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General control line discussion => Open Forum => Topic started by: Brian Massey on April 19, 2011, 09:35:34 AM
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I'm completing my second plane covered with silk. The first gave me no issues, this one is. I put the silk on wet, when it dried it pulled up nicely. After about 6 or 7 coats of clear (tauntening) it was fine. Then I sprayed the base white color (non-tautening), about 4 or 5 coats; again the silk is fine.
Then I masked and sprayed some blue trim, none of which was on the silk. Now, the silk has started to "relax" during the night. The past two mornings I've gone to the shop only to find the silk loose and sagging between the ribs. Yesterday I put the plane in the sun all day and by evening much of the loosness had started to pull out; but a night in the shop and it's back.
It's 5mm silk, and an all dope finish.
The nights are down to the low 50's; there is no rain, but the air is damp enough for the lawn to be wet from dew. My first silk plane hangs in the shop with no issues.
Any ideas what might be happening, or what I may have done wrong?
Brian
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I've never had a problem like this. Not to ask the obvious, but did you put the silk on with the thread running spanwise?
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Hi Brian,
This is one for the knowledge books if it gets figured out. Only possibility that I can easily come up with is which way the weave was running when you attached the silk like Larry asked.
Personally, I never had a silk covering job loosen after all that and humidity, etc., around here can be all types of extremes. I will add that I use more "shrinking" dope on silk than on silkspan, probably double the amount. I never use over 4 coats of high shrink on the open bays of silkspan but I will use 6-8 on silk. I use everything thinned 50/50 so it cut that in half if you are using full strength. Mainly because it takes more material to fill silk, and I just got in the habit of using high shrink to fill it. Plus, silkspan pulls tighter as it drys than silk. I do pull the covering material as tight as I can while putting it on, and keep both sides wet while covering. Then put a coat of dope on the opposite side as quickly as possible when filling it with the high shrink.
One thought is to use a heat gun like when using polyspan. Do one bay on the bottom then one on the top, working out from the center. This might help to cure the dope and tighten up the silk. Low temp and work quickly to not cause any charring, etc..
Hope the problem gets solved!
Big Bear
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I've never had a problem like this. Not to ask the obvious, but did you put the silk on with the thread running spanwise?
I did if I got the idea right; I layed out the silk so that the length of the bolt it was cut from is running spanwise on the wing. I repeat, I think I did, or at least I thought I did. Looking at the sags, sure makes me wonder.
Brian
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Matters little, Brian, as long as the hotdogs are running the length of the bun, and not crosswise... 010! Steve
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I had a similar problem on a Sig Twister. Good and tight until a second coat of color, then sag city. I could get itto tighten with a heat gun but as soon asit cooled back to sagging. I finally decided that I failed to get the sizing rinsed out properly. After a couple of years, it will finally hold tight.
Bigiron
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It'll stop doing it in a couple of years when its gassed of completely . ???
Weelll , might take six months .Blankety Butrate on S6 twisted it for 2 years.
Did you put it on WET , / damped with water .to pre - shrink as it dries ?
Definately humidity / dampness related .
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Ive seen it before. It'll go away when it drys out up there. my cuz in sac sez he's afraid he goona grow gills soon if it dont stop raining. In 1961 toshi asked me to enter a Dyna-soar 1/2 a A freeflight ror hin. when we got to willow grove Pa. the humidity was so high the tissue loosened up to the the point it was un flyable. I displayed on the workbench so he could get some exposier that way. Then after people critisized that loose covering. I put it away. Any of the old timers can tell you Toshi matsuda was among the best ever decorators and finshers with just dope and tissue. jim
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Hang it in the house for X time?
Lowest humidity...possibly.
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I use regular taughtening dope and have never seen this problem. This thread confirms you policy. The silk itself does not shrink. You need to have the dope shrink if you want a tight covering job.
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I think if you bring it in the house for a week it will shrink back out like said above. It just takes time. Using a heat gun will take it out, but after a short time it will be back. One thing that does help it seems is to put mine in my van out in the sun for a couple of days. That will generally shrink it up and it will stay shrunk. Dope continues to shrink for a long time. My last 6 planes have been silked completely, and I am still learning. The Dharma, and Thai silk, are a very tight weave, and do need to be pulled pretty tight when putting it on. I thin the first few coats of clear taughtning butyrate about 60 to 70%. That does 2 things. It keeps the blobs to a minimum, and soaks in to the silk for good adhesion.
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Some people know I use Poly-ester material from Cloth World a local store that caters to the ladies that like to sew. I had one plane that the material would not shrink up like it has on other planes. Finally cleaned it up and put four more coats of Clear Brodak Dope thinned to where I could brush it. This was not done in one sitting. A day after the final coat the material was drum tight.
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Last night I put up my Eazy-up in the shop and hung plastic drop cloths on all sides. I put the plane (still on the paint stand) inside and turned on a small space heater. I thought that would "do it". This morning it wasn't as warm in the tent as I thought it would be, and the silk not as tight. Guess I turned it on too low.
Thanks for all the comments, I was ready to give up and just fly it without really finishing it, but now I think I'll go ahead and finish masking and put on the last color hoping that it will pull up eventually.
I'm going to spray some red over parts of the open bays, and then hit it will clear. I'll use tautening clear for the final clear coats. Will that help pull tight even if it's over non-taut color dope??
Thanks again all!
Brian
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Jim Kraft
I was going to suggest the Van/Sun idea but this can raise humidity in some situations, leaving the windows cracked
helps. I keep old Dodge window van and old Suburban for this.
The slower dope curing time in low humidity(house) would be best long term?
My last silk cover job was around 1973 or so.
Crushed the wing on the Sneaker. HB~>
Brian
Let it cure good and tight before adding more paint. This will make it worse.
Heaters usually add humidity air conditioners remove it.(that the water dripping out of unit)
David
Screwing up airplanes for nearly half a century.