dmcmike

My Feedback: (14)

ok, now i'm po'd! everything looked great after I had put the silk on. It went on wet.. doped around the edges, and shrunk up great. Now I put thinned clear on, and it relaxed like mad... hmm.. makes me wonder about the silk. any thoughts? I know BobHH said that it took about 5 coats to 'start to shrink up', but if I have to put that much on, it'll weigh a ton. I'm going to give Brodak a call in the morning, see if he's got any ideas. Chip_Mull, check yer email.. I'm about ready to round file this silk! this might turn into the 'Silk and Dopey thread!'... just might have to give the Stits stuff a try after all!

Jim Thomerson

I have never had any problem with the Esaki type silk not shrinking. It is much thinner and perhaps more open. The first coat of thinned dope leaves numerous 'pinholes". I think the Thai silk may seal much easier. On another forum someone suggested that thinner fumes are trapped inside the wing and the dope thus takes a long time to completely dry and shrink. I've not used Brodak dope and have no idea how much it shrinks. On structures of any size I make holes between sections and make them open to the outside someplace. My idea being when the airplane sits in the sun and heats up inside, the hot air can get out. Same would be true for thinner fumes.

Phlip

I've not used silk, but I've had the same thing happen with silkspan ... and time did the trick. Perhaps Jim's idea that thinner fumes trapped inside might be the problem is correct, adding to the drying time. Once the first coat dried and it shrunk up, subsequent coats weren't as bad.

Don't be too worried 'til you've slept on it.

Phil

LesUyeda

MCMike: Take a deep breath, relax, have a tall one, and wait. The only thing you need to worry about is sag to the extent that it sticks to places you don't want it to. If your dope was non-taughtening, it will take longer. It is really time, not the number of coats. I seldom use more than 2, and then spot touch up where the silk has not completely sealed.

Les

dmcmike

My Feedback: (14)

thanks for the encouragement Les... I did some research on some of my other covering options. I've used super coverite in the past, and really liked it, but it seems to be on perpetual backorder. After reading about many of the poly coverings, I decided to give the Stits system a shot, and ordered the fabric and their adhesive today. I'm going to leave one of my elevators covered with the silk for the time being, just to see if it does shrink up. Still planning on using the Brodak Dope for the final finishing since i've already got some $$$ in it. Hopefully, I can find something to do with 10 yards of silk. I haven't totally given up on the silk, and think that i might need to use a different dope, i.e. nitrate, for the first couple of coats in order to get it to shrink up properly

Now, I'll just wait until the Stits fabric gets here... and yes, i'll probably have several 'tall ones!'

stay tuned, this is gonna get interesting!

mcmike

BobHH

My Feedback: (18)

mcmike, sorry to hear you had the same problem. I just finished up a little single channel pulser with the Esaki silk and everything tightened up great with the Sig butyrate clear. I only us nitrate on the small balsa surfaces where I don't want any shrinking thus no warping. I seal everything after wards with Lustracoat clear. Seems to hold up to the 35% nitro well.

As for pre-washing the silk I may try that sometime. Again mine did tighten up after a few more coats. I did try an experiment on 2 identical wings. I used the Esaki on one wing and the Tai on another. After close weighing both came out within 1.5 oz difference than the other. The Esaki took some heavy doping to seal the weave. I use a foam brush for clearing and it seems to fill the weave a bit better. Why not try a few more coats on one of the elevators and see if it will tighen up.

I have been covering with silk too for a long time. From tiny 1/2A to giant scale. I believe silk properly applied has great strength. We even use to silk the bottom of our Quickie 500 wing years ago for the added strength. Some guys would even lay them between chair and sit on them to show the strength!!

Bob Harris

LesUyeda

MCMike: Do not dispair. You will not get the same "look" out of heat shrink, as you do with silk and dope. The heat shrink will stay tangent to the surfaces, and not wrap in around the corners, and the material itself is heavier.

I went to great troubles to build a DR-1 Fin/rudder out of aluminum tubing, just like the real one. I used what was then Super Coverite, and found that I had wasted my time. I might as well used a flat piece of balsa and rounded the edges. Super Coverite was great stuff until the EPA got ahold of it. They reformulated, and have never gotten it right.

