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Help with Closing the Elevator Tip

Nihon_Ni

Well Known Member
I've been struggling to figure out a suitable way to close the forward edge of my RV-8 elevator tips. The edges of the E-714 Counterweight where it meets the Counterbalance Skin are square whereas the E-713 Counterbalance Skin is rounded. DWGs 4 and 5 indicate this is the intended design, but as I've researched VAF for tips on this detail, I can't figure out how folks have closed the forward end of the elevator tip without the closure extending well forward of the Counterbalance Skin.



I don't want to bond the tip to the elevator, so I'm looking for a solution where the fiberglass tip will conform to the Counterbalance Skin. I think there's sufficient mass on the right Counterweight to carve the corners down so that I can add a layer of fiberglass that will create a elevator tip that is flush with the Counterbalance Skin. However, the left Counterweight doesn't seem to have enough excess weight to allow removal of the edges unless I added the removed mass to the back side of the Counterweight.

Does anyone have a tip on how to close the elevator tips to match the Counterbalance Skin?

Thanks,
Rob
 
Tightly tape the counterweight and spray with release agent (PVA, polyvinyl alcohol). You do have to trim the lead slightly to the shape of the aluminum.

Feather (taper the glass) of the leading edge of the tip to give some bonding area for new glass.

Assemble tip to the prepared elevator (with dried release agent so it comes apart again).

Lay up (epoxy / glass) the leading edge of the counterbalance overlapping onto the feathered edge of the tip. Let cure.

Hold your breath while you remove the tip, trim and sand to final shape...

I installed mine with nutplates so I could easily get in to adjust balance.

 
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Just make a spacer to go between the weight and the skin
You can use a piece of .032 scrap and dimple the two holes to make a single spacer, like a big washer to move the weight in. Or use two pieces to get what ever thickness you need.
 
If the elevator tips are supposed to be riveted on with CS4-4 blind rivets, how are you supposed to access the mass balance so that it is specific to your final elevator weight? Do you just rivet the tips on later after paint then paint over the individual rivets?
Tom.
 
If the elevator tips are supposed to be riveted on with CS4-4 blind rivets, how are you supposed to access the mass balance so that it is specific to your final elevator weight? Do you just rivet the tips on later after paint then paint over the individual rivets?
Tom.

Put a platenut on the inside (i.e., outboard side) of the forward tooling on the rib hole so that you can add a bolt and washers (usually large fender washers) after painting.
 
It's ok to trim the lead. Reshape it on both the left and right elevator to clear the desired fiberglass cap. If you want the cap to release, cover the lead with clear tape, plastic sandwich wrap, aluminum foil, or spray PVA. Scarf on the new ends as below. After painting, balance the elevators separately by adding weight to the inboard side of E-704/704. Use the nutplate-and-washers method, or determine the necessary weight and make an appropriate steel plate to install there with blind rivets.

 
Thanks for all the input! Armed with this fresh perspective, I went back to work on the problem this morning.

Just make a spacer to go between the weight and the skin
You can use a piece of .032 scrap and dimple the two holes to make a single spacer, like a big washer to move the weight in. Or use two pieces to get what ever thickness you need.

I removed the screws to insert a spacer, but the dimpled countersinks in the Counterbalance Skin are preventing removal of the Counterweight. It's tight enough in there that if I force the lead weight out I'll ruin the dimples. This would have been a good option during construction, but I'm not sure I can retrofit it.

If the elevator tips are supposed to be riveted on with CS4-4 blind rivets, how are you supposed to access the mass balance so that it is specific to your final elevator weight? Do you just rivet the tips on later after paint then paint over the individual rivets?
Tom.

The plans say to drill them from the inside once the elevator is painted: The best approach is probably to leave the counterweights a little heavy, then drill the inboard side of the counterweight with a series of small holes until the elevator balances.

Ron & Dan, the method you've suggested seems to be my best bet. As I looked at the weights this morning, I realized I'll have to remove a fair amount of lead in order to get the shape of it to match the Counterbalance Skin once several layers of fiberglass are added and the corners are floxed. Perhaps it would be easier to just lop off about 1/4" of lead off the leading edge of the Counterweight to give me some room to create a fiberglass tip and match the contour of the metal skin?

