Does anyone know how to determine the leading-edge radius of an airfoil using just the x y coordinates.
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 You could just do a curve fit and then find it analytically...
 I know you can do it in XFoil... ie: 1) Start XFoil 2) type "NACA 0012" 3) type "OPER" 4) hit "enter/return" key 5) type "GDES" 6) a window pops up:

 I knew I'd find it eventually... had to find my book first. Essentially, if you have a NACA 4 series then NACA ABCD, where CD gives the max thickness, t. Then: $R_{LE}=1.1019t^{2}$
 And if all you have is x-y coordinates then you should be able to find 't' by the thickness distribution (assuming you know it's a NACA 4-series) $\pm y_{t}=\frac{t}{0.20}\left(0.29690 \sqrt{x}-0.12600x-0.35160x^{2}+0.28430x^{3}-0.10150x^{4}\right)$ The source: Theory of wing sections: including a summary of airfoil data By Ira H. Abbott, Albert Edward Von Doenhoff