Aiaa 2001–0016 Lateral Track Control Law for Aerosonde Uav

Aerosonde is a small autonomous aircraft (UAV) designed for meteorological sampling along a specified flight plan. This aircraft is currently being used by the Flight Systems Laboratory at the University of Washington as a test-bed for the development of a rapid control-law prototyping platform based on Matlab/Simulink/Real-Time Workshop environment. To accurately track a set of pre-planned flight segments, an automatic lateral-track control law was developed and implemented in Aerosonde I. However, the early design of the lateral track control-law was found to have unsatisfactory tracking performance in the presence of large cross-track distance errors, and/or when the aircraft is pointing away from the desired flight plan segment. The track performance was subsequently improved by the use of complex decision logics imbedded in the custom autopilot software, thereby making the controller unsuitable for future UAV projects. A new nonlinear lateral track control law has been proposed and results are presented in this paper. It will be shown that with the new design which does not require complex switching decision logics, the aircraft is able to stably track a flight plan segment starting from any initial conditions. In high wind situations, lateral tracking and stability are achieved with a modified control law that directly utilizes the wind information. Performance of the overall lateral track control law has been verified in nonlinear flight simulations. Nomenclature UAV Unmanned Air Vehicle GPS Global Positioning System MEX Matlab Executable DOF Degrees of Freedom X track Along-track distance (m) Y track Cross-track distance (m) ˙ X track = dX track /dt Along-track velocity (m/s) ˙ Y track = dY track /dt Cross-track velocity (m/s) U Airspeed (m/s) W Wind speed (m/s) r CMD Yaw-rate command (rad/s) Ψ Aircraft heading (rad) Ψ w Wind direction (rad) Ψ 12 Track line heading (rad) ∆ Discrete-time step (s)