I just finished a 1/3 scale biplane. I attached the koverall with nitrate dope and followed it up with 3 more coats over the whole plane. After priming (no pinholes), I painted it a dark camo scheme. Everything looks great inside the shop. I went to the field today and put it in the sun to run the motor. Much to my dismay... the open bays sagged. I thought it was the dark paint job. I even cut a hole in one of the cockpit floors to let the heat escape.. As soon as I take it out of the sun.... everything tightens up again... What gives with this? I thought Koverall gets better and tighter with age? Please make sense of this for me

The first thing that comes to my mind is the tightness of the covering prior to paint. Did you heat shrink the Koverall prior to your sealing coats of dope? Koverall shrinks drum tight and having used it on everything from a .10 size plane through giant scale I have never seen it sag regardless of the weather. My planes have seen all kinds of extremes from sitting in my freezing cold trailer to sitting in the sun in 95 degree heat with 90% humidity and Koverall is the only material I have seen that doesn't sag or wrinkle. I love the stuff.

If you did neglect to shrink it you may be able to shrink it still just be careful not to damage the paint with the heat.

Brian

Thanks Brian. I used a heat gun and then an iron before doping the weave. After doping, I tapped on it like a drum with a pencil lightly. I remember saying to myself "tight as a drum". I let the dope sit for a week before scuffing it for primer

You should never use a heat gun to shrink polyester fabric. Always use a calibrated iron. The 21st Century iron has temp marks on it but should still be checked the first time. Polyester fabric shrinks 5 per cent at 250 degrees F and 10 to 12 per cent at 350 degrees F. At about 400 degrees it begins to lose its memory. At 426 it melts. With a heat gun, you never know what temp you actually hit. Yes it shrinks but how much?

Check out http://www.stits.com/RC_Model_instru...html#shrinking for a summary on heat shrinking fabric.

The dope sold now days shrinks very little unless you specify "Tautening" dope. We rarely use tautening dope because it doesn't chemically bond and as it tightens it may pull away from the polyester fabric. I know following posts will deny that has happened in 75 years of modeling. Mostly because we used to use silk and dope or silkspan which we depended on the dope to shrink and tauten for us. When full scale switched to polyester fabric we found out it doesn't chemically bond hence the need for Nitrate dope first. Then, Ray Stits came along and gave us a system that all chemically bonds from start to finish and dope faded into a barely used method. Only the "I have used dope for 50 years and never had a problem" guys are the only ones that use dope. We are now into the 21st Century and have some vastly improved techniques.

If you shrunk your covering, then I am not sure what the problem could be. I have never heard of this happening before. I have always used a heat gun for the majority of the shrinking on Koverall and have never experienced a problem with a loss of fabric "memory". This may be a problem related more to 21st Century Fabric, which I was NEVER able to shrink as tightly as Koverall. It would always sag and wrinkle horribly. I also doubt your dope is a problem. Since we use heat to shrink the Koverall rather than dope the fabric should already be tight before the dope is applied. The dope simply seals the fabric for primer and paint.

I have never used the Stits system so I can't say whether it is a better way or not, but that wasn't the info you were seeking either. I use plain ol' Sig Nitrate dope which is non-shrinking. I hope you get the problem worked out. I wish I could tell you what caused this but that is a new one for me.

Brian

I think you are right Brian. I've never experienced this before either. I always thought that the dope "locks" in the Koverall once shrunk. I really dislike iron on coverings as it bubbles and sags (for me at least). This is a first. I really can't see why heat from the sun loosens the tightness.

I can place my hand on the covering in the sun.... I mean it dosn't burn my hand and make me want to pull it away...Its hot mind you but not 400 degree hot. When I cut that hole in the cockpit floor, I did feel the heat that was trapped inside.

When she is brought in the shade, you can actually watch the sags go away in a few moments

Zpainter as Chip Mull said it is risky to use a heat gun on polyester as there is the chance of overheating areas in the fabric. Once that happens the fabric in that area will relax no matter what and allow the taut areas around it to wrinkle.

I have noticed from time to time that polyester will shrink when cooled and do as you have described when it heats.
I have also noticed that even though the new non taut dope formulas shrink very little that over a period of 60 to 90 days the fabric does get tighter and the wrinkles fade away.
Disappointing though it may be right now, I would wait for a couple of months before I tried anything drastic.
For the modeler Koverall is still a great product and is usually happy with just about anything that you put on it.
The one thing that I would have done is use Stixit rather than Nitrate to attach it as it has non tendency to soften when sucessive coats of nitrate have been applied allowing the fabric to creep.

Thanks Gremlin Castle. I really did not use the heat gun all that much except in the beginning to shrink the inside of the perimeter. I did not "lay into it" and heat the living hell out of it either. I followed up with a new iron at 350, and then doped the fabric down to the wood and followed up with 3 caots overall. But I am glad you have seen this before as I have not. I brought the wing outside today and put it in the sun. I have not done this since I finished painting it. Well the wing wrinkled not 10 seconds later. I felt it and was hot, but then all of a sudden it started tighening up again. I brought it in the shop and went for my camera. as I would have posted a picture. When I did the "experiment" again....... The wing did not wrinkle but the fuse did. I sure hope that wing stays that way

I sure am hopeful that this might resove itself in a month or 2 like you said. I've been at this bipe for 6 months and the season is now

I have an update. After the experience with the heat of the sun and how the Koverall first expanded and sagged, and then tightening back up somewhat. I went back to the shop and pulled out my heatgun. I heated the Koverall and worked the gun, going over spots that had sagged before. I worked over those areas good! Everything tightened up. Today I brought it outside and left it in the sun. I was happy with the results........no wrinkle or sloppy covering! I am going to maiden on Thursday. If problems occur with the covering I will post again.......so no news is good news

This hobby is Bi-polar, but I do enjoy it so

the koverall needs to be heat shrunk and tighten up before filling the weave with anything, I used a heating iron on med heat ran longways from bay to bay.stayed taut all through filling the weave and paint.

I love Sig Koverall and use it up to 1/4 scale. Just follow the factory instructions.For 1/3 scale and up, I use polyester dress lining from JoAnn fabrics, it's very similar to koverall, but a slightly heavier weave.Iron only to shrink the fabric - no heat guns allowed.Fill the weave with dope,modgepodge,polycrylic minwax, Lustrekote paint sticks to it great!Happy doping! John R.

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