Help with Closing the Elevator Tip
 

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.

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.

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.

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.

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...

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

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!

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?