Underactuated Waypoint Tracking of a Fixed-Wing UAV*

In this paper a new method of performing waypoint tracking is shown for underactuated fixed-wing uavs. The position error can be mapped onto the desired axis using a desired rotation matrix, while the velocity error can be mapped to the desired axis using a desired angular velocity. With all errors defined along one axis, the tracking problem is easily solved using only one thruster. A velocity controller is derived which makes sure that the uav tracks a desired total velocity moving towards the next waypoint, while a sliding surface attitude controller is designed to track the desired attitude. The impact of saturation on the attitude controller is also studied where it is shown that the actuators will desaturate in finite time, through a change in the reference trajectory. Using both controllers, a solution to the problem of waypoint tracking of an underactuated uav is proposed, and simulations have been performed that support the theoretical results.