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General control line discussion => Open Forum => Topic started by: Darwin Ulledahl on July 02, 2016, 09:20:47 AM
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Having no fun with the China silk. Thought I'd give it a try after 49 yrs. Need advise on applying it on wing. I wet it with water and stretched onto wing panel with clear dope as I've done in past. Looked great next day nice and tight. After applying coat of clear dope expecting continued taut, the silk expanded and stayed loose and sagy (What gives). Even tried tautening dope for one more coat and same results. Totally opposite results I was expecting. Silk is expanding instead of shrinking. HB~>
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Pull it tighter when it's wet. Let it dry completely before doping.
MM
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Spray thinner on it and hit it with a hair drier
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Which dope are you using for the first coat? I tried using Sig Lite Coat and had the same results as you. I'm going to Sig Supercoat
as it has more shrinkage.
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You said your silk was tight after drying so your silk is OK. Use very thin coats of a shrink type only for the first thin coats.
Ty's suggestions are correct. Many will say to use thick first coats but that causes run through and poor drying, loose covering.
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I had a covering job that looked like that on my "13". It was flown at VSC one year. I use butyrate from start to finish. I was about to grab the iron and decided I would try one mote coat. I think it was number 10. I thin dope so it brushes easy. Hung up to cure and next morning it was drum tight. After all theses years it is still tight.
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Which dope are you using for the first coat? I tried using Sig Lite Coat and had the same results as you. I'm going to Sig Supercoat
as it has more shrinkage.
Using brodak buterate dope and then randoph buterate tautening dope to see if it would tighten up even a little. Interesting when brushed on 50/50 mix it tightens up while wet and then back to sag when dry. This also happen when I tried the lighter 5mm silk. This was a test panel so I will certainly rip this off and try again with all these suggestions. Note:The last time back in 1970 I was using aero gloss clear dope straight out of the jar.
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DO NOT USE THINNER AND HAIR DRYER UNLESS YOU WANT A FIRE
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Huh. i must not be doing it right
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Ty, when I lived in southern Missouri, I asked Dad if we were pronouncing it right, he stated, "It depends if you live in the southern half or the northern half". So I learned to say it like Missouree. It became Missourah when I moved back to the KC area. But I still hear pronounced both ways. LL~ LL~
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Darwin, just curious, but how high was the humidity when you applied the dope to the silk?. This will cause it to act like yours. I guess you need to set it in that famous Kansas sun and wind for a day so it will shrink tight. Just be sure to anchor it so it does not end up in Missourah D>K LL~ LL~( I lived in St Louis for 17 years and never did understand how pronounce it so every one was happy) D>K
I considered the humidity low. Been very dry around here these day's. Tried re coating with just thinner and then more dope outside in garage and indoors air conditioned with no difference. Tightens up when I use heat gun then sags out when cooled.
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Sounds like you got ripped off on the silk. Even poly-ester cloth tightens up after a while.
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This is a mystery! You pulled the wet silk tight. It was tight when dry. Brodak clear?
The first couple coats might look awful! ---Until about 1 hour, when it usually (always) tightens up again. After a couple of brushed coats, I begin spraying clear. It doesn't get loose after the first couple coats.
Silk expands when wet. So that even when dried out, you can still wet it again and it will expand the same amount. So it isn't a matter of a "one time shrink" situation.
It isn't necessary to pull the wet silk really tight, but it does make a nicer job of it.
(Just thought: I always give the wood frame 3 or 4 coats of clear so that the silk will stick well).
F.C.
I've used silk from Thai Silks in (Los Altos, CA) with good results.
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Keep in mind silk/silkspan does not actually shrink much. Wetting it relaxes it and you pull the wrinkles out and when it dries it goes back to original shape and seems that it shrunk.
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Keep in mind silk/silkspan does not actually shrink much. Wetting it relaxes it and you pull the wrinkles out and when it dries it goes back to original shape and seems that it shrunk.
I applied the silk to the Gee Bee Z fuselage, rudder, stab and elevators dry. I pulled it tight as I went along, actually used CA to hold it in place.
Some coats of dope later and no wrinkles.
I might try a whole wing that way.
Charles