Significance of fuel selection for hypersonic vehicle range

Optimization studies of engine-integrated hypersonic aircraft for both crui sing 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 r esults in configurations that cannot take advantage of high-lift aerodynami cs, especially when they operate at high dynamic pressures for airbreathing propulsion. Hydrogen has been the fuel of choice for hypersonic flight bec ause of its rapid burning rate, high specific energy content, and good heat transfer properties for active cooling and recuperation. In contrast, hydr ocarbon fuels have much longer burn times and substantially lower specific energies, although they have substantial 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 a nd geometric scaling are used to show that with hydrocarbon fuels, which ha ve an order of magnitude greater density than hydrogen, hypersonic cruiser designs can take greater advantage of optimal aerodynamics. As such, hydroc arbon engine-integrated vehicles may have comparable or superior cruise ran ge performance in comparison to cryogenically fueled designs.