I weighed the 5/8" section I cut off (the remainder of which is about 1/4" wide) and it's 4 oz. I could drill two holes in the outboard section of the weight and screw the removed piece to the aft side of the Counterweight. (I assume I'd want to also epoxy the removed piece to the back side to aide in securing it.) Or I could just add weight to the E-703/704 web as Dan suggested, but it would require a bit more weight if I added it aft of the Counterweight location.



Of course, all this would have been easier to do before I had riveted the counterbalance arm, but alas...
 
I agree with Dan, no need to move the weight. His diagrams are quite exaggerated for clarity.

Dan shows adding sheet fibreglass or plywood ahead of the lead, but you can also just wrap the new glass around the lead.

You only need to trim the lead to about 1/16 - 3/32 inside the final outer fibreglass surface. Imagine that you are using the lead itself as a mould, because you are.

Look at the midline of the aluminum part that wraps the lead, in line with the screws. I'll bet that the outer surface of that is about 1/16 forward of the lead, just about what you need for the glass. Trim the lead to continue that offset up and down around the corners of the lead that are currently outside of the aluminum. Make it a nice curve, the shape you want the tip to be.

Once you have the lead the shape you want, you tape it and the aluminum further out than you are going to glass, apply PVA so it will release easily, re install the scarfed fibreglass tip, and do the lay up. I did not use flox, just several layers of fairly light cloth to make up about 1/16 thickness. It goes around corners easier if you cut it on a diagonal, and you can use several pieces if it does not want to lay down... You will sand off the excess later...

If you have a builder in the area that has done it before, get him to give you a hand, it's not that difficult once you figure it out...

There is a tooling hole in the counterbalance just aft of where the lead is. If you install a 3/16 nutplate there on the inboard side, you can later install a stack of fender washers inside the tip for final balance. I installed nutplates and screwed the tips on after paint. (Some guys put the washers on the inboard side, but the possibility of that bolt coming loose and jamming the elevator would not let me sleep at night...)

Good luck!
 
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5/8"? I was thinking "round off the corners". The new glass end will only be about 1/16" thick.

The 5/8" is the forward section of the right counterweight that I cut off according to the plans.

I'll plan to just round the corners and leading edge to get the 1/16" recess. How many layers of cloth do you suggest?
 
Back to work!

Thanks Dan & Ron for your tips. I'm headed back to the airplane factory and will just round the corners of the counterweight and use it as a form for my fiberglass.

Rob
 
I had a big day in the factory today and I'm happy with the results. As suggested, I removed some material from the corners of the Counterweights to follow the contour of the Counterbalance Skin, with an allowance for a few layers of fiberglass. I used the notch I cut off the flange of the elevator tip as a guide for how much material I needed to remove in order to make the new fiberglass cap flush with the counterbalance skin.



The right elevator is still a bit nose heavy, but the left elevator was a little under after today's nose job surgery, so I added a platenut to the inside of the E-703/704 web centered on the tooling hole, and used the lead I removed from the right Counterbalance to add more weight to the left side.

With a little luck, my fiberglass supplies will arrive from ACS tomorrow, and I'll finish the job.

Thanks for all the assistance!
 
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Looks good Rob...

A suggestion would be to taper back the gelcoat a little more, particularly on the inner edge, to a point where the glass is flush with the aluminum. Right now the glass is a little proud... There is a black mark on the aluminum close to where it seems to come flush...

You might also want to install some sort of fasteners to make sure that the tip is in it's final position and will not be pulled to a different shape when you install them later... Maybe clecos or a few temporary pop rivets?

Don't forget release agent or it will be there permanently!
 
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Ron,

I was wondering how far I should sand off the gelcoat, and wasn't sure how much I need for proper adhesion of the new glass to the old.

If you're looking at the black mark in the bottom right photo, that's the mark I had for the aft edge of the counterweight. I noticed the Vans tip is bulging a bit around the counterweight and I think it needs sanded on the inside to relieve a bit of outward pressure.

