Lift enhancement and drag reduction technologies of solar powered unmanned aerial vehicles in near space: Review

Near space solar powered UAVs are special aircraft falling in between aircraft and spacecraft. Due to the constraints by the photoelectric conversion efficiency of solar cells and the energy density of energy storage cells, improving the aerodynamic efficiency and propeller propulsion efficiency of solar UAVs in nearby space is an important technical means to ensure the mission execution ability and permanent flight capability of this type of UAV platform. However, the low Reynolds number effect has brought serious difficulties and challenges to the research and design goals of increasing lift and reducing drag for the aircraft, as well as energy conservation and consumption reduction. In response to this issue, this article investigates the current research status of lift enhancement and drag reduction technologies for solar powered UAVs in near space from five aspects: airfoil design, aerodynamic layout design, propeller/wing aerodynamic coupling design, flow control technology, and propeller efficiency design. It summarizes the technical routes of existing lift enhancement and drag reduction measures, and analyzes the advantages and disadvantages of different lift enhancement and drag reduction methods. Finally, suggestions are offered for the development of near space solar UAV lift enhancement and drag reduction technologies.