Influencing Critical Mach (Increase M_crit)

Goal

To fly faster without incurring the penalties of Drag Divergence and Shock Stall. We want to increase $M_{crit}$.

Design Features

1. Sweepback (Flecha): The most effective method.
   • Decomposes velocity into a spanwise component (doesn't accelerate much) and a chordwise component (accelerates flow).
   • Effective Mach number seen by the aerofoil is lower ($M_{eff} = M \times \cos(\text{sweep angle})$).
   • Disadvantage: Poor low-speed lift, tip stall tendency.
2. Thin Wings (Low Thickness/Chord Ratio):
   • Less curvature means less acceleration of airflow over the wing.
   • The peak velocity is lower, delaying the formation of a shock.
   • Disadvantage: Less fuel volume, heavier structure needed.
3. Supercritical Aerofoil:
   • Flattened upper surface: Reduces velocity peak.
   • Cambered rear section: Recovers lift at the rear.
   • Result: A weaker shock wave that forms further aft.
4. Area Rule (Waisting):
   • "Coke bottle" fuselage shape. Smooths the cross-sectional area distribution of the aircraft to reduce wave drag.
5. Vortex Generators:
   • Small vanes that re-energize the boundary layer. They don't increase $M_{crit}$ itself, but they delay Shock Stall (separation behind the shock).