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Tip: Fiberglass Fabrication

DanH

Legacy Member
Mentor
I've noticed quite a few RV builders are a unsure about fabricating glass components. I thought it might be useful if they could see a part fabricated from scratch. Those who are already comfortable working with glass should probably click elsewhere now.

My RV-8 is a fastback; the raised turtledeck requires a new intersection fairing for the tail surfaces. No way the Van's fairing will fit.

First step is to develop a shape. You can use whatever works. Clay is popular. I used pour-in-place foam this time, and a few cut back chunks of an old Van's fairing. Tape off the aluminum to protect it and shape your medium as required. The Golden Rule of all composite fabrication is "Time spent getting the shape right early in the process pays large dividends in time and weight later". Do whatever it takes to get your form as perfect as possible.

Emp%20Fairing%20Foam.JPG


Next cover the shape with plastic tape. Put a coat of wax on the tape.

Emp%20Fairing%20Tape.JPG


Now proceed with layup. This is four plies of 9 oz crowfoot. You want crowfoot (not plain weave) or similar for this kind of shape because it forms nicely on concave or convex shapes. Get it well saturated, alternate overlaps between sides (like at the front of this part), work out air bubbles before applying the next layer. Stippling with a brush will work; I have a composite roller that I love for compacting plies and removing bubbles. In this photo I've covered the layup with saturated peel ply; it is ordinary polyester aircraft fabric left over from other projects.

Emp%20Fairing%20Layup.JPG


Here's the cured, raw glass part, after ripping off the peel ply fabric. Because I used peel ply, the glass surface requires no sanding prior to bonding additional sections or coating with micro. Just knock off any high spots with a vixen file or coarse paper and move on to the next step.

Emp%20Fairing%20Peeled.JPG


If ya'll like this stuff I'll post further steps as I proceed.
 
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Great!

DanH

This is a great addition!

As a fiberglass neophyte a complete listing of all items used would be most helpful! What epoxies, hardeners, flox, etc, etc, etc. This is one area that's hard to get good how-to information.

Thanks for the information! and keep it coming!

--
Michael
 
Pierre,
<<Where do you buy pour-in-place foam?>>

Right now I'm trying the 4 lb density from:

http://www.shopmaninc.com/foam.html

Previously I had used clay, block foam, plaster, balsa, anything that would hold a shape. Only trick I've noted with pour-in-place foam is that you can't fool with it when you pour it. If you try to spread it or move it around in any way you wind up with varying density thoughout the cured blob. That makes it harder to sand to shape with accuracy.
 
Another Source

Dan,
Thanks for sharing this project for our training.
Also, Kitplanes magazine started a series in May 07 titled "Build Your Skills: Composites (Part 1)". It is still ongoing...
 
<<listing of all items used would be most helpful!>>

Well, let's see now.....

My favorite general use cloth is 8.9 oz 8-harness satin weave, Wicks #7781 or Spruce #7781-60. Heavy weight, so it builds fast. "8 harness" means the weave is seven over, one under. That allows the crossed tows to shift in relation to each other. As a result, you can wrap 7781 around compound surfaces with ease.

West 105 epoxy and slow hardener (206) works fine. I keep a little fast hardener (205) around but I don't use it for layup work.

Pick up a 4' x 4' sheet of 1/2 plywood, the kind with a smooth, almost plastic finish on one face. That's your cutting board. Use a "pizza cutter" rotary fabric knife, Spruce #01-00299 or better.

General supplies: Order 3 oz and 8 oz unwaxed cups, a box of mixing sticks, and a box of latex gloves. Also order some flox, cab-o-sil (fumed silica), and micro balloons. Buy a box of cheap 1" brushes at Harbor Freight or similar.

I measure all my epoxy/hardener proportions by weight, using an old balance beam gram scale. A gram scale allow me to mix any quantity from 10 to 500 grams with perfect accuracy, meaning I don't waste expensive epoxy and I've never had a cure failure. Pumps suck (literally). You can't mix small quantities by volume with great accuracy, and a few bubbles ruins the mix ratio. Besides, scales work for proseal, structural adhesive, and any epoxy ratio.

"Real" peel-ply is nylon so it can be used in an autoclave. Polyester works for room-temp cure. Leftover fabric scraps salvaged from your biplane buddy will do fine at the basic level.

