines on the ground towards regular Pre-Conditioned Air Units, to make it possible for cooling the airplane with Sub-Freezing Pre-Conditioned Air (Geurts, 2015). With this method, air is pumped into the airplane that is below zero degrees. I was involved in apron work that is needed by these cooling systems.

WORKING FOR DEERNS AT ABU DHABI INTERNATIONAL AIRPORT Abu Dhabi is the capital of the United Arab Emirates (UAE), which rests on one-tenth of the world’s oil. It is known for its glittering luxury hotels, recent ten-billion-dollar bailout of its neighbor Dubai, branches of the Louvre and Guggenheim Museums, and an extension of New York University. These institutions have positioned the city for an international entrance. To become less dependent on the oil industry, the country has a vision for 2030 to have a focus on tourism and business towards a more sustainable economy. Infrastructure development is a priority area and a pillar of this Abu Dhabi policy agenda. Their aim is to become one of the major airport hubs within the region and a hub for flight routes worldwide, with Etihad as the main airline operator. It needs to compete with already existing large airports in the region such as Dubai and Doha, where Emirates and Qatar Airways, respectively, dominate the market. To bring this vision to reality, the new runway and midfield terminal in between the already existing runway are under construction. The terminal building will have a surface of 700000m2, 1500000m2 of apron and taxiway pavement, and 65 aircraft stands, of which many are designed to serve the A380. This makes it one of the largest terminal buildings under construction in the world. The airport aims to enable an annual passenger flow of around 35 million with the possibility to extend to 45 million over the years by the opening of another South Air Terminal. The central space will be an area with the rooftop at a 56m height and with a span of 320m to handle the passenger flow. It was a great opportunity to be part of a project of this size, which you can probably only find in countries where oil is literally cheaper than water. It is also a great experience to see all the cultures working together - every day 18,000 people ranging from designers, contractors, and coordinators work on the

site. As is the case for every project - especially for this size and complexity - teamwork is very important for clear communications, to deal with unforeseen circumstances and last moment changes on demand. The goal is to have the airport finished before the Expo Dubai 2020. Before the new airport can be fully operated, all implemented systems are tested and airport weaknesses must be resolved in fire safety issues, baggage handling, and security. This process of turning the newly constructed building into a fully functioning airport, that needs to operate business right from day one, is a big and important task. This process of testing is known as Operational Readiness, Activation and Transition (ORAT). This will be the next phase after the construction is finished.

THE UNITED ARAB EMIRATES Looking back on my internship, I am happy to say that it has been a complete success. It was a very enriching experience to live and work in a country, which is extreme in many ways. Islam is the official religion of the UAE and Arabic is the official language, although English and Hindi are widely spoken. The Emirates became a country that accepted modernity, but is still based on strong Islamic roots. The combination of Abu Dhabi’s location in a desert - a good place to go for jeep racing, and to see the most beautiful sunset in the world – and its timeless feeling, I enjoyed my free time outside work. Don't forget to visit the Qasr Al Sarab hotel when you visit the UAE, it is located in between sand dunes of 200m height. Also, Dubai is only an hour’s drive from Abu Dhabi. There you can do things that you cannot do elsewhere in the world and witness more concrete examples of the UAE culture clashes. I encourage future students to take the step so that their internship may prove to be as academically and personally enriching as it has been for me. References [1] Deerns Midfield Terminal Complex Abu Dhabi International Airport. www. Trade Mission, 30-03-2015.



DEVELOPING ARIANE VI The history and outlook of Europe’s access to space ESA


Arjan Vermeulen, BSc Aerospace Engineering, TU Delft

Untouched by the news coverage of galactic colonization projects like NASA’s Space Launch System (SLS) or the Interplanetary Transport System (ITS) of SpaceX, ESA is designing a new launcher: Ariane VI. This article will delve into the past of the Ariane family, its newest member, and its technical and economic future.


n 1965, France became the third space power in the world, through the launch of its Diamant A. Shortly followed the Diamant B, as these rockets were not suitable for the larger payloads demanded by the market. In 1963, a predecessor of ESA, the European Launcher Development Organization, started working on the Europa rocket, which was ultimately abandoned due to technical problems.

EUROPE’S ACCESS TO SPACE After years of debating, in 1973, the newly formed ESA started working on a new expendable launch system. The reason was simple: without its own launcher, Europe would not have independent access to space, making the realization of a space program impossible. The goal was to be capable of launching two communication satellites in a geosynchronous orbit with one launch, thereby reducing costs. The launcher was named “Ariane”, after the Greek princess that helped Theseus find his way out of the labyrinth. The naming was symbolically apt as this rocket led Europe out of its own struggle. The first flight of the Ariane rocket was scheduled for December 15,1979. However, in front 28


of a large audience, the engine ignited, and then stopped functioning. The first launch took place approximately one week later. On December 24, 1979, at 14:14 local time, The Ariane rocket lifted off from Kourou, French Guiana, starting Europe’s venture into space. Shortly afterwards, the Ariane II and III were developed, to be able to cope with the demand of increasingly larger payloads that needed to be launched into orbit. These rockets, together with the Ariane I, performed numerous successful flights up until 1989. In the meantime, the demand for larger launchers with larger thrust kept rising, leading to ESA developing a new launcher: the Ariane IV. In many regards, the Ariane IV was an evolution from the earlier models: the first stage was enlarged significantly, holding 210 tons of propellant instead of the 145 tons used by the Ariane III. In addition, a range of solid and liquid fueled strap-on boosters were developed to increase the payload capacity. This led to the Ariane IV being capable of launching payloads up to 4.3 tons to GTO, Geostationary Transfer Orbit, compared to the 1.7 tons of the Ariane I. The Ariane IV ended up carrying out 113 of its

116 launches successfully and holding 50% of the commercial market share, solidifying Europe’s presence as a big player in the launcher industry. This trend continued with the conception of Ariane V, currently the main workhorse of Europe’s space program. It provides six to seven launches per year and has an impressive record of 92 successful launches, with only two failures. However, a shift in the market caused by other launcher manufacturers, is making the Ariane V launcher an uncompetitive choice. Currently, Ariane V launches to GTO can cost up to $200 million while a launch of the SpaceX Falcon 9 can cost around $62 million. This discrepancy has led Europe to start developing a new launcher in 2014.

A NEW LAUNCHER The Ariane VI, with its first launch scheduled for 2020, has set out with one primary goal: halving the operational costs of the Ariane V, while maintaining its reliability. The design features just two stages, compared to the three stages used by previous models. The lower stage uses the Vulcain engines developed for the Ariane V rocket to reduce cost and increase reliability, providing 1,370kN of thrust. The upper stage uses the newly developed Vinci engine, providing 180kN of thrust, and has the capability of restarting up to five times. In the configu-


Exploring Spacecraft Sizing” on March 6 2018! Looking forward, the Ariane VI offers plenty of opportunities for further developments. The most exciting among these is “Project Adeline”, a concept to partially reuse the first stage of the launcher through the addition of wings. This allows the costly components, such as engines and avionics, to land and be incorporated into a new rocket. This could further reduce the launch cost up to a factor of two and vastly increase the launch cadence. Project Adeline is set to be incorporated into the second version of the Ariane VI, known as the Ariane NEXT, starting between 2025 and 2030.

ration with four strap-on boosters, the Ariane VI is capable of launching up to two satellites with a combined mass of 12000kg to GTO, at the cost of €90 million. The development of the Ariane VI is currently in full progress: an industrial review of the preliminary design of the launcher was already completed in 2016, and was given the go-ahead to continue with the development. The project is a collaboration between Airbus Defense and Space and ArianeSpace. There are currently two main areas of ongoing progress. The first are two parallel test tracks of the second stage Vinci engine. This is a further development of the P120C Solid Rocket Booster, which was adapted from the first stage used by the small Vega launcher. The other is the construction of the Ariane VI launch complex in Kourou, French Guiana. The latter is where a large portion of the economic risk lies: the construction of an entirely new launch facility constitutes a large part of the monetary investment; it would be futile if Ariane VI underpearforms on the commercial market. After its first flight in late 2020, the Ariane VI is set to fully replace the Ariane V by 2023. The launch cadence is planned to be once a month, thrusting ESA into competition with the amount of launches carried out by its most daunting competitor: Elon Musk’s SpaceX. Us-

ing the two booster variant, Ariane VI could put satellites into LEO, Low Earth Orbit, or, as with the European navigation system GALILEO, into MEO, Medium Earth Orbit. The four booster variant could be used to haul larger payloads up to GEO, Geosynchronous Equatorial Orbit, and the re-ignitable second stage allows for controlled placement of multiple satellites in a single launch.

FUTURE PERSPECTIVES As rockets change, so does the market. Wellknown developments include SpaceX with its very economical and partially-reusable Falcon 9. The current Falcon 9 Full Thrust is capable of launching 5.5 tons to GEO, in its reusable configuration. In addition, SpaceX is set to launch its Falcon 9 Heavy at the start of 2018. Other prime competitors of the Ariane VI include the Russian Proton M, capable of launching 6.3 tons to GEO at a similar price as SpaceX. Besides the large rockets, there is a newer market, the one of the small launchers. This includes launchers like ArianeSpace’s own Vega rocket, as well as newer companies, such as Rocket Lab with their Electron rocket. These companies provide similar services to LEO and sun-synchronous orbit for medium-sized satellites, at a fraction of the cost of a traditional launch. Should this shift in the design philosophy of spacecraft interest you, make sure to visit the VSV Symposium “Rescaling Limits,

An evolution, a necessity, a good all-rounder: these properties make Ariane VI a prime example of the current developments in astronautics. It is being developed with the goal of being inexpensive and market competitive, rather than being one of the maximum-capacity behemoths seen in the past. If one couples this trend with the emerging market of smaller satellites and the emergence of smaller spaceflight companies, it becomes clear that the Ariane VI might not just be a work of technological marvel; ESA’s newest launcher might be an economic victory as well. References [1] ESA. Ariane 6. Retrieved December 12, 2017, from [2] Airbus and Safran Propose New Ariane 6 Design, Reorganization of Europe's Rocket Industry. (2015, March 08). Retrieved December 13, 2017, from [3]ESA. A look at the past. Retrieved December 10, 2017, from The Space Department The Space Department promotes astronautics among the students and employees of the faculty of Aerospace Engineering at Delft University Technology by organizing lectures and excursions.




