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Using Carbon Fibre on Models

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Tosh McCaber19/07/2020 11:54:17
186 forum posts
24 photos

I left the game for a few years, and have now returned to a myriad of modern innovations, which I'm gradually catching up with. I wonder if I can start a discussion relating to carbon fibre elements, and its use for spars and reinforcing, as opposed to our old balsa, spruce spars, and other areas where it can be used. Obviously, there are the high cost, all carbon, moulded gliders. However, wher do you use carbon fibre? To start- some questions:

Are there any sources that can give relative size comparisons between, say, spruce, etc spars vs carbon fibre?

Where do I shop for carbon spars and other components?

What is an appropriate glue for carbon?

Etc, etc?

Martin_K19/07/2020 13:55:09
187 forum posts

I have recently completed my first build using carbon fibre, tube for main spar, rod leading edge, and throwing peg (DLG). This demanded my first use of cyano adhesive, medium where I wanted a bead of glue in addition to what penetrated the joint and thin where I hoped the glue would all penetrate the joint. Parts pinned to the board dry fitted, then glued when happy with the geometry.

I doubt the construction would have been possible without laser cut ribs. How could you accurately hand cut elliptical holes in ribs that are not at 90 degrees to the main spar?

After two flying sessions all the joints were still sound except the throwing peg in the wing tip. I originally glued that with epoxy but most of the glue got pushed out when I inserted the peg though it's hole. I re-glued it dry fitted with thin cyano, which survived my most recent (third) outing with the 'plane.

I see this technique as complementary to all wood construction.

DCW19/07/2020 15:05:42
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98 forum posts
66 photos

Hi Tosh.

Inserting carbon fibre tubes into a main spar or even the rear of a fuselage means a lighter structure can be built. A typical metre length of 8x6mm tube would cost about £8. With carbon tubes the smaller number refers to the internal diameter. I recently refurbished and electrified my Hambleton Pterasoarus, a 3mtr. tail less design. This aircraft was built in 1990 and has flown many hours, but the spars by now may have become brittle, so carbon tubes were epoxied against the spars with 1/8" sq. spruce above and below the tubes to help the epoxy resin glue.

The tubes were placed at the most vulnerable part of the spar. Below is the aircraft awaiting the insertion of the tubes.pterasoarus re-furb.jpg

Edited By DCW on 19/07/2020 15:06:48

Tosh McCaber19/07/2020 15:20:58
186 forum posts
24 photos

Hi Martin, DCW,

Martin, which glider were you building? Thanks for the info re tube sizes, DCW. Where do you source your cf from?

DCW19/07/2020 15:31:36
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98 forum posts
66 photos

Hi Tosh,

CF rods or tubes obtainable from:

Leeds model centre, Sussex model centre, Pegasus models, etc. Good idea to shop around.

David

Martin_K19/07/2020 15:43:45
187 forum posts
Posted by Tosh McCaber on 19/07/2020 15:20:58:

Martin, which glider were you building?

Tosh, my carbon/balsa/ply glider is a Vick Alt DLG (kit). I posted photos in the Forum members' new models thread. Scroll down to posting on 12/07. Looking at the pictures, the tail boom is, of course, also a carbon tube.

(Trimming the 'plane is proving difficult, I am still refining it).

Tosh McCaber19/07/2020 16:50:43
186 forum posts
24 photos

Oops Didn't mean to post!

 

Edited By Tosh McCaber on 19/07/2020 16:51:55

Tosh McCaber19/07/2020 16:51:11
186 forum posts
24 photos

Thx for the info David.

Tosh McCaber19/07/2020 16:54:06
186 forum posts
24 photos

Looks like an interesting build Martin! Just as well for the pre-cut laser parts!  Looks good- I hope that you sort out the trim.

A bit of a steal from Hyperflight- their kits usually run in the high hundreds to thousands of pounds!

Edited By Tosh McCaber on 19/07/2020 16:57:14

kc19/07/2020 16:54:52
6635 forum posts
173 photos

What about using carbon fibre tows to reinforce a balsa spar etc?

Tosh McCaber19/07/2020 17:03:47
186 forum posts
24 photos

Some 20 years ago , I actually did build,a very large X country glider- 12' wingspan x 14" chord, using that technique- carbon fibre and Kevlar tows on top of the spruce spars, long before the advent of moulded cf spars and rods. Great flyer! Nostalgia! Still hanging up at high level in my workshop. Must get it back down!

 

Edited By Tosh McCaber on 19/07/2020 17:04:44

perttime19/07/2020 17:15:57
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182 forum posts
11 photos

Flat carbon strip can be good for spars too. 0.5 x 6 x 1000 mm, for example. On a small model that could be embedded in a foam wing vertically, or glued to the side of a balsa spar. On a larger model, you'd glue it to the outside of a balsa upper and lower spar.

Cliff Bastow19/07/2020 18:06:35
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916 forum posts
464 photos

If you take a look at Ramy Rc on you tube he has started building whole air-frames in carbon fiber, and very nice they look too.

robert chamberlain14/08/2020 01:35:41
160 forum posts

for positive G reinforcement I would think carbon ribbon would be glued to the bottom of the spar,---yes?

Bob C

conrad taggart14/08/2020 07:36:18
108 forum posts
5 photos

For everything composite these guys are excellent. Some good videos and question and answers under the various items in terms of use and prep.

**LINK**

Tosh McCaber14/08/2020 07:40:47
186 forum posts
24 photos

That's how I did it many years ago- a bit messy (and maybe a bit hit and miss!), but it worked on my very large cross country glider.

Lima Hotel Foxtrot14/08/2020 10:29:06
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397 forum posts

Addlestone Models have (and can get hold of) CF tube, rod, strip, batten, RHS and tissue. 

Edited By Lima Hotel Foxtrot on 14/08/2020 10:29:58

Tosh McCaber14/08/2020 10:58:04
186 forum posts
24 photos

Thanks- that's excelent guys- a good selection of outlets to go with!

Still wondering- are there any sources/ articles that can give relative size comparisons between the old fashioned spruce, etc spars vs carbon fibre?

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