I prefer MEK for cleanup. Yeah, wear gloves.

A pair of barber's scissors (the thin pointy kind) work well for trimming wet cloth, all steel so you can wipe them with MEK for cleanup...no plastic handles. Spruce and Wicks sell a variety of layup rollers, stipple or ribbed. Mine is nylon, ribbed, about 2" diameter.

Composite "files" are any good grade of sandpaper glued to blocks or tubes with 3M spray-can contact adhesive. 40, 80, and 120 grits are useful.
 
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Awesome, keep up the show. It looks like you get a seamless transition from fairing to VS & HS to Fuselage sufaces. Do you use any mold release to make the fairing removable?
 
Previously I had used clay, block foam, plaster, balsa, anything that would hold a shape. Only trick I've noted with pour-in-place foam is that you can't fool with it when you pour it. If you try to spread it or move it around in any way you wind up with varying density thoughout the cured blob. That makes it harder to sand to shape with accuracy.

I think you might find the blue Polystyrene foam easier to use. I still have a few chucks left over from my Long-EZ days. This stuff is very rigid but sands really, really easy. I cut it into blocks with a hand saw and fit it into the nooks and crannys that I want to fill. A dab of 5-minute epoxy holds it in place and then you can sand it to shape. It usually seperates in big pieces and is easily removed. No need to use any wax or mold release agent. Just let the cloth stick to the foam and when you remove the part, the foam easily sands away from the glass.
 
Dan

I am almost to the same stage on my RV 7 and I want to rework it some, please go on with the lesson, it helps a lot. CJ
 
The next step is to graft some additional glass; the fairing needed to be extended down to the lower edge of the longeron and back under the stabilizer an inch or two.

Emp%20Fairing%20Graft.JPG


Grafting glass means sanding a scarf joint, just like a plywood joint in a wood wing skin. Use your 40 grit sanding block to feather the edge in a long bevel, and then bond glass plies something like you see below. Either A or B is fine for the layup. Sand to C. D is wrong as a soup sandwich:

Scarf%20Joints.jpg


Next step is a final trim; carefully lay out the edges you want and cut them with an ordinary pair of metal snips (works fine up to about six plies of 9 oz glass). The snips crush the glass slightly along the cut, so cut just outside the line and 80 grit the edge to the final profile.

Emp%20Fairing%20Trimmed.JPG


Here is a quick tool shot. Sanding boards and tubes are primary for shaping and finishing. I make mine in many sizes with 3/4" birch ply, aluminum or PVC tube, or anything else handy with a shape like the profile I want to sand. Attach a good grade of paper with 3M contact adhesive. You can also see the pizza cutter, layup roller, vixen file, etc.

Emp%20Fairing%20Tools.JPG


Knock down any high spots, thin any thick edges (like where you had fabric overlaps), and open any trapped air bubbles one ply of glass below the surface. Since peel ply was used over the original layup there is no need to sand the entire surface. If you have a bead blast cabinet, a quick pass will nicely prep any remaining glossy spots. Mix up a big batch of dry micro (glass microbubbles added to mixed epoxy, consistency of firm cake frosting or peanut butter). Spread it all out on the glass as soon as you get it mixed or it will exotherm in the pot. (If spread out so it's not in a blob, it will have the normal cure time for the epoxy mix. Can't put it all on the part? No problem; dump the whole cup on a sheet of plastic.) Use a squeegee to spread a nice thick layer everywhere on the part, much like frosting a cake. Another Rule: Better to apply too much than too little; adding more to thin spots later tends to result in uneven sanding density.

Emp%20Fairing%20Micro.JPG


In about 24 hours it is "Hi ho, hi ho, off to sand I go"
 
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Fast forward a week or so and the coat of micro is sanded. This is your big shot at getting shape and surface contour spot on, because any further contour changes will be with sprayed primer-filler and measured in .001's". Sand with small blocks and tubes for surface flatness. Avoid "finger sanding" (holding the paper in your bare hand), which tends to form high and low spots. A lot of what you see here was done with 80 grit on a 6" length of 1-1/2 PVC pipe, stroked at an angle to its length. Flat areas got a small flat block. Clear the dust as you go so you can really see the surface. I usually sit on a short shop stool with a shop vac running and the hose end on the floor between my feet. If you haven't already, get "drywall filter bags" for your shop vac at the home supply store. Don't depend entirely on your eyes; your fingertips will tell you more than you can see. This sanding took about 4 hours. It is the tedious part of moldless composite construction. Parts with multiple contours like this one are the hardest to sand correctly.

