Safety Control Design with Flight Envelope Protection and Reference Command Generation

When confronting different levels of aircraft actuator faults, a safety control system without considering the postfault performance degradation raises the probability of flight incidents. This article presents a safety control scheme against actuator malfunctions, on the basis of flight envelope protection and reference command regeneration. First, with respect to a high-fidelity aircraft model, a flight envelope estimation method is developed to respect to the state limits of postfault aircraft (i.e., trim and maneuvering envelopes). Simultaneously, in an attempt to alleviate the burden of the damaged actuators, a degraded reference command is online regenerated, thus, maintaining the closed-loop aircraft within the safe flight envelope. Second, a sliding mode control scheme with the integration of a prescribed performance function is proposed to track the degraded reference command. When comparing to the existing control schemes, the gap between safety control and reference command regeneration is bridged to ameliorate practical flight safety. Finally, comparative simulation studies, based on the high-fidelity Boeing 747 longitudinal model, are conducted to examine the effectiveness of the proposed scheme.