Trajectory tracking of an underactuated fixed-wing UAV

This paper presents a solution to the problem of trajectory tracking for a fixed-wing UAV. With its inherent actuator constraints, a fixed-wing UAV is not able to track an arbitrary trajectory, such that a guidance scheme is required in order to solve the trajectory tracking problem. In this paper, this is solved by first designing a virtual saturated control law that makes the position and velocity errors go to zero. Then the outputs from the virtual control law are mapped onto actuated variables that can be tracked using the available actuators. To that end, a model-based proportional speed controller and a quaternion-based sliding surface controller are presented, making all the errors go to zero. The solution is proved using Lyapunov theory and is validated through simulations where a fixed-wing UAV tracks a circular trajectory.