The development of hypersonic vehicle control algorithms requires the accurate prediction of vehicle aerodynamic loads. This paper focuses on finding time-accurate unsteady loads due to the oscillation of multiple vehicle elastic modes. The reduced-order modeling methodology consists of using convolution of modal step responses along with a correction factor to take different oscillation amplitudes, flight conditions, and nonlinear aerodynamic effects due to multi-modal oscillations into account. Thus, the model is valid over a range of conditions rather than one specific set of conditions upon which it is constructed. When compared with CFD simulations, the errors are shown to be relatively small in most cases over a range of Mach numbers, modal frequencies, and modal oscillation amplitudes. Also, an error estimation methodology is developed to give a general sense beforehand as to the errors expected to be incurred through the use of the model.
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