Emp%20Fairing%20Sanded.JPG


Next was spotting and drilling the locations for the mounting screws, then tapping or installing nutplates as required. With the part screwed into place you can now see any spots along the edges that need some liquid shim to close gaps to zero. Although the part was made to the airplane, screwing it down may shift things a little, same as a Van's pre-made fairing. Here's how to get that gap-less look. Roughen the underside of the flanges with 80 grit. Tape the metal surfaces with a neat strip of packing tape. Mix epoxy with cabosil to the consistency of toothpaste. Apply a bead along the underside of the fairing flanges, screw it to the airframe, and allow it to cure. After cure, sand the edges to their final contour, a nice half-round.

Here's the trimmed and sanded fairing, waiting for the shim to cure. You can just see some shim mix squeezing out from under the edge:

Emp%20Fairing%20Shim.JPG


Next was three squeegee coats of epoxy to kill pinholes and fill the surface. Brush or roll on, squeegee off, wait until it gets firm (but not cured), apply another coat.

Emp%20Fairing%20Squeegee%20Coat.JPG


I elected to also make some matching fairing strips for the underside of the stabilizer. The proceedure is all the same, with two differences. For a long narrow part like this, it is handy to use fiberglass tape (4' wide in this case), rather than cut glass fabric. Saturating glass with epoxy while working upside down with a brush would be a pain in the butt, so do it on the bench between two layers of 4 mil plastic sheet. Just lay down plastic, stack up four layers of tape precut to length, pour lots of epoxy on it, and cover it with another layer of plastic. Use a roller or squeegee to work resin into the cloth, working excess resin off to the side. When you're happy with it, cut right through the plastic with your pizza cutter, leaving a strip of impregnated fabric sandwiched between two sheets of plastic. Peel one side and stick it in place on the taped airframe, peel the other side, stipple out the trapped air with the tip of a brush, and add some peel ply.

Emp%20Fairing%20Underside.JPG
 
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Nice thread..

We just bought some new wheel pants for our -6 and will need new intersection fairings..

I have been thinking about giving them a go myself...
 
Been a while (other projects), but here's the last bit.

After cure, the epoxy-squeeged fairing was sanded with a soft block (firm foam) and 400 grit. This is the last chance to get it slick and all surfaces flat, although big corrections are not possible without cutting through the epoxy "skin". Don't sand through the epoxy skin, or you'll open new pinholes.

If at this point you see a surface wave or wiggle and you're not happy, you have two choices. If a high spot, cut it down, re-coat, cure, and sand lightly again. If it is a low spot, scuff the surface, fill with micro, sand to contour, squeegee with neat epoxy, and you're back to the same point. If a low spot is really shallow, it can be fixed in the paint process, shooting with K36 or a similar high-build primer/surfacer after an epoxy primer tie coat, then doing a bit more contour sanding. However, remember that high build primers like K36 only add a few 0.001's per coat. Don't fall prey to the old "I'll fix it later" or the "The painter will fix it". Chances are he won't.

As a final step in fabrication, I shoot a light coat of epoxy primer as a pinhole and defect check. Primer makes defects stand out. You can see everything, fix anything, and consider the part truly done, rather than getting surprised later. When the project shifts to full time painting, the lightly primed parts get a scuff pass with 400 grit, wiped clean, and go into the paint booth for a fresh primer coat and color coats.

Here are the primed emp fairing parts:

Emp%20Fairing%20Primed.JPG


The pinhole total after priming was four, all on the big fairing. At this stage, just wipe almost any filler into the individual pinhole with a fingertip, then skim sand so all that remains is the filler down in the hole.

