# When the angle of attack is increased does the air flowing below it slow down [duplicate]

So the air above the wing flows faster. So it creates low pressure above the wing. The air flow below the wing, is it slowed down by the increased angle of attack or does it stay the same? So is the higher pressure on the bottom of the wing relatively higher then the bottom or does the airflow on the bottom slow down beucase if the increased angle of attack?

In high alpha flight it is not uncommon to have compression below the wing, which would increase the pressure, and act in concert with the Bernoulli Effect on the top of the wing. The effect on the underside of the wing could also correctly be called a form of Bernoulli Effect.

There need not be any compression on the underside for there to be lift on the top side of the wing. However in higher angles of attack there is compression, which supplements the lift.

This is an old Bernoulli explanation of how wings work that is miss-leading or just plain wrong. The air is not moving, the wing is. So to answer your question, since the air is not moving.. it can't slow down.

As the wing moves forward, the air is compressed under the wing and decompressed above it. That difference in pressure causes lift. The angle of attack changes the relative amounts of each till you reach a point where the air becomes turbulent above the wing. At that point the lift becomes erratic and drag goes through the roof.

A simple analogy can be demonstrated by taking sand or talcum powder and sprinkling it over a table or sheet of cardboard or whatever. Then take a cardboard cut-out of the cross section of a wing and sliding it flat across the sand in the normal wing like direction. The sand under the wing will clump together and form a line of sand along the bottom side of the wing. The sand above the wing will be moved away from the wing leaving a void above the wing.

Now, of course, air is not like sand, and hates a vacuum, and will rush back in to fill the void above the wing. However in order to do so it is "stretched" forming low pressure above the wing. Similarly the air under the wing tries to get out of the way and equalize itself, but in the meantime it is compressed and has a higher pressure.

It is this difference in pressure that causes a net force up through the wing to provide lift.

• how is the air below the wing getting compressed and how is the air above the wing getting decompressed? – Itzyoboi Nov 2 '17 at 19:06
• @Itzyoboi because the air has to move out of the way of the wing and as such the underside may be compressed. Meanwhile the topside of the wing forms a drop in pressure as air has to move to fill in the gap left by the wing as it passes. – Trevor_G Nov 2 '17 at 19:13
• All motion is relative. "Simce the air is not moving, it can't slow down." It can be pushed backwards before the wing arrives, which it does. – Koyovis Nov 2 '17 at 22:18
• @Koyovis yes indeed it does. But that is not the same as the classic Bernoulli model either. – Trevor_G Nov 2 '17 at 22:58
• The old "Bernoulli" explanation is a poor explanation, but not for the reasons stated here. The alternative explanation (using sand as an example) is an even worse explanation, debunked many years ago. – David K Nov 5 '17 at 6:14