Flight Dynamic Characteristics of a Scramjet-Powered Generic Hypersonic Vehicle

Flight dynamic characteristics of scramjet-powered hypersonic air vehicles are unique and have major differences with those of a conventional aircraft. These special characteristics are due to the tightly integrated engine-airframe lifting body - an X-43 like - configuration which is the universally accepted geometry for this class of vehicles. With this configuration the propulsion system is completely integrated in the fuselage and the forebody is used to compress air and deliver it to the inlet of the engine. As the result of this aerodynamically optimized shape there is significant interaction between the aerodynamic and propulsion forces. The long, slender shape of these vehicles results in low structural modes, which are not far from the aircraft rigid-body modes, and additionally interact with the aerodynamics and the propulsion system. For all these reasons flight dynamics and control of these vehicles pose special challenges. This paper uses the model of a full-scale scramjet-powered generic hypersonic vehicle to highlight special dynamic characteristics of this class of vehicles. The model is a CFD-based two-dimensional airbreathing generic hypersonic flight vehicle (CSULA-GHV). The nonlinear longitudinal equations of motion are derived using the inverse square law gravitational model, and the centripetal acceleration. A Matlab model with complete aerodynamic and propulsion look up tables is used for simulation studies. The vehicle's flexible dynamics are included in this model as changes in the angle of attack and elevon effectiveness. Couplings between various dynamics are discussed and quantified and their effects on the flight dynamics of the vehicle are presented. Special dynamic characteristics such as pitch command- flight path angle decouple are presented. Transfer functions relating response of the vehicle to various commands are presented and discussed.