Elevator fiberglass tip question

[ChrisL]

I have trimmed the elevator tip so that it fits properly around the lead counterweight, but I have run into another problem. It seems that when i insert the tip, the counterweight arm rib stops the tip from being inserted all the way, leaving a 1/8 gap all around. If I squeeze the tip, I can get it in all the way, but then the flutes on the counterweight arm then push the tip down and away from the predrilled holes on the skin.

Also, measuring the distance from the predrilled holes to the counterweight rib, I get only .20 instead of the required .25, so it seems like trimming the edge of the tip won't work either.

Any ideas?

[DanH]

Ahhh yes, reality vs plans. Reality always wins.

I suspect Van's specifies an edge distance because the glass itself it quite weak in shear at the rivet hole and they anticipate builders attaching the part with pop rivets only. Without enough edge distance the rivet holes in the glass might tear out. A loose stabilizer cap might jam the elevator, or a loose elevator cap might give you some interesting trim forces.

Since reality says you must trim the the glass, you must toughen the mechanical joint. The popular method seems to be roughening the inside of the flange on the glass and bonding roughened aluminum strips to the inside. Now your pop rivets go through skin, glass and the aluminum strips. Some even use nutplates and screws.

Another approach would be to bond the the tips directly to the skin. Roughen the inside of the skin and the outside of the glass flange (best is removing the gel coat) and coat both parts with an epoxy during assembly. West is probably ok; add some cabosil so it doesn't creep out of the joint before cure. Fanatics might use something like Hysol, and I wouldn't be surprised if some have used proseal. If you intend to give your tips the "fill and blend" treatment, you can also lay one ply of glass fabric across the outside of the joint.

[FredMagare]

Sand it down more. The joggled portion of the tip need not go that far. Also, don't rivet in place until it's sealed. (The mistake I made.)

Mine seem reasonably secure with no additional reinforcement.

[ChrisL]

Sounds good - I guess unless anyone has other ideas, I will trim the edge so that it lines up properly. This will put the center of the prepunched holes on the elevator arms at .20" from the edge of the fiberglass, so I will beef this area up with some epoxied aluminum strips. I will be laying glass and filling over this joint anyways, so that should help with the possible loss of shear resistance due to the edge distance.

Anyone have a good website showing this whole fiberglass tip process?

Thanks,
Chirs