The epoxy coating works. Just for contrast, here's a shot of the inside of the part, a pinhole horror for sure:

Emp%20Fairing%20Pinholes.JPG


In addition to the squeeged West method, I like System Three ClearCoat, a very low viscosity epoxy intended for soaking into wood surfaces. I've used a lot of it on past projects. For example, two bushed coats will completely waterproof the inside of plywood leading edges on wood wings and ailerons; much more effective than the usual epoxy varnish. A single brushed coat with a cheap chip brush works well for sealing fiberglass. Pot life is about 45 minutes, plenty of time to chase all the loose brush stands out of the epoxy. No worry about brush marks, ClearCoat flows out smooth. The resulting epoxy skin is pretty thick (a few .001's) and sands very well. I did all the tail tips and the upper gear leg fairings this way. Here's a shot of a tip after primer:

Emp%20Tip%20Primed.JPG


I also roll ClearCoat on large surfaces, much like you do with PF Smooth Prime and others.

So, that's glass fabrication and finishing at my shop, at this time. There are always new things to learn and new methods to try. Plenty of ways to skin the cat; you do what you like. The point here is that none of it is rocket science. Anybody can do it, so don't be bashful.
 
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Postscript.

Previously I mentioned spraying K36 or a similar high-build primer to correct any minor surface imperfection found after shooting a thin epoxy primer coat as a test. Well, I've got one end of the shop set up to paint now, so a bunch of small parts (and a few big ones) are in the final stretch.....last chance time.

If you held the tail fairing up to a glare light and sighted along it at a very flat angle to the surface, you could see some minor waves. The goal is an optically flat surface, so some high-build and blocking was in order. The part got a good scuff with with 400 wet, and when fully dry and clean, a coat of DPLF epoxy primer followed by two wet coats of K36.

The term "blocking" means using a sanding block with a firm surface to flatten the panel, cutting the high spots without dipping into the low spots. Simple on a flat panel, not so easy with a collection of compound curves. This fairing was done with 400 wet wrapped around a medium-firm foam tube about 3" in diameter. A harder tube will block better, but the softer tube can be squeezed a little for the smaller radius spots; do what works to flatten the surface. Don't slide a sanding tube along it's long axis; you'll just cut a groove. The motion is more like a roll combined with a slide 30-45 degrees off the long axis. A tube has one straight axis on it's surface; use it to cut. Use light pressure; don't push the paper down into the low spots. Do not "finger sand" (hold the paper in your bare hand) except for minor edge work; you must use a block of some kind if you expect to bridge the low spots and flatten the surface.

And finally, the good part...wash, dry, lightly wipe with a tack rag and shoot paint. This is PPG DBC followed by DCU2021 urethane clear. If you're a serious nut case (or pick up a little dust and/or orange peel), let it cure and then color sand. Lots of variations, but in general it means sanding with 1500-2000-2500 grit wet, then buffing with 3000 grit polishing compound followed by a finishing compound. www.vansairforce.com/community/showthread.php?t=60631

Ok, that's it, from scratch to finished. Hope it helped someone.
Emp%20Fairing%20Painted1.JPG


Emp%20Fairing.jpg
 
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Great info Dan, and thanks for helping me on the phone.

I'm gonna give this thread a bump so others can see how to do it.
 
tip from a fiberglass builder......

Great write up! I am building a Lancair ES composite plane. Two additional tips from the dark side!

1) Rather than doing the 4 BID layup on the part, lay out a piece of 2 mil poly on your workbench. Lay 2 layers of your cloth down....2 sets of 2 layers each; already cut to your rough shape. Mix your epoxy and pour onto the 2 sets of cloth. Go get a soda. Let gravity work most of the epoxy down through the layup. When full saturated, fold the rest of the poly over top and use a plastic squeegee to purge all the excess epoxy and the bubbles out. Get the bubbles out here as it is much easier here than on the part.

Cut your shapes out with a roller cutter. Put 2 BID #1 on top of 2 BID #2. You can do all 4 BID at once, but it takes a lot longer... my limit is usually 3 BID at a time, although I would prob. do this as 1 - 4 BID.

Pull the top layer of poly off and apply to your mold part. Work out whatever small bubbles may be left with a stippling brush and/or roller, then pull the top (2nd) layer of poly off. Work to shape and add peel ply as discussed before. You will like!

#2 You probably don't ned the wax over the release tape.

Have fun.

This is a great forum and I get a lot of useful info from it. Thanks to all.

