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Old Yesterday, 04:47 PM
"Butchering Balsa since 1971"
CashRC's Avatar
USA, TX, McKinney
Joined Dec 2003
1,062 Posts
Help!
Tissue trim over doped silk..

Hi ya'll, need some help I recently inherited Martyg's Comet Clipper..Marty moved to Seattle, and didnt want to take the plane with him. I got it as an ARF...silked and doped, needing final assembly, weight and balance, and trim. It's silked and doped with nitrate dope, and my thinking is using Japanes tissue for trim. Any pointers on the best way to go about it? I've built tissue covered rubber models in the past, but I've never laid down tissue over doped silk. Any ideas more than welcome.
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Old Today, 02:01 AM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
Joined Sep 2007
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Should be just like applying tissue trim over tissue Cash. Obviously you will use nitrate dope as per the basic finish, cut the trim to size/shape (I like to make cardboard templates if the shape is in any way complex and cut with a NEW scalpal blade), lay it in place and dope down either with very thin dope or just plain thinners (which reactivates the base dope), working from the inside to the outside to smooth out any bubbles. If the tissue is not perfectly flat, iron it first to remove any creases with a warm domestic iron.

If the trim is straightforward - e.g. a leading edge stripe - I will sometimes wet the tissue by drawing it over a water bath, which helps in removing any wrinkles and also helps the dope/thinners to penetrate, but with complex cut-out shapes you can't do this, and as an alternative I use a perfume spray, lay the tissue shape in place and gently mist it with water.

Afterwards give the tissue trim areas a couple of coats of thinned dope overlapping the edges to make sure it is all sealed down and finished to match the rest of the airframe.

It goes without saying, BTW, that the basic silk finish should have had all it's dope applied before applying the trim - if it isn't completely finished the trim pplication can cause the silk to slacken off at first and this can cause wrinkle issues.
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Old Today, 11:40 AM
"Butchering Balsa since 1971"
CashRC's Avatar
USA, TX, McKinney
Joined Dec 2003
1,062 Posts
Thank you sir...I already have some nitrate and thinner coming from Brodak, and marty had some test panels he built and covered, so I can paractice a bit before I get started on the real thing..
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Old Today, 01:09 PM
I like real wooden aeroplanes!
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South-west France
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Very good plan to practice on the test panels Cash. Good luck and let us see the finished model.
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Old Today, 01:23 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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The present tissue we get these days is too "crinkly" to lay down well. I find that I get the best results if I lay the tissue in place then VERY LIGHTLY mist it with some water. You want just enough to make the paper go limp and not enough to be what anyone would consider as wet.

The thinner is then brushed over the tissue so it soaks through and softens the dope underneath and that is what sticks the tissue down.

In all these ways it's just like putting tissue over tissue just like Sundancer says.

One thing I find helps on the base if it's been allowed to sit for weeks or months is to "soften" the dope with a fresh top coat or even just brush or airbrush on some thinner. Getting some softness into the sealing coat in this way makes the base dope respond better to the thinner applied down through the trim tissue.

Don't "tack" the tissue down at all. It undergoes some size changes with the mist used to dampen it and when the thinner displaces the moisture. Instead just lay it down, mist lightly and then start from an area where "registration" to line up with some feature is the most important. From that point work out to the end(s) with the thinner. On longer pieces I find it helps to start it off with a patch of thinner to bond it and then to pick up the far ends(s) a little and work the length down. Less risk of the tissue "piling up" and forming folds that way.

With really narrow trim the dampness can make the tissue distort easily from tension. So straight lines are harder. But if you fudge the strip of tissue this way and that lightly as you thinner it onto the base covering you can get a pretty good lay.

If you have to lift the trim up and re-position it at all unless you do it immediately in the wake of the thinner brush you'll find that you need to flood the area with more thinner to soften the bond. But it can be done. If it is sticky at all don't force it or the lightly dampened tissue will distort badly. Instead flood the spot to be lifted with thinner and hold a very light tension and the tissue will lift easily in a second or two.

Because it stretches slightly when dampened you'll find that doing something like scallops where the points should line up with the ribs is a challenge. To make it work allow for about a 1/32 growth for every two inches of length. And even then much will still depend on the sag between ribs of the base covering. If you want a trim like that it's best to make up an 18 inch test strip and lay it in place after misting and see how it bonds down. Then flood it with thinner right away and lift it. This is also a good test to see if the tissue will stretch and form to the compound curves of the sags depending on the base covering shape. Or simply avoid a scalloped trim scheme for now....

Good luck and post pictures of it when you're done.
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