On the design of a small solar powered unmanned aerial vehicle

Unmanned aerial vehicles are seeing increasing use in a variety of applications including warfare, imaging, communication, search and rescue, meteorology, agriculture, and more. For most applications, flight endurance on the order of days, weeks, or even years is desirable. Photovoltaic cells represent an emerging and viable method of powering unmanned aerial vehicles on such long endurance flights. This study investigates the design optimization of a small solar powered unmanned aerial vehicle. The aircraft is intended to weigh less than twenty pounds and to fly for 24 hours at low altitude over Sacramento, California during the summer months of May through September. Photovoltaic technology and the characterization of a thin-film photovoltaic cell are reviewed. The majority of the paper describes the methods used to implement a continuous design approach in which the battery pack power, photovoltaic efficiency, and aircraft weight were determined for a given aspect ratio and wing loading. The optimum aspect ratio and wing loading to minimize both battery pack power and photovoltaic efficiency are identified and the final design is discussed. The results indicate that aspect ratio exhibits a strong inverse relationship with aircraft weight, wing loading is directly related to minimum required photovoltaic efficiency, and that minimum aircraft weight does not translate to minimum power required.