Lateral-Directional Coupling and Unsteady Aerodynamic Effects of Hypersonic Vehicles

Results from a joint research program of the Institutes of Fluid Dynamics and of Flight Mechanics and Flight Control of the Technical University of Munich on a two-stage space transportation system are presented. The unsteady aerodynamics resulting from an orbital stage at stage separation e ow conditions at Mach number 6.8 are e rst discussed. Unsteady e owe elds associated with yaw and roll oscillations of the orbital stage at a certain distanceabovethecarrierstageareinvestigated.Thecalculationsarebased ona e nitevolumemethodforreal-time solutions of the unsteady Euler equations. Theresultsfocus on pressuredistributions and aerodynamic coefe cients providing an essentialmeansforcarrying outstabilityand control investigations.Inthesecond part, e ightmechanics stability and control problems are addressed considering key issues of lateral ‐directional dynamics. Inherent vehicle characteristics can show specie c stability and e ying quality dee ciencies in hypersonic e ight, concerning a partially unstable dutch roll mode with high roll ‐yaw coupling and weak roll damping. There is also a coupling of the roll and spiral poles for certain cone gurations, yielding a slow, eventually unstable oscillation called lateral phugoid. Reasons and effects for the stability dee ciencies are discussed, including conditions of existence for the lateral phugoid.