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reinforcing a foam wing (combat) with CF

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Old 08-03-2004, 11:02 PM
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artandscience
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Default reinforcing a foam wing (combat) with CF

I'm building the wing for my .25-powered Gremlin combat plane and
am planning on reinforcing the wing with judicious use of CF. Namely, some CF
laminate (0.07) on the LE and some CF tape over the spars joining the wing halves. I'll use 30-minute epoxy and saturate the CF and wing areas.

Anyone have any advice/cautions about doing this? I want to keep the wing light (as per RACores instructions)..

cheers,
S.
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Old 08-04-2004, 07:51 AM
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Ed Smith
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Default RE: reinforcing a foam wing (combat) with CF

If you are going to saturate with 30 min epoxy, there goes any weight saving.

We often read about laying carbon plate strips flat on the wing. Sure this may add some strength by it's very presence. However in my opinion it is virtualy useless used like this.

This is how I use it. I use the .014 carbon laminate. On my Q500 racing wings I use a piece of carbon 1" wide X 24" long, this is the spar. With an X-Acto saw I cut a slot in the foam core, pour some epoxy in it, paint some epoxy on both sides of the spar and slip it into the slot. I now have a 1" deep wing spar. I then skin the wing. A 1" deep spar a tight fit in the slot will not break and it weighs next to nothing. The same piece of carbon laying flat can be bent into a circle. Try doing it edgewise. This will illustrate the obvious.

Laying tape on the spars to strengthen the wing joint will do nothing. Sliding and gluieng a piece of the laminate down either side if the spar at the joint position, as a shear plate will do far more for you.

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Old 08-04-2004, 02:27 PM
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artandscience
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Default RE: reinforcing a foam wing (combat) with CF

Well, it's a combat plane so the idea of the CF was to protect the wing a bit too. I like your idea of using the laminate as an extra spar. I'll try that. I'm thinking of trying the CF tape over the LE spar (as a protector as much as a strengthener). Do you still think that would be pointless?

I shouldn't have said "saturate" in my previous post. I was planning on thinning the finishing epoxy and brushing that on (judiciously) over the leading edge and fibreglass cloth in the landing area (and over the spars themselves).

Would you use CF tape on such a wing at all if you were doing it? It seems like the center section of the wing will be pretty stiff/strong because of the spars and the fuse embedded in it (no to mention the fibreglassing).
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Old 08-05-2004, 01:26 PM
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Default RE: reinforcing a foam wing (combat) with CF

not too many combat regulars go to the expense of using cf in the leading edge. I much easier/cheaper/lighter method is to wrap the le from root to tip with the Scotch Extreme application Bi-directional (BI-DI) available from most office supply stores...
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Old 08-05-2004, 04:44 PM
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Default RE: reinforcing a foam wing (combat) with CF

If you're trying to 'bulletproof' your wing then CF isn't a great idea. Carbon is great for stiffness but bad for toughness. The current trend among the majority of the competitive combat guys is 1/8" diameter FG rods for spars covered with BD tape and a 3/16" diameter FG rod along the LE. Cover the whole shebang with rip stop nylon and you'll have a very tough wing...or cover it with packing tape or Ultracote. I use packing tape because it's fast and cheap.

-Tom
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Old 08-05-2004, 05:05 PM
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artandscience
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Default RE: reinforcing a foam wing (combat) with CF

A little help here.. what are FG rods (fibreglass?)--get it from a kite store?

I presume BD is the aforementioned Scotch Extreme Application Bi-Directional tape?
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Old 08-08-2004, 06:51 PM
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Default RE: reinforcing a foam wing (combat) with CF

You got it. One source for fiberglass rods is [link=http://www.kitebuilder.com/catalog/index.php?cPath=33_66&osCsid=1b5ea3afd4e9c104ddd818b45417b45c]HERE[/link] although there are others.

JESTER
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