Launch trajectory control of a flying wing with vertical takeoff capability for airborne wind energy systems

Airborne wind energy (AWE) is an emerging technology that harnesses wind power using tethered flight systems. Maximum power output is sought out for operations ranging from low to high wind velocities. A flying wing is a promising airborne wind energy flight system since it is reduced to the wing as the primary lift-generating component to achieve a highly efficient, aerodynamic flight. For takeoff within a limited space, the flying wing is capable of vertical takeoff in a tailsitter configuration. This thesis presents a trajectory controller that controls the aerodynamic velocity of the flying wing from vertical hover to horizontal forward flight while maintaining a constant height. This flight trajectory marks the beginning of the launching phase of the airborne wind energy system, which places high demands on the flight controller for low power consumption and particularly high wind robustness. The flight controller achieves a thrust-efficient launch trajectory with sufficient control reserves for operations including a dynamic wind field. It incorporates the specific constraints imposed by the tether connection and the limited flight envelope of the flight system. The stabilization of the natural instabilities of the flight system's attitude is a necessary criterion that is inherently integrated into the control architecture. A straight flight path along the wind vector with a yaw-roll motion is outlined as a solution to keep the flight system within controllable limits. Based on a detailed analysis of trim states, the operating points from vertical takeoff to horizontal forward flight are carefully selected under consideration of control reserves and thrust requirements. The focus is on the velocity controller, which employs LQR control and integrates all flight axes to explicitly control the velocities along this selected flight path of commanded operating points. The launch trajectory controller enables dynamic operation and adapts the orientation of the flight system to a rotating wind vector to maintain flight within the flight envelope. The trajectory controller is thoroughly validated using nonlinear simulation results. Accurate disturbance rejection in response to a rotating wind field is in particular decisive during the initial hover flight phase. Simulation and flight test results demonstrate the effectiveness of the flight trajectory controller during this flight phase under wind conditions, which is complemented by a robustness analysis to verify stable flight.