Flight Dynamics of a Hypersonic Vehicle During Inlet Un-start

The aerodynamics and the stability and control characteristics of a hypersonic vehicle that is has an un-started inlet are addressed. The vehicle considered is a generic scramjetpowered ∞ight test vehicle with a 3D, inward-turning inlet and cruciform flns for control. An analysis of aerodynamic prediction methods for the vehicle with inlet started are given and shows that engineering methods are satisfactory for predicting the external aerodynamics when compared to CFD. However, during un-start, the engineering methods do not capture the efiect of the normal shock that stands outside the inlet; therefore, CFD is necessary to assess the vehicle aerodynamics. An analysis of the open-loop ∞ight dynamics of the vehicle was performed for both the started and un-started inlet. A nominal control law to track a commanded ∞ight-path angle is designed using the started inlet aerodynamics. It is shown that the un-started inlet destabilizes the controller, with a rather large time-to-double, but the aircraft angle-of-attack transient settles rather quickly, which should allow for the inlet to be re-started.