Maximizing Lift-to-Drag and Thrust-to-Drag Ratios for Trimmed Hypersonic Vehicles

Ways to maximize the lift-to-drag (L/D) and the thrust-to-drag (T/D) ratios of hypersonic vehicles are computed using the reduced-order model Michigan-AFRL Scramjet in Vehicle (MASIV). The 84 geometries considered are variations of a generic X-43 for seven chord lengths and three span lengths of the two horizontal stabilizers, and four engine widths. For all cases the vehicle is trimmed for cruise at Mach 8. Computed for each geometry were T/D,L/D, angle of attack, deflection angle of the horizontal stabilizer, specific impulse, and engine equivalence ratio. It was found that the "lifting body" design (with small horizontal stabilizers) has a larger L/D than a wing-body design. Large horizontal stabilizers may not be desirable at hypersonic speeds because, while they reduce the angle of attack and reduce the wave drag, the added length of leading edges increases viscous drag. In addition, the optimum acceleration history was computed that minimizes the fuel required for an ascent, for different geometries. Selecting a large dynamic pressure trajectory was found to significantly minimize the fuel required. The scope of the work is limited to aerodynamics, and it does not consider either vehicle stability or control.