Fiberglassing the empennage tips on your RV airplane
by Bob Collins and Darwin Barrie
Long-time RV-building friend Darwin Barrie helped me out a few years ago when I first inquired about fiberglassing the tips on an RV airplane. At the time, I was messing around with the Whelen light that goes in the rudder. I never did get around to actually attaching the tip to the rudder, which is one of my goals for this summer.
I have, however, been finishing up the final assembly of the empennage in anticipation of spending the coming winter working on the electrical system and engine (which we mounted a few weeks ago), so I've had a good reason to look up Darwin's original reply on the YahooGroups RV site.
I'm reprinting portions of it here, adidng pictures, and my own description.
You'll need a quart of West Systems epoxy, the fast cure hardener (provides plenty of time to work) the metered pumps, 410 micro filler, 30 minute epoxy from a hobby shop or home store. (Get the 5 or 6 oz bottles)
Luckily, there's a West Systems store in nearby Stillwater, Minnesota. The place is expensive (hey, they cater to a yachting crowd), but it's sure a lot better than paying shipping and handling charges. Don't even think about using anything other than West, which you can also find at boat shops around you, I'm sure. I bought both a quart of the fast hardener and the slow hardener. At least for the elevator tips, I'd recommend going with the slow hardener. When I attached an elevator tip, by the time I finished pop riveting it on, the remaining filler in a cup was hard.
This process can be slowed by spreading the peanut-butter-like slop on some aluminum foil or something similar, rather than leaving it in the cup.
Rage auto body filler, Everycoat 416 glazing compound.
I think that SuperFil, which you can get from Aircraft Spruce, is also acceptable here.
I do not like using the sheets of glass and cutting strips. These are tough to work with especially when you haven't worked with glass much.
I recommend contacting www.cstsales.com and ordering fiberglass tapes.
I found this to be valuable advice, too. With the edges of the fiberglass "bound," you don't get quite so much flying around of strips of glass. Since I did the canopy fairing first, I found these useful for that as well. Buy a lot.
For all of my tail work I used 1" wide tape. For the front of the windscreen I used 1", 2" and 3" tapes.
For the tail glass, cut the flange on the glass so the piece will fit flush to the part you are working on.
Darwin's not talking about your fiberglass cloth, here (at least I don't think so). He's talking about the actual tip. If you haven't built your tail pieces yet, here's a tip of a different sort: Pay attention to the plans! They tell you to trim the outer rib flanges on the elevator and horizontal stabilizer. If you don't do this you'll have a gap when you go to to attach your fiberglass tips and the only way you can alleviate this is to sand the tips until the tip fits flush. The problem with this is that there then isn't enough fiberglass to rivet into and have edge distance. In my cases, there was none. However I made metal strips for inside the tip for the rivet to attach to, and I just let it overhang the edge of the fiberglass tip.
Make sure the glass isn't hitting on the rib when it is in place.
Sand the flange and an area about 1.5" from the joggle with at least 100 grit paper.
The joggle is the "indented" part of the fiberglass tip meant to slip under the skin of the horizontal stabilizer, vertical stabilizer, rudder, or elevator. I believe DWG 5PP shows the details.
Also sand the inside of the glass, the inside of the metal pieces, and an area about 2" from the edge on the outer skin.
Cut some strips of .032 for backing strips on the inside of the glass. Rough these up and epoxy in place.
I used Gorilla Glue to attach those strips and lots of small C clamps. But I could have just as easily used the West epoxy. You can never have enough C clamps. Just getting started on your RV build? Buy lots of C-clamps. Be sure you clean all of these parts with acetone before you do anything.
If you have you'll need to countersink the glass. I used a Dremel with tapered stone. If you use a countersink bit or deburring bit it will be worthless for metal when done.
True that. I bought a second countersink bit and used it just for fiberglass. I did the same with drill bits for both the fiberglass and stainless steel.
If you haven't dimpled you can countersink the metal for the CS4 pop rivets with a deburring tool. Do this until t he rivet is flush. The CS4-4's have a very thin head that doesn't take much to countersink.
