Reduced-order models for integrated aeroservoelastic optimization

Recent developments of modal-based aeroservoelastic modeling techniques extended the applicability of the modal approach to almost all of the aeroservoelasticity related aspects of aircraft structural and control design. The various techniques are reviewed and combined for an integrated design optimization scheme, where stress, static-aeroelastic, closed-loop nutter, control margins, time response, and continuous gust constraints are treated with a common basic model. The structure is represented in the basic model by a set of low-frequency normal modes of a baseline design. Design changes are adequately addressed without changing the generalized coordinates. Typical difficulties of the modal approach are alleviated by various optional fictitious-mass and modal-perturbation techniques. Static modes can be added during the optimization process for better convergence to the optimal solution. Minimum-state rational approximation of the unsteady aerodynamics leads to an efficient state-space model that can be augmented by any combination of linear-control components. A physical weighting algorithm is used to improve the aerodynamic approximations and to select modes for truncation or residualization. The reduced-size models and the associated analytic sensitivities to design changes facilitate extremely efficient and adequately accurate on-line optimization sessions.