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back to article PARIS gets doped up

The model aircraft enthusiasts following our Paper Aircraft Released Into Space (PARIS) programme will be relieved to learn we've finally cracked the Vulture 1-X skinning poser. Last month we spent a not inconsiderable amount of time faffing about with various methods of cladding our aircraft, including a PVA/water mix applied …

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Solarfilm?

Not thought about using Solarfilm?

It's Iron on and heat shrink so it might be too much for the frame to take, but as you have tried everything else, why not this?

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Silver badge

Because it's plastic, not paper?

I'm going to guess that while the release mechanisms and tracking hardware can get away with not being made from dead trees, the covering is a significant part of the aircraft itself.

Plus it does tend to shrink to rather drum-tight levels, yes. And require perhaps rather more heat than a paper straw would like.

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Linux

cold test

Might be worth a bit of freezer testing to make sure the doped covering won't crack up as it cools on its way to launch altitude.

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Anonymous Coward

Also...

...condensation when warming up again is worth thinking about: paper warps (insert StarTrek joke)

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Bronze badge

What about

spray lacquer? less brushing involved.

might only seal the top layers rather than soaking throughout the paper though.

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Anonymous Coward

Already suggested...

Apparently it doesn't adhere well to paper.

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Reinforced tissue

I wouldn't bother with photocopier paper: its made of fairly short fibres, which means its weak, and full of inert fillers which are heavy and don't add any strength. Finally, nitrocellulose dope won't penetrate it very easily. The better answer is to dope on another layer of tissue when the first is dry. The dope in both layers will stick together and proper model covering tissue is strong for its weight due to the longer fibres in it. In the days when you could still buy both heavy and light modelspan we knew that double covering a wing with two layers of light modelspan was easier, stronger and lighter than using a single layer of heavy model span. As a bonus, you get a much smoother surface too. Some covering tips:

- don't use the dope at full strength. Thinning it 50:50 with cellulose thinners makes it a lot easier to work with because it wets the tissue more easily. Two or three coats of 50:50 dope will completely fill the pinholes in the tissue.

- wetting the tissue with a damp cloth or spraying it with water will make wrinkle-free covering much easier. Or, put the tissue on dry using dope to stick it to the framework. When the dope has dried, spray the tissue with water. Let it dry out completely, which gives a nice, smooth covering, and only then brush on the first coat of dope. Let each layer dry and the solvent evaporate before applying the next. One coat a day gives a much better result than two or three in a day.

- well doped tissue is extremely weatherproof - over the years balsa and tissue models have been flown on ice and in rain during competitions many, many times. If they are well doped you get little or no water in the wings even when its pissing down.

In case you're wondering, I'm not suggesting the above to save weight though it will. I still think weight is fairly irrelevant to your mission compared with the strength and torsional stiffness of the airframe. Properly doped double covering adds a lot of stiffness. You'll be surprised how much stiffer a tissue covered wing is compared with the bare structure.

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Wet wet water...

That's the way to do it - gentle mist spray of water and let it dry to shrink the tissue, then (thinned) shrinking dope to taughten it, then (thinned) non-shrinking dope when it's tight enough. Too much shrinking dope though will crush the supports...

As it happens, just got back from the model shop with half a litre of various dopes and thinners.

On a side note - am I the only one concerned that there may be issues with the *electronics* pack cooling down too much? Batteries in particular? I rather think you may need at the very least insulation around the payload, and possibly a heating element too.

Who do you know with an industrial freezer? -20C minimum? Although... at high enough altitude the heat loss may be more from radiation than conduction/convection to air. Any experts here?

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Epoxy on the stressed areas

For what it's worth: when I built slope soarers (gliders wot get some rough landings as most good sites tend to be in the hills), I found that the slow-curing epoxy was wonderful stuff if you applied it to the area of interest and then warmed it with a hairdryer. Not only does this stink to high-heaven (a pre-requisite for any modelling, I gather) it can be worked with a paintbrush into all the little gaps and cracks - perfect for wetting the glass fibre mat I was using around the nose but I'd suggest equally good at securing the office paper to the LE and so on - there's also no need to dope the paper with this method. What you'll end up with is a surface that's both smooth and very secured to the underlying structure.

Test this on a small sample first: you'd be surprised how liquid 24 hour epoxy gets when it's warm and it'll catch you out the first time! Avoid the 1 hour stuff at all costs: you don't have enough play time before it goes off.

Where's the PARIS icon, then? ;-)

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Would FR-2 be cheating?

As in the stuff cheap consumer pcbs are made off? It's called "synthetic resin bonded paper" and according to me Wiki Powers the clue is in the title. Triangles and struts ahoy!!! Dammit - I want wee missiles under the wings - it might even help with the C of G and stability thing etc

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Paris Hilton

More! More! We're still not satisfied!

Ah the first snaps of PARIS in the raw, taut skin so soft and supple... mmmm. Oh yeah, so, when are the best pics coming, from full frontal to blushing bashful beauty... you know what we want. ;)

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Rice paper

Rice paper (mulberry paper) was used to clad model airplanes back when I was a wee kid. It is strong and doesn't stretch. You could try this.

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Wings

I can imagine you are having trouble with bending straws for the wings.

What about cardboard profiles and latteral straws?

See: http://www.flying.doitproperly.co.uk/balsa-plane.jpg

If you're having strength issues, maybe you could cover the wings with several layers of polyester resin coated newspaper.

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Boffin

Composite Technology

Perhaps the best way to wing it is to think outside the cardbord box..

maybe using a plastic/plaster mold as you would with fibreglass or carbon fibre but using paper mache (cross ply tishue paper strips) with internal straws acting as spars.

More work making the moulds but a really good paper wing.

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