Which of the following is a valid compressibility effect when crossing the critical Mach number, with correct answer at the second option?

Which of the following is a valid compressibility effect when crossing the critical Mach number, with correct answer at the second option?

• A. Increased Fuel Consumption
• B. Drag Increases
• C. Increased Stall Speed
• D. No Effect on Instrument Accuracy

Answer: (B)

As speed reaches and exceeds the critical Mach number, air around the airplane becomes noticeably compressible and shock waves form on the wing and other surfaces. Those shocks create a rapid rise in pressure and a region of flow separation, producing wave drag. The result is a clear increase in overall drag when you go into transonic speeds. This direct compressibility effect is what you’re testing. Other options don’t describe what happens from a compressibility standpoint: stall speed is tied to lift and angle of attack, not the onset of compressibility at transonic speeds; instrument accuracy isn’t the primary effect of crossing the critical Mach number in normal flight (though some pitot-static readings can be affected, it’s not the main point here); while higher drag can lead to higher fuel burn, the immediate, defining compressibility effect is the drag increase due to shock-induced wave drag.

As speed reaches and exceeds the critical Mach number, air around the airplane becomes noticeably compressible and shock waves form on the wing and other surfaces. Those shocks create a rapid rise in pressure and a region of flow separation, producing wave drag. The result is a clear increase in overall drag when you go into transonic speeds. This direct compressibility effect is what you’re testing.

Other options don’t describe what happens from a compressibility standpoint: stall speed is tied to lift and angle of attack, not the onset of compressibility at transonic speeds; instrument accuracy isn’t the primary effect of crossing the critical Mach number in normal flight (though some pitot-static readings can be affected, it’s not the main point here); while higher drag can lead to higher fuel burn, the immediate, defining compressibility effect is the drag increase due to shock-induced wave drag.