Browsing by Author "Le Roux, Cornelus Tjaart"

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    Autonomous landing of a fixed-wing unmanned aerial vehicle onto a moving platform
    (Stellenbosch : Stellenbosch University, 2016-12) Le Roux, Cornelus Tjaart; Engelbrecht, J. A. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    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 to be representative of a remotely controlled off-the-shelf model vehicle, outfitted with a custom computer controlling unit. To create a more representative environmental simulation, the existing wind model was expanded to conform to military standards. The Total Energy Control System (TECS) was studied and used as the main longitudinal controller. The inner loop of the traditional TECS architecture was replaced with a normal specific acceleration controller. The specific energy and energy distribution controllers were developed based on this modified architecture using a simplified design loop. The outer altitude and airspeed loops were designed using a heuristic method. Conventional classical control designs were used for the lateral controllers. A Dutch roll damper was used to reduce yaw rate oscillations and improve lateral stability. A roll angle controller was used to regulate the bank angle and allow steering of the aircraft. An aggressive cross-track controller was developed to improve steady state tracking performance. Due to inherent problems in this design, an additional heading and guidance control system was designed and included. A switching scheme was proposed and implemented to provide a safe transition from one controller to the other. The integrated system was verified in hardware-in-the-loop simulations using a Monte-Carlo style approach for both stationary landing point and moving platform landings. It was able to achieve good accuracy in the longitudinal axis and exceptional accuracy in the lateral axis under various environmental disturbances. Overall, the system was able to hit the moving target with an 86% success rate. Limited flight testing showed that the energy-based longitudinal controllers performed more poorly in practice than in simulation, likely due to insufficient structural vibration damping and subsequent poor acceleration measurements. This is problematic because the energy controllers are very reliant on good acceleration control. The lateral controllers that were tested performed as designed and were therefore practically verified. It is concluded that this project can be used as a foundation for an energy-based landing system. Improvements are proposed that can aid future projects to enhance the system performance.