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Old Jun 16, 2009, 08:58 PM
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Question
Should I Seal a Balsa Airplane frame ?

I am at a point where I could seal my airframe and not worry about moisture warpage. But I do not know if I really need to seal up the frame to keep it dry from humidity.
I am considering a light coat of Varathane to seal it. The covering will seal the outside, I am talking about the inside of the fuse and wings.

CH
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Old Jun 16, 2009, 09:08 PM
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Quote:
Originally Posted by Chophop
I am at a point where I could seal my airframe and not worry about moisture warpage. But I do not know if I really need to seal up the frame to keep it dry from humidity.
I am considering a light coat of Varathane to seal it. The covering will seal the outside, I am talking about the inside of the fuse and wings.

CH
It's been my experience with wood working that a light coat of anything doesn't prevent moisture penetration in wood. It usually takes several applications of a fairly thick outer coating (paint, sealer, varnish, etc) to prevent moisture from working itself into the wood.

Just my observations

Chuck
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Old Jun 16, 2009, 09:22 PM
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Is the weight worth it ?

CH
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Old Jun 16, 2009, 09:28 PM
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?Hey now,
Not if you're going to use varathane. Way too heavy. you could however use nitrate dope, hader to find these days, but very light and moisture resistant.
Of course if you don't live in a swamp or fly in fog all the time you shouldn't really need it.
RobII
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Old Jun 16, 2009, 10:20 PM
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It's sort of foggy and misty in the mornings here from spring through mid July. That's why I asked. I remember seeing some models at the club that were sealed with something, sort of yellowish.

CH
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Old Jun 16, 2009, 10:24 PM
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As long as you let the plane sit after each flight then you shouldn't need any coatings. I've flown my MM Slipso sport pylon racer, uncovered/unglassed (bare balsa frame) in fog just about each time I flew it (30 times or so) and didn't notice any rotting or anything.
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Old Jun 16, 2009, 10:34 PM
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A month or so back, I flew my Lil'Squirt over wet lawns, and moisture from the grass got into the balsa. There was clearly some deformation of the balsa as a result -- mostly in the spars and top surface of one of the wings.

Most of the bending went away when the wood dried, but some remains. It hasn't affected the plane's performance, as far as I can tell. If I wanted this plane to look perfect and stay that way, I might have sealed it, but then again, that would have added weight. Lightness is more important than good looks.
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Old Jun 16, 2009, 10:51 PM
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Quote:
Originally Posted by Chophop
Is the weight worth it ?

CH
Generally no, its not worth the weight.

There have been 40 to 70 year old models found stored in attics with good frameworks. Usually the ancient tissue-dope or silk-dope covering has shattered.

I have seen some 25+ year old monokote covered planes that the structure was fine, but usually the covering has turned brittle when its that old.

You are practically guaranteed for the "shelf paper" grade ARF covering to have shrunk and become very brittle after 15 years. Sometimes as little as 2 years...

It doesn't take much attention to storage for the wood structure to survive a LONG time. Just don't let it get wet. The covering will be the first thing to fail if there's been no fuel soaking.

Humidity changes that don't produce mold generally don't do damage to balsa. Might warp the frame a bit but you can steam it straight.

*********************

That lil Squirt can easilly be steamed straight again.
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Old Jun 17, 2009, 04:47 AM
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Wet warping the fuselage sheeting got me concerned. Sounds like most people do not see a problem with bare internal balsa.

CH
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Old Jun 17, 2009, 06:27 AM
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This old sucker is 44 yrs old and is as straight now as it was when I built it. Top Flite Hustler.

Gord.
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Old Jun 17, 2009, 10:46 AM
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This old sucker is 44 yrs old and is as straight now as it was when I built it. Top Flite Hustler.

Gord.
Nice

How many re-coverings?
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Old Jun 17, 2009, 11:22 AM
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If I'm covering with tissue, silk, polyspan or litespan, I give the frame work a couple or three coats of clear dope. I use Sig Lite-coat.

If I'm covering with any kind of plastic film I do not dope anything (except around the engine where you might want fuel proofing).

I've never had too much trouble with warping afet the plane was completed. I live in S.E. Michigan. We don't get the kind of humidity that some places do but it sure isn't dry around here either!
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Old Jun 17, 2009, 05:51 PM
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Up until about 15 yrs ago, the Hustler was covered with Silkspan and dope, then covered with Monocote. K&B 21 DF motor up front. I should electrify it.
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Old Jun 18, 2009, 04:33 AM
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Wood needs to 'breathe' so just concentrate on getting a good covering on the outside with no gaps to let moisture in. If you seal both the inside AND outside then if any moisture does get in it has no means of drying out and it will rot the wood...saw many a wooden model boat hull which had been sealed inside and out suffer in this way.

Steve
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Old Jun 18, 2009, 05:33 AM
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It's been about 80*F lately, so I'm building it with the window open and under the average humidity. So maybe in winter when it dries up some, it may shift some, but the gamble is on it returning to where it was in summer.

CH
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