# 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? – DeltaLima Dec 15 '17 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? – Marius Dec 15 '17 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 – pericynthion Nov 1 '18 at 17:07