Greeshma Gowda, Editor Leonardo Times

In the last quarter of 2016, I travelled to Toulouse, France to do an internship in the Department of Mechanics, Structures and Materials of ISAE SUPAERO. I worked on a non-linear transient fluid-structure interaction approach using surrogate models for an industrial application to aircraft fairing vibrations. As part of the internship program for the Aerospace Engineering Master, I was given a chance to explore my interests and work in a different country. I was fortunate enough to get a position in the ‘Départment Mécanique des Structures et Matériaux’ (DMSM) of ISAE SUPAERO in Toulouse, La Ville Rose, for five months, back in September 2016. Being an intern in the world’s first dedicated aerospace school, the homeground for many pioneers of aviation and aerodynamics, was an overwhelming experience. The campus has over 200 research students working towards the growth of scientific knowledge and performing cutting edge research. I was working on a project to develop a fast, accurate method for Fluid-Structure Interaction (FSI) calculations for the Flap Track Fairings (FTF) of an A380.



FSI calculations involve finding solutions for coupled fluid and structure equations. This process can be computationally intensive and time-consuming depending on the complexity of the phenomena, and FTF is no exception to this, as their behavior is highly non-linear and depends on the source of the excitation. For instance, their position makes them susceptible to high vibrations caused from the engine discharge during take-off, but this was not taken into account during the design process. Because of this, reinforcement, servicing, and repair had to be done on existing systems. In order to get accurate calculations in a short amount of time, this particular FSI problem required to be studied extensively, and specifically the ability to predict the vibration loads. In order to address the issue of complexity, a solution method had to be developed us-

ing MSC Nastran and elsA, as the structural solver and aerodynnamic solver, respectively. These would generate a database of pressure distributions around the FTF. For the aeroelastic loop, to support complex 3D shapes like FTF, there needs to be a tool which reduces the dimension of the database of aerodynamic pressures. Once the database is reduced, an efficient interpolation technique is needed to interpolate the data for other positions of the FTF, apart from the data obtained from elsA. My work involved the development of the reduction and integration tools. This meant I would be dealing with Model Order Reduction and interpolation on manifolds, both of which were fairly new concepts for me. This called for an extensive bibliographic survey which lasted around five weeks. During this phase of the internship, I gained the required knowledge on Proper Orthogonal Decomposition and Dynamic Mode Decomposition, which were used to create the reduction tool, and also the basics of differential geometry and manifolds required for the in-


MAVs or wind tunnel tests. There were many seminars, as well as technical symposiums held by EUROAVIA and other student associations, which helped build an atmosphere where students have the opportunity to interact directly with the people from various aerospace organizations. Along with the ISAE SUPAERO and Ecole Nationale de L’Aviation Civile (ENAC) campuses, Toulouse is the hub of many European aerospace organizations. It is home to the Airbus Group, the French aerospace lab ONERA, the French government's space agency CNES, Thales Alenia, and many other prominent aerospace establishments, which makes it a very attractive place to be for students aspiring to create a career in the industry. The Aerospace Valley, as it’s called, is a magnet to young professionals from around the world.

terpolation tool. After the bibliographic study phase, I got my hands on the previously obtained pressure database and started building the models. The five-month long internship wasn't exactly a straightforward journey. The first few objectives were successfully achieved, but I encountered a few hurdles while developing the interpolation model due to the very low accuracy of the model. However, with the guidance of a few research students who were well-versed in the subject, I was able to develop the model. Working in ISAE SUPAERO, which has over six research departments equipped with state of the art facilities, was a valuable experience. The campus is always buzzing with enthusiastic students, much like TU Delft. Between lunch and coffee breaks with fellow interns and students, there was a great amount of interaction between all of us. There were interns from various countries working at the university and our discussions varied from our research to the more gener-

al topics like the culture and heritage of our respective countries. These conversations not only helped us socialize, but also helped relieve stress, allowing us to go back to work in a more refreshed state of mind. The working environment in the research labs is both very relaxed and inspiring. Students could approach the concerned research assistants or postdoctoral candidates with their problems and rarely be disappointed. If all else failed, the professors responsible would help solve the issues, no matter how busy their schedules were. I worked in a cluster of buildings which also housed the Department of Aerodynamics, Energetics, and Propulsion. This allowed me to interact with students and researchers involved with various interesting projects such as shock-wave boundary layer interaction, aeroacoustic optimization of wind turbine blades, external aerodynamics of the micro UAV MAVion, and other innovative concepts. I loved spending time at the Micro Air Vehicle lab as there was always something interesting happening there, such as test flights of

Apart from being the center of the European aerospace industry, La Ville Rose had a lot to offer for the travel and photography enthusiast in me. Toulouse houses two UNESCO World Heritage sites, the Canal du Midi, and the Basilica of St. Sernin. The town also has a number of other sites of historical and cultural significance. The Garonne River and the pink brick buildings together paint an unforgettable picture in the onlookers' mind. The neighboring towns of Albi and Carcassonne are some other UNESCO World Heritage sites which are worth visiting. A visit to the Pyrenees is also a must-do on the list. The breathtaking view of the mountains cannot be captured with words. There are even some adventure sports centers in the mountain ranges that operate during winter. I however, couldn’t convince myself to try skiing for the first time in my life. This internship has been a very enriching experience. Apart from having an opportunity to work with experienced professionals on an interesting topic, this internship also gave me the chance to work on my social and communication skills. From struggling to find English speaking people to being able to strike a conversation in broken French, I have come a long way and also made few good friends en route. I left Toulouse not just with more knowledge on Fluid-Structure Interaction, but also with the warm wishes of my new friends.



FLOW RECONSTRUCTION Flow reconstruction using Bayesian inference with model reduction AERODYNAMICS

Federica D'Onofrio, Ir. Aerospace Engineering, TU Delft

The reconstruction of full flow-fields from limited measurements is performed. The eventual goal is the post-processing of planar-PIV velocity-data available in a slice, into an approximation of the complete 3D flow-field that was present in the experiment. This is achieved with the use of CFD and a statistical approach (Bayes theorem) of data assimilation.


he separating flows present highly unsteady vorticial structures. The widely used RANS equations are based on uncertain model parameters and are often present with the suppression of separation and overprediction of separation bubbles (Balakumar, Park and Pierce, 2014). Under a statistical point of view, the most probable values of the model’s parameters are to exploit the misfits between CFD results and observed data from the slice of the domain which was found. For this purpose, Bayes' theorem is employed, and the inverse problem is solved. The posteriori information is explored through Markov Chain Monte Carlo (MCMC) iterations at an affordable computational cost, adopting model reduction techniques. Finally, the posterior predictive distribution (ppd) is used and the flow-field is fully reconstructed.

METHODOLOGY The branch of uncertainty quantification and 32


data assimilation is drawing more and more attention nowadays. Despite the complexity of RANS equations, involving systems of PDE, empirically based coefficients are still adopted to solve the closure problems. Moreover, the huge computational effort required to solve those PDE systems for industrial flow cases does not allow all the turbulent scales to be resolved and often their approximations, such as wall models, are used. Consequently, CFD results are unsatisfactory under particular flow conditions, when large recirculation regions and highly unsteady motions are present. What if the information from the experiments was used to manipulate the numerical models in order to match the observed data? When describing a physical system, inverse modeling consists of inferring information about the model parameters from observed data. One approach consists of a statistical description over the model parameter space

through probability density functions (pdfs). Bayes' theorem is used for this purpose, as it combines the prior state of information about the parameters and the mathematical laws that describe the physical system. The outcome of the inverse problem is a posterior pdf whose main features, i.e. mean and maxima, have to be computed during the so-called calibration process. The complexity of the process depends on the dimensionality of the model parameter space, i.e. one or more model parameters may exist. When the set of model parameters presents a large dimensionality, the calibration process requires cumbersome computations and if the posterior function has more than one maximum, the complexity increases. A commonly used method adopted in these cases for the calibration is represented by the MCMC method. In this method, random samples of the posterior probability density are produced. In regions where the samples are denser, a higher probability is expected. The procedure described is applied to flow problems. The physical system under consideration is the flow and the mathematical laws are represented by the RANS equations,


Figure 1 - Horizontal and vertical velocity profiles at the location in the flow domain where the inverse problem is applied.

combined with a closure turbulence model. In this case, k-Ďľ is adopted. The choice of model parameters is made considering the uncertainties of the problem under consideration. On one hand the closure coefficients are affected by uncertainty, as their values are determined, either empirically or from fundamental flow cases. Adhering to previous works (Edeling, 2015), not all the closure coefficients of k-Ďľ are treated as independent model parameters, but they are distinguished between dependent and independent ones. On the other hand, physical parameters can also be considered uncertain. Considering separating flows, the separation point is an uncertain variable to be manipulated, whose most probable value has to be found. Once the model parameters are chosen the inverse problem can be set up and the posterior explored. A huge number of samples are needed in order to explore the posterior distribution and obtain reliable information. When a random sample is produced at each MCMC iteration, a new flow solution is computed. This means that, if at each iteration the CFD solver was used then the calibration process would be unaffordable. Consequently, the new flow solution will be computed offline,

Figure 2 - Horizontal velocity profiles after ppd application. not involving CFD, but using using surrogate models obtained with reduced order model (ROM) techniques. The performance of the two different techniques, POD and Isomap, is investigated. The methodology implemented is tested on the periodic hill problem. This represents a

benchmark case for turbulent flows separating from curved surfaces. The separation is followed by a flat plate reattachment, showing a huge recirculation bubble. These gross features are reproduced by RANS but the presence of a highly unsteady shear layer makes the prediction of separation and reattachment points largely inaccurate. In order to LEONARDO TIMES N°1 2018


The most interesting result is represented by the pdf of the reattachment location, as in Figure 4. On the x-axis the reattachment point is reported. Whereas, the default RANS without the step predicts an early reattachment, forcing the separation and manipulating the closure coefficients allowing them to reproduce the reattachment point, as predicted by the LES. To sum up, closure coefficients are manipulated and separated, forcing them to accurately reproduce the flow solution (in terms of velocity), close to the point where the inverse problem is applied. In this way it was possible to reproduce the reattachment point, but the method was unable to accurately predict the solution elsewhere.