There's a bit of gap between the outer edge of the counterweight and the inside of the fiberglass tip. Should I fill this with flox when I cover the front, or leave the gap to aid in removing the finished product?

Your comment about fasteners -- I drilled the tips to #30 and installed clecos prior to shaping the tips, but took them off to check the balance when I took the lower two photos. I think that's what you mean, right?
 
The left elevator is still a bit nose heavy, but the right elevator was a little under after today's nose job surgery, so I added a platenut to the inside of the E-703/704 web centered on the tooling hole, and used the lead I removed from the left Counterbalance to add more weight to the right side.

YMMV, but I found, as expected, that when the elevators are perfectly balanced during construction, they were unbalanced and required more weight (using the platenuts/bolts/washers) on both sides *after* painting.

Having those platenuts on both sides made final balancing straightforward...a stack of 4 or 5 large fender washers and a bolt on each side. Easy peasy and simple to check during each preflight...400+ hours and not a hint of loosening.
 
A suggestion would be to taper back the gelcoat a little more, particularly on the inner edge, to a point where the glass is flush with the aluminum. Right now the glass is a little proud... There is a black mark on the aluminum close to where it seems to come flush...

How's this?





After closer examination this morning I decided not to sand it from the inside and just kept shaping the outside.
 
Simple rule Rob...if it's a structural bond, remove all the gelcoat, primer, etc. If it's merely cosmetic, gelcoat doesn't matter.

I consider this fairing to be structural, due to the potential for control jam. More of a mindset than an engineering truth.

How far back to remove gelcoat? No good rule, but it's hard to go wrong with more, as there is going to be a filler application later anyway.

BTW, if you're not going to do a floxed-core corner, I'd cut the original glass back to about where the black line is in the prior photos, then scarf. The new layups won't like being bent over the current edge.

The advantage to a cored corner is that it allows shaping the corner radius before laying down any glass fabric. Here the glass-to-glass scarf joints are primary, so micro would core for shape just as well. However, cored corners are not strictly necessary....lots of ways to skin a cat.
 
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Trimming lead

Any tips for shaping lead?

Just curious what you used to trim the lead. I'm at about the same stage and don't really like getting small pieces of lead shavings all over (I have small kids who like to see what I'm doing) so I hesitate using a file. I was thinking about using a sharp knife to shave larger pieces off but then the resulting surface would be fairly irregular.
 
As Dan sugggested, tapering back the gelcoat a bit more is a good idea structurally. Dan also picked up on your latest pics that show too sharp a radius near the tip. Glass layup is reluctant to stick to a radius less than about 1/4", so you'd need to grind back more like you've done inboard.

If you want a sharper radius, that is where flox comes in handy cause it will conform to a sharp corner if that's what you want.

As Dan says, lotsa ways to skin a cat...
 
Any tips for shaping lead?

Just curious what you used to trim the lead. I'm at about the same stage and don't really like getting small pieces of lead shavings all over (I have small kids who like to see what I'm doing) so I hesitate using a file. I was thinking about using a sharp knife to shave larger pieces off but then the resulting surface would be fairly irregular.

I just used files to do the shaping work. I didn't try using a knife, so I can't speak to it.

MarineEA6BNFO

;)
 
Update

Here's a few pics after this morning's work.





Any tips on how to get fabric to conform to the curve on three sides? Perhaps I need to use two strips in a diagonal fashion?

It finally dawned on me during this process that the plans call for the tips to be bonded to the counterweights, and then I guess you just shape the lead/fiberglass tip together and that's how you close it. Perhaps that was obvious to other builders, but I didn't get it until I had already taken away too much lead to use that option.
 
"Any tips on how to get fabric to conform to the curve on three sides? Perhaps I need to use two strips in a diagonal fashion?"

The over-riding rule with fibreglass is to do what you need to do to make it work... How sharp a curve you can coax cloth around depends on the weight and the weave of the material. The industry has evolved significantly since I made a living at it and others can better suggest the most flexible weaves.

You may want to take a piece of wood and mock up a "tip" with similar shapes to practice on...

Your tool box includes the following techniques, all may not apply to this tip...

- recognize shapes that are even possible with one piece of material. There's no way you could wrap this tip with one piece with the fabrics I am familiar with. Two would be a minimum.

