Joshua's RV-9A Project

Finishing up random elevator tasks today…mounted, drilled, primed, and riveted the brackets for the trim tab motor, then set it aside for now. Mounted the trim tab and marvelled at the moving part! Pulled all the plastic off the empennage components for storage, and took a crack at hanging the elevators on the horizontal stabilizer.

I adjusted the rod-end bearings to their proper length and reamed out the holes in the brackets for the bolts (the powdercoat clogs the holes somewhat). It was here that I discovered an issue…

It seems that when both elevator counterbalance assemblies are clamped “in trail” (aligned with the horizontal stabilizer), the right trailing edge is about a half inch higher than the left. They’re both straight, and the gap is consistent along the whole length. Playing around with a 4′ level, I checked both elevators for flatness and eventually came to the belief that the right elevator is twisted. The result is that either the TE’s match, and the counterbalances are split, or the counterbalances match, and the trailing edges are split.

I did some searching on the various online resources, including VAF and builder logs, and it seems that this problem isn’t unheard of. The opinions on its solution vary widely, however-some state that it’s no problem at all, others say it will cause a rolling moment which will always need opposite aileron to counteract it. Some claim it can be fixed by drilling out some rivets and “massaging” the end rib, others report they built a whole new elevator. RV-9A builder Mike Hoover had a similar problem which he wrote about on his build log (related thread at VAF), and included advice he received from Van’s:

Talked with Scott at Vans about the misaligned TE on the elevators as they are currently mounted on the HS. He suggested three alternatives: 1) leave as is, if any undesirable flight characterists, then use the second alternative. He said this happens frequently to varying degrees and may not be that noticeable in flight. 2) Align the TEs, reposition elevator horn bolt holes as required and accept the downward position of the left elevator counterbalance or the upward position of the right one. 3) Remove the elevators, find where any twist is that is causing the misalignment, [and] work the twist out by using more rivets, which will result in the elevator having pre-loaded stresses.

I believe he had already drilled his elevator control horns when this problem was noticed, which put his counterbalance arms in trail, but left his TE’s split. I would be able to go directly to option #2, which would align the TE’s and split the counterbalances. In any event, I have sent an email to Van’s builder support, and await their response. I suspect it will be some variant of the above, and the problem is not as big as I imagine it to be. From the above linked VAF thread:

I ended up with about 3/8 vans said, you won’t know it during flight, many rv’s have this problem, (we all start on the emp) also he said only you will know it so at the fly in’s or when you go somewhere other might see it, just tie the stick back with the seat belt so they are not aligned and no one will ever know. build on..

OTOH, if I need a new elevator…well, that’s life I suppose.

This entry was posted on Friday, June 27th, 2008 at 7:34 pm and is filed under Elevators. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.