Past the critical Mach speed, a common compressibility effect is which of the following?

• A. Engine Surge
• B. Drag Increases
• C. Increased Wing Area
• D. Stable Flight at High Speed

Answer: (B)

Past the critical Mach speed, the flow over the aircraft becomes significantly compressible and shock waves form on surfaces like the wing. Those shocks cause a sharp increase in pressure differences and generate substantial wave drag, so the total drag rises rapidly as speed increases into the transonic regime. This drag rise is the typical, noticeable compressibility effect you see near and beyond the critical Mach number. Engine surge is an engine stability issue, not an airframe compressibility effect; wing area is fixed by design and doesn’t increase with speed; while high-speed flight can introduce other stability concerns, the common compressibility phenomenon here is the rapid drag increase due to shock-induced wave drag.