Abstract: A research on load segmentation envelope design and layer optimization method is carried out for quasi-equal strength design and optimization of an unmanned aerial vehicle composite main wing box. The load segmentation distribution of the quasi-equal strength front spar of the main wing box is calculated using load envelope method with constant step. The initial layer structure of the front and rear spar is given. The finite element model of the main wing box is built. The strength, stiffness and stability of the main wing box are checked based on the results of finite element analysis. The optimized layer constructions of the front and rear spars and the skin are presented. It is shown that it is very convenient to calculate the segmented load of the front and rear spar using load segmentation method with constant step. The layer optimization design of the segmented main wing box can be done efficiently based on the initial layer construction design using the classical laminate theory and structure mechanical check by finite element method. Under the compression load caused by maximum positive lift, local buckling occurs easily at the wing root of the upper skin and the front spar’s upper strip, especially for the high-aspect-ratio wing box. The weight of the main wing box can be cut down by 5.23% through reducing the layers of the lower chord of the front and rear spar and the lower skin.

Key words: UAV, composite, main wing box, design optimization, finite element