Several procedures for the simultaneous aerodynamic-structural design optimization of aircraft wings are investigated. These procedures include efficient methods for optimization and sensitivity calculations that are applied to two specific design examples. The first is a subsonic transport aircraft with a composite forwardswept wing. The aerodynamic modeling for this case is provided by vortex-lattice theory and the structural model initially utilizes finite-element analyses. Even with efficient sensitivity methods, the approximate optimization problem still requires a large computational effort. To reduce this cost, a variable-complexity model for the structural analyses is introduced. First, an algebraic equation model for wing weight is used in the optimization procedure to obtain an aerodynamic design that approximately accounts for the effects of wing geometry on wing weight. Then this design is refined by simultaneous aerodynamic-structural optimization based on the finite-element analysis. The net effect of this dual structural model is a substantial reduction in optimization costs.

The second example is the wing design of a supersonic High-Speed Civil Transport (HSCT). For this case, the simple wing-weight equations for structures are retained. For the aerodynamics, a variable-complexity model was introduced with the complex models provided by volumetric wave drag analysis and panel methods. In addition, simple algebraic models for wave and drag due to lift provide inexpensive approximations during most of the optimization cycles. With the minimization of the costly complex sensitivity calculations, a reduction in optimization costs is realized.