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Carbon Fibre Wing joining cuff

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Old 04-30-2003, 10:38 AM
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zippo
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Default Carbon Fibre Wing joining cuff

I'm currently building a model with a foam wing and I'm thinking that rather than us the normal glass tape and epoxy method, I want to make a CF cuff that fits around the wing.

Making the cuff really isn't a problem. I will use CF tape, laminated up on OHP film. When its just going 'green I will cut it to size and mold it around the wing. When set, the film will be removed and the 'cuff' epoxied in place. In this way I hope to achieve a really nice looking wing joint.

I have made various bits and pieces in this way before and the surface finish is pretty close to perfect. One bit was a wing LE band protector - and it was real easy to make. So I think extending the idea to a full wing 'cuff' will work just as well.

However - I do not think that I have heard or seen anything like this being done before. So I'm a bit worried that it might not be a very safe thing to do. I obviously don't want is a weak wing joint.

Can anyone offer and advice?
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Old 04-30-2003, 05:39 PM
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Default Re: Carbon Fibre Wing joining cuff

Im having a tough time understanding what youre trying to accomplish & what 'cuff' means.

A cf reinforcing band in the center section will be stronger that the equivalent cloth weight glass band if you are talking about simple material substitution.

If you are trying to acheive better surface cosmetics, that doesnt really have anything to do with cf vrs glass, thats just a surface treatment of the resin/matrix layup along the lines as youve described.

If you mean the cf cuff is some kind of external shell that holds the R/L panels into place during flight but is plug-in & removable similar in concept to spar & socket style plug in wings, well thats a different animal.
- wont work for tapered wings because, well.. its taperd
- no incidence adjustment control like the round spar & socket method
- the cuff is holding the wing in a potentially bad structural manner. The wing bending moment is exponentially higher towards the root, I can see where the edge of the cuff might make a conveniant pivot point stress area for the skin to kink.

A 'full length cuff' hmmm... that sounds like a glassed wing skin surface

Maybe try & explain what youre trying to accomplish and/or a picture & a more direct answer can follow.
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Old 04-30-2003, 08:36 PM
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Default Carbon Fibre Wing joining cuff

Hi Zippo!

What you are attempting might be more work than is really necessary. If you are using very light carbon it might work, but if it's a CF tape (5.8 oz), then the material is much heavier than what's really required.

For joining wings you'd be better off using a 0.5 oz CF omnidirectional 'veil' or 'tissue'...this stuff is very thin and very light. I use this in conjunction with a 0.7 oz fiberglass cloth cut on a 45 degree bias.

Here's what I do:
1. Cut the CF and FG to size (cut the FG slightly larger so you can 'feather' the edges)
2. Lightly mist the bottoms of the pieces with spray adhesive
3. Smooth them out on the wing eliminating bubbles and wrinkles
4. Wet the layup out with laminating epoxy
5. If necessary, blot the piece after its' wet out with toilet paper to remove any excess resin.
6. Let cure, lightly sand, then fill the weave with thinned-out lightweight spackle.
7. Sand with 320 grit and then you're ready to apply covering

I also like to apply masking tape about 1/16" from the edge of the glass before wetting-out to keep the epoxy from getting spread out too far.

The strength of the 0.5 oz CF / 0.7 oz FG is comparable to 4 oz glass tape and a helluva lot lighter! It won't provide you with the glossy woven carbon fiber look, but who looks at wing joints anyway? The layup described will be very thin and barely noticeable beneath the covering.

-Tom
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