[luckyrob]

I'm trying to recreate an airfoil as a camber line and apply thin airfoil theory to it, however I'm having some issues with the NACA 4 digit camber line formulas.

Most sources say the camber line formula is:

Front Yc=M/P^2 *(2Px - x^2) when 0<x<P

Back Yc=M/(1-P)^2 *(1-2P+2Px-x^2) when P<x<c

However when I try to plot this in Excel using any 4 digit NACA airfoil it most definitely does not produce a camber line, more like two disjointed downward slopes. In my searching I also found this formula on Wikepedia, which I wouldn't normally trust but this actually gives a camber line as expected!?!

Front Yc=M *x/P^2 *(2P-x/c) when 0<x<P

Back Yc=M *c-x/(1-P)^2 *(1+x/c -2P) when P<x<c

Now after some rearrangement the Front formulas turn out to be identical apart from the 'c' term and the Back formulas I can't quite work out.

Anyway so I'm trying to follow the thin airfoil theory calculations to eventually find CL and moments etc but I can't follow the rest of the calcs as using the Wikepedia formulas doesn't give the same answers once differentiated. I can't understand why Wikepedia appears to be correct and every other reliable source isn't!!?!?

Can anyone shed some light on this for me please?