High-Speed Flight Without an Engine: A Unique Performance Capability Enabled by Dynamic Soaring

Abstract

Dynamic soaring is an engineless flight mode that is feasible by extracting energy from horizontally blowing shear wind. There is a possibility of extremely high speeds in wind scenarios where a thin shear layer separates a region of high wind speed from a region of zero wind, as it is the case in the leeward side of ridges. Flight mechanics and shear wind modelings are developed so that the motion of a glider can be mathematically described. The maximum speed achievable with dynamic soaring is determined, and the key factors for the speed performance are identified. Furthermore, it is shown that, depending on the wind speed, the maximum speed can reach the high-subsonic Mach number region where compressibility exerts an effect on the aerodynamic characteristics of gliders. It is found as a consequence of this effect that the drag rise due to compressibility is a limiting factor for the achievable maximum speed. Furthermore, quantities relevant for flight control and loads in high-speed dynamic soaring are identified and their effects are shown. An optimization method is used for constructing results on the high-speed performance enabled by dynamic soaring.