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Schleicher ASH31 4m

Let us all watch your new project progress.
MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

Meanwhile I'm putting together the wing-joiner.

This will have 2 carbon/Kevlar ballast tubes built-in (For steel rods, giving weight and strength) - photo.

These will be wrapped in a uni-direction carbon she'll.
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Tubes and steel rod
Tubes and steel rod
MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

The tubes are bonded together, leaving a trough in between.
This is filled with several lengths of 12k carbon tow (infused thoroughly with epoxy resin) and lightly clamped onto the wing-joiner jig.

When that's cured this can be repeated on the other side.
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MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

While the resin was curing, I made the tail-plane profiles ready for foam cutting.

3mm ply, profiles printed and then glued on with 3m 75, cut out on the fret saw.
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MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

I got a bit side-tracked from the wing joiner, and cut the elevator foam cores.

These are cut from XPS foam (the old blue foam). I used this for a couple of reasons:
1. The higher compression vs EPS allows me to use a thinner skin (than the obechi) & so allows me to fit a thin wing servo inside the profile.
2. I can also then apply a live Kevlar hinge

It didn't go entirely to plan, with the hot-wire, so had to do some sanding afterwards.
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MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

Still putting off the wing joiner!

This time it's the fuselage - sprayed on a light coat of 3m 75, then smoothed on the 100gsm twill glass fibre.
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Jolly Roger
Posts: 519
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Schleicher ASH31 4m

Post by Jolly Roger »

How exciting!

I'm really interested in how many layers of glass you'll add to the inside/outside, and which gsm values?

I asked around when I was making a lost-foam fuselage and the experienced builders suggested that for a 1/3 - 1/4 scale glider they'd use a total of around 800-1000gsm for the nose and 600-800gsm for the boom. With the balsa core approach you've used, I assume you're using a lot less glass?

Thanks for posting your build thread Mark. I've found it very informative.

Rog
Jolly Roger
Posts: 519
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Schleicher ASH31 4m

Post by Jolly Roger »

Also...as an aside, I noticed what looks like a slim home-made carbon fibre fuselage on your workbench, and I wondered if you'd used carbon fibre braid to cover it? I moulded a tail boom this morning using carbon braid over a male plug, and it seems to have gone really well. I found that pulling the braid at each end made it tighten beautifully around the plug - like those Chinese finger traps.

Rog

P.S. I'm sure it's not just me that scrutinises photos of other people's workshops. Err. Is it? :oops:
MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

Hello Rog,

The ASH31 is still TBD, probably 1 more 100gsm up front & carbon fibre on the rear. That skinny bit by the fin will have some more added.

The fuselage in the background is another experiment - balsa rear with 110gsm carbon skin (not a tube, never used it), front in glass over shaped foam (to be removed later) - I digress😀
Jolly Roger
Posts: 519
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Schleicher ASH31 4m

Post by Jolly Roger »

You have plenty going on in your workshop!

If I could make a suggestion about the narrow boom just in front of the fin (where most T-tail models snap). Carbon, although it has a very high Young Modulus and excellent strength to weight, is also very brittle and therefore prone to failing under the kind of shock-load experienced in a boom during a rough landing. For these stress-points, I've switched to aramid fabrics like Kevlar and Diolen. They have incredible tear-strength, so prevent the boom splitting, and allow a little flex so that the structure as a whole can absorb the stress as it bends.

I made a boom last week using two wraps of 200gsm Diolen plus 1 x 200gsm glass and I when I load-tested it in bending I could not break it, even at the 30mm diameter section. Out of curiosity, I took it out the test jig and tried to break it over my knee (and I'm a huge bloke) and I still couldn't break it! Also, Diolen is way cheaper than carbon and a much lower health hazard to work with.
MartinE
Posts: 54
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

That's a very good point Rog, I recall reading they have a similar strategy for the cabin crash structure on full size gliders.

I have some 100gsm Kevlar so will use that. The fun will be avoiding sanding into it and getting fuzz. Perhaps a layer of glass on top - food for thought.
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