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West Systems 403 Microfibers vs cotton flox; peel ply?

SabreFlyr

Well Known Member
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Getting ready to start on some of my tail fairings. I'll soon be cutting the big hole in the bottom of the rudder bottom fairing to clear the tailwheel spring (p. 12-04; fiberglass patch is applied to the outside and an oversize piece of glass fabric is applied inside). I've got the composite kit from ACS on backorder and it has some flox in it (last shipment they received was last November but they say it will be in stock next week; we'll see). I've also got some West Systems 403 Microfibers left over from an RC airplane project a few years ago. When I put the epoxy fillet on the inside of the patch as instructed, should I use flox as specified or the microfibers? I've never used peel ply before. Would you use it around the edges of the glass fabric applied to the inside to keep the edges of the fabric in the epoxy during the set or not bother because it's inside?
 
Getting ready to start on some of my tail fairings. I'll soon be cutting the big hole in the bottom of the rudder bottom fairing to clear the tailwheel spring (p. 12-04; fiberglass patch is applied to the outside and an oversize piece of glass fabric is applied inside). I've got the composite kit from ACS on backorder and it has some flox in it (last shipment they received was last November but they say it will be in stock next week; we'll see). I've also got some West Systems 403 Microfibers left over from an RC airplane project a few years ago. When I put the epoxy fillet on the inside of the patch as instructed, should I use flox as specified or the microfibers? I've never used peel ply before. Would you use it around the edges of the glass fabric applied to the inside to keep the edges of the fabric in the epoxy during the set or not bother because it's inside?

I just made a wetted double layer on the bench then applied it to the well sanded lower fairing. Then pushed until it made a nice gravity draped shape and left it to set. Then came back for the interior. The exterior got sanded once fully cured and the excess just disappeared as the blend was made. I would not use peel ply as it will distort the shape and cause more downstream work. The gel coat can be thick (or not) and you can remove it 1/2" around the hole and then overlap the cloth over it for sanding back flush. Glass to glass will be a better structural project.

Oh - fibers or flox would work inside as a structural blend.
 
Flox

Dan's Fiberglass thread (Sticky) is one of the best sources on here.
He has a few posts about "Scarf" joints.
Personally micro is only for filling. It's not structural.
Flox is structural but hard as rock so be aware if you need to sand it.
Fiberglass cloth will lay without Peel Ply. The Peel Ply both absorbs excess epoxy and it leaves a fractured surface ready for the next layup.
I had to cut away some of the bottom cap because the fit was so bad. I sanded the remaining edge to a scarf then layed up the new cloth increasing thickness over the joint.
I also had to split it along the bottom center fore and aft. I placed.some tape inside and filled the split with flox with the rudder up side down till it cured. Then one layer of cloth was layed up inside.
Hope that helps. Dan is the Bodishatva so hopefully he will chime in.
 
Dan's Fiberglass thread (Sticky) is one of the best sources on here.

Thanks, Larry. I've been studying that thread but there's a lot there! I'll dive back in.

I tend to think microballoons = filler, microfibers = (at least somewhat) structural = flox.

Bill, did you have any issue with the outside patch sagging applying it wet like that?
 
Layup

Thanks, Larry. I've been studying that thread but there's a lot there! I'll dive back in.

I tend to think microballoons = filler, microfibers = (at least somewhat) structural = flox.

Bill, did you have any issue with the outside patch sagging applying it wet like that?

That's correct.

Not at all but it wasn't free floating. The rudder was taped and waxed and the layup against it.
I did predict an issue with the canopy skirt on the gap between tip skin and canopy. It was resolved by filling the area with a section of clear plastic from an old poster frame.
Basically, fill the area with something as a mold.
Time spent on the mold saves hours of work later.
 
Not at all but it wasn't free floating. The rudder was taped and waxed and the layup against it.

Okay, Larry. Now you've lost me a bit. First of all, is the 7A's rudder bottom fairing done the same as the dragon tail -14? Did you make a patch like below?

