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Building Tips and technical articles. => Paint and finishing => Topic started by: Dennis Toth on August 29, 2012, 05:42:41 PM
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Guys,
I intend to use the silk on my new El Diablo and had a question about doping the covering so that it won't loosen in the sun. I have seen some painted surfaces loosen like monokote. Any ideas how to avoid the loosen?
Best, DennisT
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If in doubt, cover the plane with a white towel. H^^
Wouldn't covering it with a towel make it Really Heavy? Particularly after you put the dope on all that terry cloth? And besides, towels are cotton, not silk.
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Some of that aluminized mylar insulation would be way better than a white towel, since it's lighter, won't tend to induce warps, fuel/oil presidue can be easily removed,....and it doesn't take any dope to fill the weave. S?P Steve
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what you REALLY need is a true genuine retro "space blanket" like you could get in the 60's,, that would do the job nicely,, not to mention the chance that the "accidental " glare off it might blind your competition,, just sayin,, S?P H^^
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Like Ty said if done correct it will stay tight. The problem is many people skip the one step that is needed. Unless you have some 40 year old silk you need to wrinse it out in water. All silk make has a compound added that stops proper shrinking. It goes on tight but then gets loose when dope is applied and takes a long time to tighten up. Just wetting the silk will not get the compound out. I call it a conpound as I do not know what it is.
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I've been using Dharma silk and have never washed it. Just cut to size and put it on. Haven't had any problems of it loosening.
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Will nitrate dope shrink the silk enough? What is the difference between nitrate thinner and butyrate thinner?
Best, DennisT
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Never knew there was a difference in thinners. Of course the hobby shop only carried SIG thinner and I used it in both nitrate and butyrate. Now if there is such a thing as nitrate thinner I would not even try it in butyrate.
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Will nitrate dope shrink the silk enough? What is the difference between nitrate thinner and butyrate thinner?
Best, DennisT
HI Dennis,
While I use a LOT of nitrate, I leave the tautening of silk to high shrink butyrate. Sig Supercoat Clear (not their colors, confusing!) is pretty high shrink and that is all I use it for (shrinking open bays).
BIG Bear
RNMM/AMM
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HI Dennis,While I use a LOT of nitrate, I leave the tautening of silk to high shrink butyrate. Sig Supercoat Clear (not their colors, confusing!) is pretty high shrink and that is all I use it for (shrinking open bays).
BIG BearRNMM/AMM
Bill,
I'm curious, On a typical wing rib spacing, say 2", what amount of silk deflection, on center between the ribs, are you satisfied with?
1/16", 1/32", 1/64", none?
Is there an average measurement that someone expects to get?
Thanks in advance.
Charles
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HI Charles,
I have never heard of anyone measuring that process. I get it as tight as I can and would guess that it might be + - 1/32". Less with silkspan.......... I work extremely hard to get it as tight as I can.
BIG Bear
RNMM/AMM
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Hard to say, but I would guess as much as 1/16 with ribs 3 in apart. Maybe I will actually go measure. The droop is minimized by the usual practice of running the grain spanwise. I have seen in some old, pre WWII, freeflight stuff the advocating of putting the grain chordwise to increase droop between the ribs. No explanation, but at that time they were using fairly thick wings; RAF 32 airfoil was popular. Some designs used multispar wings to minimize the droop around the front of the airfoil, and, perhaps, do some turbulation. I did that on the first Twister I built, two 1/8 square spars, top and bottom, ahead of the main spar. As I recall, the airplane had very little glide.
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OK, so if the butyrate clear (Sig) is the shrink and you are going to use a clear finish - how many coats of butyrate and what do you do so stop it from shrinking forever and either warping the wing or ripping the silk?
Best, DennisT
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I eyeball measured the sag between three inch apart ribs on my Big Fry wing, covered tightly with silk. Toward the front of the airfoil it was 3/32 - 1/8 inch by eye with a straight edge across the ribs.
I have the impression that nitrate pretty much stops shrinking in a day or two, but as said, never completely stops. Butyrate shrinks longer. These days, on silk open bays, I use one or two, as it strikes me, coats of tautening dope and then non tautening from then on. I'm doing mostly transparent finishes, so I want the grain well filled and shiny. I use non tautening on solid surfaces. I've been doing nitrate all the way on diesel airplanes and butyrate all the way on glow airplanes.
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I just silked my Flite Streak using Butrate only. I have no sags or deflections between the ribs greater than 1/16". Some less than that.
I used no tautening dope.
Charles
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Isn't taunting silk illegal? S?P Steve
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You can taunt silk, but be careful, it could be bullying!
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Isn't taunting silk illegal? S?P Steve
Not illegal, but it could come back an haunt you.
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Hi Dennis,
For me to get really tight covering with silk I do put it on wet and stretch it as much as possible. I put the grain span wise.
I use non tautening Nitrate to apply it, it has just always has seemed to stick stuff better than butyrate. I let the silk dry completely. (apply to both sides of the wing [top and bottom] as quickly as possible and keep the first side wet until all is covered)
Then it is 4-5 coats of Sig Supercoat Clear (or equivalent Randolph) and again alternate top, bottom until all have been doped.
Then as much Sig Litecoat (or equivalent Randolph) to fill the weave.
I let all coats dry as much as possible before moving on.
BIG Bear
RNMM/AMM