Hypersonic Stability Derivative Modeling Issues

Unsteady aerodynamic modeling is important for hypersonic vehicles when predicting stability derivatives. Specifically the unsteady viscous boundary layer needs to be considered and has a direct effect on the phugoid dynamics. In addition, linear piston theory does not apply to an engineintegrated vehicle and should only be used for the vehicle shape. It is also shown that the longitudinal dynamic derivatives (those derivatives that are a function of  and pitch rate) may be neglected with little change to the overall transfer function. This was done by examining XB-70 and X-15 data using a sum of squares method based on low order equivalent systems and also by examining the terms in the short period transfer functions.