A general design methodology for year-round solar-powered stratospheric UAVs from low to middle latitudes

A design methodology for configuration sizing of solar-powered UAVs is established, which could be equally applied to all configurations capable of year-round operations in the stratosphere at low and middle latitudes. In general, the configurations are classified into two representative types-the conventional and the wing-sail. The wing-sail configuration employs sail tails that can rotate around individual roll axes to maximize solar energy absorption, and photovoltaic (PV) modules are coupled to the wing and only one side of each sail tail. The configuration sizes are treated as key design variables, including wingspan, aspect ratio of wing, and area ratio of sail tails to the wing. The established methodology mainly contains two parts. The first part parameterizes energy absorption and energy consumption, mass components and aerodynamic efficiency. The second part employs an optimal approach to obtain a group of optimized solutions. Then, the methodology is applied to analyze conceptual parameters at different latitudes for both configurations. Finally, a solar powered stratospheric UAV concept of wing-sail configuration, PoXiao, is proposed for year-round operation at middle latitudes. Its energy performance is investigated to validate the operational altitude and latitude capabilities throughout a whole year and demonstrate the utility of the design methodology. The characteristics of stability and control for the wing-sail configuration is also preliminary analyzed.