måndag 13 augusti 2012

See How It Does Not Fly

See How It Flies: A New Spin on the Perceptions, Procedures and Principle of Flight by John S. Denker sells the the old Kutta-Zhukovsky circulation theory of lift:
  • In real flight situations, precisely enough circulation will be established so that the rear stagnation line is right at the trailing edge, so no air needs to turn the corner there. 
  • The general rule — called the Kutta condition — is that the air hates to turn the corner at a sharp trailing edge. 
  • To a first approxmation, the air hates to turn the corner at anysharp edge, because the high velocity there creates a lot of friction. 
  • For ordinary wings, that’s all we need to know, because the trailing edge is the only sharp edge.
  • The funny thing is that if the trailing edge is sharp, an airfoil will work even if the leading edge is sharp, too. This explains why dime-store balsa-wood gliders work, even with sharp leading edges.
  • It is a bit of a mystery why the air hates turning a corner at the trailing edge, and doesn’t mind so much turning a sharp corner at the leading edge — but that’s the way it is.
  • In any case, the rule is:The air wants to flow cleanly off the trailing edge.
We see the Kutta condition being motivated by viscosity. Yet another piece of evidence of collapsed aerodynamics science and education. 

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