Smooth a Curve from an Airfoil


(Gmoreno) #1

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…

Drawing a perfect Aerodynamic Airfoil
(Pascal Golay) #2

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.


(Gmoreno) #3

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!

(Gmoreno) #4

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!

(Pascal Golay) #5

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’.


(Gmoreno) #6

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!

(Pascal Golay) #7

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)


(Gmoreno) #8

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!

#9 I highly recommend this method.

(Gmoreno) #10

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.

(Gmoreno) #12

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.

(Gmoreno) #14

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.