Abstract: Ultra-long endurance solar powered Unmanned Aerial Vehicle (UAV) has attracted wide attention due to its characteristics of high efficiency, energy saving, and unlimited cruise in principle. However, its unique design indicators and mission characteristics also impose higher requirements for key technologies. High coupling of multiple design elements means that the overall design method is different from that of conventional aircraft. Low-density and low-speed flight conditions contribute to aerodynamic characteristics of a significantly low Reynolds number. Flexible wings with large aspect ratio bring complex aeroelastic problems. The characteristics of low wing load and large wind disturbance increase the difficulty of control. Extreme flight environments and demanding mission indicators pose new challenges to energy and power systems. The high dependence on energy opens up the research direction of flight trajectory optimization. This paper summarizes the research status of key technologies of the ultra-long-endurance solar UAVs. On this basis, the difficulties in key technologies are explained, and the future trend of ultra-long endurance solar UAV is illustrated.

Key words: solar UAV, conceptual design, aerodynamics design, aeroelasticity and gust mitigation, flight control, energy and power, flight trajectory optimization