Silk Wrinkles

Covered a plane with 5 momme silk (from Thai silks), wet, and it dried with not even the smallest wrinkle anywhere and no warps. Then I put on one coat of Brodak clear thinned 50/50, and it developed severe wrinkling near the leading and trailing edges, and in the tips. The wrinkles run parallel to the ribs. The grain of the silk is parallel to the spars.

First, any clues as to what I did wrong? Second, how do I fix it?
I don't ever remember this happening before, but it has been a few years, you know. Steam, maybe would fix it?

As a solution to your present problem, I guess I would try to brush a little thinner on those areas where it wrinkled and see if I could then pull it out tight. If so, then go back and dope down the leading and trailing edges with a second layer of relatively thick dope, before covering the whole thing. No guarantees, however, that this will work.

After having the same problems last year, I found that I had to recover as a last resort.

To avoid this problem here is an idea for the future. First of all, this isn't my thought, but from a fellow that has been covering airplanes for just about 40 years. He suggested using candle wax or a light colored crayon on ribs that haven't been doped. Use the dope on LE, TE, center section and wingtips.

Apply the wax moderately on the sanded ribs and when the silk shrinks you won't get the wrinkles that you're discribing. Use light coats of dope until the silk is sealed and then you can apply more liberally.

Of course you still have to make sure that the silk didn't slip during the initial application. Like others, I've been there, done that!

Try to have a good day and good luck in removing the wrinkles.

It could have been a variety of things, but one of the main reasons for using cap strips is to help the covering lay over the structure more smoothly AND to allow the covering to stick to the ribs better. Silk is both easier to use than silkspan in certain ways, and a lot harder in others. I like using silk, but in my opinion it does add half again, or even more, labor to the finishing process!

K.

Bill, makes sense and I'll do that next time. To Jake and Leonard, with a little serendipity, it's working.

I tried the thinner, and the silk would not budge. (Remember, my Big, Strong, Handsome wife was holding the other end of the silk when we put it on, and I gave it an over-coat at the leading and trailing edges before doping the bays.)

What did work was the thinner! Even though I could not loosen the panels, the thinner took the wrinkles out like magic. Maybe not completely yet, but I experimented with three bays and a wingtip, and they have stayed taut for two hours now. Bottom line, I don't think the silk ever moved after the application, and this is a materials problem. I'll do the whole wing and see what happens.

Leonard, maybe silkspan next time!

I appreciate your thoughts! I was fortunate to own a fabric covered airplane some years ago and you are right about the stitching to each rib!

I hadn't thought about the billowing of the silk at all, but you brought up a very valid point. Thanks!

LAST EDITED ON Apr-30-01 AT 10:18 PM (EST)

I was thinking the steam iron would be a good thing to try. I would give it a good steaming with YOUR steam iron (surely your strong and handsome wife wouldn't use one!) perhaps followed by a hair dryer treatment. For one thing, steam and heat always will affect a wing, even if temporarily ... and it wouldn't do anything that would prevent any of the other ideas from working. Thinner would be my second thing to try...liberally applied and allowed to dry slowly, or if that didn't work, then over a lightbulb. Something has to work. It sounds to me like there may be some "other" fibers in the silk or maybe Brodak's clear is a low shrink type? You wouldn't have used any retarder or plasticizer? I agree with Jake about waxing the ribs. Don't! Steve

Thanks a lot. I suspected it was a material problem, and thanks for confirming it. I am still not sure whether to leave it on or not. At 6:00 PM tomorrow, I'll have razor blade in hand and make a decision.

Convinced me of one thing, though. This is my last silk plane. It is silkspan forevermore.

(Thanks to Leonard for being polite and not shouting, "If you had listened to me, you wouldn't be in this mess!")

The wingtips did have some of the problem of slippage that Leonard and Jak noted. I am still convinced the rest was due to the silk. The Big, Strong, Handsome Wife suspects some kind of fire retardent as the culprit which has changed silk over the years.

Don't get put off silk too easily, I have used it for years, and will continue to. It is far easier to use on open bay structures than silkspan, especially on compound curves, and more puncture resistant. I quit using silkspan years ago, except for a few cases on sheet surfaces. Are you guys absolutely sure this is a problem with the silk, and not with the butyrate dope?
I have used mostly Aerogloss (which is really an acrylic lacquer) through the years on silk with zero problems of the type you mention.
I tried Sig dope, and had some of the same troubles you mentioned, none with AG. I haven't tried Brodak yet, but I did buy some 5mm Thai silk, and I'll let you all know how it works with the Aerogloss.

I was just checking a silk covered plane the other night and found where fuel has leaked into the wing. I had used Thai-Silk's 5mm on that model and many coats of Brodak's dope.

