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Best technique for covering backside of empennage fiberglass fairings

rvator51

Well Known Member
I am getting ready to fill in the back sides of the empannage fiberglass fairings. I had heard that people use balsa wood to make a plug that fits inside the fiberglass fairing and then glue it in? And then fiberglass over it.

Is that still the preferred way to go or is there a better way to do it?
 
That will work. I laid up some flat fiberglass (about 6 plies I think), cut to fit, put a flox fillet in and then filled in with micro...brushed on neat resin after. Many ways to do this. Foam also works as a foundation although it may absorb water
 
This is new to me... why does the fairing need to be filled in?

And what is the extent of it?

Dave
RV-3B, now on the fuselage
 
That will work. I laid up some flat fiberglass (about 6 plies I think), cut to fit, put a flox fillet in and then filled in with micro...brushed on neat resin after. Many ways to do this. Foam also works as a foundation although it may absorb water

I did a two (2) ply layup on a single layer of plastic trash bag, covered with single layer of plastic trash bag. Once cure, I cut it to fit inside the tips. I glued it in the tip with a few drops of 5-minute Epoxy then used flox on the inside with a layer or two of glass. I then added more glass on the outside after cure.

This is new to me... why does the fairing need to be filled in?

And what is the extent of it?

Dave
RV-3B, now on the fuselage

Typically many guys follow the plans and close out the open area that the tips create when they are attached to the VS, HS, and elevators.
 
The method I have used for many years and as described in the RV-14 plans...

- Use a piece of waxed aluminum to make a thin laminate with two layers of cloth and resin. If the close out piece is not flat, the metal can be bent/shaped to result in a laminate piece that will match the opening you are intending to seal.

- Once it is cured cut out the filler piece so that it is approx. 1/6" bigger around perimeter of the fairing opening.

- Sand the interior (non smooth) surface of the lay-up, and about 1" back from the edge of the fairing for additional bonding/glass lay-up later.

-With the fairing clecoed in place and tape/etc. being used to hold it in the desired finished shape, wet the edge of the fairing with resin... and hold the laminate in place with tape to the fairing until the resin fully cures.

-Uncleco and remove the fairing. Apply a fillet of flox mixture around the interior corner/intersection point between the laminate and the fairing. While the flox is still wet, add one more layer of glass to the inside of the laminate, large enough that it laps onto the fairing by about 1". Cleco the fairing back onto the airframe while it fully cures.

- Sand the excess laminate flush to the fairing on the outside and radius the corner as desired (possible because of the flox fillet on the inside).

This all takes very little time, is strong, light, and best of all doesn't require tedious futzing with shaping a filler piece of balsa or foam to properly fit the inside. It does require that you have a way to keep the main fairing in the desired shape/position but that is easy to do with tape and wood sticks if needed.
 
- Use a piece of waxed aluminum to make a thin laminate with two layers of cloth and resin. If the close out piece is not flat, the metal can be bent/shaped to result in a laminate piece that will match the opening you are intending to seal.

- Once it is cured cut out the filler piece so that it is approx. 1/6" bigger around perimeter of the fairing opening.

- Sand the interior (non smooth) surface of the lay-up, and about 1" back from the edge of the fairing for additional bonding/glass lay-up later.

-With the fairing clecoed in place and tape/etc. being used to hold it in the desired finished shape, wet the edge of the fairing with resin... and hold the laminate in place with tape to the fairing until the resin fully cures.

-Uncleco and remove the fairing. Apply a fillet of flox mixture around the interior corner/intersection point between the laminate and the fairing. While the flox is still wet, add one more layer of glass to the inside of the laminate, large enough that it laps onto the fairing by about 1". Cleco the fairing back onto the airframe while it fully cures.

- Sand the excess laminate flush to the fairing on the outside and radius the corner as desired (possible because of the flox fillet on the inside).

Picture, general concept. I like some scarfed glass on mine.



 
I used aluminum sheet from the trim bundle to fill the back of the fairings. Easy to work with. Free. Lightweight. Strong.

Photos are here.

I used epoxy with flox to bond them in place, then used epoxy with micro on the outside to fill it out smoothly.

IMG_1870-M.jpg
 
Picture, general concept. I like some scarfed glass on mine.

Yea, there needs to be some overlap beyond just the edge bonding.
That is why I make the laminate thin and add another one or two layers (depending on cloth thickness) on the inside, lapping onto the original fairing.

Thanks for adding the sketches... makes it much simpler to understand.
 
Feedback and advice on my horizontal stabilizer tip fairings fitting

Hello, The sheet metal work requires less artistic sculpting than the tip fairings. I am not a sculptor. Can some people review my trimming and provide me feedback and advice before I fine tune them.

I could smooth these out a bit or I could build up the elevator tip fairing to be square and flat and that would make the horizontal stab tip fairings easier and flat as well.

Once I have them trimmed I will cut a foam piece and insert and smooth it over and lay-up the glass over it.

I could also take a compass and scribe a line even with the Elevator tip and trim to it.

1-IMG_4467.jpg


2-IMG_4468.jpg


3-IMG_4469.jpg


4-IMG_4470.jpg


The underside view.


