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Glassing an aluminum gear leg fairing tab

ac_oldman

Active Member
I have five questions about fiberglassing:

- when fiberglassing aluminum onto roughed up fiberglass, should I squeegee
or thin the layer of pure epoxy applied w/ paintbrush to coat the metal?

- when making a layup onto an existing fiberglass part, is it ok to wipe away
excess epoxy with a paper towel?

- Is floxing the appropriate method to build up a ramp to a metal piece
placed over existing fiberglass so another ply can be layed up on top?

- Is floxing between rows of rivets-to-nowhere a good idea to prevent
air bubbles if another ply is to be layed up on top?

- What does properly cured floxed epoxy look like - is it kind of a white
haze under a non-floxed layup? does anyone have photos of flox'd work?


Background:

The gear leg fairings on my RV-3 are hollow fiberglass.
They have a 1.5"x4" aluminum tab to attach to the gear leg, similar to the tab
shown for the aluminum fairings in the RV-3 plans. The tab has 6 "rivets to
nowhere", and it (was) attached to the fairing with a layer of fiberglass that
was broken recently when the fairings were removed. The outer fairings have
what appear to be wear holes where the rivets to nowhere sit snugly.

I'm attempting to re-glass the aluminum tabs back to the fairing.
I have not done fiberglass work before.

I made a test piece with a similar configuration and it seems ok, please let me
know if you have suggestions on what I might do differently.

#1 - remove old fiberglass/epoxy from metal tab. sand w/ 220 grit paper.

#2 - sand inside of fairing where the tab is to be replaced w/ 60 grit paper until rough.

#3 - cut two squares of 7725 bidi, one perp to selvedge, one at 45 deg.
dimensions approx 3in wider and 1.5in taller than portion of tab to attach to fairing.

#4 - mix one pump of west 105 resin w/ one pump 206 hardner. mix for 1min.
within 4 min:

#5 - coat outer fairing where tab is to be attached, and metal tab top and bottom with epoxy.
unclear: how thick should this be? Should I squeegee it thinner?

#6 - place tab onto outer fairing. align wear holes w/ rivets-to-nowhere.
support hanging end with a layer of wax paper'd cardboard to prevent
hanging.

#7 - add flox to remaining resin so that flox makes mixture stand up w/ a
paintbrush. If > 3min has elapsed, mix a new batch for this.

#8 - apply floxd epoxy w/ paintbrush to build up a "ramp" up to the side of
the aluminum tab. Also apply flox w/ paintbrush to ramp up to the "rivets to
nowhere" so that the glass can lay ontop of it without forming a bubble.

#9 - mix one pump west 105 resin, w/ one pump 206 hardner, mix for 1min.

#10- - apply 1 square of 8oz 7725 bidi parallel/perp to aluminum strip, overlap sides & end by ~1.5in.
- squeegee to soak up epoxy from underneath.
- apply extra epoxy if necessary
- squeegee it out
unclear: how to prevent excess from making a mess on existing fairing - wipe w/ paper towel?

#11 - apply 1 square of 8oz 7725 bidi at 45deg to aluminum strip, overlap sides & end by ~1.5in.
- squeegee to soak up expoxy from underneath
- apply extra epoxy if necessary
- pump a new mixture if it's been >= 4min since mixing.

wait 24hrs.
 
I sometimes apply a very thin coat of epoxy resin over the area to make sure I get into all the small voids but you get the best bond with your flox if the fibers in the flox contact the surfaces you are bonding. A wet coat of resin would keep the fibers away from that surface.
Yes the extra resin should be wicked up after the fiberglass is applied. Try drying up your brush on the edge of your resin container and then going over the wet areas on your layup. With a dry (brush not full of resin, same brush you used to apply the resin) , it will pick up the extra resin.
Fiberglass is at it's strongest strength when all the fibers have enough resin to wet them out and no more. More resin make the layup brittle, that's why vacuum bagging is so good. It removes all the extra resin and leaves the layup totally wetted out.
 
I have five questions about fiberglassing:

- when fiberglassing aluminum onto roughed up fiberglass, should I squeegee
or thin the layer of pure epoxy applied w/ paintbrush to coat the metal?

Precoating roughened glass is usually not required.
If pre-coated, the surface need not be more than damp...paint on some epoxy, wipe off excess.

