Beyond the critical Mach speed, what is a recognized compressibility effect?

Beyond the critical Mach speed, what is a recognized compressibility effect?

• A. Drag Increases
• B. No Change in Flight Characteristics
• C. Control Difficulties
• D. Instant Stall

Answer: (C)

When airspeed passes the critical Mach number, flow becomes highly compressible and shock waves form on the airfoil. These shocks change the pressure distribution and the way the wing and tail respond to control inputs. The most noticeable result from a pilot’s perspective is control difficulties: the shock-affected flow reduces the effectiveness of the control surfaces, making pitch, roll, and yaw less responsive and more difficult to manage, especially near high Mach and in abrupt maneuvering. Drag rise from wave drag does occur with compressibility, but the question’s focus is on how handling is affected, which is why control difficulties is the best answer. Instant stall isn’t an immediate or guaranteed consequence of exceeding the critical Mach speed, and saying there’s no change in flight characteristics contradicts the known effects of compressibility.

When airspeed passes the critical Mach number, flow becomes highly compressible and shock waves form on the airfoil. These shocks change the pressure distribution and the way the wing and tail respond to control inputs. The most noticeable result from a pilot’s perspective is control difficulties: the shock-affected flow reduces the effectiveness of the control surfaces, making pitch, roll, and yaw less responsive and more difficult to manage, especially near high Mach and in abrupt maneuvering.

Drag rise from wave drag does occur with compressibility, but the question’s focus is on how handling is affected, which is why control difficulties is the best answer. Instant stall isn’t an immediate or guaranteed consequence of exceeding the critical Mach speed, and saying there’s no change in flight characteristics contradicts the known effects of compressibility.