Surrogate Aerodynamic Model for Initial Sizing of Solar High-Altitude Long-Endurance UAV

This study proposes a surrogate model that yields significant reduction in aerodynamic calculation for the initial sizing of the high-altitude long-endurance solar unmanned aerial vehicle (UAV) that uses solar and regenerative fuel cells. In contrast to the traditional aerodynamic surrogate model that correlates the wing drag with wing area, aspect ratio, and flight speed, the proposed surrogate model simplifies the correlation using the Reynolds number. As a result, the significant numerical error that the previous model suffers is removed, and considerable reduction in calculation time is achieved. Furthermore, the proposed model eliminates the cumbersome invocation of the aerodynamic analysis tool for altitude changes. In addition, this study conducts case studies of initial sizing using the proposed surrogate model and investigates the effects of flight date, wing area, and solar cell efficiency on the optimal configuration, which yields minimum weight under the constraints that consider the daily energy required for cruising and energy available in the daytime, i.e., power balance, nighttime energy balance, and $C_L$ limit.