Regards,

Gordon
 
What's the best way to close the fiberglass tail tips?
I've been thinking I would fit them, drill & cleco, and 'glass across the outside of the open end to hold the shape so it won't spring open when removed, then remove the part and glass in a few layers from the inside.
Then grind off the original outside layer and fill the imperfections.
But I'm thinking there must be a better way?
 
Stab tip closeout

Scott, we carved some medium weight open cell foam to fit the inside of the tip fairings. The piece was set back from the edge of the tip about 1/8", and epoxied in to achieve a slightly "inset" look to the closeout surface.

Then the exposed foam surface was glassed in with a couple layers of 5.8 oz S-glass. The S-glass edges were trimmed to fit the opening without any hangover. Finally, I laid in a little radius of micro to the inside peripheral corners to hide the glass edges and give it a nicer look.

empennage02.jpg
 
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Easy as 1-2-3.....

Cut a sheet of core material to fit the opening. It can be almost anything which bonds well using epoxy. I used some 1/16" aircraft plywood; ply makes good core, as does foam, glass laminate scrap, etc. Another good choice is a few plies of glass, formerly laid and cured on a flat surface. Grab some 5-minute epoxy and tack glue the core into place with the tips clecoed on the control surface and the fixed surface, so that any mismatch between them can be jigged out. Contour is locked once the caps are in.

Cure 15 minutes, remove the tip, wipe a flox filet on the inside. Not shown here, but you can add two plies of fabric on the inside, over the flox while it is still wet...adds impact resistance.

When cured, round the outside corners and add at least one ply of fabric. Two is better. When cured, sand to blend.

Bill's very nice concave ends are a simple variation of the above. That's the kind of thing which makes this game so much fun.

HS%20Caps.jpg


Emp%20Tip%20Primed.JPG
 
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Dan, I know it's been said before but I can't remember, is it necessary to remove the gel coat from the exterior of the tip before doing step 3?
 
Thanks Dan & Bill;
I'm seeing Bill's concave part closeout on the stab, and a rounded Dan closeout on the counterweight for a nicely nested fit!
As always, Keep sharing, we all benefit! :)
 
Dan, I know it's been said before but I can't remember, is it necessary to remove the gel coat from the exterior of the tip before doing step 3?

Epoxy will stick to gel coat just fine. However, the gel coat itself is weak, so it should be removed for a serious structural bond. Put another way, remove it where you intend to bond fabric.
 
Peel ply

Just reading through your great thread on fiberglass. There are two things I don't understand;
You talk about applying saturated peel ply. Please explain the saturated part. The second thing is that you say the part doesn't need sanding before applying more fabric. Is that because the peel ply gives it enough tooth for the new layer to grab?
Thanks for answering my dumb questions.
 
re the peel ply, i think he was just saying he laid the peel ply down on the fg fabric and it soaked up resin and became saturated.

remember, this part is not structural. If you were doing a structural part on a composite plane you would sand down the surface left by the peel ply to just see the fabric underneath if you needed to bond more fabric
 
You talk about applying saturated peel ply. Please explain the saturated part. The second thing is that you say the part doesn't need sanding before applying more fabric. Is that because the peel ply gives it enough tooth for the new layer to grab?

Let's assume you just finished wetting out 4 plies of fiberglass fabric. Immediately add one additional layer of polyester or nylon peel ply fabric. Wet it out exactly as you did the 4 fiberglass plies. Just treat it as you would another fiberglass fabric layer; fully saturated with wet epoxy, no trapped air bubbles. The only real difference is that you may need to apply it in small sections; the peel ply fabric won't conform to compound curves.

Later when fully cured grab an edge of the peel ply and rip it cleanly off the surface of the glass laminate. Pull off any loose fibers, then do any necessary touch up sanding where you might have allowed an air bubble. The surface needs no other prep prior to bonding new material. Ripping off the peel ply fabric left a "fractured" epoxy surface quite suitable for bonding...yes, tooth.
 
That was a quick reply! Gotta love this forum.
I finished up with peel ply this evening and right now it looks like h***.
Can't wait til it cures so I can see the result.
Thanks for the help.
 
