Nonlinear integral sliding mode fault tolerant longitudinal aircraft control

This paper presents a nonlinear fault tolerant scheme for longitudinal control of an aircraft. The proposed approach uses an integral sliding mode control allocation scheme which can be built around any existing controller. In nominal fault free conditions, only the baseline controller and the primary control surface associated with it will be active. When faults/failures occur in the control surfaces, the proposed sliding mode control allocation scheme becomes active to provide extra robustness, and to redistribute the control signals to the redundant secondary control surfaces. In this paper the baseline controller considered is an existing backstepping one from the literature, designed for flight path angle tracking based on the nonlinear equations of motion. The simulations on a high fidelity aircraft benchmark model show good results for nominal and fault/failure conditions even in the presence of unmodelled dynamics.