Update of the X-29 High-Angle-of-Attack Program

The X-29A forward-swept wing flight research aircraft flight envelope was expanded to 66°-angle of attack in 1990. This work was accomplished at the NASA Dryden Flight Research Facility in Edwards, California, using Grumman aircraft and United States Air Force personnel assistance. The flight envelope expansion was accomplished through a carefully planned buildup approach using the number 2 X-29 aircraft and a well documented high-angle-of-attack database established from wind-tunnel results, radio controlled subscale drop model results, and from previous X-29 aircraft number 1 flight data below 22.5°-angle of attack. Following the flight envelope expansion, a military utility evaluation was conducted to investigate the tactical utility of the X-29 configurations at high-angle-of-attack, slow-speed flight conditions. This paper provides an overall management view and perspective of the expansion process, the technical problems encountered, and the results obtained when compared to the initial predictions.

Initially, emphasis was placed on aerodynamic parameter identification for the flight envelope expansion process and simulation studies preceding each research flight. However, the approach of using only parameter identification to update the simulation's aerodynamic database had to be altered significantly because of concerns when aircraft performance differed significantly from expectations. The technique was changed to allow the aircraft to lead the simulation results. Better aircraft controllability was encountered when compared to the initial simulation studies up to 45°-angle of attack with a slow-speed flight envelope virtually free of wing rock. The X-29 aircraft proved to have slow-speed high-angle-of-attack flying qualities equal to or better than some of the current day United States high-performance aircraft.