5-IMG_4471.jpg


6-IMG_4472.jpg


Thank You
 
There are lots of ways to skin this cat. In your situation, it appears that the horizontal stab tips have a little more span than they need to match the elevator tips.

With that in mind, you can apply flox in any holes you've drilled in the elevator tips, slide them outboard slightly to match the stabilizer tip, then re-drill. You'll have a valley to fill between the elevator tip and elevator.

Another option would be to "move" the joggle in the stabilizer tips. You can do that by using a sanding block or a file with the abrasive side up against the joggle line, and tape on the side that lays flat on the flange on the fiberglass. You simply sand (or file) the joggle back to a point where it fits in a way so the HS tip and elevator tip match.

Another way is to apply a bunch of filler to the elevator tips. You'd want to sand through the gel-coat in any areas you wanted to build up with filler. You might also want to apply a layer of fiberglass cloth over the filler.

Again, lots of ways to address this...
 
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Thank you but what abuot the gap between the two pieces

I had noticed the protruding tip past the elevator, but I thought the difference was OK. Based on your observations, I must be wrong. I will pull the elevator tip out as you suggested.

Could you comment the trimming of the gap between the two pieces. I wish it was straight but it is not and pulling the elevator trim out will make it a bit worse...unless I pull the trailing side out enough to straighten it. Hmm time to fiddle.
 
I had noticed the protruding tip past the elevator, but I thought the difference was OK. Based on your observations, I must be wrong. I will pull the elevator tip out as you suggested.

Could you comment the trimming of the gap between the two pieces. I wish it was straight but it is not and pulling the elevator trim out will make it a bit worse...unless I pull the trailing side out enough to straighten it. Hmm time to fiddle.

Fit and finish is all up to the builder. It'll fly just fine either way.

What I did to finish off the elevator to my satisfaction, then closed the HS end to match the elevator. I also applied a fairly heavy coat of micro to the aft part of the HS tip, taped a 1/8" thick piece of baffle seal material over the front of the elevator tip, and wiggled the elevator to "mold" the micro to the elevator tip. There's probably a better way.
 
The method I have used for many years and as described in the RV-14 plans...

- Use a piece of waxed aluminum to make a thin laminate with two layers of cloth and resin. If the close out piece is not flat, the metal can be bent/shaped to result in a laminate piece that will match the opening you are intending to seal.

- Once it is cured cut out the filler piece so that it is approx. 1/6" bigger around perimeter of the fairing opening.

- Sand the interior (non smooth) surface of the lay-up, and about 1" back from the edge of the fairing for additional bonding/glass lay-up later.

-With the fairing clecoed in place and tape/etc. being used to hold it in the desired finished shape, wet the edge of the fairing with resin... and hold the laminate in place with tape to the fairing until the resin fully cures.

-Uncleco and remove the fairing. Apply a fillet of flox mixture around the interior corner/intersection point between the laminate and the fairing. While the flox is still wet, add one more layer of glass to the inside of the laminate, large enough that it laps onto the fairing by about 1". Cleco the fairing back onto the airframe while it fully cures.

- Sand the excess laminate flush to the fairing on the outside and radius the corner as desired (possible because of the flox fillet on the inside).

This all takes very little time, is strong, light, and best of all doesn't require tedious futzing with shaping a filler piece of balsa or foam to properly fit the inside. It does require that you have a way to keep the main fairing in the desired shape/position but that is easy to do with tape and wood sticks if needed.

This worked out fine for me, except I had a bit less gap on one side than I needed - I had to shape it a bit to have full elevator clearance. I laid up an extra layer inside and shaped it, filled as needed and sanded it smooth.
 
This is new to me... why does the fairing need to be filled in?
And what is the extent of it?
Dave
RV-3B, now on the fuselage

Disclaimer #1: I'm building an RV-9 not an RV-3, although they are related.

I'm gonna go out on a limb here Dave cause (Disclaimer #2:) I really don't know but.....

I believe the ends are filled because, at speed, the air rushing over the parts and then past the open cavity would create a turbulence. That turbulence could cause the part to oscillate, wobble and potentially break. Or worse, force the empennage to start to oscillate and get damaged.

(Another disclaimer) Again, I really don't know but if Van's says puts it in the build, well, they have their reasons. I suppose that if the gap was at a very close tolerance the air wouldn't have a chance to do anything nasty. However, if the parts were built that close together there would be no room for movement.

Having said all that - best thing to do is call or write Van's and ask.

My $0.01
 
This is new to me... why does the fairing need to be filled in?

And what is the extent of it?

Dave
RV-3B, now on the fuselage

David, I am closing my tips now and was researching some methods of closing the end cavities. I found a comment by the late Bob Axsom (RV6A) where he stated that closing the ends of the HS and forward (counterweight section) of his elevator gave him 3 kts. Knowing Bobs dedication to data and speed it is to be believed. I don't know about your 3, but the Rockets also square off the elevator and hs ends, usually with some threaded standoffs and a .025 plate tightly fitted.
So, the short answer is speed with a maybe thrown in for RV's other than 6's and 7's. It may be different for elevators with a counterweight that extends to the LE of the HS. I like to think in terms of efficiency, so I will be claiming better MPG. ;) YMMV - Ha!
 
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