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I'm currently taking aerodynmics course.In the classical thin airfoil theory. we saw that both for symmetric and non-symmetric airfoils the term $dc_l/d\alpha= 2\pi$. But in the preceding chapter, calculation of aerodynamic center, if we calculate aerodynamic center with using values of Lift and Moment about the quarter chord, there appear the following equation:

0=$\dfrac{dc_l}{d\alpha}(x_{ac}-0.25)+\dfrac{d{c_{m,c/4}}}{d\alpha}$

However, the problem is that, in the example question, the solution is like the following:

  • There are given two values of $c_l$ and $c_{m,c/4}$ for different angle of attacks.
  • $\dfrac{dc_l}{d\alpha}$ calculation is being done by applying finite difference for these two values.

Finally, I don't understand why we do not use the value of $2\pi$ directly.

Thanks for advance :)

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  • $\begingroup$ You might be better off asking this on Physics.SE. $\endgroup$ – ZeroOne Jan 14 at 16:56

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