Optimization of composite wing structure for a flying wing aircraft subject to multi constraints

This paper presents a minimum weight optimization of a composite wing structure subject to multi constraints including strength, damage tolerance and aeroelastic stability. Based on preliminary design data, the investigation demonstrated an efficient optimization approach of a composite wing structure modeled by FEM in the detailed design phase for a flying wing aircraft. For potential application, the structure modeling and optimization process has been performed by full use of the commercial software MSC Nastran, which is widely employed in aerospace industry. First the wing structure FE model is divided into number of design zones along the span. A pre-process was proposed to group all plies in the same fiber orientation within one zone into a stack laminate and share one design variable. In each zone, the number of design variable in terms of skin ply thickness is reduced to the same number of fiber orientations used in the wing skin laminate. After the optimization, a post process was performed to trim the ply thickness and reset the skin laminate layup under the design and manufacture constraint. To keep the final design on the safe side, the thickness of an optimized ply is normally increased to the standard figure in the trim process. Consequently the trimmed structure weight is slightly increased after the post-process. However a practical optimum design of the composite wing structure in detailed FE model can be obtained. For the composite wing example, numerical results show that the optimized structure weight has been reduced by 16.3%. The results also show that the optimization approach is much efficient with little accuracy penalty.