Autonomous landing of a fixed-wing unmanned aerial vehicle onto a moving platform

[摘要] ENGLISH ABSTRACT: This thesis presents the analysis, design, simulation, implementation and partial practical flight testing of a flight control system to achieve accurate autonomous landing of a fixed-wing unmanned aerial vehicle onto a moving platform.A landing strategy is proposed that is based on real aircraft scenarios and scaled down tobe representative of a remotely controlled off-the-shelf model vehicle, outfitted with a customcomputer controlling unit. To create a more representative environmental simulation, theexisting wind model was expanded to conform to military standards.The Total Energy Control System (TECS) was studied and used as the main longitudinalcontroller. The inner loop of the traditional TECS architecture was replaced with a normalspecific acceleration controller. The specific energy and energy distribution controllers weredeveloped based on this modified architecture using a simplified design loop. The outer altitudeand airspeed loops were designed using a heuristic method.Conventional classical control designs were used for the lateral controllers. A Dutch rolldamper was used to reduce yaw rate oscillations and improve lateral stability. A roll anglecontroller was used to regulate the bank angle and allow steering of the aircraft. An aggressivecross-track controller was developed to improve steady state tracking performance. Dueto inherent problems in this design, an additional heading and guidance control system wasdesigned and included. A switching scheme was proposed and implemented to provide a safetransition from one controller to the other.The integrated system was verified in hardware-in-the-loop simulations using a Monte-Carlostyle approach for both stationary landing point and moving platform landings. It was ableto achieve good accuracy in the longitudinal axis and exceptional accuracy in the lateral axisunder various environmental disturbances. Overall, the system was able to hit the movingtarget with an 86% success rate.Limited flight testing showed that the energy-based longitudinal controllers performed morepoorly in practice than in simulation, likely due to insufficient structural vibration damping andsubsequent poor acceleration measurements. This is problematic because the energy controllersare very reliant on good acceleration control. The lateral controllers that were tested performedas designed and were therefore practically verified.It is concluded that this project can be used as a foundation for an energy-based landingsystem. Improvements are proposed that can aid future projects to enhance the systemperformance.

[发布机构] Stellenbosch University