Figure 3 - Vertical velocity profiles after ppd application.

The analysis was conducted focusing on the velocity profiles, as the eventual goal is to start from the planar PIV data and post-process them for a three-dimensional flow-field reconstruction. The inverse problem solution was computed taking into account the velocity magnitude. Because of the predominance of the horizontal velocity in terms of order of magnitude, the accuracy in the vertical velocity representation is lower. This fact can be avoided for example, using the vorticity instead of the magnitude. The periodic hill physics is extremely complex to be represented through RANS; simpler cases, i.e. 2D flow around the cylinder, can be considered in order to test the methodology and obtain better results. It is also possible to deal with 3D cases, i.e. wheel, but the parameter space dimensionality is expected to be larger. However, the method developed allows to apply the MCMC analysis in a cheaper way. The CFD solver is called only for the ROM construction and this process represents the 0.01% of the time required if MCMC was run using CFD at every iteration.

Figure 4 - Reattachment point pdf. study the uncertainty of the separation point, separation is forced through a step, whose location and height are the uncertain model parameters to be calibrated together with the k-ϵ closure coefficients. When applied to the inverse problem, the observed data is represented by the validated LES data from (Breuer, et al., 2008). The inverse problem is applied to the location highlighted in Figures 2 and 3 by a dashed line. The most probable values of model parameters in order to match LES data at that location are found after the MCMC calibration. The ppd is then computed and the full flow solution is found with the previously calibrated values of the model parameters.

RESULTS AND CONCLUSIONS The results from the MCMC iterations are the pdfs of the model parameters. The peaks indicate the most probable values of the model 34


parameters. For each parameter, a range of variation was chosen at the beginning. The solution at the location where the inverse problem is solved, in terms of horizontal and vertical velocity profiles, is depicted in Figure 1, where the red shaded area represents the 90% confidence interval and the red line, the mean solution after the calibration. Clearly there is an improvement in the horizontal velocity profile prediction with respect to the default RANS solution without that step. The application of the ppd allows for the reconstruction of the horizontal and vertical velocity profiles at other locations in the flow domain. The result of this is depicted in Figures 2 and 3. The dashed line is where the inverse problem has been applied. Moving away from this position the accuracy of the flow reconstruction drops, meaning that the results of the flow reconstruction depend strictly on the point where the calibration is performed.

If you have further ideas or want to contribute to this research as a graduate student, contact the author for further information by email fvm. References [1] Balakumar, P., Park, G., Pierce, B.,2014. DNS LES and wall-modeled LES of separating flow over periodic hills. In: Center for Turbulence Research Proceedings of the Summer Program 2014. 407-415. [2] Breuer, M., Peller, N., Rapp, C., Manhart, M., 2008. Flow over periodic hills – Numerical and experimental study in a wide range of Reynolds numbers. Computers and Fluids Vol. 38, Issue2. Available through [Accessed: March 2017] [3] Edeling,W., 2015. Quantification of modelling uncertainties in turbulent flow simulations. Ph. D. Delft University of Technology.

LONG-HAUL, LOW-COST Will it take off globally?

Low-cost airlines are a common sight at airports across the world. However, budget air travel seems mostly limited to short and medium-haul. Intercontinental routes are served mainly by legacy carriers, and for a long time have shut out low-cost carriers. Nevertheless, some airlines are trying to tap into these routes. PIONEERING LOW-COST, LONGHAUL The desire to travel across the pond at competitive prices emerged in recent decades. In 1966, British airline entrepreneur Sir Freddie Laker founded Laker Airways. After initially operating charter flights, he saw a demand for low-cost transatlantic travel. However, getting approval from the regulatory bodies proved difficult. Aviation regulators were protective of their own markets, and authorities feared the low fares would undercut the position of legacy carriers. Laker claimed that his airline would tap into a newly-created demand, instead of poaching passengers from existing airlines. Nevertheless, it took years before regulations were relaxed. Finally, in 1977 the Laker Airway’s subsidiary, Skytrain, became the world’s second low-




Ralph van Sunten, MSc Student Aerospace Engineering, TU Delft

cost, long-haul airline with flights between London Gatwick and New York JFK. Besides skimping on the on-board services, the airline saved cost by reducing engine wear and tear and thus maintenance costs. This was achieved by reduced thrust take-offs and faster climbs. Laker also managed to increase the range of the aircraft by further weight-saving measures. Despite its break into the industry, Skytrain could not cope with an economic recession in the early 80s. A price war broke out among the large carriers such as British Airways, TWA, and PanAm. Despite of the initial competitiveness of Laker’s fares, there was not sufficient passenger demand and the airline lacked the equity its competitors did have. In February 1982, the airline collapsed.

THE RISE OF TRANSATLANTIC LOW-COST After the failure of Laker’s Skytrain, the intent for creating a successor did not fade. Ryanair was one of the airlines that, repeatedly, announced transatlantic flights based on its European success story. But as is often the case with Michael O’Leary’s plans, it never materialized. Airlines such as Icelandair and Wow Air started operations which used Reykjavik as a transit point between European and American gateways, offering lower fares than legacy carriers. This model consolidated passengers on routes that did not have high enough demand for a direct flight. The advent of the Boeing 787 Dreamliner changed this. Scandinavian carrier Norwegian initiated and expanded direct pointto-point flights from Europe to North America. The higher efficiency of the Dreamliner together with a capacity in the sweet spot for these routings enabled a profitable operation. Furthermore, Norwegian managed to copy the model that worked brilliantly for continental low-cost flights: flying to secLEONARDO TIMES N°1 2018



ondary airports. For instance, using Stewart instead of New York and Oakland instead of San Francisco. These airports offer smaller facilities and, therefore, lower cost. Although a more distant location is less convenient for travellers, a lower ticket price will make them more willing to accept this. After growing the operation, Norwegian also introduced flights to major gateways such as JFK, Boston, Fort Lauderdale, and Seattle. The new goal of Norwegian is to start flights using narrow bodies, such as the Boeing 737 MAX, from Europe to the East Coast of the US.

TRYING OUT EUROPE-ASIA Airlines have not only experimented with discounted flying between Europe and the US. Air Asia is one of the world’s largest low-cost airlines. Led by multi-billionaire Tony Fernandes, the airline has a dominant market position in Southeast Asia, with local spinoffs in Indonesia, Thailand, Japan, and the Philippines. Air Asia X launched in 2007 and was aimed to expand Air Asia’s network beyond regional flights. Using the Airbus A340 aircraft, the airline connected Kuala Lumpur with Gold Coast, Australia, and later London and Paris. In 2012, the carrier suspended flights to Europe. The 4-engined airplane lacked the efficiency to cope with increased fuel prices. The company hinted on a return on the London to Kuala Lumpur route in early 2017, using more fuel-economic aircraft. However, Fernandes announced in June that the flight is not relevant after all and that Air Asia X will focus on shorter routes.

SUBSIDIARIES FOR COMPETITION In a trend to catch up with dedicated lowcost carriers on intercontinental flights, many legacy airlines have started subsidiaries to recapture market share. By offering independent products, airlines can cater to both premium, leisure, and budget travellers without affecting the full-service brand of the parent company. For example, SWISS started Edelweiss and Lufthansa has Eurowings. These spinoffs focus primarily on holiday destinations. LEVEL, the subsidiary of IAG, the parent company of British Airways and Iberia, 36


was founded to compete directly with carriers like Norwegian on major routes. From its base in Barcelona, LEVEL’s initial destinations were Oakland, Los Angeles, and Buenos Aires. The airline also announced flights from Paris Orly to Montréal, Boston, and Newark in 2018. Air France-KLM is also launching a subsidiary airline to compete for budget-minded travellers. JOON will start long-haul operations in early 2018 with an initial destination list of Fortaleza, Cape Town, and Seychelles. On these low-yield destinations, Air France had trouble to generate a profitable operation. The French airline, however, will initially utilize former Air France Airbus A340s. Additionally, because of union disputes, the cockpit crew will have the same pay conditions as Air France pilots, and only the cabin crew will operate under more frugal conditions. The on-board service is not completely no-frills either, with features such as free drinks and entertainment. The question remains whether JOON can thrive in the low-cost carrier regime when it does not appear to genuinely reduce on costs.

