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Using CAD to generate ribs for geodetic wing

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Using CAD to generate ribs for geodetic wing

Old 01-16-2004, 08:42 AM
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arthurwerner
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Default Using CAD to generate ribs for geodetic wing

I really like the way a geodetic wing looks like. As they should also be able to resist torsion quite well, I guess it is time to try to make one.

For a wing without taper, it is quite easy to do. However for a wing with taper it gets much more difficult, and I have spent hours looking at it and trying to come up with the gonio that should succesfully describe the riblengths. This is complicated, as the rootfacing rib is longer than the tipfacing rib - and I didn't manage..

I have no knowledge at all about Autocad or something like that, but I have a feeling it should be possible to:

a) Export the root rib as DXF from Profili
b) Export the tip rib as DXF from Profili
c) Import both in a CAD program
d) Layout a wing planform in the CAD program that has those two ribs at the end
e) 'Slice' that structure at any angle to produce the rib at that location and that angle.

I have attached an image below: what I am after is the dimension of the rib as shown by the diagonal red/blue lines.

So my question is:

Is this really possible in CAD?
How? (I can export the ribs as DXF)
If so, is there any free or shareware program that I can do this with? What should I look for?

Thanks for any help
Arthur
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Old 01-16-2004, 12:18 PM
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SeditiousCanary
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Default RE: Using CAD to generate ribs for geodetic wing

I suspect I can do it easily enough if you gave me the airfoil you wanted to use. If you have the file already, make sure they are "closed" and I will see what I can do this weekend.
Also, let me know what dimensions you are looking for as far as wingspan, root chord, tipchord and any other dimensions which may be a factor.
Old 01-16-2004, 12:45 PM
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Default RE: Using CAD to generate ribs for geodetic wing

I see what you mean.....

It's easy to stretch the ribs out to the correct length but there is another factor that comes into play. With the ribs running spanwise on a tapered wing the effective depth will have to change along the length of the rib to reflect the thickness of the airfoil at that position of the wing. In effect you would have to lengthen the ribs to suit the position and then you would have to taper their depth to match the change in airfoil thickness from the leading edge to trailing edge chord stations.

Yep, this sounds like a fine time to forget the whole idea and go have a nap.....

In truth what most folks would do is just lengthen the ribs, hand cut each one (or set up the laser) and build the wing. Once finished a few strokes with a big sanding block would even up any differences. Perhaps leaving the ribs a trifle fat to allow for the sanding.

And yes they DO look very nice with the light showing through.
Old 01-16-2004, 01:05 PM
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Tall Paul
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Default RE: Using CAD to generate ribs for geodetic wing

Select the rib for the wing section you want... 10% thick say.
Determine the angle the geodetic rib will have relative to a normal (90°) rib.
Finger out the true length of the geodetic rib.
Hypotenuse..
Draw up the rib and -stretch- the horizontal component that amount, leaving the vertical component at 100% of the "normal" rib.
The wing will still be 10% thick.
Old 01-17-2004, 03:17 AM
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DanSavage
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Default RE: Using CAD to generate ribs for geodetic wing

ORIGINAL: arthurwerner

Is this really possible in CAD?
How? (I can export the ribs as DXF)
If I were to do this in CAD, I would do it in 3D CAD.

1) Make a 3D wing.
2) Copy the 3D wing to another layer.
3) Dice the 3D wing along a diagonal rib.
4) Trace the edge of the wing to get a rib.
5) Repeat steps 2 through 4 until all ribs are diced and traced.

If you were familiar with the CAD program, it would probably only take an hour or so to do.

Dan
Old 01-18-2004, 02:59 PM
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arthurwerner
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Default RE: Using CAD to generate ribs for geodetic wing

Thanks for the replies:

@SeditiousCanary - thanks for the offer, and I might take you up on it. But reading the posts below - this might be quite some work and I might be asking too much.

@BMatthews - You are describing the exact problem that made me look at CAD rather than gonio.

@ TallPaul - I tried that route and it works fine for constant chord sections. But it is flawed for a tapered wing section - as the rootfacing end will not only be longer than the tipfacing end, but also itself be tapered as it 'passes' different thickness wing sections.

@DanSavage - I think you are describing the way this needs to be done. I am lacking any current CAD experience but not unwilling to dive into this. Would a package like TurboCad be able to do this, or do I need something more advanced or 3D?

Thanks,
Arthur
Old 01-18-2004, 05:14 PM
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claude vuattoux
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Default RE: Using CAD to generate ribs for geodetic wing

i am a modeler an expert with autocad
the only way to do this is to use mechanical desktop from autodesk

1 generate a surface revolution ( start rib end en rib )

use a a fonction to slice the volume the genrate volume by a plane perpandicular to your desired rib
the slice function will generate a 3d polyline a the intersection ( it will be your rib )

if i have time this week i will try do do it
Old 01-18-2004, 05:47 PM
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BMatthews
 
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Default RE: Using CAD to generate ribs for geodetic wing

The new Version 9 and up TurboCAD's handle 3D in a much more intuitive way. I tried 3D with my old Ver 7 and it was terrifying to use. With the new Version 9 I just got I did a rotated airfoil sectioned drum (ducted prop shroud) and rendered it into full living color in the first few moments of opening the program for the first time. I still haven't bothered with 3 D yet but it sure looks like this will make it a lot easier.
Old 01-20-2004, 01:31 PM
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DanSavage
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Default RE: Using CAD to generate ribs for geodetic wing

ORIGINAL: arthurwerner
@DanSavage - I think you are describing the way this needs to be done. I am lacking any current CAD experience but not unwilling to dive into this. Would a package like TurboCad be able to do this, or do I need something more advanced or 3D?
You're welcome. Sorry for taking so long to respond.

I've never used TurboCAD, so I wouldn't be able to comment on it's 3D capabilities.

The only 3D package I've used for model airplane design is DesignCAD 3D and DesignCAD 3D MAX. Either of these two packages would be able to easily accomplish what I've described. I did a quick test in DC3 MAX and it's a straightforward process which is pretty much as I described it above. I created a 3D wing, then diced a diagonal rib from it.

While the original DC3 isn't available any more, you can buy DesignCAD 3D MAX from most computer chain stores like CompUSA for under $100. If you happen to catch it on sale, you can even buy it for under $50.

Dan

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