Flight testing flutter suppression on a small flexible flying-wing aircraft

High aspect ratio lightweight and flexible aircraft have high lift-to-drag ratios and low mass; all leading to low fuel burn. As aircraft become more flexible, rigid-body and structural dynamics become highly coupled, posing challenges in aircraft design, modeling, and control. Due to significant structural flexibility, active flutter suppression is required for these aircraft to maintain stability and performance in the desired operational flight envelope. A small unmanned flexible flying-wing aircraft built for aeroelastic research has been used to validate active flutter suppression flight control. Three different flutter suppression controllers were designed using a flight-test-validated aeroelastic aircraft model. These three independently-designed controllers were tested via a series of flights where the vehicle velocity was incrementally increased up to and above the aircraft open-loop flutter boundary. The tests involved both open-and closed-loop flights at lower speeds and closed-loop-only flights at higher speeds. Frequency-domain system identification was used to identify critical aircraft modal frequencies and damping ratios from the test data to confirm predicted control performance, and to further validate model accuracy, including estimation of the critical open-loop flutter point using flight test data. The results of these flight tests demonstrate that the flutter boundary can be successfully expanded using active control.