EXPANSION TO AND FROM ASIA Currently, long-haul low-cost airlines focus primarily on the Europe-US market and some other destinations where leisure travellers are looking for cheap flights, such as Bangkok. Connections between Europe and Asia are generally less popular. Although Air Asia X failed on these routes, the current generation of aircraft may enable profitable flights. Scoot, a spinoff from Singapore Airlines, is planning to start service to Berlin Tegel with the Dreamliner. However, they prefer flying these aircraft on regional routes. Certainly, there is a large demand for flights between major Asian cities where the use of widebodies is warranted. These flights can be operated multiple times a day. An aircraft seat can only be sold once, and flying multiple flights a day means more streams of revenue, especially on routes with a high load factor. Also, it truly is much more difficult to lower

fares on flights from Europe to Asia. Whereas flights to North America are in the 6-8 hour range from the major European hubs, flights to Hong Kong, Singapore, Kuala Lumpur or Jakarta vary from 10-14 hours. Savings from reducing the on-board services are limited, and some fixed operating costs are inevitable. With increasing distance, the fuel cost component increases substantially, hence why long-haul flights used to be very hard to turn a profit on. The 787, A350 and A380 have improved efficiency on these very long flights, but not to the extent to slash prices as is done on short and medium haul flights. Despite this, the tables are turning. With Singapore Airlines’ subsidiary Scoot planning flights to Berlin using a Boeing 787 and service to Athens launched earlier this year, there may be hope for this market. Singapore is also connected to London Gatwick by means of a 4-times-weekly flight operated by Norwegian. It shows there is clearly interest among airlines to expand to Asia. Routes offered currently are limited, but if further advances are made in the efficiency of aircraft flying long-haul, it will be a matter of time before low-cost flights to Asia are as common as to North America. References The Aviation Department The Aviation Department of the Society of Aerospace Engineering Students VSV ‘Leonardo da Vinci’ fulfills the needs of aviation enthusiasts by organising activities like lectures and excursions in the Netherlands and abroad.

BOBSLEIGH AERODYNAMICS Near-wake flow topology on a two-man bobsleigh WHISTLER BLACKCOMB


Pallav Pattnaik, MSc student Aerospace Engineering, TU Delft

This work investigates the flow field in the near wake of a 1:5.5 bobsleigh model by means of stereoscopic particle image velocimetry. The time-averaged flow field reveals two counter-rotating vortices and a strong downwash between them. From the velocity field, the aerodynamic drag is retrieved invoking the conservation of momentum. This approach enables relating the aerodynamic loads to the flow structures responsible for them.


rag measurements on bluff-bodies such as bobsleighs using force balance systems have been in prevalence for several decades. These studies, however, do not reveal anything on the flow behavior around the body. In the recent past, various flow visualization techniques have been applied to investigate the flow behavior

around bobsleighs. Even though these studies have highlighted the qualitative flow features, there is a lack of deep insight into the wake flow topology and the behavior of the flow structures that are formed in the highly three-dimensional flow. This lack of knowledge raises a lot of challenges in the understanding of the wake flow of bobsleighs.

Bobsleighing is one of the most popular winter Olympic sports that has gained a lot of attention in the field of speed sports owing to the nature of its close and exciting races. The margin for victory in a typical bobsleigh race is only a few hundredths of a second [1]. Thus, modern-day bobsleigh designers seek superior aerodynamic designs to gain a competitive advantage. This is the focus of an ongoing research project at the Aerodynamics Laboratory of TU Delft, for which this thesis was a stepping-stone. The answer to the lack of knowledge in this field of bobsleigh aerodynamics LEONARDO TIMES N°1 2018



lies in the understanding of the flow around a bobsleigh. More precisely, how can we visualize this flow in order to understand it?

METHODOLOGY The flow around an object is visualized using an experimental technique known as flow visualization wherein tracer particles are introduced into the medium (think of putting ink drops in water). Further quantitative information can be deduced from flow visualization by recording the light scattered by these tracer particles onto subsequent image frames and then analyzing these image pairs in order to obtain the displacement field of the tracer particles. This is known as Particle Image Velocimetry (PIV). In case the recording of the flow field is performed with two cameras placed at an angle between them, then this technique is known as Stereoscopic PIV. Figure 1 - Experimental setup. In order to perform stereoscopic PIV experiments in the wake of a bobsleigh, a 3D printed scaled model (see Figure 1) was used. The model features two main parts namely the front cowling (3D printed) and the rear cowling (made from PVC) along with a wooden crew model. The bobsleigh model was mounted on a test bench setup in the M-tunnel at the Low Speed Laboratory. Micron-sized fog particles were used as tracer particles in these experiments and the measurements are performed at 20 m/s. A high-powered laser and two CCD cameras in stereoscopic configuration were setup to illuminate a plane in the wake of the bobsleigh model and capture time-resolved images of the tracer particles. Apart from the PIV instruments, the drag forces were also measured using a wind tunnel balance in order to draw comparisons. The complete experimental setup is shown in Figure 1.

RESULTS The raw images were processed with the stereoscopic PIV algorithm and post-processed to obtain statistically converged velocity fields in the wake of the bobsleigh model. Figure 2 shows the converged results. These velocity fields were obtained for the first time using stereoscopic PIV technique. This technique provides clarity on the formation of the flow structures in the wake and produces more accurate results as compared to other conventional drag measurements techniques.

NEAR WAKE FLOW TOPOLOGY The near wake of the bobsleigh model at z/D = 2 shows a large momentum deficit downstream of the model and the formation of two counter-rotating vortices. The latter is due to the rotation of the flow from the sides of the bobsleigh surface towards the inside of the rear cowling. Between the two vortices, a clear downwash is visible at the plane of symmetry of the model (see Figure 2-left). The two vortices are symmetrical with respect to the symmetry plane and have 38


approximately the same intensity (Figure 2-right).

NEAR WAKE FLOW TOPOLOGY AT DIFFERENT NOSE ROTATION ANGLES The mean flow topology in the near wake of the bobsleigh is investigated for different front-cowling rotation angles. The front cowling is rotated towards the left of the model from 0 to 20 with steps of 5. The time-averaged velocity contours in Figure 3-left to Figure 5-left suggest that as the angle of rotation increases, the momentum deficit initially reduces (the wake shrinks, mainly from the right side), and then slightly increases (the wake enlarges on the top-right). At smaller rotation angles, when the increase in frontal area is not significant, the area uncovered by the front cowling increases and more fluid passes through to the wake directly without any blockage from the crew model. Hence the momentum deficit decreases. As the nose is rotated to higher angles, the increase in frontal area dominates over the increase in the area uncovered by nose rotation due to additional blockage by the crew model. As a result, the momentum deficit increases marginally. From the vorticity contours in Figure 3-right to Figure 5-right, it is observed that the strength of the left vortex does not change significantly with the increase in angle of misalignment of the front cowling. As the nose is rotated to the left and the angle is increased, the flow at the left side of the bobsleigh separates from the front cowling and reattaches onto the rear cowling. However, due to the length of the rear cowling (approximately 2.25 D), the flow after reattachment recovers to a condition similar to that in the absence of flow separation. Hence, close to the model’s trailing edge, the flow on the left side of the bobsleigh is only marginally affected by the front cowling rotation. As a result, the left vortex shows only minor differences with re-

spect to the 0 front-cowling rotation case, as can be observed in Figure 6-left, where the peak vorticity of the left vortex is nearly unchanged with the angle of misalignment of the front cowling. Conversely, the peak vorticity of the right vortex decreases by 40% from 0 to 20 (Figure 6-left). As the nose angle increases, the area uncovered by the front cowling increases and more fluid passes through to the wake directly. As a consequence, the pressure difference between the side of the bobsleigh and the inside of the rear cowling decreases, thus reducing the strength of the right vortex.

AERODYNAMIC DRAG Figure 6-right shows the comparison of the drag coefficient obtained from balance measurements and stereoscopic PIV. The latter is obtained from time-averaged results over 500 uncorrelated samples at plane z/D = 2. The drag coefficient is evaluated with a frontal area equal to that of the reference case (0 rotation). For the computation of the momentum deficit from the PIV results, the flow velocity upstream of the model must be known. If this velocity is set equal to the freestream velocity (20 m/s), the drag coefficient is underestimated by about 10% with respect to the balance measurements (PIV-uncorrected result of figure 6-right). However, due to the expansion of the jet at the exit of the test section, the flow velocity in front of the model is lower than the free-stream velocity. In this work, a velocity correction based on the work of Merker and Wiedemann [2] has been applied (PIV-corrected result figure 6-right). Upon applying the correction, a difference of 2% to 3% is observed between the balance measurement and the corrected PIV drag coefficient. The uncertainty on the drag coefficient obtained from PIV is evaluated using the error propagation formula [3]. Since the momentum term accounts for the major contribution to the overall drag, the uncertainty of the Reynolds stress term and the

pressure term is neglected. The error bars indicate the expanded uncertainty on the drag coefficient evaluated at 95% confidence level. The drag evaluated from PIV confirms the balance measurements, within the margin of error.


Figure 2 - Time-averaged velocity (left) and vorticity (right) fields at plane z/D =2. For sake of clarity, one every three vectors is shown both in the x- and in the y-direction.


Figure 3 - Time-averaged velocity (left) and vorticity (right) fields at plane z/D =2 for no nose rotation.


Figure 4 - Time-averaged velocity (left) and vorticity (right) fields at plane z/D =2 for nose rotation of 10째.

The plot in figure 6-right shows that the aerodynamic drag first decreases for front-cowling rotations below 5 and then increases. The initial reduction in aerodynamic drag is due to the fact that from 0 to 5, a jet flow occurs in the wake due to the fluid passing through the area uncovered by the nose rotation; such jet flow energizes the wake. However, as the angle increases further from 5 to 20, the increase in frontal area plays a dominant role in lowering the wake velocities and increasing the momentum deficit. This counteracts the advantageous jet-effect within the wake and in turn increases the drag.

