Design and Development of a Backstepping Controller Autopilot for Fixed-wing UAVs

Backstepping is one of the most promising advanced control laws developed for xed-wing Unmanned Aerial Vehicles (UAVs). Its nonlinearity combined with adaptation guarantees adequate performance over the whole ight envelope even when the aircraft model is not exact. In the literature, there are several attempts to apply a backstepping controller to aspects of xed-wing UAV ight. Few of them attempt a simultaneous longitudinal and latero-directional aircraft control, and the majority of these have not been implemented in a real-time controller. In this paper a backstepping approach able to control longitudinal and latero-directional motions is presented. Rapidly changing inner-loop variables are controlled with non-adaptive backstepping, less dynamic outer-loop variables are controlled with PID gains. The controller is evaluated through softwarein-the-loop simulation in both continuous and discrete time domains, in the rst case on two aircraft with di erent capabilities. The behavior with parametric uncertainties in the aircraft model or in presence of noise is also tested. The results of a real-time implementation on a microcontroller are presented and its performance is evaluated through hardwarein-the-loop simulation. Overall, the proposed backstepping controller has good performance on the aircraft evaluated for complex maneuvers involving control of multiple changing variables simultaneously.