On the low speed longitudinal stability of hypersonic waveriders

Abstract

The development of hypersonic civilian transport aircraft requires solutions to a number of challenging problems in the areas of aerothermodynamics, control, aeroelasticity, propulsion and others encountered at high Mach number flight. The desire for good aerodynamic performance at high Mach numbers results in slender vehicle designs called waveriders. The stability and handling of waverider shapes at the low speeds at the take-off and landing phases of flight is not well studied. This thesis covers static and dynamic CFD simulations of the Hexafly-Int glider which have been used to obtain longitudinal stability derivatives at low speeds. Complementary static and free-to-pitch dynamic wind tunnel testing, are used to validate the CFD computations. A final chapter on the optimisation of waverider designs including low speed longitudinal stability is presented to show the impacts of this additional requirement on the hypersonic design space. The static wind tunnel testing has identified stability issues relating to the location of the centre of gravity. The design centre of gravity which is suitable for the Hexafly-Int vehicle at Mach 7.2 is found to be too far aft which results in instability at low speeds. In addition, the dynamic testing in the wind tunnel shows that the pitch damping is inadequate at low speeds. The CFD simulations agree well with the wind tunnel test results validating the use of CFD tools for determining dynamic stability derivatives of this class of slender vehicle in the design process. To alleviate the low speed stability issue of hypersonic vehicles, a waverider shape optimisation study has been carried out to understand what shapes will produce better low speed stability behaviour. These shapes are found to produce lower aerodynamic efficiency at high speeds which suggests that a design compromise between low speed stability and high speed performance is required at the outset of hypersonic waverider design