The pics are blue Thai silk. No wrinkles (except one little corner). I use nitrate dope on all that the silk will touch, until I get a slight gloss. Then I know the contact areas will not leach dope from the final application. Wet the silk and attach the perimeter with nitrate. Let dry. Take a heavier mix of taughtening nitrate and apply two coats, letting dry in between. I go back and touch up anything that has not sealed. Then I am ready for color. The white trim is butyrate. You can tell by the lack of gloss that I really don't have that much dope on this silk, and it is obviously shrunken up nicely.

My clear is Randolph, and the white was Certified. Brodak gets their dope from Randolph.

Hang in there MCMike.

Les

p.s. The red wing in the background is also Thai silk. The wrinkle on the wingtip is from a crash.

dmcmike

My Feedback: (14)

I probably ought to start a new thread, since I've decided to forgo the 'silk & dope' and have gone over to the 'Stits & Dope' approach! I ordered 6 yards of Stits covering and the Poly-tak to apply it from F&M (thanks Chip!), which arrived yesterday. After a thorough search through Wally world, Menards, and a couple of other paint and hardware stores, I finally managed to find a quart of MEK, which is needed to thin the Poly-tak adhesive for the covering. I started this afternoon (yeah, I took off from work a bit 'early') by covering one of the elevators, just to see how things would go. The instructions available on-line, and packaged with the materials, spell things out very well. I thinned a small amount of Poly-tak with a brushful or two of MEK, just so it was brushable. Brush about 8" along the edge of the frame to be covered, and apply the covering, working the poly-tak up through the weave. You've got to work in small increments, because the adhesive dries pretty quickly. I trusted the directions, and didn't have to pull the covering super tight, just basically smoothed it out. Once I got the top and bottom of the elevator covered, I got out the trust covering iron, checked the temp with an infra-red meter just to verify a 250d setting, and shrank up the covering. Nice! so far so good. After debating about what to do next, I decided to give Chip a call at F&M just to make sure that it was ok to use the Brodak Butyrate that I had already purchased to seal and finish the Stits product. He gave me the go ahead, saying that if you start with a specific product, to stay with it. So now I've got a direction to go. Went around the edges with a rag wet down with MEK, just to get some of the excess Poly-tak off of the cloth, but not enough to pull it loose. Then I put on the first coat of brodak clear, thinned about 40% dope to 60% thinner, and applied it to the covering. Well, so far, things are looking much better than the previous result. No sagging, just a nice, taught covering! I've still got a little bit of sanding that I need to do before I get much more of the covering on, but I'll be taking more pics and posting them.

If anyone has any doubts about the Stits system, i'd like to squish 'em like a bug right now! This stuff is nice! I compared the weight to the silk I had purchased, and while the Stits may be slightly (very slightly) heavier than the silk, I sure can't tell. If I can get access to a precision scale, I'll weigh a yard of silk versus a yard of Stits, just for hoots and giggles, and let everyone know. I'm thinking that in the end, the Stits may even turn out to be a bit lighter, since not as many coats of clear will be needed to get it to shrink tight, just enough to fill the weave.

Anyways, here's some pics of my results so far...

FrancisPerson

I have had good luck with Aerodyne dope http://www.freeflightmodels.com/

Francis

LesUyeda

MCMike. I'm sorry that you gave up on the silk/dope, but I am happy for you that you found something you could be happy with.

I used some Koverall once upon a time (very similar to the Stits method) and swore that for the work involved, I would go back to silk.

Les

dmcmike

My Feedback: (14)

I'm finding that it's very similar to Koverall too. I wouldn't say i've given up on the silk, yet. I've got an old Dively kit of a Skybolt that i'll probably try it on again, only make sure I get some dope that will shrink! I think that's the problem. I think if I go to a shrinking nitrate for the base and first couple of critical coats, it'll be ok. So far, this Stits covering is going pretty quickly, and is actually pretty easy to do.