What happens aerodynamically as speed approaches the critical Mach number?

What happens aerodynamically as speed approaches the critical Mach number?

• A. Shock waves form on the wing surface, causing a rapid rise in drag and potential loss of lift or control effectiveness.
• B. Stall occurs at low AoA.
• C. Engine throttles automatically adjust.
• D. Lift becomes zero.

Answer: (A)

As speed approaches the critical Mach number, compressibility effects become dominant and the flow over the wing begins to reach supersonic speeds locally while still subsonic overall. This creates a shock wave on the wing surface, usually on the upper cambered part. The shock causes a sharp rise in pressure and a sudden increase in wave drag. It also tends to disrupt the boundary layer, leading to flow separation that reduces lift and can degrade control effectiveness. This combination—a rapid drag rise due to the shock and potential loss of lift or control authority from the altered pressure distribution—matches what happens in this speed regime. The other ideas don’t describe this aerodynamic shift: stall is tied to high angle of attack, engine throttling isn’t an automatic physics effect of Mach numbers, and lift typically doesn’t fall to zero solely because you’re near the critical Mach number.

As speed approaches the critical Mach number, compressibility effects become dominant and the flow over the wing begins to reach supersonic speeds locally while still subsonic overall. This creates a shock wave on the wing surface, usually on the upper cambered part. The shock causes a sharp rise in pressure and a sudden increase in wave drag. It also tends to disrupt the boundary layer, leading to flow separation that reduces lift and can degrade control effectiveness. This combination—a rapid drag rise due to the shock and potential loss of lift or control authority from the altered pressure distribution—matches what happens in this speed regime. The other ideas don’t describe this aerodynamic shift: stall is tied to high angle of attack, engine throttling isn’t an automatic physics effect of Mach numbers, and lift typically doesn’t fall to zero solely because you’re near the critical Mach number.