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Building Tips and technical articles. => Building techniques => Topic started by: Bill Little on January 29, 2007, 08:12:49 PM
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HI All,
Has anyone used Poly Span over the "kept foam" wing system?
I do not have any iron on covering, haven't used any in over 15 years. I have been given a set of wing panels which have the LE, TE, center section, and cap strips applied to the foam. I need to cover this! I am worried about a dope finish going through the poly span and getting to the foam.
TIA
Bill <><
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Bill, I have used polyspan on several stunters with Foam wings and constructed as you suggest. No problems whatsoever.
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Bill, I have used polyspan on several stunters with Foam wings and constructed as you suggest. No problems whatsoever.
Hi Keith,
Anything "special" you did the keep the clear dope from attacking the foam over the "open bays"??
Thanks!
Bill <><
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Bill,
Check your mail.
Roger
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Bill,
Check your mail.
Roger
;D
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Hello all.
Iīve used silkspan and dope, no problem at all, really donīt concern about silkspan "sagging" and touching foam, final reslult was 100% OK.
Regards.
Manuel.
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HI All,
Has anyone used Poly Span over the "kept foam" wing system?
TIA
Bill <><
Bill,
In my experience, the dope WILL attack the foam, but not to an amount that is significant. I built a Dixon "StuntWagon" which uses the 'kept foam' technique.
As you apply the first few coats of dope, look carefully and you will see a change in the *texture* of the foam directly under the open bays. Some vapor from the dope is trapped in that small cavity between the Polyspan and the foam core, but the volume is small, and the reaction with the foam is very minor.
As subsequent layers of dope are applied, eventually this reaction will diminish and stop as the Polyspan is filled. If I were to venture a guess as to how much foam was "melted" I would say probably 1/32" to 1/16", not enough to effect the structural strength of the wing.
I believe that it was Todd Lee that had this situation cause a failure of his "Mustang" wing, but in his case, he had removed much of the foam between the capstrips, which left a large void that could contain a large volume of dope vapor, and consequently, a major damage to the remaining foam and an ultimate failure. If I don't have all those facts right, please someone feel free to correct me.
Go for it, Bill.
Cheers,
Warren Wagner
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Warren,
While it wont help while doping (unless you hook up purge system n~) , I mentioned (to Bill) drilling a small vent hole in the foam, before covering, through to the "cored area", in each bay, that will provide a vent path for the trapped air. This prevents the covering from "bulging outward" when the trapped air expands in hot weather.
Roger
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There was a thread recently about PolyCrylic being useful for applying silkspan to open frameworks, and this would be a great use, IMO. #233436 is the topic number, on ~~> another forum... f~ the one that deletes posts with mention of this forum, in fact. (051) Steve
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Since your original post mentioned Polyspan, I will address that avenue. I have had some luck using Balsarite to Iron on the polyspan instead of using dope. Just make sure you dont have any scratchs in the surface of your iron, and a sock really doesnt work to well, both tend to snag the fibers in the Polyspan causing some fuzz issues.
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I' considering doing exactly what is this described here. Using Polyspan on a foam core wing with balsa LE, TE and capstrips. I plan to use Butyrate clear dope. If the thinner "relieves the foam in the open bays, so be it.
My main convern is the buildup of mass if I go ahead and put colour dope on the whole wing, in lieu of the more traditional Super MonoKote.
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I wonder; if you first painted the foam with a coat of thinned down Titebond, would that protect it from the dope fumes?
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I wonder; if you first painted the foam with a coat of thinned down Titebond, would that protect it from the dope fumes?
HI Jim,
That is an interesting idea! I was more concerned with the dope actually contacting the foam, but it seems I should be more concerned withthe fumes. (??) I am going ahead and seeing what happens, and I wil use some type of "blocking" coat on the foam.
I have used polycrylic and wasn't totally satisfied with the results. Maybe it would protect foam. Titebond is an idea.
Bill <><
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Hi Bill; That is what the R/C guys used to use, when they still built their planes. Thinned Titebond works very well to seal the foam from dope. If I remember right, I used this method on a small R/C bipe, and painted right on the foam after sealing it with the thinned Titebond.
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Hi Bill,
Man-o-man, is this timely! I came on today to post this very same question and here are some answers before I even start. I'll take all this in consideration, but do have a concern about the added weight of thinned Titebond as a sealer.
Have any of you guys compared the before and after weights of using this method? Also, it's been five airplanes since using polyspan, where's the best place to buy it now?
Thanks guys, you're way ahead of me1
Will Z@@ZZZ n~
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Hi Bill,
Man-o-man, is this timely! I came on today to post this very same question and here are some answers before I even start. I'll take all this in consideration, but do have a concern about the added weight of thinned Titebond as a sealer.
Have any of you guys compared the before and after weights of using this method? Also, it's been five airplanes since using polyspan, where's the best place to buy it now?
Thanks guys, you're way ahead of me1
Will Z@@ZZZ n~
Hi Will,
I hope all is well with you!
Tom Morris still handles the Polyspan. I think Control Line Central does, too. ???
What are you working on?
Bill <><
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Thanks Bill,
I typed out a reply and then forgot to post it - just another sign of mental rogor mortis setting in! I wrestled for a long time with what semi-scale ship to build for my new PA75 but finally settled on building another Ephesian! That was my old twin boomer; 710 squares, 72 oz on a VF46/pipe. It flew great, even at that weight, and this one has a LOT of changes to improve the handling and keep the weight down. y1
My health has improved greatly, PTL, and I'm looking forward to a good season!
Blessings,
Will