Question for Fiberglass guru's

Rick_A · #1 07-08-2008, 03:32 PM

I'm working on my windshield faring (slider). The plexi fit was not very good, so I had some large gaps to fill. I filled in the gaps with flox and did some shaping with the flox to give myself a nicely shaped base to lay the glass on.

I got a bit carried away with the shaping and didn't leave much bare aluminum or plexi exposed to bond the glass to. I'm now in the process of sanding back the flox to expose some metal and plexi. Sanding back the flox is slow going.

My question is: What is the minimum amount of metal and plexi that I need to get a strong bond around the edges?

RV7Guy · #2 07-08-2008, 03:56 PM

I'd shoot for 2-3". You can do about 2 on the plexi portion and a 2-3 on the metal. As long as you have a good bond with the flox compound the glass cloth will lock it all in.

osxuser · #3 07-08-2008, 07:09 PM

The flox itself, if done right is pretty strong, just make sure that the taper into the metal/plexi is nice and smooth, no pockets when you layup over it. Should be ok with 2" like Darwin said.

Mike S · #4 07-08-2008, 07:29 PM

Quote:

Originally Posted by osxuser

The flox itself, if done right is pretty strong, just make sure that the taper into the metal/plexi is nice and smooth, no pockets when you layup over it. Should be ok with 2" like Darwin said.

It would really help if you can do a layup on both sides ---inner/outer---- of the floxed joint. Just be wary of sharp edged corners. Use more flox/epoxy to blend if needed. Just be sparing-----weight will build up rapidly.

Flox is basically structural, but can be brittle.

Rick_A · #5 07-08-2008, 08:11 PM

Since the flox is already in, I'm trying to figure out how much I need to remove so that I get enough glass to plexi/metal bond and still have a fairing that looks good.

The metal is a little easier since I can just move the edge of the glass forward but I don't want to go too far forward. The plexi is a bit harder because I don't want to go too far up the windshield. Since I have "clips" embedded in the flox, I need some flox on the plexi to fair in the clips.

In both cases, 1" vs 2" vs 3" make huge difference in the overall shape of the fairing. Thus my effort to determine how much is enough. So far it sound like 2 inches.

rv72004 · #6 07-08-2008, 11:53 PM

If the preparation of the surfaces was done correctly the glass cloth will stick to the flox without fail. The flox will stick like crazy as well to the metal and plexi. Remember if mixed correctly , flox is a structural compound, unlike qcell.
If I had 1/2 inch cloth either side I would be happy.

If it bothers you make up a few small test sample pieces and see what I mean when you try tear them appart.

Finley Atherton · #7 07-09-2008, 01:31 AM

Rick,
IMHO having flox between the glass and the plexi/aluminum is about as good as having the glass directly on the plexi/aluminium. I don't think you would need to sand back the flox very far (others may disagree!).
I built the tip up so I am not sure if this applies but I guess you are talking about the plexi to the fwd top aluminum skin??
How you have done it, buy letting the flox set is OK and may be the best method if the gaps are really big. However if I was doing it I would have put in just enough flox to fill the gaps and to provide a joggle/bump free surface for the glass and then immediately do the glass lay ups before the flox had set. Once set, rough up with coarse sand paper, brush on a THIN layer of epoxy then apply a generous layer of dry micro over the whole lay up extending on to the aluminum, shape as best as possible and when set, sand to the desired profile.
When doing the lay up, from memory the plans say to start with the narrowest piece of glass and end with the widest. If I was doing it again I think I would do it the other way around, starting with the widest lay up first. I found that a small bubble of air often got trapped at the edges of the glass where the wider lay up over lapped the narrower one below. This became a problem when sanding to get the desired shape as the void could be exposed creating more areas to fill. I have not heard of others having this problem, so maybe it was just me.

Fin
9A
Vari-Eze

DanH · #8 07-09-2008, 06:44 AM

<<IMHO having flox between the glass and the plexi/aluminum is about as good as having the glass directly on the plexi/aluminium.>>

Mine too. The bond strength of a fabric/epoxy-to-plexiglass joint, and flox/epoxy-to-plexiglass joint is identical. Same for the aluminum bonds. Bond strength is governed by the epoxy properties, surface prep, and mechanical factors like shear and peel.

The tensile strength of flox/epoxy and fabric/epoxy is governed by the strength of the fibers, cotton in the case of flox and glass in the case of fabric. Glass is higher, but I think the issue is moot here. Bond strength appears to be the primary factor in this case, and flox/epoxy is plenty tough anyway.

<<My question is: What is the minimum amount of metal and plexi that I need to get a strong bond around the edges? >>

The minimum? Truth is, nobody knows the minimum for sure.

David-aviator · #9 07-09-2008, 07:22 AM

For those reading this thread for information, flox is very difficult to sand. If the job is a simple fill, use micro balloons instead of cotton flox and mix it as dry as possible. It weighs less and is much easier to sand. Also, covering the filled area with squeegeed peel ply before cure will speed up the sanding process. Just remember to remove the peel ply before proceeding.....years ago an EZ had a winglet collapse in flight and the investigation revealed peel ply was still in place beneath a major lay up.....not good.

I agree with the last few responses, flox is structural. It won't be coming loose from metal or plexi glass and its sanded surface is as good a bond for the lay up as anything.

Finley Atherton · #10 07-09-2008, 05:23 PM

Quote:

Originally Posted by David-aviator

For those reading this thread for information, flox is very difficult to sand. If the job is a simple fill, use micro balloons instead of cotton flox and mix it as dry as possible. It weighs less and is much easier to sand. Also, covering the filled area with squeegeed peel ply before cure will speed up the sanding process. Just remember to remove the peel ply before proceeding.....years ago an EZ had a winglet collapse in flight and the investigation revealed peel ply was still in place beneath a major lay up.....not good.

I agree with the last few responses, flox is structural. It won't be coming loose from metal or plexi glass and its sanded surface is as good a bond for the lay up as anything.

Peel ply is good stuff and can also be used as an alternative to sanding in preparation for a subsequent lay up or micro fill. I must admit though that I usually lightly rough up the surface somewhat after removing the peel ply "just to make sure". The easiest way to prepare a lay up for a subsequent micro fill is to simply apply the fill while the lay up is still "tacky". So for the plexi to fwd top skin, fill the gaps with flox, immediately lay up the glass strips, wait a couple of hours or so depending on the temp and cure rate of the epoxy then apply the dry micro directly onto the glass lay up while it is still tacky.
Just had a look in my old Vari Eze manufacturing manual and the instructions for flox to metal are, "When using flox to bond a metal part be sure to sand the metal dull with 220 grit sandpaper and paint pure mixed epoxy (no flox) on the metal part". I would use the same instructions when applying micro directly to metal.

Fin
9A
Vari Eze