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Author Topic: Polyspan and dope over fiberglass/epoxy wing  (Read 1520 times)

Offline Mike Callas

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Polyspan and dope over fiberglass/epoxy wing
« on: October 25, 2011, 01:13:00 PM »
Can I apply polyspan with dope over a wing that has some fiberglass cloth reinforcing the center section??
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Offline Tim Wescott

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #1 on: October 25, 2011, 01:24:58 PM »
I would thing that, first, polyspan and dope over fiberglass is redundant from a strength standpoint, and second, that dope may not stick well to epoxy.

So I guess the real answer is that it won't make much difference one way or another, unless the glassed section extends outside of the fuselage (as if, for instance, it's a profile plane).
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Offline Mike Callas

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #2 on: October 25, 2011, 02:42:04 PM »
Quote from: Tim Wescott on October 25, 2011, 01:24:58 PM
I would thing that, first, polyspan and dope over fiberglass is redundant from a strength standpoint, and second, that dope may not stick well to epoxy.

So I guess the real answer is that it won't make much difference one way or another, unless the glassed section extends outside of the fuselage (as if, for instance, it's a profile plane).

Tim,
That was my initial concern. Should I dope on the fiberglass cloth instead of epoxy?
And yes, it is a profile racer called a Super fly. It is a Dave Braun, not Curtis Mayfield design

Thanks

Mike
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Offline Tim Wescott

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #3 on: October 25, 2011, 02:48:20 PM »
First: take what I say with a grain of salt; I'm guessing.

Second: Your best bet would be if there were a primer out there that would stick to the epoxy, and offer a surface to which the dope would stick.  Second best would be to sand the epoxy/glass with fairly rough paper (100 dry) so that it's smooth but has a lot of "tooth" that the dope will stick OK.

But if someone who actually has mileage with this would speak up, that'd be nice!
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Offline Allan Perret

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #4 on: October 25, 2011, 04:12:45 PM »
Yes it would be better to use dope for the glass if you are going to follow with dope and polyspan covering.  I have done just that in past.  You can also use an extra layer (or two) of polyspan in the center section to strengthen it. 
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Offline Claudio Chacon

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #5 on: October 25, 2011, 04:18:07 PM »
Hi,
I do that in every wing I build. Epoxied fiberglass over the center section and then Polyspan over the whole thing. Never had any adhesion problems whatsoever with the Polyspan (no peeling, no bubbles, no nothing)
Sand the epoxied area first with #360 grit trying not to leave shiny spots in order to provide some tooth and that's it.
By the way, I use nitrate dope.
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Offline Allan Perret

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #6 on: October 26, 2011, 06:34:37 AM »
Let me correct myself.  Above I said it would be "better" to use dope for the center glass if following with a doped on covering.  By that I did not mean that it would be stronger, but that it would be easier to use dope for both the glass and covering with nearly the same strength as using epoxy for the glass.
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Offline john e. holliday

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #7 on: October 28, 2011, 06:50:12 PM »
Maybe the guys don't notice it, but I have found that epoxy used to put down glass cloth cures with a slight oily surface.  Sanding will sometimes remove it.  I also use acetone or a thinner to clean the surface before using any other stuff on top of it.   Never had a problem with dope as long as I cleaned/sanded the epoxy. H^^
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Offline Bill Little

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Re: Polyspan and dope over fiberglass/epoxy wing
« Reply #8 on: October 30, 2011, 04:05:50 AM »
Quote from: john e. holliday on October 28, 2011, 06:50:12 PM
Maybe the guys don't notice it, but I have found that epoxy used to put down glass cloth cures with a slight oily surface.  Sanding will sometimes remove it.  I also use acetone or a thinner to clean the surface before using any other stuff on top of it.   Never had a problem with dope as long as I cleaned/sanded the epoxy. H^^

I agree, Doc. y1  ;D

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