Sliding mode control of fixed-wing UAVs in windy environments

In this paper, a fully nonlinear aircraft dynamic model in the presence of wind is introduced. Assuming the wind vortex hypothesis, the equations of motion are formulated in a novel nonlinear control system form that is affine in control input for the chosen aircraft model. A sliding mode controller is subsequently developed where the position of the throttle is used to control the air velocity and the aileron, elevator, and rudder deflections are employed to control the rest of the dynamics. It is shown that the full state converges to the desired values even in the presence of the uncertainties imposed by the wind. The applicability of the controller design is illustrated through simulations in the presence of uncertainties.