I know it's a common old school practice, but thinning epoxy with a solvent is never a good idea.


- when making a layup onto an existing fiberglass part, is it ok to wipe away
excess epoxy with a paper towel?

Yes.

- Is floxing the appropriate method to build up a ramp to a metal piece
placed over existing fiberglass so another ply can be layed up on top?

Yes, definitely.

- Is floxing between rows of rivets-to-nowhere a good idea to prevent
air bubbles if another ply is to be layed up on top?

If "rivets-to-no-where" means the heads stick up
so as to hold the subsequent glass fabric application up off the surface like tent poles, then yes indeed, flox to fill the voids prior to fabric.


- What does properly cured floxed epoxy look like - is it kind of a white
haze under a non-floxed layup? does anyone have photos of flox'd work?

Yes, white. Mix some epoxy, add some flow, put a few blobs on waxed paper, let it cure two days. Put on good safety glasses and try to destroy the blobs...hammer, pliers, saw, whatever you like. You'll gain a practical respect for the properties of flox.


Background:

The gear leg fairings on my RV-3 are hollow fiberglass.
They have a 1.5"x4" aluminum tab to attach to the gear leg, similar to the tab
shown for the aluminum fairings in the RV-3 plans. The tab has 6 "rivets to
nowhere", and it (was) attached to the fairing with a layer of fiberglass that
was broken recently when the fairings were removed. The outer fairings have
what appear to be wear holes where the rivets to nowhere sit snugly.

I'm attempting to re-glass the aluminum tabs back to the fairing.
I have not done fiberglass work before.

I made a test piece with a similar configuration and it seems ok, please let me
know if you have suggestions on what I might do differently.

#1 - remove old fiberglass/epoxy from metal tab. sand w/ 220 grit paper.
#2 - sand inside of fairing where the tab is to be replaced w/ 60 grit paper until rough.
#3 - cut two squares of 7725 bidi, one perp to selvedge, one at 45 deg.
dimensions approx 3in wider and 1.5in taller than portion of tab to attach to fairing.
#4 - mix one pump of west 105 resin w/ one pump 206 hardner. mix for 1min.

When working in small quantities, mixing by weight is more accurate. Not sayin' you cannot use the pumps, but...

within 4 min:

West 206 is slow hardener, so no real tight time frame here.


#5 - coat outer fairing where tab is to be attached, and metal tab top and bottom with epoxy.
unclear: how thick should this be? Should I squeegee it thinner?

Instead, wipe a thin layer of flox onto the fairing surface, then firmly press the metal tab into the wet flox. Press firmly so as much as possible squeezes out the sides

#6 - place tab onto outer fairing. align wear holes w/ rivets-to-nowhere.
support hanging end with a layer of wax paper'd cardboard to prevent
hanging.

#7 - add flox to remaining resin so that flox makes mixture stand up w/ a
paintbrush. If > 3min has elapsed, mix a new batch for this.

Mix epoxy, pour some off in a second cup, add flox or micro or cabo as desired. Now you have two cups ready to go.

#8 - apply floxd epoxy w/ paintbrush to build up a "ramp" up to the side of
the aluminum tab. Also apply flox w/ paintbrush to ramp up to the "rivets to
nowhere" so that the glass can lay ontop of it without forming a bubble.

Flox doesn't paint very well. Most of the time you'll wipe it into place with a squeegee, since you want the profile to be accurate. I like hotel key cards.

#9 - mix one pump west 105 resin, w/ one pump 206 hardner, mix for 1min.

If needed

#10- - apply 1 square of 8oz 7725 bidi parallel/perp to aluminum strip, overlap sides & end by ~1.5in.
- squeegee to soak up epoxy from underneath.
- apply extra epoxy if necessary
- squeegee it out
unclear: how to prevent excess from making a mess on existing fairing - wipe w/ paper towel?

#11 - apply 1 square of 8oz 7725 bidi at 45deg to aluminum strip, overlap sides & end by ~1.5in.
- squeegee to soak up expoxy from underneath
- apply extra epoxy if necessary
- pump a new mixture if it's been >= 4min since mixing.

Easy to wet out both plies, stacked, at the same time, but do what works for you.
 
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