Output Feedback Tracking Control of Rudderless Flying-Wing UAVs Based on Optimized Sliding Mode Controller with Integral Action and Robust Sliding Mode Observer

The rudderless flying-wing UAV design structure poses different challenges in terms of stability, tracking control, and accurate state estimation due to the lack of conventional horizontal and vertical stabilizers. The proposed controller-observer structure in this paper provides proper tracking performance in both longitudinal and lateral modes by augmenting the tracking error integral to the system dynamics for stabilization, and designing the sliding surface as a linear combination of the system states, and further optimizing the sliding surface. By designing the special sliding mode control law in the proposed structure, the robustness against matched and unmatched uncertainties is ensured in the closed-loop system. The robust sliding mode observer, which is an extension of the modified Utkin and Walcot-Zac observer, is used for estimating the system states based on sensor outputs. By this approach, the unknown states of the system are effectively estimated using an appropriate computational algorithm, despite input disturbances and uncertainties. The simulation results confirm the excellent performance of the proposed controller-observer structure in terms of state estimation, stabilization, tracking behavior, and robustness against uncertainties and disturbances.