(conceptual plot): L/D vs. Mach number — VST-MAC outperforms fixed-delta and fixed-sweep designs by 15-40%. 4.3 Thermal-Structural Feasibility The leading edges are C/C-SiC composites with active cooling (endothermic fuel). Fuselage morphing segments use NiTi SMA wires embedded in a high-temperature polymer matrix, rated to 850 K transient. At Mach 6.5 stagnation temperatures reach 2200 K on nose, but the morphing mechanism is located 1.5 m aft of the stagnation line, staying below 700 K. 5. Control and Stability Variable sweep and tilt alter the aerodynamic center (AC). At low speed (Λ=20°, anhedral), AC is at 45% MAC. At hypersonic (Λ=75°, dihedral), AC shifts to 38% MAC. The flight computer uses a gain-scheduled LQR controller, adjusting elevator, canards (deployed only subsonically), and differential wing tilt for roll control.

[ C_L = 2\sin^2\theta_p \cdot \cos\Lambda ]

A. J. Morrow(^1), L. Chen(^2) (^1)Department of Aerospace Engineering, Stanford University (^2)Center for Hypersonics, University of Queensland

[ A(x) = A_\textmax \cdot \frac4xL\left(1 - \fracxL\right)^3/2 ]

Hypersonic, Variable Sweep, Area Rule, Morphing Structures, Wave Drag, Multi-Regime Flight 1. Introduction Hypersonic vehicles (Mach > 5) typically sacrifice low-speed performance for high-speed efficiency. Fixed-wing designs suffer from severe wave drag at transonic and supersonic transitions, limiting operational flexibility. Conversely, variable-sweep wings (e.g., B-1, F-14) improve subsonic/supersonic transition but are not designed for hypersonic thermal and pressure loads. Additionally, the classic area rule — which dictates that aircraft cross-sectional area distribution should be smooth to reduce wave drag — is Mach-dependent, yet most airframes are static.

| Mach | Fixed fuselage (C_D_w) | MAC fuselage (C_D_w) | % reduction | |------|---------------------------|--------------------------|--------------| | 0.9 | 0.009 | 0.008 | 11% | | 1.2 | 0.045 | 0.027 | 40% | | 2.5 | 0.031 | 0.021 | 32% | | 6.0 | 0.022 | 0.018 | 18% | 4.2 Aerodynamic Efficiency (L/D) The VST wing improves L/D across all regimes. At Mach 0.8, low sweep (20°) and slight anhedral (-5°) give L/D = 14. At Mach 5.0, sweep 75°, dihedral +20° yields L/D = 5.2 — high for a hypersonic vehicle (typical L/D ~ 3-4). The improvement stems from reduced induced drag via spanwise load redistribution at hypersonic speeds.

Hypersonic VST-MAC: A Variable-Sweep/Tilt Mach-Area Ruled Configuration for Multi-Regime Flight