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Nonlinear Autopilot Design for Fixed-Wing UAV Using Disturbance Observer Based Backstepping

This paper focuses on the design of a robust nonlinear autopilot for fixed-wing unmanned aerial vehicle. A disturbance observer based backstepping control method is proposed to deal with nonlinearities and uncertainties simultaneously. The nonlinear baseline controllers for airspeed, altitude, and roll angle command tracking and sideslip angle regulation are constructed recursively based on backstepping. Nonlinear disturbance observers are designed to obtain the estimations of the lumped disturbances from wind disturbance and aerodynamic uncertainties. As a result, robust performance of the autopilot is achieved by incorporating those estimates into the feedback baseline controllers to compensate for the adverse effects duo to disturbances. Results of numerical simulations demonstrate that the proposed method is particularly beneficial in terms of the command tracking accuracy and the robustness against disturbances and uncertainties.