Thermal centering control for autonomous soaring: Stability analysis and flight test results

Abstract

This paper addresses the challenge of using autonomous soaring gliders to search for and exploit thermal lift to extend the gliders' endurance. For this purpose, a simple thermal centering controller is proposed. The paper includes theoretical analysis of stability and convergence properties of this controller. Using an exponential Gaussian function to represent the updraft field of a thermal, the Lyapunov type analysis shows the proposed controller to be asymptotically stable and determines its region of attraction. The size of the region of attraction is shown to be a function of the feedback gain that can be adjusted for any given strength and geometry of thermal. The paper additionally presents simulation and flight test results that verify the performance of the proposed controller. The results of the flight trials also confirm the feasibility and effectiveness of using autonomous thermal soaring to extend endurance for unmanned gliders. © 2011 by Klas Andersson.