Hypersonic flight experience

Abstract

The flight test results from the X-15, Asset, Prime, Reentry F and Shuttle Orbiter flight research programmes are reviewed and compared with theory and ground- based experiments. Primary emphasis is placed on our present capability to predict aerodynamic coefficients and stability derivatives, and distributions of surface pressure and aerodynamic heating rate for typical orbital and sub-orbital hypersonic vehicles. Overall, this comparison demonstrates the feasibility of designing hypersonic vehicles based on tests in conventional perfect-gas wind tunnels supplemented by state-of-the-art CFD analysis. At Mach numbers up to approximately 8, real-gas effects are small and Mach number/Reynolds number simulation is sufficient to insure accurate prediction of aerodynamic characteristics. At higher mach numbers, real-gas effects become important but appear to affect primarily pitching moment and to have little influence on other aerodynamic characteristics. Viscous interaction effects appear to be well correlated by the viscous interaction parameter V̄' ∞ , and to affect primarily axial force. With the exception of RCS jet interactions, stability and control derivatives are well predicted throughout the hypersonic flight régime. State-of-the-art aerodynamic heating techniques appear to give accurate predictions for laminar and fully turbulent attached flows so long as there are no strong shock interactions or non-equilibrium chemistry effects. For such flows, heating rate distributions depend only weakly on Mach number for M ∞ ≥ 8 and hence M ∞ ≈ 8-10 wind tunnel results can be used throughout the hypersonic speed range. For high- speed, high-altitude flight, surface catalycity effects can have a major influence on heating rates but modern, finite-rate boundary layer analyses are capable of predicting major trends. The major remaining challenges are the accurate prediction of: (1) real-gas effects on longitudinal trim, (2) the effectiveness of blended high altitude control systems, (3) shock interaction heating, (4) heating rates for separated vortex-dominated leeside flows, and (5) boundary layer transition and relaminarzation. Finally, it is pointed out that there are no flight data on the propulsion-airframe integration effects that are so important for airbreathing launch vehicles.