- lighter fabrics will conform to sharper corners, use more layers to get the thickness you want.

- for compound curves try cutting the fabric on a diagonal, it will conform to interesting shapes but is harder to handle without distorting

- cut smaller pieces and overlap. You will sand off the "lumps" later.

- keep a pair of sharp scissors handy, occasionally you may have to "dart" to get it to lay down.

- if there are sharp corners, less than 1/4" radius, mix up a stiff paste of flox or milled glass fibres. You can let it harden, sand and lay up over it, or just use it in the corners and lay up on top with cloth...

There's quite a range of ways that people do the tips. Mine are screwed in place because having access is important to me... Others bond them permanently and use filler over rivets and joint to make the transition disappear. That looks good too... It's up to you...
 
Ta Da!

It's been a while since I started work on the elevator tips, so I thought I'd give everyone an update. First, thanks for all the great input that helped guide me through this step. For the benefit of future builders I'll say that I accidentally made the tips removeable but I wasn't trying to do that. I just couldn't figure out how the plans wanted me to close the tips. I should have called the Mother Ship -- a few minutes on the phone would have saved me hours of work in the shop. By the time I finally figured out that I should just bond the tips to the counterweight it was too late as I had already removed enough lead to provide an allowance for fiberglass. Nevertheless, now that I'm on the other side of this modification, I'm happy with the results.

After I finished prepping the counterweight and elevator tips, I decided to set them aside and learn about fibreglass. I watched all the composite Hints for Homebuilders and the Van's RV-14 canopy videos (https://www.youtube.com/watch?v=EVEEcnNJJys&list=PLsHxidYW7eS2bmEfPh-zuZCXn5TXngVlY) which were really helpful. I decided my first experiments into the world of composite needed to be on something that was disposable, so before attempting the elevator tips I made a fiberglass map case, a cup holder, and caps for the other tips. I learned quite a bit with those training projects.

Project #1, the map case, ended up with a few air bubbles in it that would fail a quality test for a structural component, but for my purposes it was good enough. I used the hairspray release agent method I learned about in HFH, but the mold wouldn't release and I ended up digging the foam mold out. (The shape of the mold likely contributed to it's reluctance to release.) Sadly I had promised izzybear he could have the mold when I was finished, but I doubt he wants it now.



Project #2 was a cup holder for a custom fuel gauge mount / cup holder panel I built. I used the bottom of a wine bottle as the male mold, and covered it with electrical tape to eliminate the punt in the bottom of the bottle. This time I used five coats of Meguiar's Mold Release #8 wax and sprayed PVA on top of that, but the cured fiberglass wouldn't release from the mold and I ended up breaking the bottle to get it all out.



I also spent some time making fiberglass caps for the horizontal/vertical stab tips and enclosing the gap between the elevator and the counterbalance arms.



After I finished these projects, I felt ready to attempt the elevator tip. In case the tips wouldn't release from the mold, I decided to get all the hole and tip prep done before laying up the fiberglass (final drilling, countersinking, etc.). Worst case, I could pull off the electrical tape on the Counterbalance Arm and pop rivet the tips in place.



I covered the counterweights and counterbalance arms with electrical tape, seven coats of wax and two coats of PVA, then clecoed the tips in place. (Covering the arms was more of a precaution in case any resin dripped onto that surface.)



I cut a piece of fabric about half the size of a gallon Ziploc bag, put it inside the bag with epoxy resin and squeegeed it around to saturate the fabric. I then cut strips and triangles directly through the plastic bag like I’d seen on the videos, and laid them up on the tip. I ended up with 2-3 layers of fabric covering the counterweight. I found out that I couldn’t form a straight edge against the counterbalance arm that I was happy with, so the last layer of fabric extended over the taped and waxed counterbalance arm. After curing for about 5 hrs, I trimmed the overhang with a utility knife.



In the morning I removed the clecoes, took a deep breath and pulled outward on the trailing edge of the elevator tip. It popped right off easy as could be.



I sanded the tips smooth, added two coats of resin and glass bubbles, with sanding in between.



