Stiffness Optimization of Composite Wings with Aeroelastic Constraints

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 the mass, strength, buckling, aerodynamic twist, and aileron effectiveness. The elements of the in-plane 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, in which single or multimodal objective functions were minimized. The first numerical results for a generic wing confirmed a functional setup for multiload case stiffness optimizations with aeroelastic design responses. Stiffness-optimized unbalanced laminates demonstrated a clear advantage over balanced laminates for mass or aileron effectiveness optimizations, with constraints on strength and buckling.