What confuses me is that you at one point had a cured, molded patch that you then had to attach back to the fairing. Granted, no sagging since the hole had been taped but now you've got to get a structural bond between the two pieces.
 

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Rudder fairing trailing edges

Another question: did anyone sand the aft end of their rudder fairings to match the taper of the rudder trailing edge? I'd prefer the appearance but would fear for the weakness of the thinned fiberglass.
 
Rudder cap

Another question: did anyone sand the aft end of their rudder fairings to match the taper of the rudder trailing edge? I'd prefer the appearance but would fear for the weakness of the thinned fiberglass.

First mine is an "A" so there was no need to cut a relief. However, that's not a problem.
How I would do it...
Find center and use a compass to draw a perfect circle the size needed. Cut out the plug carefully and save it. Flip it concave side out. If it look like it will work, prep it for install. Sand all edges if both the plug and rudder cap to make a scarf joint. Secure it in place with tape or whatever works.
Layup round strips over the scarf joint. Start narrow and go wider to maybe three or four layers. Cure and sand it clean.

I did sand the cap to match the rudder. Before I do, I stand the part up and apply flox into the area and cure. No way to break through sanding. Since I split mine anyway, it got floxed.

Here's a photo of my rudder cap. Should show how I did it. Notice mine isn't slotted the same as plan. Mine slides on from aft. That section either side was cut a few inches back and replaced so it would lay flat.
20200813_102914.jpg
 
Find center and use a compass to draw a perfect circle the size needed. Cut out the plug carefully and save it. Flip it concave side out. If it look like it will work, prep it for install. Sand all edges if both the plug and rudder cap to make a scarf joint. Secure it in place with tape or whatever works.
Layup round strips over the scarf joint. Start narrow and go wider to maybe three or four layers. Cure and sand it clean.

You're then still left with a concave "dent" in the bottom of your fairing? (Not an issue. Just seeking clarity.) I presume those round strips need to be cut as circles ("doughnuts," not just round patches), right? Can't turn straight pieces that tight, I wouldn't think. This would be done inside and out, I presume. Understand that I've never tried this before; previous "glassing" work was just reinforcing an RC engine mount with heavier carbon fiber cloth.
 
Layups

You're then still left with a concave "dent" in the bottom of your fairing? (Not an issue. Just seeking clarity.) I presume those round strips need to be cut as circles ("doughnuts," not just round patches), right? Can't turn straight pieces that tight, I wouldn't think. This would be done inside and out, I presume. Understand that I've never tried this before; previous "glassing" work was just reinforcing an RC engine mount with heavier carbon fiber cloth.

It was just an idea. Simple because it should fit perfectly flipped inside out.
Yes, it would be concave. If you want it flat, that's easy. Find somehing flat that fits. Lay packing tape on it and wax it. Place it inside over the hole and secure it. Layup will be flat. You still need to sand the area around the hole into a scarf.
Basically pointing out how fiberglass can be utilized. It's very easy to work. With a hole and flat mold (Vans plan), you would just secure a flat mold inside and layup over the hole past the scarf about 1/2-1". 4-5 layers.

If you go with the concave plug, the scarf pieces could be cut as doughnuts but depending on the fabric used, strips can actually be shaped into partial circles and ends overlapped. Stagger the overlaps. Final sanding will make it smooth.
I recomend playing with some layups. Do a practice 4 layer layup on a sheet of 4mil plastic. The flat piece is useful later.
I have a "Fiberglass" page on my blog under "Favorite Links". Might help.
 
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It was just an idea. Simple because it should fit perfectly flipped inside out.

I think it surprised me for some reason but it's actually not a bad idea because of the fit. (If someone's down on the ground looking at my concave patch, they're a bit too nosy! ;)) I had also misread. I got the impression that you had done such a patch on your -7A. I later reread with a clear head.

