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I have seen some RC planes flying without any form of airfoil, the wing is literally a flat board.

What I want to understand is how lift is generated under these conditions. I understand kinetic energy is transferred from air onto the wing, pushing it up(assuming your aircraft is angled up) but I don't understand why air from above the wing doesn't cancel it out.

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  • $\begingroup$ Not the same question. $\endgroup$ Commented May 19 at 21:40
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    $\begingroup$ Have you ever stuck your flat hand out the window of your car on the freeway and played around with twisting it? $\endgroup$ Commented May 19 at 22:52
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    $\begingroup$ What is the performance of a flat plate wing? Of course this depends on the Reynolds Number (thus on the scale), as explained in the answer. $\endgroup$
    – mins
    Commented May 20 at 15:00

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When we study the lift produced by an airfoil, we add together the lift caused by the camber (the curved mean surface of the airfoil) and the lift caused by the angle of attack.

Any symmetrical airfoil (say a NACA 0012, or your flat board of an airfoil) will have zero camber, so that contribution to lift goes away.

However, the contribution due to angle of attack remains. It does not care that the shape is just a board.

The reason we prefer a nicely rounded airfoil is to delay or avoid flow separation. A flat board has sharp corners at the front that can encourage separation -- by increasing the leading edge radius of the shape, we can delay that.

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  • $\begingroup$ So what causes the lift then? Does there end up being lower air pressure above the wing due to a delay caused by time it takes to fill the void above the wing? I don't understand why upward lift isn't canceled out by downward push $\endgroup$ Commented May 19 at 21:34
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    $\begingroup$ In my experience, explanations of lift can be: simple, correct, intuitive -- but you only get to pick one. There are many discussions on ASE diving into this fundamental question. $\endgroup$ Commented May 20 at 5:01

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