Stiffness Optimization of Composite Wings with Aeroelastic Contraints

Abstract

The drive for ever more efficient aircraft structures stimulates the research to use the full potential of anisotropy of composite materials. The stiffness optimization of the upper and lower skins of a composite wing is demonstrated in this paper. The wing was optimized taking into consideration mass, strength, buckling, aerodynamic twist and aileron effectiveness. The elements of the inplane and bending stiffness matrices and laminate thicknesses were used as design variables. Static aeroelastic analysis was performed using Nastran to find the responses of the structure and their sensitivities to the design variables. The results of aeroelastic finite element analysis were processed to create efficient structural approximations of the responses. The approximations were used by a gradient based optimizer to update the design variables. The separable and continuous approximations in terms of the design variables allowed for the use of efficient parallel computing strategies, where single or multi-modal objective functions were minimized. The first numerical results for a generic wing confirmed a functional setup for multi load case stiffness optimizations with aeroelastic design responses. Stiffness optimized unbalanced laminates demonstrated a clear advantage over balanced laminates for mass or aileron effectiveness optimization, with constraints on strength and buckling.