Bio-Inspired Flaps as Flight Control Effectors for Airborne Wind Energy Harvesting Platforms: From the Lab to the Field

Abstract

This thesis investigates feather-inspired flaps as novel flight control effectors for tailless airborne wind energy harvesting (AWEH) kites. Accurate execution of aerodynamically complex maneuvers in AWEH systems requires developing high-fidelity aerodynamic models that precisely describe the system’s behavior under various operating conditions. Tailless kites pose significant aerodynamic control challenges due to the lack of conventional control surfaces. Inspired by bird covert feathers, this work explores the deployment of covert-inspired flaps on both the suction- and pressure-sides of a wing section to enhance aerodynamic control authority without a tail section. Wind tunnel force/torque measurements, particle image velocimetry experiments, and data-driven modeling are used to investigate the fundamental aerodynamic mechanisms of covert-inspired flaps under static and dynamic conditions. We demonstrate that simultaneously deflecting pressure- and suction-side flaps expand the achievable ranges of lift, drag, and pitching moment modulation compared to any single-sided configuration. We also uncover flow interaction mechanisms essential to expanding the flight control authority of the covert-inspired flaps. Results from the experiments and models show that the covert-inspired flaps are effective flight control devices during both static, steady-state flight conditions and dynamic pitch maneuvers. For dynamic pitch maneuvers, where the dynamic stall is dominant, results show that the placement and configuration of the covert-inspired flap can be tailored to amplify, maintain, or suppress the dynamic stall response of the wing section, making them multifunctional flight and flow control devices. Results from the wind tunnel experiments are then validated during free flight experiments on the Toyota Research Institute of North America (TRINA) Gen 8 AWEH kite. During flight tests, the covert-inspired flaps enabled the kite to successfully perform stability augmentation maneuvers necessary to maintain flight, as well as pumping cycle maneuvers required for energy harvesting. Finally, this thesis develops and modifies a system identification framework, previously developed for conventional aircraft, to an AWEH kite for the first time. Such a framework enables the development of accurate kite aerodynamic models and improved control laws. Thus, this thesis establishes novel bioinspired lightweight, effective, and multifunctional control effectors for tailless AWEH kites, making new pathways toward efficient high-altitude wind power generation.