Shockwaves formed on a wing will move backward until they reach the trailing edge, when they turn into oblique shocks and stop. When they're on the surface of the wing, it makes sense why they would make resistance, because they're acting like walls in a way. When the shocks reach the trailing edge, they turn into oblique shocks because the flows on the top and bottom of the wing are coming at each other at an angle and they have to turn, making a shock to do that; explained very well by this answer if I didn't make sense.

For me it doesn't make sense why the oblique shocks would make resistance for the plane at all. In the same way the wake of a plane doesn't cause it more resistance, why would the shocks make resistance? They still act like a wall (they being the oblique shocks), but the oblique shocks are kind of like a byproduct in a way, so why would they make resistance?

Basically, I don't see anything that would be 'pulling' the shocks with the plane.

Here's the oblique trailing edge shocks I was talking about. Another way to think of it : The shocks as you can see are at the very tip of the airfoil, so why would it make much resistance at all?

enter image description here

(If any of that doesn't make sense, comment and I will try to fix it. I found it hard to explain what this question is asking. Thanks)

edit : Could someone explain why this question is getting downvoted?


1 Answer 1


The oblique shocks don't cause resistance. However, they do cause a jump in pressure. That jump in pressure (on the body) is what causes the change in force.

The oblique shocks at the TE do not change the force on the body.

Here is a supersonic wedge airfoil.

enter image description here

The shock causes the pressure in region 2 to be higher than freestream (region 1). Then, the expansion fan makes for lower pressure in region 3. The final shocks make for high pressure downstream of the airfoil (not depicted).

The high pressure on the front compared to the low pressure on the back cause what we call wave drag.

All aerodynamic forces are either pressure or shear.

In an intermediate transonic case, with a shock on the top surface, like this one...

enter image description here

The shock causes the boundary layer to separate -- and that region of separation on the back of the airfoil is what really causes the drag.

From this, we see that transonic drag rise has a totally different physical origin than supersonic wave drag.

  • $\begingroup$ That’s very interesting. So the majority of the drag from the shocks isn’t always from the shock acting like a wall? $\endgroup$
    – Wyatt
    Feb 5 at 2:36
  • $\begingroup$ The shock acting like a wall causes the pressure increase. The pressure increase either causes the drag -- or causes flow separation, which causes the drag. All aerodynamic forces are pressures or shear. $\endgroup$ Feb 5 at 18:07
  • $\begingroup$ Oh okay that makes sense, thanks for your answer. Also do you know why this question got downvoted? I'd like to improve it, but I need to know why it needs improvement. $\endgroup$
    – Wyatt
    Feb 5 at 21:40

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