Unique performance characteristics of solar aircraft

Unique flight performance characteristics of solar aircraft are identified. There are substantial differences when compared to aircraft with an air-breathing propulsion system. Characteristic properties of the flight envelope of solar aircraft are determined. It is shown that solar aircraft can achieve a higher ceiling and a greater maximum speed than comparable aircraft with an air-breathing propulsion system. Furthermore, solar aircraft are dealt with which can store energy in batteries. Thus, they offer the possibility of an unlimited endurance performance. As a performance goal case, the minimization of the required battery capacity is considered in order to keep the related weight penalty as small as possible. Results from the trajectory optimization for a solar aircraft with an unlimited endurance capability are presented. They show that the optimal trajectory consists of segments with characteristic properties.