EG-0093-01
Two X-31 Enhanced Fighter Maneuverability demonstrators were test-flown during the early 1990s at NASA’s Dryden Flight Research Center, Edwards, CA, to obtain data on control in the post-stall flight regime. The X-31 program demonstrated the value of thrust vectoring – directing engine exhaust flow – coupled with advanced flight control systems, to provide controlled flight at very high angles of attack.
Angle of attack – AOA or alpha – describes the angle of an aircraft’s wings relative to the oncoming wind direction, or the path of the aircraft’s flight. In the X-31, the maximum angle of attack at which airflow could be maintained over the wings in normal flight was 30 degrees nose-up from the aircraft’s direction of flight, beyond which the aircraft would stall. Flying in the post-stall regime – flying at angles of attack greater than the maximum – was achieved in the X-31 when thrust vectoring was combined with advanced digital flight controls.
Three thrust-vectoring paddles mounted on the X-31’s airframe adjacent to the engine exhaust nozzle directed the exhaust flow to provide control in pitch and yaw. Made of carbon-carbon, the paddles could sustain temperatures of up to 1,500 degrees C for extended periods. In addition the X-31s were configured with movable forward canards and eventually with fixed aft strakes. Both supplied additional pitch control in tight maneuvering situations.
The X-31 research project produced technical data at high angles of attack. This information gave engineers and aircraft designers a better understanding of aerodynamics, effectiveness of flight controls and thrust vectoring, and airflow phenomena at high angles of attack…Learn more