CONCLUSIONS The mean flow topology of a scaled bobsleigh model is investigated using stereoscopic PIV revealing the formation of two counter-rotating vortices in the wake of the model. The comparison of the mean flow topology at two different planes shows that turbulence diffusion plays an important role in broadening the wake and reducing the peak momentum deficit. When the front cowling is rotated with respect to the rear cowling, the strength of the vortex in the direction opposite to the nose rotation decreases. Conversely, the strength of the vortex on the side of the nose rotation remains nearly constant. Finally, a rotation of the front cowling by up to 5째 yields a reduction of the aerodynamic drag by approximately 5%. For larger nose rotations, the aerodynamic drag remains approximately constant. Future work in this field may focus on application of this technique to a more realistic model of a two-man bobsleigh to study the effect of nose rotation on the aerodynamic drag.

Figure 5 - Time-averaged velocity (left) and vorticity (right) fields at plane z/D =2 for nose rotation of 20째

Interested students may get in touch with Dr. Andrea Sciacchitano (A.Sciacchitano@ If you have further ideas or want to contribute to this research as a graduate student, contact the author for further information by email References


[1] International Bobsleigh & Skeleton Federation (IBSF). Our sports: bobsleigh. http://, 2015. [Online]. Accessed: 2015-12-23. [2] E. Mercker and J. Wiedemann, On the correction of interference effects in open jet wind tunnels, Technical report, SAE Technical Paper (1996). [3] A. Sciacchitano and B. Wieneke, PIV uncertainty propagation, Meas. Sci. Technol. 27 084006 (2016).

Figure 6 - Peak vorticity at different angles of rotation of the front cowling (left) and Drag coefficient at different angles of rotation of the front cowling (right). LEONARDO TIMES N째1 2018


SUSTAINABLE AIR TRAVEL Can we make flying environmental friendly? NICO’S CORNER

Nicolò Nefri, Editor Leonardo Times

With a 5% increase in commuter traffic per year, the aviation industry is without a doubt one of the fastest growing sectors of the last century. Airlines are continuously growing and travelling by air is becoming much more effortless and affordable. However, this comes at a huge drawback to the environment.


espite the slow pace, the scenario of air travel is changing. Back in 1901, when the Wright Brothers successfully completed the first ever powered flight, government authorities were unaware of the tremendous environmental consequences that could result due to air travel: the only goal was to discover the unknown skies. With the number of passengers that travel by air expected to double over the next twenty years, there is no doubt that air travel is now playing a far more influential role in the ever-changing environment. In fact, the current pollution problem is probably the biggest and most frightening issue that humanity has ever faced. Indeed, it is not a secret that the aviation sector is seriously compromising the destiny of our future generations. As humans and as engineers we have the moral duty to take action to recover from this trend and make air travel more environmental friendly. But is there still time? As the saying goes, never say never. Aviation 40


giants and technology, such as Airbus and Tesla, are constantly looking for sustainable solutions, investing billions of their annual capital in the research and development department to seek more green opportunities. For example, Airbus has committed to the ‘UN Sustainable Development Goals’, which focus on responsible consumption and production, as well as immediate climate action. This led the company to come up with products such as the A350 XWB, which is 25% more efficient compared to its predecessor. This shifting mindset to green innovations does not apply to aviation companies alone, as everyone is involved in this world-changing phenomenon. Tesla’s CEO Elon Musk is probably the biggest promoter of the global transition to sustainable energy. In fact, Delaware’s gigafactory will most likely change the game of energy consumption, as it has been doing so for the last decade. Tesla has promised to produce enough batteries to power nearly 500 thousand vehicles by the end of the year: something we should all be really ex-

cited about. Furthermore, Musk announced the release of the new Tesla-Y model on the market in the next two years, with the goal of selling one million cars annually. The ambition of the State of California is to have only electric vehicles on the road by 2040: a goal that is hard to achieve, but definitely worth fighting for. However, Elon Musk does not seem to have a particular interest in aviation and his companies do not manufacture commercial aircraft. Hence, we will need to rely on someone else to help solve the many concerns that this industry faces.

DRAWBACKS OF THE CURRENT SYSTEM Whether you agree or disagree, the air travel business is not all peaches and dandelions. In fact, it comes with a long list of disadvantages. 3.5% of the global greenhouse gas emissions and 5% of atmospheric heating are caused by air travel: figures that seem utterly irrelevant. However, we have reached such a state of fuel pollution that these numbers canno longer be ignored. The fact that the discharge of carbon dioxide into the atmosphere has increased by 87% from 1990 to 2006 in European countries should certainly trigger something in the engineers’ thought process. But

the worse side of this tremendous statistic is that the pattern is increasing due to the growing number of passengers worldwide. “Flying from London to New York and back generates roughly the same level of emissions as the average person in the EU does by heating their home for a whole year”, reports the EU Commission on climate change. Considering there are roughly seventeen flights per day between the two metropoles, we can easily do the math: connecting the two cities by air equals seventeen years of heating a house. Insane. Here is another impressive figure: only one out of twenty-five people in East Europe has ever boarded an airplane. With the advancing economies of these emerging countries, this number is destined to be changing soon. Along with fuel emissions, another important consideration worth mentioning is the deterioration of the local air quality, particularly around airports. These are usually located near big urban areas, where the carbon footprint levels are already high. Moreover, an additional impact induced by airplanes is the extensive noise level produced by the engines of airplanes. It is often disregarded how much acoustic pollution affects the environment, both for us humans and for our beloved animal friends. Speaking of the latter, they are usually involved in fatal accidents. Think of the 2009 emergency landing by pilot Charles B. Sullenberger on the waters of Hudson River, New York City. For those unfamiliar with the incident, upon departure from LaGuardia, the plane was struck by a flock of birds. The impact caused the loss of both engines, but miraculously no one (except the flock) was injured. Following that terrifying day for the air traffic control of LaGuardia airport, thousands of Canadian Geese were captured and moved away from the sky of New York because considered too dangerous for departing and landing airplanes, as well as in danger themselves. Without losing myself into the ethics of animalists, let me come back to the purpose of this article. Approximately 40% of the annual operational capital costs of an airline is spent on fuel, which is why companies are constantly seeking possible sustainable solutions to replace the traditional fuel sources. There is clearly a

big market gap which should warrant investment, but nobody seems to have found the right answer to really cut their costs and decrease the environmental impact. Not yet at least. We are, however, getting closer.

CHANGING MINDSET Over the last decade or so, a lightbulb has been come alight: aviation enterprises have finally understood the need of marrying technological discoveries and sustainability issues. The real key is hidden in finding the appropriate balance in order to move towards a greener future. American company 3Degrees launched a sustainable program, which was first introduced at San Francisco International airport. The way it works is straightforward: in allocated kiosks in the departure area, commuters would enter their destination, the trip type (either one-way or return) and how many people they are flying with. According to this information, the software would calculate the greenhouse gas impact according to the miles travelled. For example, a return flight from SF to LA would generate approximately a quarter of a ton of greenhouse gases, precisely 259.908kg of CO2. The costumer would then purchase the amount of carbon offset equivalent to that figure, which in this case sums up to €2.87. A reasonable price to pay to save some trees, right? The profits of this program are all invested in projects directly related to the protection of the environment. For travelers from San Francisco, the offsets go to the Garcia River Forest, a redwood forest along the north coast of California. The idea behind this simple but genial idea is remarkable: you pay not to cut trees. Also, airlines are making some efforts to change the pollution trends due to aviation. In fact, their strategy for making air travel more environmental friendly is increasing the prices of tickets based on their environmental impact. For example, a typical return trip between two European cities would increase between €1.8 and €9. “Bringing aviation emissions into the EU Emissions Trading Scheme is a cost-effective solution that is good for the environment and treats all airlines equally”, says Environment Commissioner Stavros Dimas. Environmental impact is everyone’s responsibility, even air passenger carriers.

Lufthansa was recognized as the most environmental friendly company in Europe, and Virgin America was their equivalent in the United States. Here are some key tricks to consider in order to make your flying experience more sustainable for the environment: • Fly during the day: due to less warming caused by emissions, it is eco-friendlier than night flights; • Choose economy class: more people on the plane means lower carbon footprint per person; • Fly non-stop; • Fly on a newer plane; • Lower the window shades: on average, if all the passengers on an aircraft lower their shades, the temperature can decrease by 10°C; • Pack lighter: less weights means less fuel emissions. • Last but not least, offset your carbon footprint: for example, paying off the CO2 you consume.

CONCLUSION Business innovations such as those introduced by Airbus or Tesla indicate that there is the right approach for a slow changing trend in the field of air travel, so real actions must be taken. The rules are set and the game is open. It’s just a matter of time till someone comes up with the perfect plan for a sustainable approach to flying. The one hundred billion dollars question remains one: who will reign? Unfortunately, I do not know the answer. However, let me say one last thing: it would be a dream coming true seeing Elon Musk entering the fascinating world of commercial air travel. Can you imagine a Tesla airplane? You should want to travel first class on that one… References [1] [2] [3] [4] [5] [6] [7] [8] [9] LEONARDO TIMES N°1 2018


STEERED FIBER PANELS A numerical method for prediction of their properties ASM

Vibhas Mishra, Master of Science, TU Delft

Steered fiber panels have shown improved specific mechanical performance compared to straight fiber panels. However, the manufacturing of these panels leads to inevitable defects. Numerical evaluation of the effect of these defects on the properties of the panels is problematic. A comprehensive approach is discussed which could predict the amount of defects and its effects on the properties of panels.


t the moment, fiber based composites are extensively used in the aerospace industry. However, it is still a challenge to manufacture complex geometries from it. Different manufacturing technologies have evolved over the decades to make the manufacturing possible. Filament winding and automated tape layup technologies were introduced to manufacture different geometrical shapes like cylindrical, singly curved and even doubly curved geometries [1]. Simultaneously, different design solutions to exploit the full potential of fiber composite materials have also been studied. One such concept which evolved was steering of the composite fibers in a design such that it follows the load paths in the structure. The concept can lead to designs with minimum usage of material and maximum delivery of mechanical performance. This has been demonstrated by Yau et al [2]. They produced a panel containing a hole with fibers going around this hole. The panel showed better performance than the straight fiber panels in which a hole was drilled. This was because of the load path continuity and higher stiffness around the hole area. The panel with steered fiber around a hole can be viewed as a panel 42


with spatially varying stiffness properties. There are many names in literature, which have been assigned to these panels, such as variable stiffness panels, variable fiber tow panels or steered fiber composite panels. In this article they are addressed as steered fiber composite panels. Many other researchers have also shown an improvement of mechanical performance due to steering of the fibers along the load path [2-7]. Nevertheless, the problem still remains on the manufacturing side. These manufacturing challenges were somewhat compensated by automated fiber placement technology. This technology is a smart amalgam of filament winding and automated tape layup technologies [1].

