Wing sweep effects on the maximum speed performance in high-speed dynamic soaring

Dynamic soaring is an engineless flight mode that enables extremely high speeds when flying in a shear wind comprising a thin layer and a large wind speed. The speed level recently achieved approaches the high subsonic Mach number region where compressibility becomes effective. It is shown that the aerodynamic properties of straight wings, as used by gliders, yield a limitation for the achievable maximum speed in this Mach number region. Wing sweep is considered a means for enhancing the maximum speed performance, and the related aerodynamic characteristics are dealt with. A 3-degrees-of-freedom vehicle dynamics model is developed in order to solve the maximum speed problem, applying an appropriate optimization method. Furthermore, an energy-based flight mechanics model that is validated using the 3-degrees-of-freedom dynamics model results is developed for deriving analytical solutions. Thus, it is shown that the maximum speed achievable with swept wing configurations can be increased when compared with straight wing configurations. As a result, wing sweep has potential for enhancing the maximum speed performance in high-speed dynamic soaring.