Test Pilot School Instructors Conduct Research that Pushes Boundaries
By Paul Lagasse, U.S. Naval Test Pilot School Communications
T
he instructors at the U.S. Naval Test Pilot School (USNTPS) at Naval Air Station Patuxent River in Maryland are dedicated to ensuring the next generation of developmental test pilots, flight officers, and engineers gain the skills necessary for testing the aircraft and systems of tomorrow. Less widely known, but no less valuable, is their dedication to conducting original research that broadens the body of aerospace knowledge and improves flight test safety and practice.
The shadow of a U.S. Naval Test Pilot School (USNTPS) OH-58C Kiowa falls on the face of the Elevated Fixed Platform, a test platform constructed from over 100 shipping containers stacked to form a 38-foot-tall box and capped with steel plates. U.S. Navy photo by John Holder
A good example of this is a recent flight test program conducted by USNTPS rotary wing instructors John Tritschler and John Holder to evaluate the hover performance of helicopters near obstacles and inside confined areas, in order to better understand how helicopters behave when landing on and taking off from ships at sea, rooftop platforms, and other complex environments.
effects on the V-22 Osprey using dozens of anemometers affixed to the sides of the EFP to measure airflow variations. Once those tests were completed, the two USNTPS instructors learned there would be a brief window of time before the EFP was dismantled. It was an opportunity they couldn't pass up. "I saw the EFP as a target of opportunity for USNTPS," Tritschler said. "I argued that it would have been irresponsible of us as a learning institution not to take advantage of this great opportunity to create a dataset that would be useful not just for the engineering community, but also for the operational community."
Helicopter rotors generate lift in part by accelerating air downward — a phenomenon, appropriately enough, called downwash. Nearby obstacles such as buildings, hangars, and ship superstructures can bounce some of that downwash back toward the helicopter, which is called recirculation. Excessive recirculation can force a pilot to use more engine power to stay in a hover, and in some extreme instances it can even result in a loss of control. It's a situation that pilots learn to deal with through experience, but Tritschler and Holder sought to gain a more systematic understanding of downwash recirculation so that pilots could train better to deal with it.
With the approval of USNTPS commanding officer Lt. Col. Rory Feely, Holder and Tritschler developed and implemented a series of test flights with three USNTPS helicopters — a UH-72A Lakota, a UH-60L Black Hawk, and an OH-58C Kiowa — to study how recirculation affected the helicopters' performance when hovering at various predetermined locations and altitudes above and alongside the EFP's roof, walls, and corners. Once the roof and one wall have been removed as part of the dismantling process, the two pilots will return to fly a similar series of tests inside the box itself. So far, five USNTPS staff pilots have participated in the research flights along with Holder and Tritschler, providing them with valuable first-hand experience and knowledge that they can use in designing test projects of their own.
"We have been conducting flight test research programs for several years at USNTPS," Tritschler said. "This particular project came about organically from a previous project that Noddy" — that's Holder's call sign from his previous service in the Royal Navy — "and I conducted to assess the effect of sloping terrain on helicopter downwash." To conduct their research program, Holder and Tritschler took advantage of a unique opportunity: a temporary structure that had been built on a disused taxiway at NAS Patuxent River. Constructed from over 100 shipping containers stacked to form a 38-foot-tall box and capped with steel plates, the Elevated Fixed Platform (EFP) was built to test recirculation
During the tests, Holder and Tritschler varied the helicopters' rotor speeds and gross weight. "In doing so, you get a wide range of thrust conditions, and you can explore whether there are any sensitivities that effect those conditions," Tritschler explained. "We wanted to make sure that we collected data across the widest range as possible because it
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