m. a. hamed

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. 

The rudderless flying-wings are fixed-wing type UAVs without horizontal and vertical stabilizers. The robust control problem of this category of UAVs is of great importance due to strong coupling between reduced control surfaces and longitudinal/lateral mode, misbehaving dynamics, non-minimum phase nature of lateral mode, high sensitivity to control surface commands, disturbances, and uncertainties. The second-order super twisting sliding mode method is one of the uncertainty-resistant control algorithms, which is especially implemented in non-linear models. By combining this controller with adaptive methods, the control gains are not overestimated despite the uncertain disturbance bounds. Furthermore, by adding an integral term to the standard sliding surface equation based on the tracking error, the sliding surface is defined in PID form, which helps to increase the tracking accuracy. The comparison of the proposed method with the non-adaptive and simple adaptive super twisting sliding mode control methods demonstrates the proper performance of the proposed method in longitudinal tracking control behavior in the presence of uncertainties and disturbances.