Creating naca wing profiles

[stephengibson76]

Can anyone suggest a rhobust way to build naca wing profiles? We can get the points from a genertor but are struggling to sketch the profile without getteng reflux in the curve. We need to be able to offset the profile by at least 70% of it's height. An inventor naca generator would be nice but I guess that's a post for the customization group

[stephengibson76]

does anybody make wing shapes with inventor?

[itsparts]

Hello steve
I build wings all the time. I may not do it right, but it works for me. I start with the tip and after tip is constructed I go on the inside flat surface and make several work planes at desired measurements.
on each workplane I design the shape that I desire. after I shape all work planes I loft the whole wing.
Hope this helps.
Ed

[stephengibson76]

thanks for the reply.

'on each workplane I design the shape that I desire'

how do you sketch this wing profile? I keep finding that im getting reflux in the curve if i use a spline, (if you imagine the perfect shape, my shape wobbles + and - along that perfect shape) can you offset your wing profiles to any distance?

[itsparts]

Hello Steve
Yes. I am not at my inventor today, so I want be able to do an example till tomorrow morning. Sorry.
I start by determining my wing span that I want to achieve. I determine hieght and thickness. If the wing is going to be 20 feet long, then when I place work planes the distance in-between worplanes will be 2 feet. On each work plane I will make design taper larger from tip to where wing will mount. On each workplane you design the shape larger till desired design. you can keep the same design are change a little, if you start making changes you may need more workplanes closer together so not to distort too much. I always you loft when I design. I only have problems when I get lazy and dont do enogh workplanes. For the beat results you have to make the shape transition smoothly.
I hope this helps. If you want an example I,ll do one tomorrow.

Thanks Ed

[itsparts]

you might not need this but I thought I would send it anyway.
Might help? see attached.
Ed

[stephengibson76]

Thanks, it is a useful document. My problem is not lofting but getting the curviture on 1 profile correct. as you can see from the attached jpeg, the curviture goes from + to -

the points are taken direct from a naca generator but i cant get a nice smooth spline thru the points that doesnt have thes wobbles on it

[itsparts]

Hello
In the example it looks like the bottom schetch is reference something that is off on the top schetch. Are you sure the generator values are correct? I can only see so much from a jpeg, but that is my guess.
Thanks Big Ed

[JDMather]

A common problem with spline curves is users try to use wayyyy too many points. More points is not equal to smoother curve.

Try an experiment. Start a new sketch over your NACA sketch. Sketch a two point spline endpoints projected from your NACA sketch. Spline is straight line. Now, edit the handles to try to match your NACA along one side. Insert node where you think you need one for more control and try adjusting all three handles (you can add dimensions) to match the NACA. Repeat if necessary. My guess is that with surprisingly few points you can match the NACA well within actual possible manufacturing tolerance. (is this going to be layed up fiberglass)

[dan_inv09]

It looks to me like maybe your bottom is a mirror of the top. I have found that mirrored splines get a little weird. How's the curvature on the top spline?

[stephengibson76]

thanks JD i will try that. just out of interest, is there a way to control a spline you produce from a spreadsheet? it is going to be layed up and will have a fillet on the aft end to get rid of the knife edge

[reply2.vibh]

Try breaking the spline connections to avoid the woobles.. to offset the height you might need to shift the plane accordingly.

this video may help i guess..
http://youtu.be/uQzC-W1PwEs