ANALYTICAL AEROPROPULSIVE AEROELASTIC HYPERSONIC VEHICLE MODEL WITH DYNAMIC ANALYSIS

The determination of the dynamic characteristics of hypersonic vehicles requires an integrated approach since the propulsion system and airframe are so highly coupled. The forces and moments arise from both aerodynamic and propulsive sources, which are for these configurations hard to separate. Offered herein is a first step toward the development of such an approach that is intentionally generic and basic. Further, analytical expressions are developed to allow for characterization of the vehicle's dynamics early in the design cycle, so that configuration trade-offs may be performed with some cognizance of the attitude dynamics. The method of approach involves a two-dimensional hypersonic aerodynamic analysis utilizing Newtonian theory, coupled with a one-dimensional aero/thermo analysis of the flow in a SCRAMjet-type propulsion system. In addition, the airframe is considered to be elastic, and the structural dynamics are characterized in terms of a simple lumped-mass model of the in vacuo vibration modes. The vibration modes are coupled to the rigid-body modes through the aero/propulsive forces acting on the structure. The control effecters considered on a generic study configuration include aerodynamic pitch-control surfaces as well as engine fuel flow and diffuser area ratio. It is shown that the vehicle's aerodynamics and propulsive forces are both very significant in the evaluation of key stability derivatives that dictate the vehicle's dynamic characteristics. It is also shown that the vehicle model selected is highly unstable in pitch and exhibits strong airframe/engine/elastic coupling in the aeroelastic and attitude dynamics. With the use of literal expressions for both the system's poles and zeros as well as the stability derivatives, key vehicle dynamic characteristics are investigated. For small errors, or uncertainties, in either the aerodynamic or propulsive forces, significant errors in the frequency and damping of the dominant modes and zero locations will arise.