Scale Soaring UK

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.

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.

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.

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.

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.

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

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?

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

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.

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.