Let's assume you just finished wetting out 4 plies of fiberglass fabric. Immediately add one additional layer of polyester or nylon peel ply fabric. Wet it out exactly as you did the 4 fiberglass plies. Just treat it as you would another fiberglass fabric layer; fully saturated with wet epoxy, no trapped air bubbles. The only real difference is that you may need to apply it in small sections; the peel ply fabric won't conform to compound curves.

Later when fully cured grab an edge of the peel ply and rip it cleanly off the surface of the glass laminate. Pull off any loose fibers, then do any necessary touch up sanding where you might have allowed an air bubble. The surface needs no other prep prior to bonding new material. Ripping off the peel ply fabric left a "fractured" epoxy surface quite suitable for bonding...yes, tooth.

This sounds like a way to get a heavy part. i know there are not a lot of fiberglass parts that rv builders make, but typically even with a sandwich of plastic on a layup beforehand that lets you remove much of the excess resin, there is plenty of resin left to simply add dry peel ply and it soaks up resin from the fabric, resulting in lighter layups. you can do more than necessary and remove resin from the fg cloth if you work at it but its pretty easy to notice when that happens
 
Different uses/different results.

Peal ply is usually used when you are planning on making a structural connection to a part----- you peel ply the area where the joint will be made. Typically in mold less composite construction you would lay up a spar (as an example) then later add the leading edge. You would peel ply the mating surface of the spar.

In the case above, Dan was using peel ply to achieve a smooth finish, and to give a smooth surface to work from.

In the first example, apply the peel ply dry, just let the existing resin wet it, and in the second, do it like Dan says.

One other use is when vacuum bagging a part, you use peel ply under the bleeder cloth, before the plastic.
 
This sounds like a way to get a heavy part.

No...the excess epoxy rips off with the peel ply.

Yes, lay dry fabric onto the wet layup. Squeegee or roll to work any excess epoxy up through the peel fabric from underneath, but don't be bashful about adding more epoxy. Only wet plies are translucent. Too easy to accidently introduce delaminations (air) in the underlying layup and not see them through dry peel ply, in particular over concave sections.
 
No...the excess epoxy rips off with the peel ply.

Yes, lay dry fabric onto the wet layup. Squeegee or roll to work any excess epoxy up through the peel fabric from underneath, but don't be bashful about adding more epoxy. Only wet plies are translucent. Too easy to accidently introduce delaminations (air) in the underlying layup and not see them through dry peel ply, in particular over concave sections.

when I worked on lancairs if you didn't get the peel ply to be slightly dry compared to saturated it was considered a sign that the fiberglass/ carbon fiber had more resin than it needed, and some of the resin would remain in the lay up after the peel ply was removed. Hence you would then have a heavier layup than necessary. a big difference in a composite plane, not sure it would make much more than a couple ounces difference in the few layups on an RV.

working daily on layups it was easy to see the difference between air bubbles and a less than fully saturated peel ply. being exp planes there was not a limit (that i was aware of because we personally were able to achieve nearly 100% bubble free layups) for amount of allowed air bubbles, but we strove for zero and mostly go it. i mention that as a difference from the columbias, which i heard had no tolerance for any bubbles/ air pockets/ delams although i never worked in the columbia plant so i can not say that with certainty.
 
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peel ply in layups

It has been proven that a peel ply'ed lay-up is typically heavier... the technique I teach is; after your layup is applied, take paper towels and remove any excess epoxy from the surface of the layup, then apply a dry piece of peel ply and stipple with a DRY brush... if the peel ply quickly fills with epoxy, YOUR LAYUPS ARE TOO WET!!

Most folks use waaaaay too much resin to start with, either when wetting out a plastic sandwich lay up, or when pre-painting a part before the plastic sandwich lay up is applied.

If you have a completely saturated piece of peel ply, and you remove it, exposing an even, completely imprinted or "fractured" surface (in other words, one of those really impressive looking lay ups that impresses the average hanger looker) you are actually looking at a layer of dried resin that's on top of fiberglass or carbon. This layer is dead weight that does not have to be there. But it is pretty to look at...

Brad Simmons
Airframes Inc.
Milan, TN
 
If you have a completely saturated piece of peel ply, and you remove it, exposing an even, completely imprinted or "fractured" surface (in other words, one of those really impressive looking lay ups that impresses the average hanger looker) you are actually looking at a layer of dried resin that's on top of fiberglass or carbon. This layer is dead weight that does not have to be there. But it is pretty to look at...

