In transonic flight, what is the origin and significance of wave drag?

• A. Wave drag is negligible in transonic flight.
• B. Wave drag arises from Reynolds number effects at low speeds.
• C. Wave drag arises from compressibility and shock waves and becomes significant near and above the transonic regime.
• D. Wave drag is caused by skin friction alone.

Answer: (C)

Wave drag in transonic flight comes from compressibility effects as parts of the flow reach speeds near the speed of sound and shock waves form on the aircraft surface. These shocks create abrupt pressure changes and redistribute the flow, adding a substantial drag component known as wave drag. This becomes significant when the flow is transonic, so shock waves develop and the pressure distribution over wings and the fuselage changes rapidly. It’s not due to Reynolds number effects at low speeds, and it’s not caused by skin friction alone; skin friction is a separate, smaller drag term. The key point is that compressibility and shock waves generate wave drag, and this effect rises sharply in the transonic regime, strongly influencing aircraft performance and design.