I should have hit the PAUSEnTHINK button instead of REPLY earlier. The overlapping strips to form the circle occurred to me about five minutes later. :rolleyes:

Thanks, Larry. I'll check out your blog. Basically ALL fiberglassing ideas are new to me. :)
 
Epoxy + microballoon = filler, light but little strength
Epoxy + chopped cotton or epoxy + colloidal silica (Aerocil) = Bonding paste (flox)

I believe West 403 = chopped cotton, West 406 = Aerocil, West 407 = microballoon, West 410 = really creamy, light colored, microballoon. There are other West fillers!

All can be mixed to what ever consistency is required for the job in hand.
A chopped cotton & aerocil mix can be used. Aerocil gives a smoother mix, chopped cotton produces a stronger mix. Bonding paste is tough to sand.

Peelply is used over a layup to make the surface look better and to make the next layer stick well (otherwise must be well roughed up).

In this case it will take 4 resin processes (4 days) to finish the fairing (flowing Van's steps, although 3 & 4 could be reversed). 1/16" ply could also be used instead of making a repair patch. Repair patch (or ply) could also be stuck on with super glue or 5 minute epoxy, that would mean only 2 resin processes. I would rough up inside of repair patch and inside & outside of fairing before starting.
1) Layup the repair patch, cover with peelply, allow to cure
2) Sand away corner and glue on repair patch, allow to cure
3) Sand back edge of repair patch to fair in, rough up outside of fairing well with 60 grit, and lightly sand outside of repair patch (don't clean with alcohol, just brush and vacuum). Apply layer over the whole lot (too difficult to apply a ring), a layer of peel ply will help achieve a better finish. Allow to cure.
4) Rough up very well with 60 grit - no shiny surface where epoxy will be applied. Apply bonding paste to inside edge (glass cloth won't stick to a sharp corner) and lay up the internal layer. Allow to cure.

Outside will have to be filled before painting.
 
Epoxy + chopped cotton or epoxy + colloidal silica (Aerocil) = Bonding paste (flox)

Although both chopped cotton and fumed silica are additives often used in making a paste for bonding, "flox" is generally the name given to chopped cotton or a mixture of chopped cotton and epoxy. Think of flox as structural because it is a fiber additive.

Silica is different. It is not a fiber, but rather a powder in which each grain has a huge surface area. It is used to make mixed epoxy (and other products) thixotropic, i.e. flowable only under pressure. Mix fumed silica (Cab-o-sil, Aerosil, or any of the other "sil" trade names) into epoxy to prevent flow before cure, like when you don't want it to run out of a vertical joint.
 
Silica is different. It is not a fiber, but rather a powder in which each grain has a huge surface area. It is used to make mixed epoxy (and other products) thixotropic, i.e. flowable only under pressure. Mix fumed silica (Cab-o-sil, Aerosil, or any of the other "sil" trade names) into epoxy to prevent flow before cure, like when you don't want it to run out of a vertical joint.

Thanks, Dan. You answered the question that was just coming to mind in reading Penguin's post.

Bill, Larry, Penguin, and Dan: I appreciate all the help! I've got a lot to digest and the first thing I'm learning is how little I know. Gonna hope that the ACS composite kit does get here in the next couple of weeks and try to get through those practice pieces first before I try to fully grasp the rest. Also going to spend a lot of time in your sticky, Dan. Thus far, I've only scratched the surface.
 
Somebody here mentioned that peel ply could distort a layup. Provided there are no wrinkles, that has nit been my experience. I can’t think of a single situation where I would not use peel ply. It just makes for a neater job.

As far as flox or silica thickened epoxy being hard to sand, while it is certainly harder than micro, it doesn’t hold up to a sanding block with 40 grit or a coarse disk on an angle grinder. Of course you have to be careful not to go too far, ut I always use the coarsest grit I can get away with to knock down lumps and achieve contour. Then I worry about scratches and achieving smoothness.

Mike Arnold made some great vidoes on working with composites. Both plug making and mold making. Since he died they have been put up on youtube. Very much worth watching.
 
Mike Arnold made some great vidoes on working with composites. Both plug making and mold making. Since he died they have been put up on youtube. Very much worth watching.

Thanks for your thoughts, Scott. I'll check out MIke's videos.
 
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