Abstract: Tethered hovering unmanned aerial vehicle is a long time hovering platform which is secured by a cable serving as power supply and wideband data link. The purpose of tethered power supply method is to resolve the short time endurance problem of tradition UAV. Hovering platform is now applied in surveillance for military, public security, fire control etc. For increasing the hovering height of the UAV, the weight of structures has to be declined in the preliminary design program. Consequently, composite materials are always used in the airframe structure. Composite material has been widely used in UAV structures because of the various excellent performances, such as strength and stiffness ratio, as well as the performances in the process of manufacturing. Meanwhile, composite laminate has excellent designable property in the process of manufacturing. So, it is widely used among all the types of composite materials. In this paper, the airframe structure of a certain tethered hovering unmanned aerial vehicle is selected as the research objective, and the finite element model of a composite airframe is created. Then the mass of the structure is chosen as the objective function, the failure index are chosen as constraints, and the composite airframe structure is optimized by using the engineer software, where the results should meet the demand of strength and stiffness during the optimization. The final optimization results show that the ratio and thickness of plies of the composite material has been redesigned. Compared with the previous designing scheme, the weight of airframe is obviously reduced after the free-sizing optimization, which could achieve the objective of optimization.

Key words: tethered hovering unmanned aerial vehicle, airframe structure model, composite material, finite element model, free-sizing optimization