Brad Simmons
Airframes Inc.
Milan, TN

"But it is pretty to look at..."

Yep, and as I read Dan's post, this is the exact reason he suggested doing it that way-----this was the last step of the layup portion of constructing the part, and gives a good basis to start the finishing portion.

Having done my share of trying to fill the weave of a cured part, (so it is smooth enough to paint) by the fill/sand/fill/sand/repeat as needed method, I appreciate the time savings of Dan's recommendation. And I doubt the weight difference would be very much on a fairing like this. A wet layup wing or fuse obviously will have a much greater weight factor, not only due to the greater area, but also the weave of the cloth is usually more open, thus needing a greater amount of epoxy per unit of area.
 
"But it is pretty to look at..."

Yep, and as I read Dan's post, this is the exact reason he suggested doing it that way-----this was the last step of the layup portion of constructing the part, and gives a good basis to start the finishing portion.

Having done my share of trying to fill the weave of a cured part, (so it is smooth enough to paint) by the fill/sand/fill/sand/repeat as needed method, I appreciate the time savings of Dan's recommendation. And I doubt the weight difference would be very much on a fairing like this...


Very well said.
 
Lancairs incorporate many, many feet of interior fillet layups where skin is joined to reinforcements (stringers, spars, ribs, bulkheads, see drawing below, left side). Those layups are not subject to subsequent surface finishing or structural bonding, and there isn't any reason to care what the surface looks like when partially adhered peel ply is removed. Those the layups you're talking about Brad?

Similar joints might appear on an RV. Here's a Showplanes canopy frame:

Canopy%20Interior%20Painted.JPG


Structure is an outer skin, with bonded-in honeycomb ribs. The ribs joints get a fill wipe and glass plies. The fillet plies on these ribs did need finishing; weave coverage as well as fairing the 0.020" ply dropoff. You could do it all with micro, but a wet peel ply application fairs most of it as part of the original layup...no muss, no fuss.

Peel%20Ply%20to%20Fair.jpg
 
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Dan,
You are correct in that Lancair has moved away from the "miles" of fillet/2 bid rib construction and most everything is now "glue together" premolded flanges. Much faster, but most certainly heavier.

Realistically, how much weight would you save on say, a Lancair IV if every lay-up was peel-plyed and extra-wetted for either looks or finishing vs. taking the paper towel/dry brush method to extremes? 5/10 pounds? Now, think about what this total would be for the average RV...

Another thing to take into account is the fact that this excess resin weight that is saved will partially be offset by the weight of dry micro or Superfil or whatever filling method is chosen. But do note in the fillet/lay up drawing in Dan's post the layer of surface resin that makes the bids on the right side thicker than the similar bids on the left... if you assume this to be bids at the intersection of a horizontal and vertical stabilizer, think about how much farther up and outboard your following bodywork would extend since you have a bigger bump to hide. On the other hand, if this is a ring bulkhead lay up in a tailcone, why not make it pretty?

It's more of a mindset than anything... most folks who don't go the extra mile in one area (as it relates to saving weight) won't bother in others. That's how planes end up heavier than planned...

Brad Simmons
Airframes Inc.
Milan, TN
 
.. Now, think about what this total would be for the average RV...

5-10 ounces total?

..excess resin weight that is saved will partially be offset by the weight of dry micro or Superfil or whatever filling method is chosen.

Yep....fill it with something or look at the weave forever. Dry micro is roughly 1/2 the weight of solid epoxy, so there is some penalty for fairing drop offs with wet peel ply. On the flip side, it's fast and doesn't add up to much weight in the limited RV application.

Context is important. This thread is about a 4 ply layup of 8-harness over a male form with concave, compound curves. The tight weave traps air easily and tends to slide around when worked. The neophyte target audience is highly likely to bubble the layup, so I'm teaching saturated peel ply is translucent; they can see the problems. And it doesn't make much difference in finished weight...see below.

..do note in the fillet/lay up drawing in Dan's post the layer of surface resin that makes the bids on the right side thicker than the similar bids on the left...

