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As we know, the forces per unit length are: L=q⋅c⋅c

_{l}, D=q⋅c⋅c

_{d}, where c

_{l}and c

_{d}are the coefficients of the 2D airfoil for the given Re and α.

Now, if we rotate the infinite wing of an angle Λ, we have an infinite swept wing.

The theory says that in this case, the forces per unit length (parallel to leading edge) become: L=q⋅cos

^{2}Λ⋅c⋅c

_{l}, D=q⋅cos

^{2}Λ⋅c⋅c

_{d}.

Here is my question:

when looking up the c

_{l}and c

_{d}for the 2D airfoil, should we use:

.) the Re for the unswept wing: Re=U⋅c/ν

.) the Re normal to leading edge: Re=U⋅cosΛ⋅c/ν

.) the Re parallel to the flow: Re=U⋅(c/cosΛ)/ν