Combat planes are designed in a structured relaxed static stability to meet maneuver requirements. These planes are unstable in the longitudinal axis and require continuous active control systems with elevator control. Therefore, failures in the elevator can have vital consequences for flight safety. In this work, the performance of classical control approach against asymmetric elevator failures is investigated and it is shown that this approach is insufficient in the case of such a failure. Then, a fault-tolerant control system is proposed to cope with these failures and it is shown that this controller can successfully deal with such failures. The F-16 aircraft is taken as an example case. A detailed nonlinear dynamic model of this aircraft is presented first. In the F-16 aircraft, the elevator surfaces are in two parts, right and left, and can move independently. Therefore, to obtain a more realistic and difficult failure scenario, it is assumed that the elevator is asymmetrically defective. Two types of failures commonly observed on the elevator surfaces (freezing and floating) are aerodynamically modeled and it is shown that the pitch-rate control augmentation systems in the conventional structure cannot cope with these elevator failures. In order to overcome this problem, a fault-tolerant control system is proposed. It is shown that this controller can successfully cope with the aforementioned failures without any degradation in flight safety.
robust control, flight control, fault-tolerant control, asymmetric elevator failures, control augmentation system
93B51, 93B36, 93C35, 93D15, 93C95