MOTIVATION Automated fiber placement technology has made it possible to place bands of composite fiber tows along curvilinear paths, to create laminates with spatially varying stiffness properties called steered fiber panels. However, automated fiber placement machines can allow a minimum radius of curvature for fiber steering. This depends on machine specification and can vary from 400-1000mm. Due to this,

bands of fiber tows with the same orientation are placed next to each other to produce a ply. This placement strategy gives rise to mismatch between the two bands and leads to fiber angular distortion. It can also lead to thickness build up but, to maintain the constant thickness of the panel, fiber tows are cut perpendicular to the placement direction which gives rise to the defects called tow drop defects. Tow drop defects are resin rich areas. In recent years, optimizations of the steered fiber panels for different load cases have been studied. These studies do not account for tow drop defects during optimization. To take account of these defects on the properties of the steered fiber panels, certain finite element approaches were proposed. For applying these approaches, location and geometry of the tow drop defects need to be identified in the steered fiber panels. Based on it, property assignments to the mesh elements were done. It becomes extremely tedious to identify them when the geometries of the panels are more complex, which is the case for doubly curved surfaces, for example. Moreover, the location and geometry of tow drops are dependent on fiber angle, width of the fiber tows and number of fiber tows in a band, and can vary for different configurations of steered fiber panels. It involves excessive computational effort to determine the location and geometry of the tow drop defects in the panels and analyze it. This makes it difficult to integrate the effect of the tow drop defects into the optimization studies. Thus, there is a need

to develop a methodology which could make this integration possible.

METHODOLOGY This research focuses on developing a methodology which could take the effect of tow drop defects on the properties of different steered fiber panels into account, without knowing the location and geometry of the tow drop defects in the panels. The estimation of the tow drop defects will be done based on the fiber angle gradient present in the panels. Based on this estimation, the effect of tow drop defects will be estimated on the stiffness properties and buckling load of the different steered fiber panels. These estimations will finally be compared with the full analysis results of the steered fiber composite panels to evaluate the validity of the procedure. To achieve this goal, three major steps were performed. Firstly, a micro-mechanical model was developed, which was dependent upon the variables that the geometries of the tow drop defects were dependent on. These variables were fiber angle distortion, tow width and course width. To evaluate the effect of the tow drop defects on the properties of a ply, firstly, a baseline ply with no defects was considered. Thus, a ply with all the fibers in y-direction was considered as baseline ply. The stiffness properties of the baseline ply can be calculated analytically. Thereafter, the stiffness property of the ply with tow drop defects was evaluated through a periodic homogenization approach. The changes in the elastic properties of the ply with the defect from the baseline ply were evaluated. The weaknesses that changed the elastic properties were termed as knock-down factors. A correlation between the knock-down factors and the geometrical parameters was developed, through which the material properties of the ply with any defect configuration can be evaluated. Secondly, a complete steered fiber panel model was developed. This model could identify defects inside a panel with any fiber angle. The complete analysis was carried out by the existing finite element approach, called defect layer method. In defect layer method, the mesh elements were generated on the geometry of the panel and for each element, the volume fraction of the resin inside an element was evaluated. Based on it, properties were assigned to an element through linear interpolation. For this approach, the location and geometry of the tow drop defects in the steered fiber panels

need to be evaluated. Uniform end shortening analysis was performed on the panel. The effective elastic modulus and buckling load of the panels with different configurations were evaluated from that analysis. These results were taken as reference results and compared to the predicted results. Lastly, finite element analysis of the steered fiber panels with developed smearing methodology was done. In the smearing method, an estimation of the geometrical parameters of the tow drop defect in the steered fiber panels was made through the fiber angle gradient. Based on this, properties were assigned to the mesh elements through the correlation developed in the first stage of the thesis. From the finite element analysis, the effective elastic modulus and buckling load of the various steered fiber panels were evaluated and compared to the reference results generated in the second stage of the thesis.

RESULTS From the first phase, it was found that the knock-down factors were dependent upon the fiber angular distortion and volume fraction of the tow drop defects. The relation between the degradation in the stiffness properties of a ply with fiber angle distortion and volume fraction was found to be quadratic and linear, respectively. A function of the stiffness properties of a ply with tow drop defects was developed. This function was dependent upon the fiber angle distortion and volume fraction of the tow drop defects. An error analysis was done to compare the stiffness properties of a ply from the finite element results and the correlation. The maximum error observed in the developed correlation was 10%. From the second phase, the results were generated based on the defect layer method for different configurations and were compared to the results reported in the literature to verify the developed model. The comparison of stiffness properties and buckling load showed that the results differed by 0.9% and 2.7% from the experimental results, respectively. The model was assumed to be valid, since the error can be considered small. Lastly, for all the configurations studied, the elastic modulus evaluated through the smearing methodology was underestimated compared to the results obtained from the defect layer method. Thus, the elastic moduli were

predicted on the conservative side. This was done for two material sets, and for both material sets the maximum error observed was 5%. However, the buckling load evaluated from the smearing methodology was overestimated compared to the defect layer method results. For all configurations studied in this research, at least 50% of the effect of tow drop defects on the buckling load of the fiber steered panels was captured by the smearing methodology. Moreover, it was shown that the estimation of the tow drop defects can be done through fiber angle gradients and no determination of the tow drop defect location and geometries is required. References [1.] D.H.J.A. Lukaszewicz, C. Ward, and K. D. Potter. The engineering aspects of automated prepreg layup: History, present and future. Composites Part B: Engineering, 43(3):997– 1009, 2012. [2] S.S. Yau and T.W. Chou. Strength of woven-fabric composites with drilled and molded holes. In Composite Materials: Testing and Design (Eighth Conference), ASTM STP, Philadelphia, PA, volume 972, page 423. ASTM International, 1988. [3] B.F. Tatting, Z. Gürdal, and D. Jegley. Design and manufacture of elastically tailored tow placed plates. Technical report, NASA, Langley Research Center, Hampton, VA, NASA/CR2002-211919, 2002. [4] D.C. Jegley, B.F. Tatting, and Z. Gürdal. Optimization of elastically tailored tow-placed plates with holes. In Proceedings of the AIAA/ ASME/ASCE/AHS/ASC 44th structures, Structural Dynamics and Materials Conference, Norfolk, Va, pages 2003–1420, 2003. [5] D.C. Jegley, B.F. Tatting, and Z. Gürdal. Towsteered panels with holes subjected to compression or shear loading. In Proceedings of the 46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Austin, TX, pages 18–21, 2005. [6] C.S. Lopes, P.P. Camanho, Z. Gürdal, and B.F. Tatting. Progressive failure analysis of towplaced, variable-stiffness composite panels. International Journal of Solids and Structures, 44(25):8493–8516, 2007. [7] M.W. Hyer and H.H. Lee. The use of curvilinear fiber format to improve buckling resistance of composite plates with central circular holes. Composite Structures, 18(3):239– 261, 1991. LEONARDO TIMES N°1 2018


DUCTED TURBINES Acoustic analysis to determine suitability for urban environments GREENCHECK.NL


Luca Anselmi, MSc Sustainable Energy Technology, TU Delft

The Diffuser Augmented Wind Turbine (DAWT) is a promising concept for power harvesting in urban locations. However, its far-field noise characteristics are still unknown. A computational study through Lattice-Boltzmann Methods and Ffowcs Williams – Hawkings analogy is performed and fluid-dynamic and acoustic are compared with a corresponding un-ducted turbine.


he problem of energy generation is widely considered one of the biggest challenges humanity in the near future. On one hand, the world’s energy consumption is increasing and it is expected to continue to grow in the coming years. By 2050, the world energy requirements might even double the current energy consumption. On the other hand, the current energy production is mostly based on fossil fuels, such as oil, coal, and natural gas. These 44


production methods have been proven to affect the climate, representing a threat to the environment and future generations. Therefore, the large-scale, fast, and sustainable development of new energy production systems is needed. Wind energy has emerged recently as a reliable resource to represent a significant share of the power production.

Nowadays, most wind power comes from wind farms on land. However, onshore wind farms can be located only on specific sites, which must have abundant wind resource, respect acoustic and visual regulations, and not be too far from the locations where the energy is consumed. Since such sites are limited, other locations need to be considered. As suitable locations are limited, wind energy generation in the urban environment is gaining interest. Urban wind energy involves a smaller scale of wind energy production and has the key advantages of reducing losses in electric power transportation and the direct use of the electricity by the consumer.

[2] need complete datasets to be used as a reference, which are not available in the literature. The DonQi Urban Windmill is employed as a reference case. There is no study in literature about this design in yawed inflow condition, i.e. when the angle between the wind direction and the rotor axis (defined as yaw angle) is not zero. Acoustic effects can differ to a great extent with the presence of a yaw angle and such state is recurrent in the lifecycle of a DAWT [3]. Therefore, the DonQi Windmill needs to be simulated in yawed conditions. This lead to the following research goals: • Create a baseline setup • Analyze the fluid-dynamic flow field in nominal conditions • Analyze the performance of the DonQi turbine in yawed conditions • Analyze the noise characteristics Figure 1 - Geometry of the DonQi wind turbine.

