Browsing by Author "De Bruin, Andrew"

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    Accurate autonomous landing of a fixed-wing unmanned aircraft under crosswind conditions
    (Stellenbosch : Stellenbosch University, 2017-03) De Bruin, Andrew; Jones, Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: This thesis presents the design, implementation and verification of an autopilot system with strong disturbance rejection characteristics, capable of landing a fixed-wing unmanned aircraft accurately under crosswind conditions. All aspects of the autopilot design are considered, from first principles to the final practically verified product. A mathematical aircraft model is derived, verified and analysed in detail to ensure the design of a high-fidelity, high-bandwidth flight control system. A synergistic controller architecture is proposed, where the approach is to design a structure capable of executing one of three crosswind landing techniques, or a combination thereof, by strategically sequencing controllers throughout the landing procedure. Various landing techniques, developed for manned aircraft, are investigated and emulated by the flight control system to exploit the advantages of each and to mitigate the risks associated with crosswind landings. A highbandwidth acceleration-based control architecture was augmented with Direct Lift Control to improve gust alleviation performance in the aircraft’s longitudinal axis. A state machine was used to facilitate effective controller sequencing and continuous hierarchical monitoring through strategically planned state transitions. Monte Carlo simulations were used to develop a landing accuracy prediction system that provides statistical information regarding the expected touchdown region given certain atmospheric conditions. Results from sixteen days of flight tests demonstrate the autopilot’s success, and correspond exceptionally well with results obtained from high-fidelity hardware-in-the-loop simulations. Verification of the autopilot through practical flight testing and extensive simulations proved that the system is capable of performing crosswind landings accurate to within 0.5 m of the intended touchdown point.