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I'm a beginner in airfoil design. I just came across swept-back wings. There is a point that I couldn't understand that theory.

Why is the only perpendicular component of the airflow to the wing(component parallel to chord line) affects the shockwave formation? Why doesn't the total airflow vector(spanwise +chorwise vector component) contribute towards shockwave?

Why wouldn't the shockwave form with the total airflow vector in the swept wing? I have attached the image to show my point better The Red block shows the shockwave in the wings

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Imagine a wing that is infinitely long, and stretches from east to west. It is moving north at 400 mph. Obiously, it does not produce a shockwave, as it is moving subsonically.

Now, imagine a copy of this wing that is moving to the east at 800 mph (along its length) while still moving north at 400 mph. Other than skin effects, this wing is aerodynamically identical to the first, so it does not have shockwaves, yet it is very supersonic.

Of course, a real swept wing is not infintely long, and so there are shockwaves at nose and tip of the wing, but mid span it really does behave similarly to a wing moving much more slowly perpendicular to its leading edge.

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  • $\begingroup$ I'm talking about swept back wing. And I couldn't understand your answer. Could you brief your answer? $\endgroup$
    – Sankara Narayan
    Mar 25, 2021 at 14:49
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I propose you first read this answer.

The flow over the wing is accelerated along the pressure gradient (or orthogonal to the isobars), and this gradient is swept with the wing. Therefore, acceleration and deceleration is orthogonal to the direction of wingspan. The spanwise speed component remains unaffected.

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