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Old Sep 15, 2011, 01:23 AM
Registered User
Cromer,Norfolk, UK
Joined Nov 2006
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Idea
Another ridiculous idea? Glass skinning a built up structure...

Hello all,

This is something I have been mulling over for a while, and wondering if it would work.

Here's the idea.

Cut a foam wing, and cover with parcel tape and release agent, then cover with light glasscloth and thus create two "shells" (ie top and bottom of wing) which will be pretty light and flexible.

Wait a few days for the skins to go off.

Now lay the lower "skin" in the foam "blanks" using double sided tape.

Lay down a suitable spar onto the inside, add ribs and other bits, then top spar.

Glue "top" skin down onto the structure.

Presto, and open structure wing "skinned" in glasscloth...

The idea being it would be nearly as light as a balsa skin, and lighter than a glassed balsa skin, but would present a "ready to paint" surface, which would be more ding resistant, less prone to the "starved horse effect" and completely fuel proof.

Its probably a foolish idea, but its been rattling around in what I like to call my brain for some years now.
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Old Sep 15, 2011, 02:42 AM
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Staffs, UK
Joined Nov 2003
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I think I'm missing something here. If you've cut and glassed the exact foam wing you need what is the benefit of then throwing away the foam and fiddling about building a wooden structure to replace it ?

I can imagine that it might sort of work with a fair amount of effort but I also suspect that if you make the "shells" strong enough to build on then they'll be at least as heavy as most other sheeting methods. I can't see that you gain anything.

Perhaps just a failure in my imagination .

Steve
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Old Sep 15, 2011, 02:57 AM
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Cromer,Norfolk, UK
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There's no benefit to throwing away the foam wing really, maybe a bit of weight saving, but really, I just wondered if it could be done.

The shells would remain fairly floppy on their own until the structure was built inside, somewhat similar to the way some models use a moulded "D-box" around a built up structure.

It probably IS a foolish idea, I often have those
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Old Sep 15, 2011, 03:52 AM
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Australia, WA, Kalgoorlie
Joined Apr 2011
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Matt

Why don't you give it a go, and post the results?

Progress generally comes through innovation- which usually starts with an idea..... If it doesn't work, all you have lost is some time and a bit of building material. If it works you may just start a new trend.

You might even want to consider vac-forming the skins from thin plastic, say .020 0r .040"? Would be lighter, less hassle to make and easily repeatable, but not so rigid as 'glass.

I say go for it!

Odd
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Old Sep 15, 2011, 04:05 AM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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Technically it could work but for one thing. To actually end up lighter your skins would need to be made from the same cloth used for bagging wings. But the sort of very light cloth grades used for bagging is so light that when not supported by the foam core it's about as stiff and bend resistant as printer paper.

A "better" way would be to cut a foam core that is smaller by about 1/16 to 3/32. Then vacuum bag a sandwich of mylar sheet, peelply, resined cloth, 1/16 foam sheet, resined cloth, peel ply and finally mylar over the core. When cured you pull out the center core and remove the mylar and peelply from both inside and out. You're left with a hollow structure that is like a molded honeycomb structure. The two layers of cloth separated by the foam gives the strength of a sheeted over ribs structure. All that's missing is a main spar to fit full depth between the inner skins. No need for ribs even. But it would not be as light as the single layer of cloth and resin. But it WOULD be adequitely strong instead of the inadequite single layer on it's own.
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Old Sep 15, 2011, 09:44 AM
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Being old school, I would cover the wing with tissue, then put the light glass cloth on top of the tissue and call it good. May have to give that a try.
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Old Sep 15, 2011, 12:16 PM
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Cromer,Norfolk, UK
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I'll give it a go sometime, even if its just a trial piece, see how it goes.

Bruce, I love your method, and I have intended to do a wing like that, and probably will as I get myself back into building mode. I'm looking for this winter to be a reasonable season of balsa bashing and experiment, before I start planning a decent scale build for 2012.

Thats the plan. It won't work out like that.

Quote:
Being old school, I would cover the wing with tissue, then put the light glass cloth on top of the tissue and call it good. May have to give that a try.
Why didn't I think of that? Thats a much better idea. I need to eat more fish.
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Old Sep 16, 2011, 12:12 PM
B for Bruce
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The 'Wack, BC, Canada
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The cloth over tissue idea is a variation on a method some of the free flight guys are using where they cover the wing with thin heat shrinkable clear mylar. Then "wash" the outside with a strong degreasing solvent and use water based varnish to bond down a layer of damp tissue to the mylar. The result is strong and puncture resistant but still quite light. Certainly not as light as just tissue and dope but it's only used on bigger models where the weight isn't an issue.
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Old Sep 16, 2011, 05:41 PM
Waiting for the paint to dry.
ctrout's Avatar
Pasadena Maryland
Joined Oct 2009
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I have not posted the steps to do it but yes its works.
http://www.rcgroups.com/forums/thumb...ttach&u=286385
"Spray" sprayfoam" to the core and the glass skin and wait til tac.
the sprayfoam will be as a doubler to the thin glass and the formers will be the stress bearing to the body.
doing this without safety first can hurt you bad as the mist of sprayfoam is in the air as your breathing.
Its hard to test this with small parts but having everything layed out at the same time will help.
Clean up is also nasty.
I woulds say 8' is the smallest wing for cost.
Its just like contact glue but not as safe.
also much stonger then wood only.
Open cores are vac with blocks inside to keep the core from crushing
I do all the paint work on the inside of the skin to have a good grip over the fiberglass for the sprayfoam to stick to.
Use fiberglass of the needed oz for each area of the plane needed for stress.
you can have the layout on a waxed door blank "like a tracter trailer door.
the mid area in 9oz, wing tips with 7.6 to 4.8oz. when it set up you will see no seam.
note- cheap water paint only. the better paints"high solids" it will fail quick.
and no metal flake or matalic paints, the grip will fail.


Its a pain to get everything just right and a lot of work but you can beat the crap out of them if you get it right.
Good luck
you have it right.
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Old Sep 17, 2011, 11:07 AM
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AndyOne's Avatar
United Kingdom, Oxford
Joined Feb 2003
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Quote:
Originally Posted by BMatthews View Post
...The result is strong and puncture resistant but still quite light. Certainly not as light as just tissue and dope but it's only used on bigger models where the weight isn't an issue.
BMatthews,

Some people in the free-flight fraternity who use tissue over Mylar swear by this method because they say it is lighter than tissue alone. The reason is that there is nowhere for the dope to pool under the tissue. Pooled dope accounts for more weight than a layer of 5 micron Mylar.

A.
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Old Sep 18, 2011, 03:05 AM
It must have a machinegun
Scaledown's Avatar
Perth, Western Australia
Joined Sep 2004
1,270 Posts
Isn't a moulded competition glider effectively a glass or carbon skin with a mostly hollow inside? It seems to me that MCarlton is proposing a low tech method of producing something similar, that doesn't require a CNC milling machine.
Most of the benefit would come from skins that are thick enough and stiff enough to create a monocoque structure that doesn't rely on a heavy internal structure.
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Old Sep 18, 2011, 04:07 AM
Waiting for the paint to dry.
ctrout's Avatar
Pasadena Maryland
Joined Oct 2009
1,233 Posts
I thought when I first started to post in here it was common as dert to build this way.
all thats needed it to inter lock the open areas and build the plane in stages for the needed tapers from front to rear.
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