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The X-31 executes a high angle of attack maneuver. NASA Photo / Jim Ross

X-31A team captures von Kármán Award

By Jay Levine
X-Press Editor

An experimental aircraft project in which Dryden played a prominent role received the prestigious International Council of the Aeronautical Sciences (ICAS)-von Kármán Award for flight research spanning an ocean and two decades.

The X-31 Enhanced Fighter Maneuver-ability (EFM) program researched high angle of attack flight at angles up to 70 degrees, an unfriendly environment well beyond the aerodynamic limits of conventional aircraft. A glimpse into the aerospace future was gained through the X-31's use of thrust vectoring - using the engine's thrust to control the aircraft - and cutting-edge technologies and flight controls.

"Congratulations certainly go to Dryden's entire X-31 team. The X-31was a great program that flight-validated the utility of high angle of attack flight, allowing the X-31 to fly routinely in uncharted areas of the flight envelope. It explored the realm of high angle of attack flight, an area in which most aircraft previously could not maintain control," said Dryden's Acting Deputy Director Robert R. Meyer Jr.

The X-31 team achieved as many as five flights per day and recorded 406 flights during the Dryden portion of its research from 1992 to 1995. In all, the first international X-plane recorded a record number of flights - more than 580 sorties.

This is the front of the medal that honored the X-31 team. NASA Photo

A highlight of the X-31 program was an appearance at the 1995 Paris Air Show, where the aircraft awed spectators with aerial cartwheels that had never before been possible with traditional aircraft.

German researchers convinced Rockwell North American Aircraft (now part of The Boeing Company) and the Department of Defense to partner with them in the 1980s to explore the concept's military utility. Dryden was wrapping up work on the X-29 Swept Wing when the Defense Advanced Research Projects Agency (DARPA) asked Dryden to join the flight research team for the new bird roosting at nearby Air Force Plant 42 in Palmdale, said Gary Trippensee, who was Dryden's X-31 project manager. He retired in January 2001.

Dryden accepted the challenge, and the International Test Organization (ITO) assembled at the Center was excited by the challenges presented in studying the latest in aviation technology.

"We were flying every other day and completed maintenance on the days in between. We would try to get two to four flights a day and we twice flew five flights a day. Watching it fly could take your breath away," Trippensee recalled.

In fact, 33 times the aircraft flew four times a day; 42 times it flew three sorties a day, 48 times it flew at least two flights a day and 42 times it flew a single flight.

The back of the honor bestowed n the X-31 team looks like this. NASA Photo

"It felt so good to be a part of the program. The team had its back against the wall a few times, but it seems the more stymied the team was on something, the harder the team worked to resolve the issue and move on. The key was co-location of all the key people, who met on a daily basis," Trippensee said.

Trippensee and former Dryden Director Ken Szalai represented the Center at the July 13 award ceremony at the International Air and Space Symposium and Exposition, "The Next 100 Years," in Dayton, Ohio.

The ICAS-von Kármán Award for international cooperation in aeronautics is usually granted biannually. However, in conjunction with the Centennial of Flight year, the organization bestowed a special von Kármán on the U.S. and German Team, in which NASA was a partner. The award was presented "for over 20 years of successful Trans-Atlantic R&D (research and development) teamwork producing the first-ever International X-plane and significant breakthroughs in thrust-vectoring control."

The award was founded in 1980 in memory of Professor Theodore von Kármán, a leading figure and founding member of the ICAS, one of the greatest aeronautical scientists of the 20th century and an outspoken proponent of international scientific cooperation. The award recognizes the team of countries that contributed to the outstanding technical achievement of the program for which the team is nominated and ultimately awarded the von Kármán medal.

Dryden's Rogers Smith was lead pilot for the envelope expansion from 45-degree angle of attack to 70-degree angle of attack and the effect that expansion had on air combat situations.

"What was truly amazing was to fly the 'finished product' in simulated combat engagements against all the current top U.S. fighter aircraft. The ability to 'point the nose' of the X-31 during maneuvers at high AOA (slow speed) - almost like you were flying a helicopter - was truly remarkable," said Smith, who also will be inducted to the Lancaster Walk of Honor later this month.

NASA engineer Pat Stoliker, who served as flight control lead on the X-31 project, fondly recalled the X-31 aircraft and team.

"It was an interesting challenge to fly in a flight regime that most planes try to avoid. It was a unique opportunity to work with Germany and U.S industry. It was a top notch team of motivated, dedicated and fun-to-work-with individuals," he said.

"Challenges included dynamic entry to high angle of attack from high speed level flight and lateral asymmetries resulting from the forebody. We solved the forebody issues with a simple aerodynamic fix, and identified and validated the aerodynamics for the full envelope control system design. It was a very complex challenge because of the limitations of the wind tunnel predictions for the aircraft and (the) required parameter identification flights from 45-degree angle of attack to 70-degree angle of attack," he said.

John Bosworth, NASA X-31 chief engineer, shares the sentiment about the team's extraordinary capabilities.

"It was a highlight of my career. It was amazing. DASA (a German aerospace company), Rockwell and NASA represented three different cultures working together and we benefited from the best of each group in this fast-paced program. I think the award is well deserved. A lot of people were saying there was no way we were going to do what we did. All along there were doubters. But it was a success. When the X-31 pulled high-alpha maneuvers at the Paris Air Show, there was an audible gasp from the crowd. People thought the maneuvers would cause a crash, but it kept flying," Bosworth said.

And for then new engineer Brent Cobleight, who worked on the X-31 aerodynamics and flight dynamics, the project offered fantastic opportunities.

"It was a great growing experience for a new engineer. The flight rate for the X-31 was so high that there was a lot of work in the control room and it gave me the opportunity to work under the pressure and stress of such a high-profile program. It was one of those key experiences. I was impressed with the international team and how the walls came down and the team really worked together toward a common goal," Cobleigh said.

The X-31 program included two aircraft. X-31 number 1 was lost Jan. 19, 1995, after a single-point failure in the noseboom airspeed system.

As part of the flight research at Dryden in 1994, software was added to simulate tailless flight at supersonic speeds using thrust vectoring.

A follow-on program called VECTOR five years later studied improved operational performance. That program, as well as the most recent demonstration flight series on using thrust vectoring as a way to achieve Extremely Short Takeoff and Landing capabilities, was flown at the Naval Flight Test Center at Patuxent River, Md.