When done and ready to attach for good, mix a batch of West Systems and 410 filler into a near peanut butter consistency. You will only need one pump of epoxy and one pump of hardener for this.
Tip: If you buy plastic cups, you can use them over and over again, even though the epoxy hardens. Just squeeze it a few times and it'll pop out. There, that tip saved you about $5, but at this stage of the build -- if you're like me -- $5 is worth saving.
Butter the joggle with the mix...
... attach and piece and cleco in place. Pop rivet in place.
Use a credit card or similar material to clean off all of the epoxy that has been pushed out. Use the epoxy to fill any low areas.
When cured, block sand to clean the joint.
Use some
of the 30 minute epoxy with micro filler to fill any significant
low areas or gap in the glass/metal joint.
Sand when
cured. (Sorry, I didn't get a picture)
Use the
1" glass tape and cut a piece that overhangs the trailing edge.
For the rudder, for example, cut this piece to go to the rudder
horn. Cut another piece to go around the LE. Use a half pump of
epoxy and hardener and thin with acetone or alcohol.
Be sure
to use a container that won't melt. Clean the pieces again with
acetone.
Brush
a coat on the pieces to wet the area. Don't over do it. Now lay
the glass tape on the piece and center over the gap. Brush the
epoxy on the tape to to make it wet. Again, don't overdo it, just
get the weave wet.
Here's my
piece with some peel ply added. I did cut the mixture with acetone
slightly although I'm not yet sure why. Since my elevator is already
on, I really needed things to set up quickly before gravity could
take over on the bottom piece.
When cured
lightly sand the tape and the edges.
Here you can see, I've removed the peel ply and lightly sanded.
Mix a
small amount of Rage with the hardener. It doesn't take much hardenener.
A half dollar sized puddle only needs a BB sized amount of hardener
to make it go off in less than 10 minutes.
Use a
squeegee or credit card and fill the edges of the tape and any
other low areas. Pretty simple.
You can probably see here that I've used SuperFil. It's very light and very easy to sand. I also filled a couple of pop rivets inboard of the tip.
When cured,
block sand. If you have any significant low areas use Rage. When
you are down to final small areas to fill, use the 416 filler.
I couldn't
find anyone around here who carries Everclear, but I found a 3M/Bondo
finishing glaxe and tried that. So far, I'm not too impressed,
but it's probably because I didn't mix it right and it set up
in about 3 minutes.
After sanding
it down...
I shot it
with some filler primer...
Pretty good.
Not great. Yet. I found some areas that I sanded through the glass...
Seems like a simple
fix. I'll mix up some more filler, sand, and repeat.
This process
may take a few mixes. It is not hard to do. Work till you are
satisfied.
Boy, you've got that right, Darwin! I added some more finishing glaze and sanded some more. I still don't think I've got it right and I'm not ready to shoot more primer filler on it because I know what it's going to reveal.
And this, it seems to me, is one of the hardest parts about building an RV. It's not that this is hard, it's there we're talking an elevator tip here -- one stinking tip. Last year, when I was working on the canopy fairing, it felt like I was spending all summer on it (I took two months). Keep in mind, I can only work on the plane an hour or so a day, but this particular task -- fiberglass -- tests your standards. When you want to give up and say "good enough," the task at hand screams, "no, it's not." It's hard to work on these things and not think, "at this rate, I'll never be done."
But if the canopy fairing is any indication, at some point, you repeat the filling process for the umpteenth time, sand and -- son of a gun -- it's done! And you can be proud of it.
Booya! This is the same spot shown above after a little more finishing glaze was used.
You can't tell well here but it's super smooth. I do detect a slight rise at one point, so I'm going to go with one more round of finishing glaze and some 600 grit sandpaper.
This process works great, is very light, and extremely
durable. If you have prepped properly your bond will last the
life of the plane.
(Note: You can also find some other fiberglass tip work details on my blog, Letters From Flyover Country.)
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