I sprayed the tips with filler primer and sanded them again, repeating the process a couple of times until they were smooth and fit the elevators nicely.



My left elevator needs a little more counterweight, so now that the tips are removable I was able to add a platenut to the inside flange of the counterbalance arm and add some additional weight under the tip. I was going to put this weight on the inboard side, but now that I can get under the tip I don’t have to worry about it backing out and jamming the elevators.



Thanks again to everyone who offered advice to me on this project!
 
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Excellent work on the tips! They will look WAY better than the stock style when painted.

I am also probably going to steal your idea of the fuel gauge / cup holder in the center console. That looks pretty neat.
 
Outstanding stuff, Rob! I've been putting off the same task because I just didn't know how to get started and between your and Dan's post, I think I'm good to go.

One question...what did you use to close out the stabilizer tips? Is that a glass layup or some other material?

Dave
 
I am also probably going to steal your idea of the fuel gauge / cup holder in the center console. That looks pretty neat.

I thought that was an original idea until I walked the RV line at AirVenture last year. It took a lot longer than I expected to end up with the final result. "Stick to the plans" has been my mantra, but the occasional custom development experience is good for pride in workmanship, and to remind me to stick to the plans!
 
Outstanding stuff, Rob! I've been putting off the same task because I just didn't know how to get started and between your and Dan's post, I think I'm good to go.

One question...what did you use to close out the stabilizer tips? Is that a glass layup or some other material?

Dave

I cut out a foam rib to fit into the end of the stabilizer tip when it was clecoed in place. Once it was the right size, I covered the foam rib with a glass bubble epoxy slurry and let it cure. (One caution, make sure the foam rib doesn't cover any of the rivet holes.)



The next day, I covered a smooth piece of plywood (from my fuselage kit) with a section of 2 mil plastic drop cloth, and laid up two layers of med weight fiberglass cloth (from the list that Dan recommended) directly on the plastic. I lightly sanded the foam rib, and then bonded it to the cloth while the cloth was still wet.



The next day I peeled the glass assembly off the plastic, trimmed it to shape, and sanded it to remove any imperfections caused by the plastic. I epoxied the whole assembly into the tip, with the tip clecoed onto the stabilizer. (The glass assembly was set back about 3/16" from the trailing edge of the tip to allow clearance for the elevator tip to swing through the center.) After that cured, I filled any gaps between the foam rib/glass layer assembly and the fiberglass tip with flox and then used glass bubbles to form a fillet between the edge of the tip and the glass cap.



I'm making the VS tip removable, and I made a spare VS tip with a notch to hold my GoPro camera. I closed end the same way as above, but for the notch I made a couple pieces of two layer composite, and epoxied them in place without the foam. After they were tacked in, I made a fillet of flox, then added two layers of cloth to the inside, basically following the suggestions in the plans.







 
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You're doing great Rob. Nice neat work.

Minor note....in this installment you coated foam ribs with wet micro, then allowed them to cure, then sanded them later for bonding to a glass layup.

When glassing to a foam core, wet micro is indeed used to fill the open bubbles in the foam, greatly improving glass-to-foam adhesion. Fine cell foam may not need micro, in particular if shear and peel are not critical. If used, allowing the micro to cure just adds time and effort. Instead, squeegee on wet micro, and immediately add the glass layups. In this case, slap on some micro, smoosh the rib against the wet glass, and wipe away whatever squeezes out.
 
You're doing great Rob. Nice neat work.

Thanks Dan -- that means a lot coming from you!

Minor note....in this installment you coated foam ribs with wet micro, then allowed them to cure, then sanded them later for bonding to a glass layup.

When glassing to a foam core, wet micro is indeed used to fill the open bubbles in the foam, greatly improving glass-to-foam adhesion. Fine cell foam may not need micro, in particular if shear and peel are not critical. If used, allowing the micro to cure just adds time and effort. Instead, squeegee on wet micro, and immediately add the glass layups. In this case, slap on some micro, smoosh the rib against the wet glass, and wipe away whatever squeezes out.

Thanks for the tip. That would have cut a day's curing time out of the process. When I was doing this I understood why some builders recommended getting the quick cure hardener too.
 
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