NASA AND McDONNELL Douglasand NASA have completed the first phase of flight testing of the X-36 tailless-fighter technology demonstrator, achieving a higher angle-of-attack (AoA) than planned during the initial eight flights of the subscale unmanned aircraft.

Plans had called for the aircraft to be flown to 15 degree AoA in Phase 1, but handling qualities and stability margins proved better than predicted, allowing manoeuvres to 20 degree AoA, says programme manager Gary Jennings. The envelope will be pushed to 35 degree AoA during Phase 2 of the 25-ßight programme, with the objective of demonstrating high-AoA agility "equal to or better than" that of current fighters.

The X-36 is a 28%-scale model of a highly unstable tailless fighter with foreplanes, split ailerons and thrust vectoring. Jennings says that two flight-control software routines "proved to be very effective" in Phase 1: parameter identification, used to determine individual control-surface effectiveness, and real-time stability margin, used to monitor flight-control phase and gain margins.

The NASA-developed real-time stability-margin program "was a key element in successfully completing Phase 1 in record time."

Source: Flight International