What is a shock wave on a wing?

A shock wave is a very thin region where airflow properties change abruptly, typically forming when local airflow exceeds the speed of sound over the wing.

Why do shock waves cause drag rise on wings?

Shock waves convert kinetic energy into heat and cause a loss of total pressure, resulting in a significant increase in drag known as wave drag.

How does angle of attack (alpha) affect shock waves on wings?

Increasing angle of attack intensifies and moves the shock wave forward on the upper surface, increasing its strength and the likelihood of flow separation.

Can shock waves form on both the upper and lower wing surfaces?

Yes, at higher Mach numbers, a second shock wave can appear on the lower surface, especially at high lift coefficients.

How can asymmetric shock waves lead to Dutch roll?

At high Mach numbers, differences in shock wave formation between wings can cause asymmetric lift and yawing moments, contributing to Dutch roll instability.

Shock Waves on Wings

Hard4 min readPrinciple of Flight

Moderately Examined

Why this matters

Recognizing how shock waves form and affect wing performance is vital for pilots to anticipate drag rise, buffeting, and control issues at high speeds, ensuring safe and efficient flight near and above the speed of sound.

Shock waves on wings occur when an aircraft approaches or exceeds the speed of sound, creating abrupt changes in airflow properties over the wing. These waves form first just above the critical Mach number (Mcrit) on the upper surface, leading to significant increases in drag and changes in lift and control effectiveness. Understanding how and where shock waves develop is crucial for managing high-speed flight performance and safety.

Quick Check

Where does the first shock wave typically form on a wing as the aircraft exceeds its critical Mach number (Mcrit)?

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In depth

Explanation

What is a Shock Wave?

A shock wave is a very thin region in the airflow where pressure, temperature, and density increase suddenly, and velocity drops sharply. This discontinuity forms when airflow transitions from supersonic to subsonic speeds, typically as the local airflow over a wing exceeds the speed of sound and then is forced to slow down abruptly.

Formation and Location on Wings

Shock waves on wings first appear when the local Mach number exceeds the wing's critical Mach number (Mcrit). At this point, a weak shock wave forms on the upper surface, usually near the point of maximum thickness or just behind the leading edge. As the aircraft's Mach number increases, the shock wave grows stronger and moves aft along the wing surface.

Effects of Shock Waves

Crossing a shock wave, the airflow experiences:

A sharp rise in static pressure, temperature, and density
A sudden drop in velocity (from supersonic to subsonic)
An increase in local speed of sound due to temperature rise
A loss in total pressure, resulting in wave drag

As the Mach number continues to increase, the shock wave intensifies and may be joined by a second shock wave on the lower surface, especially at higher angles of attack (alpha) or with positive lift. The position and intensity of shock waves are influenced by Mach number, angle of attack, and control surface deflections.

Impact on Aircraft Performance

Shock waves cause a rapid increase in drag (wave drag) and can induce flow separation behind the wave, leading to buffeting and loss of control effectiveness. At high Mach numbers, asymmetric shock wave formation on each wing can contribute to Dutch roll tendencies, affecting stability and handling.

Key Points for ATPL

Shock waves are perpendicular (normal) to the local flow direction on the wing.
Their position moves aft with increasing Mach number and forward as Mach decreases.
Angle of attack and control surface deflections can shift and strengthen shock waves, impacting lift and control.
The onset and development of shock waves are central to understanding transonic and supersonic flight limitations.

The essentials

Key Points

Shock waves form when airflow over the wing exceeds the speed of sound locally.

The first shock wave appears just above Mcrit on the upper wing surface.

Shock waves cause abrupt increases in pressure, temperature, and density, and a drop in velocity.

Increasing Mach number moves the shock wave aft and strengthens it.

Angle of attack and control surface deflection can alter shock wave position and intensity.

Shock waves lead to wave drag and can cause flow separation and buffeting.

Asymmetric shock waves at high Mach can contribute to Dutch roll.

Watch out

Exam Traps & Typical Mistakes

Confusing where the first shock wave forms (it's on the upper surface, not the leading edge or lower surface).

Thinking shock waves reach maximum strength at Mcrit—they strengthen as Mach increases beyond Mcrit.

Believing shock waves always move forward with increasing Mach (they move aft).

Assuming control surface deflection has no effect on shock wave position (it can move the wave aft or forward).

Mixing up high-speed buffet (shock-induced) with low-speed buffet (stall-related).

Test yourself

Example Exam Questions

Question 2Medium

As Mach number increases above Mcrit, what happens to the position and strength of the shock wave on the wing?

Question 3Medium

What is a key aerodynamic consequence of shock wave formation on a wing at transonic speeds?

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