Thesis Examination Committee

Prof Jinglei YANG, MAE/HKUST (Chairperson)
Prof Zexiang LI, ECE/HKUST (Thesis Supervisor)
Prof Fu ZHANG, Department of Mechanical Engineering, The University of Hong Kong (Thesis Co-supervisor)
Prof Yonghua CHEN, Department of Mechanical Engineering, The University of Hong Kong (External Examiner)
Prof Michael Yu WANG, ECE/HKUST
Prof Shaojie SHEN, ECE/HKUST
Prof Long QUAN, CSE/HKUST

 
Abstract

Vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs), which can accomplish vertically takeoff and landing and, at the same time, possess the ability of high power efficiency level flight, have shown tremendous potential in various industrial applications. In this thesis, we present a quadrotor tail-sitter vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) platform which can operate autonomously in an outdoor environment. The mechanical design, dynamic modeling, vehicle controller design process, and experimental verifications are detailed. For the vehicle design, special considerations are given to the aircraft operating in an outdoor environment, where three novel designs are proposed to respectively improve the control moment, landing stability and vibration attenuation. Flight tests show that the designed vehicle has agile maneuvers, unnoticeable vibration, and robust landing ability in windy condition. For the aircraft modeling, a full-scale wind tunnel test is conducted to characterize the full envelope aerodynamics model. A hierarchical control structure, which consists of three different position controllers for the respective flight modes (namely, a fixed-wing position controller for fixed-wing mode, a rotary-wing position controller for rotary-wing mode, and a transition controller for transition mode), a tail-sitter attitude controller, and a tail-sitter mixer which allocates control moment between elevons and rotor differential thrust, is developed to fulfill both manual flight and autonomous flight. A disturbance observer (DOB) based on H_infinity synthesis is developed on top of the rotary-wing feedback position controller to improve the hovering accuracy in a windy environment. Both indoor and outdoor experiments are conducted to verify the robustness and anti-wind performance of the developed DOB. Comprehensive outdoor experiments are conducted to verify some key VTOL maneuvers (i.e. accurate hovering, stable transition) and its fully autonomous operation, including takeoff, vertical flight, transition flight, level flight, and landing, in an outdoor environment.