METHODOLOGY However, the urban environment places challenges on wind power generation. The presence of buildings increases surface roughness, leading to lower wind speeds and higher turbulence. Furthermore, the urban environment limits the maximum height of the turbine and it is subject to noise limitations. Several solutions have been proposed during the years, such as using buildings to concentrate the wind resource in the so-called Building Augmented Wind Turbines (BAWTs), and as turbines with vertical axis of rotation, named Vertical Axis Wind Turbines. Another wind turbine concept that is suitable for urban sites is the Diffuser Augmented Wind Turbine (DAWT), which is the main subject of the current research.

states that a turbine on its own cannot capture more than 59.3% of kinetic energy from the wind. However, with the inclusion of a diffuser, this limit can be overcome [1].

The DAWT is a promising concept for urban locations where the turbine is embedded into an airfoil-shaped diffuser (also called a shroud or duct), which has the function of increasing the mass flow across the rotor. Such a device is designed to overcome the low wind speeds present in urban locations. This device can exceed the Betz Limit, which indicates the maximum power that can be extracted from a wind turbine, regardless of its size or design. The law

Surprisingly, despite being well-suited for urban sites, where noise regulations are a significant limitation to power output, no acoustic study about DAWT can be found in literature.

PROBLEM STATEMENT AND RESEARCH GOALS Despite more than fifty years of research on Diffuser Augmented Wind Turbines, several crucial open questions remain. In fact, the scientific community has not agreed yet on a thorough aerodynamic theory that can explain the behavior of DAWT. The information available is relative to a wide variety of design and implementations, making it difficult to compare the results and coming to definitive conclusions.

1-D momentum models have been developed, but they are built on straightforward assumptions that cannot explain the 3-D behavior of a turbine. Semi-analytical models as the one by Bontempo and Manna

To perform the study, a computational aeroacoustics (CAA) approach was chosen. Since no CAD files are available for the turbine, the required geometry had to be created from scratch with SolidWorks based on previous work completed at NLR [4] [5] and by Van Dorst [6]. This DonQi Windmill is investigated for the availability of experimental and analytic data that are employed as a benchmark. Looking towards the solution of the flow and acoustic field, the computational software Exa PowerFLOW, which employs Lattice-Boltzmann Methods (LBM), is preferred over Ansys Fluent and other Navier-Stokes solvers. The LBM is chosen for its computational efficiency and its effectiveness in tackling the unsteady problems owing to its intrinsic low dissipation and dispersion properties [7] [8]. The acoustic data are then obtained using the Ffowcs Williams - Hawkings (FW-H) analogy, which calculates noise through the sound propagation from an integration surface where the noise sources are assumed to be located. The analogy is used in order to reduce the high amount of comLEONARDO TIMES N°1 2018


Figure 2 - Iso-surfaces of the lambda-2 criterion color-contoured with the velocity magnitude, for the ducted case (left) and the unducted case (right). putational time that a direct resolution of the acoustic pressure field would require. Following the research goals, three significant cases are created and compared: • ducted turbine, 0° yaw angle (nominal conditions) • unducted turbine, 0° yaw angle • ducted turbine, 7.5° yaw angle

COMPUTATIONAL SETUP The commercial DonQi wind turbine is used as a reference (Figure 1). The rotor has a radius of 0.75m, and three blades whose cross-section for the whole blade span is a NACA 2207 airfoil. The blade chord distribution and twist varies from 0.0435R to 0.0335R and 0.3° to 40.5°, respectively. The rotor is located in the section corresponding to the throat of the diffuser. At this location, the diameter is: Dth = 1.53m. The diffuser chord (cdiff) is 1m. The clearance between the diffuser suction side and the blade tip is 2% of R (h = 0.015m). The free-stream velocity, is set to u∞=5m/s, which is an average value for urban locations. The rotational speed of the rotor is 39.84rad/s, correspondent to a tip-speed-ratio of 6, found by Van Dorst [5] to be the optimal one for power production in such conditions. Both the diffuser and rotor blade are tripped with a zig-zag strip placed at 15% of the local blade chord and at 10% of the diffuser chord, forcing boundary layer transition. This allows avoiding artificial laminar flow and having a better comparability with future experimental results. As necessary simplifications, the geometry does not include the tower, the nacelle support structure, or the Gurney flap. The commercial software PowerFLOW is used to compute the flow field. The software solves the discrete Lattice-Boltzmann (LB) equation for a finite number of direc46


tions in the computational domain. The LB method determines the macroscopic flow variables starting from the mesoscopic kinetic equation, i.e. the LB equation. The discretization used for this particular application consists of nineteen discrete velocities in three dimensions (D3Q19). In the farfield, noise is computed by using the Ffowcs Williams-Hawkings (FW-H) integral solution. Integration is performed on the solid surfaces where the unsteady pressure is recorded with the highest frequency rate available (fs=10.235kHz) on the finest mesh resolution level (29’381voxels/cdiff). The far-field noise is computed on 160 microphones placed in four archs spaced by 90° at a distance of 8m from the diffuser center. A total of nine mesh refinement regions with resolution factor of two are employed. An anechoic outer layer is used to dampout the outward radiating and the inward reflected acoustic waves. The results are collected over six rotor revolutions, with the measurement starting after the thrust coefficient of the rotor has reached convergence.

VALIDATION The simulations have been performed with four mesh refinements, the finest one presenting 417 millions voxels and 3200 CPU hours per revolutions. However, both the fluid-dynamic and acoustic results are found not to be fully independent, with differences between the two finest simulation scales in the order of 9% of the thrust coefficient and 0 to 4dB in the sound power spectrum for nominal conditions. A finer resolution could not be simulated for computational and time constraint. A comparison of the rotor thrust coefficient and of the diffuser pressure distribution with previous experiments and analytical studies on the DonQi turbine shows that the results of the finest simulations are valuable for meaningful results.

RESULTS The power coefficient of the turbine is found to exceed the Betz limit when referring to the rotor area but not when referring to the diffuser area, in agreement with the research by Lubitz and Shomer [39]. The power and thrust augmentation of the diffuser augmented turbine compared to the bare counterpart is found to amount to several units. The reason for such behavior can be found in Figure 2, where iso-surfaces of the lambda-2 criterion for vortex-identification color-contoured with the velocity magnitude are displayed. The velocity magnitude at the rotor plane increases due to the presence of the duct as visible from the contour. Consequently, the thrust generated by the rotor increases due to the induced larger angle of attack. In addition, the rotor design is optimized for ducted conditions. The tip vortex interacts with the turbulent boundary layer, thus enhancing the intensity of the turbulent flow at the suction side. At the trailing edge of the diffuser, larger vortices are generated that convect downstream of the wake. The vortices still have a coherent structure after the diffuser outlet, in contrast with the results on the Wind Lens design, a DAWT with a large Gurney-flap at the end, from Takahashi [56]. The wake of the ducted turbine is significantly larger than that of the un-ducted case, due to higher rotor loading. Furthermore, the intense vortical activity downstream of the trailing edge of the diffuser is expected to hinder the wake mixing with the undisturbed flow, representing a problem for applications with DAWTs in series. When the DonQi Windmill is tested in conditions with a yaw angle of 7.5° ,the power produced by the blade decreases by 10.8%

Figure 3 - Directivity plot of OASPL (in dB) for the non-ducted (red) and ducted (blue) wind turbines for zero degree yaw angle. The upwind direction corresponds to θ = 0°. compared to nominal conditions. This is due to the non-axisymmetric flow at the rotor plane, which causes the thrust coefficient on the blade to vary during the revolution up to 20% in the chordwise location of maximum power. However, no stall on the blade is detected. The variation of the flow features, particularly the flow acceleration due to the duct, affect the farfield noise intensity and directivity. Directivity plots of the Overall Sound Pressure Level (OASPL) for both configurations are shown in Figure 3. The non-ducted wind turbine shows the conventional directivity plot for a wind turbine, with a region of low noise above the rotor (70° < θ < 110°), and the two zones of high noise upwind and downwind. The installation of the duct causes noise increase of about 5dB both upwind and downwind and of about 15dB in the low noise region, as an effect of the diffraction from the walls of the diffuser. The yawed case does not show a relevant increase in noise, since blade stall does not occur and the separation region on the diffuser presents low speed. The directivity in the yaw angle plane is tilted in correspondence with the turbine, while in the perpendicular plane no relevant difference with the nominal conditions is detected.

