Energy optimization and investigation for Z-shaped sun-tracking morphing-wing solar-powered UAV

To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs. (C) 2019 Elsevier Masson SAS. All rights reserved.