Significance of Fuel Selection for Hypersonic Vehicle Range

Optimization studies of engine-integrated hypersonic aircraft for both cruising and accelerating missions tend to demonstrate noticeably lower lift-to-drag ratios than those of pure aerodynamic forms. One explanation of this is that, with low-density fuels such as hydrogen, matching lift to weight results in cone gurations that cannot take advantage of high-lift aerodynamics, especially when they operate at high dynamic pressures for airbreathing propulsion. Hydrogen has been the fuel of choice for hypersonic e ight because of its rapid burning rate, high specie c energy content, and good heat transfer properties for active cooling and recuperation. In contrast, hydrocarbon fuels have much longerburn times and substantially lower specie c energies, although they havesubstantial packaging and handling advantages. To study this, range performance is evaluated in terms of fuel density for hypersonic craft with time-varying lift-over-drag ratio. Historical data and geometric scaling are used to show that with hydrocarbon fuels, which have an order of magnitude greater density than hydrogen, hypersonic cruiser designs can take greater advantage of optimal aerodynamics. As such, hydrocarbon engine-integrated vehicles may have comparable or superior cruise range performance in comparison to cryogenically fueled designs.