fireflier
Posts: 14
Joined: 4/30/2003
From: East Moline, IL, USA
Status: offline
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You are very close on your guess on the stall...a stall occurs when air separates from the top surface of the wing. This separation happens at the trailing edge first, and then works its way up to the leading edge. Why does the separation take place? As you know, changing the vector of a fluid takes a tremendous amount of energy. The higher the AOA is, the greater the vector change has to be for the air to have a laminar flow. As the air moves towards the trailing edge, it is constantly expending energy. The CAOA is the maximum vector change the air can make using its potential energy, and of course depends on the shape of the airfoil. At the CAOA, the air has just enough energy to conform to the top surface of the wing all the way to the trailing edge. If you exceed the CAOA slightly, the air uses too much energy changing vectors, and does not have enough energy at the trailing edge of the wing. This would be the birth of a stall, and the CL starts to decrease. If you increase the AOA further, of course the air uses more energy making the vector change, and runs out of energy sooner, thus making the air separate from the wing sooner. Induced drag at this point is tremendous, and the aircraft will not fly. The CL reduces very rapidly when you go beyond the CAOA, and the point where it gets to zero depends on the shape of the airfoil. As an example, though, a symmetrical airfoil that stalls at 18 deg AOA, reaches a CL of zero around 26 deg. The answer to your question about the 45 deg AOA is no, there is no lift generated. There is lift, however, at 25 deg, well above the CAOA.
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- "I just ran out of air and ideas, all at the same time!
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