The objective of this research is the preliminary design of aircraft structures for improved steady-state roll performance in the transonic regime. The control surface effectiveness (a parameter that indicates the relative rolling power produced by an aileron of a flexible aircraft with respect to the rigid aircraft) is employed for quantifying the roll performance. Control surface effectiveness is evaluated by iteratively solving the antisymmetric trim equation on roll rate. Each iteration of the trim equation necessitates the computation of nonlinear airloads. To make the multidisciplinary design optimization computationally practical, the transonic small disturbance (TSD) theory is used for the aerodynamic analysis. Transonic loads including shock effects are captured by employing the TSD theory for which the CAP-TSD program is used. For design optimization, a nongradient-based method is adopted. Control surface effectiveness variation with respect to the statistically significant structural variables (skins, spars, ribs, and posts) is approximated using the response surface method. Multidisciplinary optimization for minimum weight, with control effectiveness, stress, displacement, and frequency constraints, is performed.
