Mechanical and Aerospace Engineering, Henry Samueli School of Engineering, University of California, Irvine

Recovery of aircraft from post stall regimes to normal low angle-of-attack flight regime is a challenging problem for all aircraft. The aircraft model which is used to generate results for this presentation has unstable and unpredictable post stall behaviour. As a result, a completely different and unconventional methodology has been used for recovery of the aircraft. In this methodology, a nonlinear controller is first designed at high angles-of-attack. This controller is connected by the pilot after the departure of the aircraft and the controller drives the aircraft to a well-defined spin condition. Thus, the controller makes the post stall aircraft behaviour predictable. Then a set of automatic recovery inputs is designed to reduce aircraft rotations and to lower the angle-of-attack. The present aircraft model is unstable at low angle-of-attack flight conditions as well and therefore to stabilize the aircraft to a low angle-of-attack level flight, another controller is designed. The high angle-of-attack controller is disconnected and the low angle-of-attack controller is connected automatically during the recovery process. The entire methodology is tested using extensive non-linear six degree-of-freedom simulations. This presentation shall include a large number of simulation results that establish the efficacy of the technique.