Rudder Binding

I'm looking for a bit of advice from those that have gone before me. I think I know what needs to be done but I'm curious to hear other thoughts.

I am in the process of hanging my rudder on my RV-8 for the last time until paint. All alignment has been done, the front splice plate has been riveted on, and the aft spar has been drilled and bolted on.

I now realize that I have a slight bow in the Vertical spar hinges. There is about 3/64 of a gap at the center hinge when I put a straight edge from end to end.

I have been adjusting the bearings on the rudder for the last day and a half. I can get it to hang and move with no bind until I tighten each of the nuts down on the bolts. I am able to tighten with the top or the bottom along with the center snugly with little drag but when I tighten the last one down, there is a noticeable drag with the rudder. The bolts fall in so the bearings seem aligned yet I still have the problem.

I measured the thread distance for the center bearing and I have a little less than half of the threads in the nut plate. If I remember right, half of the threads need to be in the nut plate so that might be the answer to my question.

Options that I see so far are:

1) Keep adjusting the bearings and see if I can get it to move bind free.

2) drill out the front splice plate of the VS, realign, and replace the plate. (Vans says you can use 4 AN3 bolts here instead of riveting if preferred).

3) replace the upper or lower hinge brackets on the VS with a fabricate piece and drill to the new line using the top two as alignment. I'm not sure thats not more difficult than number 2.

Thoughts?

Thanks for your time.

jump4way said:

I now realize that I have a slight bow in the Vertical spar hinges. There is about 3/64 of a gap at the center hinge when I put a straight edge from end to end.

Click to expand...

With this discovery there is no point in doing any adjusting of the rod ends.

I know it is not what you want to hear but the only way to fix it is to redo the fwd spar attach plate.

All three hinge point have to be in perfect alignment to avoid binding and to prevent a forced flexing of the rudder as it swings (one of the causes of rudder skin cracks).

Shim...

If I understand you correctly, I had the same problem. The holes in the brackets on the aft of the horizontal stabilizer were slightly out of alignment. On mine, the center holes were slightly too far aft (or the top and bottom holes were slightly too far forward.

If the holes in the HS brackets are out of alignment, it is impossible to align the bearings because when the rudder swings to the side the bearing holes will become out of alignment from side to side.

I strung a piece of fishing line down through the holes in the brackets so I could measure how far out of alignment they were. I made a 0.015? thick, triangle shaped shim that goes between the bottom of the horizontal stabilizer and the back of the fuselage where the three bolts are.

To align the holes in the bearings, I got a 3/16? rod from Ace Hardware (I believe it is called piano wire) . I slid the rod through all three bearings. This allowed me to measure the distance from the rod to the spar in the rudder with calipers so I could precisely adjust the bearings to the lengths specified on the drawings.

After I installed the shim and got the bearings aligned per the drawings the rudder swings very easy w/o binding.

Hop this helps, good luck,

Thanks for the input so far. Bill, I think my situation is the same only opposite to yours. My VS aft spar is bowing in the opposite direction. A shim in the area you describe would make the problem worse.

Scott, I have been thinking the same thing. I hate to get a couple of years down the road and find a cracked spar.... or worse.

Thanks to those that have contributed so far. If anyone else sees a solution, I'm all ears.

Bummer

It's a bummer, but I think you're right. Re make the attach plate and you will be glad you did.

Good luck,

My approach here (8A project) was to delay the drilling/riveting of the attachment of the VS front spar and the F884 attach plate until the end of the process. First was to drill the attach plate to the HS to be sure of good edge distance on those bolt holes. Same for the bolt hole connections of the VS into the F812 bulkhead. Then, I attached the rudder to the VS on the bench. Should be no binding at this point. Now, with the VS/rudder assembly on the fuse, and also the attach plate bolted in, the rudder itself positions the VS front spar on the attach plate so that the rudder movement will be stop to stop travel without binding. Then, I drilled the rivet holes for the attach plate/front spar.
Lot of sweat and scrapped work figuring this out, so thought I would get it into archives in case it might help somebody else.

Cliff Dominey
Alvin, Texas

Shim the VS front spar-to-HS front spar? IIRC, that's what I did...just a thin plate between the two spars...