Failure sensitivity and robustness in reconfigurable flight control systems

This paper is concerned with the design of reconfigurable flight control systems furnished with aerodynamic redundancy. Our focus is directed towards dealing with the aircraft surface impairment such as locked, float, or missing surfaces. We propose a control design criterion that facilitates the detection of failures without compromising the required performance robustness. Details are carried out for the design of the pitch axis controller of an experimental highly maneuverable aircraft, where redundancy in the control authority is provided by both the elevens and the canards. The goal is to explain our design procedure and to demonstrate enhanced overall system fault tolerance. The design effort is focused on the selection of controllers that can differentiate their effects on failures that require a control reconfiguration from the effects on other uncertainties that do not require a control reconfiguration. The key idea for achieving such differentiation is to examine the FDI (failure detection and isolation) performance index of controllers from a parameterized set that attains a certain control performance index. The scenario with a loss of surface effectiveness is simulated for the aircraft model. The deviation in the control law designed variance of the residual signal is shown to be most neglected in the processe of failures