Auto-landing of fixed wing unmanned aerial vehicles using the backstepping control

The control of the unmanned aerial vehicles is a difficult problem because of their light weight and the strong coupling between the longitudinal and lateral modes. Motivated by this, a backstepping and dynamic inversion-based automatic landing system is designed in this paper for the flight control of a fixed wing unmanned aerial vehicle subject to wind shears, atmospheric disturbances, and wind gusts. Two backstepping-based controllers are designed for the stabilization of the attitude angles, while the controller associated to the forward velocity uses the dynamic inversion technique to obtain a constant forward velocity during all the three stages of landing. To provide an estimation of the wind shears, atmospheric turbulences, and wind gusts, a nonlinear disturbance observer is introduced in the control architecture. The lateral deviation with respect to the runway is canceled while the unmanned aerial vehicle maintains its desired trajectory slope angle. The novel adaptive automatic landing system is software implemented and validated by complex numerical simulations; the results of the numerical simulations prove the stability and robustness of the new control architecture for different initial conditions and wind type disturbances.