Original URL: http://www.theregister.co.uk/2010/07/23/paris_skin/

PARIS skins up with Rizlas and dope

Well, tissue paper and PVA...

By Lester Haines

Posted in SPB, 23rd July 2010 11:00 GMT

Work continues apace down at the Paper Aircraft Released Into Space (PARIS) workshop, where we've been looking at just how to skin our Vulture 1-X vehicle.

Before we get to that, though, we're delighted to announce that our audacious upper atmosphere project now officially exists, because Wikipedia says so.

Lovely. Now, on with the skinning. We were tickled by suggestions last week that we might fancy putting something together with silver Rizlas and dope. Sadly, the former are a bit hard to come by round here, and in any case they're just 20 microns thick, so we'll be needing something a little more substantial.

Like tissue paper, for instance. We did a couple of initial tests with this and spray lacquer, but the lacquer wouldn't bond with the straws properly, and the paper just pulled away as it dried.

Well, we always favoured PVA anyway, so here's our high-tech skinning kit, posing with a section of test structure:

Skinning kit, with tissue paper, glue, and test structure frame

We started off by gently rubbing the surface of the straws with a bit of P180 grade wet and dry - just enough to rough up the surface where the paper was going to make contact.

We then applied pure PVA to the straws, a 50-50 mixture of PVA and water to the tissue paper, and stretched it over the frame. When it dried, the result was pretty well perfect:

One layer of tissue paper stretched over frame

All well and good, but the model makers among you will be aware just how fragile this covering is - far too fragile to survive an ascent to 20,000 metres.

Why not add another layer of tissue paper then? Not a good idea, since although it looks plausible-ish from the outside...

The structure with a second layer of tissue paper applied

...the inner face tells a different story:

The inside view of the two-ply skin, showing wrinkling

Okay then, we thought, let's apply three plys of tissue paper in a single operation:

Three layers of tissue paper applied at once over frame

Not bad, but it's pretty well impossible to prevent wrinkling...

The dried three layers of tissue paper

...which becomes more evident if you later coat the surface with a layer of pure PVA.

Three layers of tissue paper treated with an extra coat of PVA

At this point, it was pretty obvious that to get a decent thickness of skin without a load of faffing about, we'd be better off using plain old paper - in this case bog-standard 80 gsm printer paper:

Paper stretched over a test frame

Take our word for it, this works a treat. It dries taut and accepts a final coat of PVA without losing its composure. Here's a rear view of the finished skin - tighter than a nun's naughty bits and sufficiently strong to take a few knocks:

The tightened paper over the frame

Using standard A4 sheets of paper does, of course, offer an additional benefit, since you can print on it before deployment, meaning you don't have to paint on graphics and stuff after skinning.

Just so you know, the above test section survived 12 hours in the freezer without adverse affect. We're still running a few more tests to get the optimum result, but reckon this is the way to go.

And since our skinning snaps are not the most scintillating to come out of the PARIS project to date, we'll conclude with this teaser of a mock-up section of wing structure...

A mock-up of a section of wing spar

More details on that shortly. ®

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