CONCLUSIONS AND RECOMMENDATIONS The fluid-dynamic analysis reveals that the presence of the diffuser accelerates the flow in the tip region, resulting in a significant increase of the thrust and the power

produced by the turbine. In correspondence, the tip vortices present a higher intensity. The presence of a yaw angle creates a non-axisymmetric velocity pattern at the rotor disk, resulting in a power drop of 10.8% but not in stall. The addition of the diffuser to the bare turbine causes a noise increase and a more uniform noise distribution. This effect is ascribed to the higher flow speed in the tip region and to the diffraction of acoustic waves by the diffuser. Increasing the yaw angle to 7.5° is found not to have a relevant impact on the far-field noise. For the future, it is suggested to create a fairer comparison between a DAWT with rotor and diffuser optimized to work in ducted conditions an optimized bare rotor, whose rotor disk area is equal to the diffuser exit area. All the phenomena related to the tip vortices formation are strongly related to the tip clearance. By varying this value, it should be possible to obtain a configuration with a trade-off between noise generation and power production. An investigation on the effect of the Gurney flap, commonly claimed to be beneficial for power production, on the noise emissions would be of interest and lead to a joint optimization with the diffuser. References [1] A. von Betz. “Energieumsetzungen in Venturidusen”. Die Naturwissenschaften, 10, 160–164, 1929. [2] R. Bontempo and M. Manna. “Solution of the flow over a non-uniform heavily loaded

ducted actuator disk”, J. Fluid Mech. (2013), vol. 728, pp. 163 195. [3] S. Oerlemans. “An explanation for enhanced amplitude modulation of wind turbine noise”. NLR, Report NLR-CR-2011-071. [4] National Aerospace Laboratory (NLR). “Evaluatie en verbetering van de prestaties van een kleinschalige diffusor augmented wind turbine (dawt); 1e fase”. 2008. [5] National Aerospace Laboratory (NLR). “Ontwerp van een kleinschalige diffosor augmented wind turbine (dawt); 2e fase”. 2008. [6] F.A. Van Dorst. “An improved design for a diffuser augmented wind turbine”. Master Thesis, Delft University of Technology, 2011. [7] G. A. Brès, F. Pérot, and D. M. Freed. “Properties of the Lattice-Boltzmann Method for Acoustics”. 15th AIAA/CEAS Aeroacoustics Conference, AIAA Paper 20093395, May 2009. [8] S. Marié, D. Ricot, and P. Sagaut. “Comparison Between Lattice Boltzmann Method and Navier Stokes High Order Schemes for Computational Aeroacoustics”. Journal of Computational Physics, Vol. 228, No. 4, 2009, pp. 1056–1070. [9] W.D. Lubitz and A. Shomer. “Wind loads and efficiency of a diffuser augmented wind turbine (DAWT)”. Proceedings of The Canadian Society for Mechanical Engineering International Congress 2014, 2014. [10] S. Takahashi, Y. Hata, Y. Ohya, T. Karasudani, and T. Uchida. “Behavior of the blade tip vortices of a wind turbine equipped with a brimmed-diffuser shroud”. Energies 2012, 5, 5229-5242.



AIRCRAFT MANUFACTURING LA Building a real aircraft at the Faculty of Aerospace Engineering AML


Martina N. Stavreva, MSc Student, Aerospace Engineering

To those who did their Bachelors in Aerospace Engineering at TU Delft: remember that first lecture of Introduction to Aerospace Engineering, when Professor Hoekstra asked us to build a paper aircraft and fly it around the room? I remember him saying something like: “You just built the first and maybe last aircraft in your career.” He was mostly correct, as a large part of the students do not end up working in aviation design, and I just thought: “I really hope he’s wrong.”


ooking at the curriculum of the Bachelor and Master programs in the faculty of Aerospace Engineering, one can see various courses covering the statics, dynamics, aerodynamics, structures, as well as the system design of an aircraft. However, it all seems a bit too theoretical, no? We can derive relations and perform calculations, but do we really understand the mechanics of such a complex machine? Even though we are very lucky to have the theoretical knowledge, which allows us to analyze complex problems, there remains a piece of the puzzle missing regarding the 48


facilities to test such concepts on small scale aircraft components. Yes, we have manufactured simple specimens, but we have not had the chance of producing a real aircraft part, let alone something that is going to fly.

MOTIVATION The world of aviation offers a few fields one can specialize in, namely research, design, manufacturing, and maintenance. Most of these have been covered within the 5-year Aerospace Engineering curriculum, but construction and certification are only briefly present.

Looking at the current state of aviation, the main aircraft manufacturers, Airbus and Boeing, have already proposed and developed various designs that serve the numerous needs of transport aviation. Even though the predictions can vary a bit, everyone is certain about one thing: the demand for air transportation is steadily increasing and the biggest challenge for manufacturers is how to accommodate it [1]. The focus now is on optimizing the production process of aircraft so that a twofold increase in expected demand within twenty years is met. Therefore, there is a strong need for engineers who are able to perform and supervise this. But how does one master those skills?

THE PROJECT This is where the course of Aircraft Manufacturing Laboratory (AML) comes in. The kickoff for our team was in November 2016 and it features the production of a two-seat all-metal side-by-side airplane, namely the Van’s



The AML team. RV-12. The construction is performed under the supervision of four staff members from the departments of Aerospace Structures and Materials and Flight Performance and Propulsion. The course is an elective available to every master track from the faculty of Aerospace Engineering. Since the skills and knowledge you will gain belong to the AE curriculum, unlike other student projects, you get 6 ECTS for participating. One might think that its sole aim is to: “Get this built!” But again, just as everything in aerospace, it is much more intricate than initially imagined. The study goals are a list of six points varying from teaching the students to operate within an aircraft manufacturing setting, to keeping the production and administration up to a level that can meet industry standards. Moreover, everyone is responsible for the organization of not only their own work, but also of the rest of the team, as everything needs to be quality controlled throughout the process. The organization features a team of students

working on the aircraft for roughly 20 weeks. After that, a new team takes over. The biggest challenge is seen in the fact that the overall learning curve of the project is not constantly increasing. This is due to the fact that, by the time the current team gains experience and knowledge on the production techniques, it is exchanged with a new, fresh and inexperienced team. Of course, no one is thrown in the deep end from day one, a heavy handover procedure is yet another requirement for each team. Everyone should be able to pass as much knowledge to the newcomers, which practice is also strongly present in the industry. Nevertheless, what is going to be the end result?

THE AIRCRAFT The RV-12 is unique for meeting the certification standards of the Light Sport Aircraft category and being eligible to be licensed as such. Moreover, the wings are quickly and easily removable, which allows for easier transportation and can be kept off-airport.

However, this feature could potentially benefit the implementation and testing of different modifications, a major attraction to students and staff in the faculty. The engine of the aircraft is a Rotax 912ULS 100HP engine that is the most widely used engine in the world for Light Sport Aircraft. It is known for its durability, reliability, acceptable price, and the fact that it can use both unleaded gasoline or 100LL. The control and wiring connections are automatic and an ignition interlock is featured, which prevents the engine from starting in case the wings are not properly installed. Moreover, the propeller is the light and smooth Sensenich that contributes to the low empty weight of the aircraft. The latter in return results in having the possibility of high useful load, passengers and luggage and a large fuel tank, which is not common for Light Sport Category aircraft [2]. But how does it work?

THE MANUFACTURING PROCESS There is space in the Aircraft Hall dedicated LEONARDO TIMES N°1 2018



Figure 1 - Organization of the lab space dedicated to AML. and every single step can be traced back to the responsible “engineer”, just like in large manufacturing lines. Moreover, at important stages of the manufacturing, such as section closings and at the end of each twenty weeks, licensed inspectors check the aircraft in order to ensure that everything is still in order.

GROUP ORGANIZATION Another very important feature of the project is the group organization. Next to the construction, each member has a personal role in the team. Every group is free to choose how to distribute the tasks as long as the functions are covered and the efficiency of the project is ensured. Group 2 riveting the horizontal tail. for AML only. It is equipped with all the tools needed for the production as well as an office where all organizational procedures as well as the ones related to the documentation are carried out. The layout can be seen in Figure 1. If any additional equipment is needed, the team can go to the main lab and ask responsible mechanics for advice and help at any time. In 2016, the faculty ordered the aircraft kit, which contains all required parts and is supported by an extensive production manual. The latter is divided into sections and gives the specific order in which the construction to be carried out. The first team that started February 2017 was responsible for receiving the kit, checking if everything is in order and setting up the basic documentation procedures. Then the construction was initiated by building the empennage: the horizontal and vertical tails as well as the rudder and the trim tab. This was taken over by Team 2 who finalized the horizontal tail and carried on with the fuselage tail cone. Now, Team 3 is aiming to finish the tail cone, assemble it with the empennage and prepare for the next group to come. We aim to make it possible for Team 4 50


to start working on the wing spars as soon as they have completed their handover. One may think: “Aren’t you guys a bit slow? For twenty weeks you can definitely do better!” And this would be very much true if the sole task of the project was manufacturing. However, it should be noted that there is another high point within the project: one should work with a high degree of precision. Things like: “This looks like it is straight to me” do not imply. One needs to make sure everything is exact to the smallest detail. For example, it is common practice that more than one or two people are involved when you drill a hole. Even though this might seem a bit excessive, at the end of the day, you sign the document saying that you drilled this hole or you performed the independent quality check and you take full responsibility for it. It might sound surreal, but every time you do it, the thought “I worked on something that is going to fly, I am responsible for it”, always comes in mind. Thankfully, the procedures established by Team 1 and Team 2, which of course are in constant revision, do not leave room for mistakes as everything is thoroughly checked

In general there are seven main roles: Head of Project Hours, Health & Safety, Public Relations, Construction Lead, Quality Control Lead, Tooling Lead and Project Manager. Each of them has their own specific tasks and requires certain skills. It is up to the team to decide what is the best distribution and who is the best fit for the role.

CONCLUSION Aircraft Manufacturing Laboratory is an exciting course for the Master students at the faculty of Aerospace Engineering, TU Delft, that offers the possibility to learn how a real manufacturing environment operates, to experience and understand the importance of certification standards in both production and documentation as well as to work in a diverse team. Moreover, the expected result: building an aircraft that is to be certified and flown, is more than motivational and is a one-time opportunity, which surely nobody wants to miss! If you have any additional questions, do not hesitate to contact us on or any of the responsible instructors. References [1]Boeing Commercial Airplanes, “Current Market Outlook 2017-2036” [2]

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Would you like to develop your talents and your competencies? At NLR youâ&#x20AC;&#x2122;ll get all the space you need! NLR - Netherlands Aerospace Centre

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THE WORLD’S LEADING TIER 1 AEROSPACE SUPPLIER GKN Aerospace acquired Fokker in 2015. Fokker’s outstanding people and technologies are now fully integrated into GKN Aerospace. The result is a stronger GKN Aerospace business with enhanced market leadership positions, increased exposure to key growth platforms, a more comprehensive global manufacturing footprint and stronger technological offerings.

Leonardo Times February 2018  
Leonardo Times February 2018