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PostPosted: Mon Aug 29, 2011 10:33 am
by GPW
... or just avoid the fiberglass .... :thinking:

PostPosted: Mon Aug 29, 2011 12:41 pm
by Wobbly Wheels
Thanks for posting that Harry.
The best results I've had have come from a tip given by another poster on there who was quoting Burt Rutan:
"The bottom layer should be an epoxy "slurry" consisting of a loose mixture of microballoons and epoxy"


I've used cabosil for that rather than microballoons but, given that he's building airframes, microballons make more sense to keep the weight down.

As far as the temps go, I do agree with a lighter color but for a it of a different reason. Dark hulls in warmer latitudes have an obvious tendency to warm up, which will soften the epoxy.
I also play around a bit with knifemaking and when I want to change handle scales I've glued on, I just boil them. Boiling water doesn't hurt the blade's temper but once the steel warms up those scales fall right off without leaving a residue on the tang.
I wouldn't think there would be enough heat transfer through the layup to warm the foam to melting temp, especially since the epoxy itself would begin to be compromised at a temperature of a coffee in a styrofoam cup.

I would be more concerned about foam damage from exotherm stacking during layup. If you apply another unit (layer) over one that's kicking off, it will accelerate the gel time. Towards the end of the gel period is when the most heat seems to be given off. That's (for me at least) about the time it takes to get the next unit on. Now you've got two exothermic reactions at the same time and the foam's R value is allowing that heat to dissipate through only one side of the layup. That's a perfect recipe for blisters.

I've had runaway layups that have actually started smoking, I've seen melted mixing pots and I've had one shop catch fire (though that was from a glasser leaving a pot of catalyzed vinylester in a cabinet).
I will be using multiple units over blue foam on mine, so this is definitely something to think about, but I wouldn't call it an insurmountable obstacle.

Then again, I'm not an expert...just a long winded amateur !

GPW, you aren't suggesting we stop trying ways to make foamies better are you ?!? :shock: :lol:

PostPosted: Mon Aug 29, 2011 1:41 pm
by atahoekid
Oh bother!!! :( :( :( Just when I thought I had everything worked out. :cry: :cry: I can't get the link to load. Can someone provide me the bullet points?

Is it the epoxy or the fiberglass that would be the problem? Melting at 150??? Oh Crap!!! :shock: :shock: :shock:

Is it the same issue if I'm using TB2 instead of epoxy with the fiberglass?

Now I'm very confused :? :?

PostPosted: Mon Aug 29, 2011 1:59 pm
by Wobbly Wheels
Not to worry Mel, it's the epoxy that kicks out the heat.
TBII will be fine.

PostPosted: Mon Aug 29, 2011 3:49 pm
by atahoekid
That big exhaling sound you just heard was me. Wow, that's a relief :worship: Thank God!

RE: Foam & Fiberglass

PostPosted: Mon Aug 29, 2011 4:24 pm
by mezmo
Hi Harry Segelken,

Thanks for posting that link. I just perused it lightly but it seems to
be another good source of info & experience to draw from, especially
concerning building with foam.

One point some bring up is structural foams vs the cheaper insulation
types. It seems a subject worth looking into.

Also one of their forum members ["Hovermaster"] suggested an aircraft
composite book on it that is reasonably priced at:

http://www.aircraftspruce.com/catalog/b ... ldless.php

Looks to be interesting.

Cheers,
Norm/mezmo

PostPosted: Tue Aug 30, 2011 9:12 am
by eaglesdare
i think if epoxy and fiberglass are your thing, its ok to use.

some of us, wanted cheap and easy (non toxic) materials.


nothing wrong with either.

RE: Fiberglass Delamination

PostPosted: Wed Aug 31, 2011 6:14 am
by mezmo
One thing I gleaned off the hovercraft link was that the aircraft
foam and fiberglass compositors always make an slurry of microballons
and epoxy/resin and apply that to the foam first, then the epoxy/resin
to embed the fiberglass in and such. evidently it seals the foam somehow
and greatly increases the adhesion for the fiberglass. It's supposedly all
explained in that book that I posted the link for and is based on methods
the great experimental aircraft designer Burt Rutan used.

Cheers,
Norm/mezmo

PostPosted: Wed Aug 31, 2011 9:55 am
by GPW
I guess that's the Beauty of foam construction ... you can take it as far as you want to ... No Limits to what you can do or use ... All in what's Best for You !!! 8)

RE: Links

PostPosted: Wed Aug 31, 2011 3:51 pm
by mezmo
Hi Harry Segelken,

Once again, thanks for the great links!

The Rutan booklet is great.

Cheers,
Norm/mezmo