Silkspan and Tissue Covering

I have completed a slow flier from plans and shown at www.indoorflyingmodel.com. It is the 'Chickadee'.
The author used ' litespan' covering which requires the application of heat
for adhesion. It is not avilable locally. Also, the use of heat is foreign to me.
I have tissue and some silkspan. I do not think the structure will withstand water shrinking of the covering. However, I think it will need doping for strength.
I have not covered a model in many years, so I am wondering if doping either or both of these will result in shrinkage as much as that when using water.
Thanks, Jim.
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My recollection (from the 60s) is "no."
I remember getting warped surfaces from wet silkspan. But you can unwarp the surfaces using a light application of steam vapor. Or pin or prop them in such a way that they are forced to dry straight.
You might be able to get litespan from Hobby Lobby:
http://www.hobby-lobby.com /
                    Marty
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On Fri, 09 Oct 2009 13:31:12 -0400, Martin X. Moleski, SJ wrote:

Litespan is great stuff. Some dope (nitrate) shrinks, some (butyrate) doesn't. Most color dope is butyrate, but you can use nitrate to intentionally shrink a covering, so it's available.
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Oh, yes, I've read about that effect, come to think of it.
I must have used butyrate when I was a kid ...
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On Thu, 08 Oct 2009 20:42:27 -0400, JFL34 wrote:

Tissue won't shrink when you dope it with butyrate dope.
You can get nicely controlled shrinkage with 99% and 91% rubbing alcohol -- the tissue reacts to the water in the alcohol (and the water the alcohol pulls out of the air) but not to the alcohol itself. Moreover, the effect is somewhat cumulative, so you can sneak up on the right degree of shrinkage. I just don't use water on tissue anymore, except when I'm applying tissue wet to solid wood.
Silkspan takes _lots_ of dope to seal (surely you remember that!). I wouldn't use it on a model so light, not because of shrinkage but because of the weight of the necessary dope.
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Tim Wescott wrote:

I don't know about the modern butyrate dopes, but I used both Pactra and Sig clear butyrate dope back in the '60s to tauten tissue and silkspan. Enamel paints wouldn't tauten tissue, it would lay limp unless one doped them first, but then enamels (spray) are much heavier.

Not for a light finish they don't. I brushed on several coats of clear, then a colour coat. Colour coat adds weight, if not necessary leave the colour off. If one really wants a light finish, using fine woven silk is lighter than silkspan and more tear resistant. For electric models, one doesn't need to seal the weave entirely like with a gas model.
However, I am impressed with the modern synthetic heat shrink materials. They do produce a lighter finish.
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For strength I'd cover it with silkspan, then use the 90-99% rubbing alcohol to control/get the amount of shrinkage I want. Finally spray it with Krylon or a urethane clear spray of some type. You can use a glossy or semi-gloss to get the finish you want. Most paints with colors will add addition weight.
Richard
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On Sat, 10 Oct 2009 13:01:48 -0700, rszanti wrote:

My experience with silkspan is that quite unlike tissue it doesn't shrink overall if you put it on dry and wet it -- you have to put it on wet and let it dry.
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<snip>

I believe silkspan actually expands slightly when it gets wet, then it will shrink as it dries.
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wrote in

I think that's why you put it on wet--fitted while stretched, it then dries taut.
BTDT, was not an expert, but saw OK results.
A long time ago in a faraway place ... ;o)
                Marty
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I realize silkspan doesn't shrink much, at least not like tissue, but it has worked for me. In fact I have a test panel I did some time ago laying next to me on the work bench - it's still tight. The SS was applied using glue stick, then sprayed with 70% Isopropyl Alcohol.
I suppose if the initial covering work was overly slack, the SS may not tighten up enough to eliminate all the wrinkles.
Richard
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I've never had tissue or silkspan loosen up on me. I've always, except for a few years in the USAF where nitrate dope was available gratis, used butyrate dope to apply said coverings. But, I soaked it in water from the sink and laid down a coat of dope on the framework before applying the covering. Then, after pulling it tight, I applied butyrate dope. My problem has been that fifteen to twenty years after covering, the covering splits.
Ed Cregger
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