# How to find coordinates of the geometric center of a NACA 4-digit airfoil?

For a project that my team and I are working on, we are using Autodesk Inventor Professional 2018 (student license) for 3D modelling. We are working on NACA airfoils.

I need to create an airfoil within an airfoil so that the thickness distribution is uniform at around (10/12/15)mm.

To do this modelling, I've used two methods, neither of which is satisfactory. Please advise if using geometric center of airfoil is better than aerodynamic center. And how to find it. Please suggest any other method to get the uniform thickness distribution.

1. Use a NACA 6415, c=600mm and NACA 6412, c=580mm. Superimpose their aerodynamic centres.

• The issue with this method is that thickness is more at Trailing Edge (TE) than at Leading Edge (LE).
2. Use a NACA 6415, c=600mm and scale it down to 0.85 with respect to the aerodynamic centre.

• Issue with this is that the thickness variation is too high.

Cross posted at researchgate

• Hello user27602, welcome to Aviation.SE. I see that at researchgate you have added images to clarify your problem. Can you add them here as well please? Dec 15, 2017 at 9:13
• I was trying to do the same thing last year but was using either the mathematical formulation of the NACA 4-digit profile or CATIA (for which, DS seems to be giving away a free academic license every October). While I needed to do some special handling of the LE and TE areas, I could make a thick skin at the thickness I wanted. It's not Inventor, but you could import the points and spline them from the mathematical formulation. Would that be of interest? Dec 15, 2017 at 13:39
• The CAD software should have a function for this that's independent of the shape. This is often called "offset". e.g. for Inventor, youtube.com/watch?v=JaXqqy4o2mQ Nov 1, 2018 at 17:07

I guess you wish to create a halo.

You can use Airfoil Tools' NACA 4 digit generator ( http://airfoiltools.com/airfoil/naca4digit ) to generate your NACA shape. It also features a plotter were you can set chord and halo thickness. Positive values for internal halo and negative for external. Internal halos are interesting to build wing ribbons.

Airfoil Tools generated NACA 6415

NACA 6415 600mm chord with 15mm halo (JPG)

Airfoil Tool's NACA 4 Digit generator