Smooth a Curve from an Airfoil

Hi all,
I know this is a very simple question… but important to me…

What would be the best way to “smooth” a curve for an airfoil that I just copied from a PictureFrame? I would like a command that smoothes as max as possible all the borders, since I will use this curve later for a surface…

Hello - really the best is to redraw it carefully with as simple a degree 5 curves as you can.You can probably make each half with maybe 10 control points if you edit carefully.
AirfoilTest.3dm (70.0 KB) - V5 now.


Perfect. Thank you very much Pascal… Is 5 degrees the best? I mean, is it better than 3 deg?

I also discovered another command which is RebuildCrvNonUniform, which looks quite practical.

Another question that I have… once I do a Sweep 2 rails or Curve Network to get a surface, is it better for the quality of the surface to put a small amount of Tolerance?? I mean, is it better for the quality purpose to put 0.0001 than 0.01?

Thanks a lot!

I’m sorry Pascal, I have the version 5 for Mac and cannot open your file since it was saved in a newer version. Could you be so kind to convert it to v. 5.0?

Many thanks!

Hello - I would trace the thing similar to the curve I posted above then, assuming all the profiles are about the same, copy this curve to the other locations and scale/edit to match the curve there. Then Loft all the curves and see what that gets you - a loft through (structurally) identical curves gives the simplest cleanest surface. I’d use degree 5, yes, in preference to 3, here, as it has greater internal ‘smoothness’.


Great Pascal… I could open it now… understood.

So basically, it would be better to have less control points so the curves are smoother, right? Many thanks… I will try now to Loft the surface, instead of doing a Curve Network to compare both surfaces.

Many thanks!

Right - here’s a little bit more careful version (at the nose) where the CurvatureGraph is cleaner across the leading edge.

First version on the right.

AirfoilTest.3dm (72.5 KB)


Much better…

Great!! this is what I was looking for… a command to check the quality of my curves.

Thank you very much for your time and patience!
:slight_smile: I highly recommend this method.

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This method is very interesting… I read it completely and I appreciate your time to post it since I also import my airfoils from Profili 2…


Breaking the airfoil into simple smooth sections. Makes fuselage and tip blends so much easier.

There is a Plug-in that he uses, which is called CosSpacing… I downloaded from them, but I am not able to make it work in my Mac version 5.0. Is it only for Windows?

By the way, do you work also with T-Splines?

This is the attachment for the plug-in:

CosSpacing.rhp (40 KB)

I think it’s pc only. You can also split the curve manually then rebuild the sections as degree 5 spans. Then point edit and curve deviation (compared to the original naca data) to get an acceptable result.

I rarely use t-splines. I find it so much faster to model with surfaces now.

Hi all,
Is there any way to make work the Script that I posted before for MAC?

For the ones working with airfoils, please read this post:

I would like to make it work with the “FULL COSINE SPACING” as Strosfear is saying in his previous e-mail, but there is no command for doing this directly… or is it?

Many thanks.

What version of Rhino for Mac are you using and do you still need the CosSpacing plug-in or equivalent functionality?