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Old Sep 27, 2012, 06:49 PM
Be the duck. Whaaaa?
UberZogster's Avatar
United States, CA, Guerneville
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Covering

I decided to bring this question over here because I figure I might get more answers.

I am currently covering a plane for the first time and ran into something that I wasn't expecting. When I tried to shrink the covering it turned my part into a rudder shaped balloon. The covering tutorial over in Builders Workshop says to drill vent holes in your ribs and somewhere to the outside. Okay that makes sense, the glue is off gassing when heated causing the covering to balloon and the holes allow the gas to escape.

While thinking about drilling holes in ribs and other parts to allow venting I thought about the fact that people act like your glider is going to break when you put pins through the parts while assembling. So why would it not be okay to stick pins in parts and be okay to drill holes for venting? Assuming everyone doesn't drill holes what do you do to prevent airplane shaped balloons?
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Old Sep 27, 2012, 07:04 PM
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This doesn't seem to happen to me. Perhaps you build more carefully and there are less gaps to let the air out! A pin may split the wood, a reasonable drill is less likely to. I suspect if you put a pin through the middle of the rib, where it's nice and wide, you won't get splits. If you put it near an edge, you may have problems. It's still a good idea to avoid high stress areas when you are making holes. Not always obvious which are the low stress areas, I'll admit.

You can put pinholes in the covering when you get bubbles that form over sheeted areas. This will happen less if you use low heat to stick the covering down first.

I don't think the glue off-gasses very much, I think the air inside gets hot and expands.
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Old Sep 27, 2012, 07:28 PM
Brett
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Never had that happen to me either. Could it be that you have the iron set to high? What brand covering are you using?
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Old Sep 27, 2012, 07:30 PM
Be the duck. Whaaaa?
UberZogster's Avatar
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I am using Monokote and I have my iron set to 275F as the paper instructs.
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Old Sep 27, 2012, 07:39 PM
Brett
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The weird thing is, if the covering is puff out like a balloon that kinda implies it's not actually shrinking.
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Old Sep 27, 2012, 08:23 PM
Be the duck. Whaaaa?
UberZogster's Avatar
United States, CA, Guerneville
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When it completely cools it is a tad tighter than it was but nothing like you would actually want it. I poked holes (with a pin) in the rudder covering and it kinda shrunk but nothing even close to "drum tight". It also has a ton of wrinkles, definitely not something to be proud of .
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Old Sep 27, 2012, 09:03 PM
Brett
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Dumb question, but did you remember to peel off the backing?
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Old Sep 27, 2012, 09:09 PM
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I said this didn't happen to me, but I've seen hints of it, a little minor puffing that goes down, leaving the covering tight.

With the wrinkles, it often helps to pull out all the edges as tight as you can and stick down with low heat before shrinking. When you shrink, use a lot of heat. Almost enough to melt the stuff if you leave the iron in one place for too long. If it folds over itself, you may need to replace that part.

I have heard bad things about recent Monokote, but have not experienced it myself as I have many rolls of the old stuff around. Consensus seems to favor Ultrakote. But I wouldn' t give up just yet if I were you.

BTW, long ago I covered part of a model with the backing left on. It can be done, but it's not easy. And I don't remember it puffing.
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Old Sep 27, 2012, 09:30 PM
Be the duck. Whaaaa?
UberZogster's Avatar
United States, CA, Guerneville
Joined Mar 2012
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I did remember to take the backing off. As for the wrinkles I did have the covering tight with a couple (2) large wrinkles. Now it has a ton of small wrinkles. Humm I wonder if I'm just not using enough heat.

I'm working on the wing now so we will see what happens .
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Old Sep 27, 2012, 09:37 PM
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Quote:
Originally Posted by UberZogster View Post
I decided to bring this question over here because I figure I might get more answers.

I am currently covering a plane for the first time and ran into something that I wasn't expecting. When I tried to shrink the covering it turned my part into a rudder shaped balloon. The covering tutorial over in Builders Workshop says to drill vent holes in your ribs and somewhere to the outside. Okay that makes sense, the glue is off gassing when heated causing the covering to balloon and the holes allow the gas to escape.

While thinking about drilling holes in ribs and other parts to allow venting I thought about the fact that people act like your glider is going to break when you put pins through the parts while assembling. So why would it not be okay to stick pins in parts and be okay to drill holes for venting? Assuming everyone doesn't drill holes what do you do to prevent airplane shaped balloons?
After the wing is covered, but before shrinking the open areas, I like to take a pin and make one hole through the covering on the open structure, usually where the rib meets the trailing edge next to each rib.

So, each covered bay (that is possibly sealed tight) is given a single pin hole. Then there will be no balooning.

Craig
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Old Sep 27, 2012, 10:31 PM
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Monokote can take a lot of heat, and will shrink quite a bit more as you go up in temperature. Turning the iron up to 350 is not a problem and will usually get any stubborn wrinkles out of an open structure. For solid surfaces it's best to either iron it on at a lower temperature to avoid bubbles, or only iron the edges and use a heat gun for everywhere else.

Jim
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Old Sep 27, 2012, 10:39 PM
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Quote:
Originally Posted by lincoln View Post
I don't think the glue off-gasses very much, I think the air inside gets hot and expands.
The good news there would be that once the air cools down, the rudder shaped balloon problem will be gone, and instead you'll have a saggy covering job.

Jim
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Old Sep 27, 2012, 10:45 PM
Be the duck. Whaaaa?
UberZogster's Avatar
United States, CA, Guerneville
Joined Mar 2012
312 Posts
Quote:
Originally Posted by craigrrr View Post
After the wing is covered, but before shrinking the open areas, I like to take a pin and make one hole through the covering on the open structure, usually where the rib meets the trailing edge next to each rib.

So, each covered bay (that is possibly sealed tight) is given a single pin hole. Then there will be no balooning.

Craig
That sounds exactly like what I ended up doing on the rudder, except I made a hole on both sides.

Quote:
Originally Posted by GliderJim View Post
The good news there would be that once the air cools down, the rudder shaped balloon problem will be gone, and instead you'll have a saggy covering job.

Jim
I think it is mostly the air expanding as it does (mostly) go back down. Yes it does end up with a saggy covering.
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Old Sep 28, 2012, 12:25 AM
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Uberz brought this question over here because very few people on the Electric sailplane forum have little building skill's.
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Old Sep 28, 2012, 11:31 AM
Be the duck. Whaaaa?
UberZogster's Avatar
United States, CA, Guerneville
Joined Mar 2012
312 Posts
Was this on the electric forum as well? I actually felt that there are more people here than the builders workshop where the covering for beginners thread is.
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