Not really. I like to quantify things, so just for the heck of it I made four test coupons yesterday. First step was to wet out 2 plies of 8.9 oz 8-harness between 4 mil plastic sheets, then work it hard with a roller to remove excess epoxy. Cut it into four sections and pulled the top plastic sheet from each.

(1) The first was allowed to cure as-is.

(2) The second was blotted severely with a paper towel.

(3) The third got 1.7 oz dacron peel ply, and was blotted firmly with a paper towel to pull excess resin up from the layup.

(4) The fourth got identical peel ply and blotting, then additional epoxy was poured on top to make the peel ply sloppy wet.....more than you would ever use to simply make it fully translucent.

After cure each sample was cut into a five inch square and the two peel ply samples were stripped. The four coupons were clamped together and the edges were sanded so all were perfectly identical in size.

As-is weighed 20 grams. The blotted/no peel ply coupon was 18 grams. No surprise. When cured the blotted coupon showed several white dry patches; I'd call it right at the edge of the old 10% rule for acceptable. Maximum lightness for sure. Without peel ply both samples had heavy weave pattern to cover with some subsequent filler step, but both would require heavy sanding to prep for bond. You would cut into the top glass fabric layer.

The blotted peel ply coupon (3) was 19 grams. The blotted then soaked coupon (4) was 20 grams. The blotted/dry peel sample, like (2) above, showed some dryness but again within the acceptable range. Coupon (4) showed no white patches. Both were of course bond-ready without further prep.

The 1-coupon sample is arguably too small to call the results absolute, but it's a reasonable guide. Works out to be about 5.76 grams per square foot of laminate, about 2/10ths of an ounce.
 
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Dan:


As if evidence was needed this will remind me never to get into an argument with you about Fiberglass technique.

And reminds me why I'm glad I'm building an aluminum airframe...
 
I like being a Neophyte - has quite a natty ring to it............ :D

I guess I belong to the latter description rather than the former :rolleyes:


A neophyte is a beginner.

In the context of Christianity, the term often refers to:

1. New convert to the religion, in the Catholic and Orthodox Churches an adult convert is considered a neophyte for one year after conversion. Roman Catholic neophytes are considered full members of the Church, but may not act as sponsors for others planning to join,
2. Newly ordained priest,
3. Person who recently took a monastic vow.

Neophyte may also refer to:

* In ecology, a neophyte is a plant species recently introduced to an area (in contrast to an archaeophyte, a long-established introduced species).
* In fraternities, it is a person that is a new convert or member of a secret fraternal organization, a beginner or novice member of the organization, or a recent convert (rookie/freshman) to the fraternal organization.
 
Dan, great test! It goes to show that the differences are mighty small.

I used to teach one of the Sportair courses, and I found that there's more than one way to skin a cat... if you are comfortable with a method, and you can get a desired result, stick with it!

Thanks for going to the effort to test this. FWIW, we did a similar test a few years ago with similar results. I did not have any dry spots but that's probably due to the fact that I have blotted a lot of layups. But in the end, the same results. I think our lightest effort was about 10% below the average.

Regards,

Brad Simmons
Airframes Inc.
Milan, TN
 
..we did a similar test a few years ago with similar results. I did not have any dry spots but that's probably due to the fact that I have blotted a lot of layups. But in the end, the same results. I think our lightest effort was about 10% below the average.

That's more or less where these samples fall. With the "no peel ply" samples (1 and 2), the heavily blotted coupon weighs 10% less than the unblotted coupon. The overall fiber-to-resin ratio looks reasonable, 48 to 54% fiber, but these were rolled-between-plastic wetouts. You're certainly right to stress caution about allowing brush wet-outs to become way too wet. The use of peel-ply over them as a sort of bleeder sheet to consolidate plies and pick up excess resin is a good tip.

The difference in the "with peel ply" samples was 5%. The little dry patches seem to be minor surface starvation.

No structural effect except to make a hidden layup lighter, your goal and all good. I suspect any sort of subsequent wipe with micro or resin is going to bleed enough resin back into the surface to eliminate them.
 
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Dan,

Your fiberglass work is much better than mine :) I'd like to "practice" some and if you would post a list of materials, I would be greatful. I would like to use the west system in my work.

Thanks
Chris
 
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