Model Forum / Radio Controlled / Air Models / September 2007

Nice pix.

BTDT.  Pix here:

http://picasaweb.google.com/martin.moleski/Rec_models_rc_air

I used the heaviest fiberglass I have.  Two layers of
3/4 oz. should be fine.

I think I used medium CA on the exposed fiberglass first,
thinking it would soak in better than epoxy.  YMMV.

I probably also roughed up the gel coat to try to get
a better bond for the epoxy/fiberglass band-aid.

Scratch that--I put the band-aid on with medium CA, too.
I didn't want to mess around with epoxy, I guess.

The other places where the gel coat got broken off,
I used CA & microballoons (first repair--my crash)
and epoxy and microballoons (a friend's crash).

All of that stuff looks horrible both in the picture
and in Real Life (tm), but it's under the wing and
doesn't show in the air.  

I've used epoxy and CA with fiberglass.  Both seem
to work well.

Some folks spray the cloth with ... uh ... 3M Super 77 contact
cement.  I haven't tried that.

If you use a sharp knife (#11, new blade), a straightedge
that you can press down right where you're making the
cut (a piece of aluminum works OK), cut on the bias
(a 45-degree angle away from the way the weave, and use
a soft cutting surface (I have one of those green
self-healing pads), you can minimize the fraying.

Painting is optional.  I believe in Ugly Insurance myself
(as you can clearly see in the pix).

We broke it.  We fixed it.  It still flies.  If
anyone complains about how bad the plane looks, I'm
willing to let them take it home and improve it all
they want.

                Marty

I have used silk and fiberglass resin to repair cowls. Sand and clean
the area to be repaired, paint on a thin coat of the resin, lay down the
silk where you want it, then paint on a thin coat of resin over that
working it through the silk. Two layers of silk or any other light thin
strong fabric will work. A light thin cloth will form to the curves easier.

Epoxy is to thick and dries too quickly to effectively do this and
thinning epoxy with acetone is a pain in the a.s. Fiberglass resin is
already thin and easy to work with. It's available at Walmart for $10.97
for a quart. You mix 10 drops of hardner per ounce of resin, at least
you do with the can I got. Work with 2 to 4 ounces at a time in a
plastic mixing cup. I just use cheap 50 cent brushes and throw them away
when I am done. You can use acetone to clean the brush out if you don't
want to use a cheap brush.

You don't have to use epoxy with the fiberglass cloth. You can wrap a
piece of saran wrap around your finger and push medium or thick CA into
the cloth. Saves lots of time. Is usually lighter and is much, much quicker.

Ed Cregger

On 15 Sep, 19:57, "Doug McLaren" <dougmc+usenet-20070...@frenzied.us>
wrote:

Fill in any gouges with some filler and smooth the surface.  I like
wall board compound.  Let it dry real well before sanding.  If needed,
prestabalize the break with a drop of CA to make the structure rigid
while you work on it.  Your final surface will be no better then what
you start with so get it smooth before you get out the epoxy.

Cut the glass cloth on the bias to reduce fraying to a minimum.  It is
better to use two or four layers of a light cloth vs one layer of
heavier cloth to get smooth fits.  Use a finishing epoxy for the best
results.  Stuff like ZPoxy is real easy to work with.  West system
products are too viscous for best results in model work.  They will
work but are a pain in the .......  Rough the whole surface you are
bonding to then just wet it with epoxy and lay the cloth over the wet
surface.  Work just enough epoxy into the cloth to wet it out then lay
the second layer over it.  Work on the second layer with a plastic
tool you can get at any auto parts store or an old credit card for
putting on body putty to work excess epoxy into the second layer.
Usually what you put down to wet the first layer is enough to wet a
second layer also.  Clean the card right after use with acetone or MEK
or you will only use it once.  Ethanol will also work but is slower
and not as good.

Finally cover the whole area with peal ply.  Peal ply is simply a
polyester cloth.  I have used scraps of polyester woven cloth from my
wifes sewing bin in emergencies and it works fine.  If you have a big
bend in the part being patched it will work better then the heavier
commercial peal ply.  Let it cure 24 hours or more and peal off the
peal ply and you will have a smooth surface.  Much smoother then you
can get with a regular layup.  You need enough epoxy in the glass to
wet the peal ply out fairly well.  But beginners always have more then
enough epoxy that this is not a problem.  Make sure it is polyester if
you are using scrap cloth.  Easy to do by testing and seeing if it
will peal off the cured surface cleanly.  Any cotton in the cloth will
be a disastor.

Will the patch be invisiable?  Nope.  But it will not have rough edges
and splinters sticking out that will grab a hunk out of your hand like
a fish hook.  And there is no stronger patch you can make for the tiny
weight you added unless you go to carbon cloth.  This will work on any
plastic or wood.

Fast, very strong, easy, neat.  I have stuck a fuse busted clear in
half back together this way and been flying in 48 hours.