In this paper, robust fault tolerant longitudinal control of an aircraft in the presence of external disturbances with actuator fault/failure is proposed. This is accomplished using nonlinear dynamic inversion (NDI) based controller robustified by uncertainty and disturbance estimator (UDE) technique with control allocation scheme. The control allocation scheme redistributes the control command from the primary actuator to the secondary actuator if fault/failure occurs in the primary actuator. The UDE technique estimates the effect of external disturbance and the estimate is used to robustify the nominal controller. The proposed control scheme makes the plant less sensitive to external disturbances under fault/failure free as well as fault/failure condition. The effectiveness of the proposed control scheme is demonstrated through numerical simulation.
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