After finishing the model I added many coats of clear dope and it has baffled me as to why I got a soiled spot. The plane is solid and the leakage area looks like glass. The spot is on the wing planking. I've been scratching my head as to why the problem occurred, until I read your post.

I'll watch for the same problem on the two planes I'm about to cover now. As for the soiled wing on the previous plane, I'll just add a couple of more coats of clear on the leakage spot, just to lessen an increase of fuel soaking before I fly it this year.

Thanks for the tip!

Ed;

The only #3 that I saw on the Thai silks list was a 17mm Shantung silk. Is this the one Joe Wagner is using? Seems kind of heavy....

No retarder. (Well, I did go to school in one of those real short yellow buses.) I did add some steam to the equation, but after some playing around, just used a teakettle.

It looks good for a while, then relapses. Ed's note below may explain all.

C/L folks seem to be wedded to materials and techniques I used forty years ago building airplanes, silk, silkspan, and butyrate dope. Good stuff all, but for 99% of us there are better materials that can turn up a sturdy flyable airplane without the fragility and associated patching of these materials. It seems as if sport builder/flyers have followed the contest stunter techniques when they are inappropriate to their needs. I've been using Polyspan (and I think Model Research Labs sells a 'generic' but identical product) on open-bay wings and stringered fuselage areas on my r/c airplanes very successfully. Nitrate dope to adhere, heat shrink with an iron, and finish to suit. There's no sagging problems and no fiddling with a finish. A few coats of nitrate, colorcoat with Krylon, clearcoat with Lusterkote clear to fuelproof, and done. Sand in between coats as appropriate. The folks who value perfection in finish and are willing to spend a kazillion hours getting it do not need to worry about the topic here, they already have techniques to get what they want. The other 99% of us are better served by a straightforward finish and go fly the airplane. The spun polyester is vastly stronger and more puncture resistant than teabag paper or silk, and suits me nicely. It does not get fuzzy unless the person doing the finish does something silly with sandpaper. Picky perfectionists can fuss about its finishability, but a rattle-can finish atop unwrinkled and unpatched spun polyester looks good to me for my learning machines, and can be relatively quick and straightforward to apply. But again, my opinion.

I am an old Indian.

But thanks for sharing.

I had exactly the same problem you descibed (except using Sig Supercoat Dope). I was about ready to cut it off, but thought I'd throw the wing in the car. Well we had some 70+ degree days here in the Chicaco area (=80+ in the car), and guess what? The covering tightened up right nicely. Took the wing back down into the cold damp basement, and it kept taut. Put some more coats of SuperCoat on the wing, each time bringing it out of the basement to hang upstairs in the house (with temperatures in the 70 degree range)---not too popular with the wife tho.

As regards to the leakage problems described below, I don't see how the fuel is penetrating the dope layer in the first place. I don't look forward to this happening!

We'll see what happens

Razor blade is in the pocket for another day. Wing is in the trunk.

I'll let you know.

Well, I ended up cutting off the silk and putting on silkspan. I now have silk capstrips, whatever that is worth.

Alan -- your "trunk of the car" trick did indeed work. I could have salvaged the covering job with your hint, but it was still a little tacky looking, and I went for the gold.

Leonard and Jake -- Yeah, I lost the wingtips, and maybe some of the bays. These were indeed my errors. Even with silkspan I will be far more careful in the future.

Lessons for All -- Silk ain't what it used to be. This problem was a combination of poor craftsmanship and silk that doesn't behave the way it should. I suppose we could all choose 10 pound per square inch synthetics and be right happy. That darned Leonard, as usual, is on the mark, and silkspan is the best answer for most of us. I don't like the RC alternative covering options.

And I STILL think what you actually had is a dope problem, and not a silk problem. Unless they have changed the DNA on the little suckers that spin the fibres, silk is the same as it has been for uncounted thousands of years. IF there is any "sizing" or treatment added after weaving, that might cause a problem, but the fact that your's shrank tight when first applied tells me it is the dope. I had the same problem with SIG butyrate and silkspan by the way, so don't think you are off the hook with silkspan. I am getting ready to cover a couple models with 5mm Thai silk and Aerogloss, I'll let you know how they come out.

Ya know, covering is just one of those "givens" that separates the modelers from the rest of the world. I was more than a little embarrassed to tell this tale. Make sure you tell me the end of your story with the 5mm silk and Aerogloss. Hard to believe it is a Brodak dope failure, but I try to keep an open mind. Something other than my skill was involved. I freely admit to skill problems on the tips, but the between bay wrinkles are still a mystery, and related to some of the materials involved.

Oh yeah, the silkspan is perfect, no wrinkles, and it looks like a sheet of glass with just one coat of clear. Please follow up, as I would like to do some more silk on another project, but for now I am "scairt".