NACA 6 digit maximum thickness position ?

Is there any equation to determine the max thickness position over chord for a symetric 6 digit NACA profile, starting from the profile name only?
I made a simple parametric, table-driven SolidWorks file to modelate traditional fin keels in 3D, interpolated between two different 6 series profiles, at variable maximum thickness %. It works fine but that equation could make things easier.

 

If you have the ability to use the @IF function in your table you can possibly do this.

If you are simply looking for something like "The third digit indicates the chordwise location of max thickness" then you are out of luck.

 

Oops, wrong airfoil

 

Not true, see Wipikidia for a quick look or : http://www.pdas.com/naca456pdas.html

In the above page is a link to the naca documents that give the formulas for constructing the six series. you could use that to make your own max thickness formula.

 

I believe 6-series NACA foils are thickest at 34.9% chord.

 

Some are, some aren't.

63 series are at 35%.

64 series at 40%.

64 (2) and (4) series at 35%.

64A series at 40%.

65 series at 40%.

66 series at 45%

 

I was thinking on a simple formula to relate the second digit with its maximum thickness chord position. This are the related empirical numbers I found:
63: 35%
64: 37.5%
65: 40%
66: 45%
67: 48.75%
all percents from nouse

attached .dxf with some 6 series

 

No. The NACA 4- and 5-digit sections used a formula to determine the thickness distributions, but the NACA 6-series sections were designed differently.

The NACA 6-series sections were designed by specifying the pressure distribution and then calculating the shape that gave that pressure distribution. The pressure distribution was constant (flat "rooftop") back to the location indicated by the second digit, and then tapered linearly to the trailing edge. This results in the maximum thickness being somewhat near to the break in the pressure distribution, but there's not an easy formula to determine the precise location.

You can develop empirical approximations, of course, and that may be fine for your purpose.