Fault tolerant control for aircraft control surface failures

In recent years, fault tolerant flight control systems have gained an increased interest for high performance military aircraft as well as civil aircraft. Fault tolerant control systems can be described as either active or passive. An active fault tolerant control system has to either reconfigure or adapt the controller in response to a failure. In contrast, a passive fault tolerant control system uses a fixed controller which achieves acceptable performance for a presumed set of failures.; A passive fault tolerant flight control law is designed for the F/A-18 aircraft which achieves acceptable handling qualities for a class of control surface failures. The class of failures includes the symmetric failure of any one control surface being stuck at its trim value. A comparison is made of an eigenstructure assignment gain designed for the unfailed aircraft with a fault tolerant multiobjective optimization gain. We show that the time responses for the unfailed aircraft using the eigenstructure assignment gain and the fault tolerant gain are identical. Furthermore, the fault tolerant gain achieves MIL-F-8785C specifications for all failure conditions.; An active fault tolerant control law is designed by using direct model reference adaptive control for multi-input multi-output plants. We augment the plant with a feedforward compensator such that the inverse feedforward stabilizes the plant over the set of allowable failures. We prove that the augmented output error is asymptotically vanishing for a loss of control effectiveness failure. A novel state space approach for computing the feedforward compensator is proposed. We demonstrate the use of our algorithm by application to a three input model of the linearized lateral dynamics of the F/A-18 aircraft.