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Rudder Rod-End Bearings - Help

D

DaveHadfield

Member
Our RV-6a was purchased with some minor hangar rash damage along the lower edge. It wasn't a show-stopper, but it was ugly, and we recently found a new-built rudder that appears in perfect shape. So we bought it.

After taking off the existing rudder, I removed the rod-end bearings, and was shocked to find the middle one only held in with 3 full turns. Not very far! And the top one only 5 full turns.

rod ends ours sm.jpg


Also, the new rudder doesn't quite have the same clearance, and might require these to be turned out slightly.

So, I'd like to buy new ones, slightly longer. But the A-Spruce bearing order page is very confusing, and shows no actual sizes.

After some research, I think I want to simply get 2 more of the lower one, a GMM-3M-680.

Is that available at A-Spruce? I don't see it.

And, since we bought the airplane, and don't have plans, is there a problem with increased length -- will the longer shank hit something behind the nut-plate?

Thanks,

Dave
 
Welcome to VAF!

Dave, welcome aboard the good ship VAF.

Congrats on your new bird :D

In addition to the above, you need to be sure the jam nut is snugged up when you install the rod end into the nutplate.

There is also a service bulletin out to check for cracks in the spar where the nutplate mounts. http://www.vansairforce.com/community/showthread.php?t=109464

http://www.vansairforce.com/community/showthread.php?t=104551

Also, there is a service bulletin about checking for cracks in the stab spar center area. http://www.vansaircraft.com/pdf/sb014-01-31.pdf

There are a couple threads going about these things, check the "Ongoing Maintenance" forum.
 
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Might want to investigate why the specified length rod ends don't work. The fin and rudder spars should be a finite distance apart, so while a longer shank looks like a good fix at first, it does increase the overhung load on the rod end, reduces stiffness in the system, and increases the load behind the hinge line - All bad from a flutter perspective.
 
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The plans - later CAD versions - call for Heim MD3614 for the upper two locations and MD3616 for the lower spot.

http://www.rbcbearings.com/literature/pdfs/Rodends-Aerospace-M-M.pdf

Your photos look like the correct parts.

Perhaps the "rolled" portion of your rudder skin is not closed enough?

Or the steel mating hinge parts on the vertical fin are not to the correct dimension?

Dimensions - vertical fin spar to hole center

Lower 1 7/16
middle 1 9/32
top 1 1/4
 
Per plans RV6 dimensions of rudder leading edge

I think Gil may have a point...having almost completed the entire empennage for RV6 #2 some of the dimensions are fresh in mind.

At the lower end of the rudder the distance between with forward side of the rudder spar and and the outside edge of the rolled leading edge is 1 3/4". The same distance at the very top end of the rudder is 1 5/8".
 
Dave, I found the same thing on my 6A. I bought the longer bearings but the width of the bearing is wider than the original short bearings. It would spread the hinge ears on the vert. stab. too far, so I had to grind the bearing width down to fit properly. I own a machine shop, so I have the capability to do this on my surface grinder. With a fixture to hold the hole perpendicular to the ground surfaces I was able to maintain perfect parallel surfaces on the bearing. A machine shop with a surface grinder should be able to do this.
 
Wow. What a response. I don't think I've ever experienced such quick and helpful replies anywhere, on any forum, at any time. Thanks!

To respond...

Thanks for the part numbers.

Yes, we had a good look for cracks as per the bulletins -- all good.

I agree, the shorter the rod length the less stress on the whole hinge. We'll have a look at the fit again, and adjust whatever we can.

I will indeed tighten the jam nut. I can see that that's what keeps it rigid against the nut plate. If it was loose, the assembly would "work" more. Probably crack sooner.

Thanks for the dimensions, and the plans info. And for clearing up what's behind the plate (nothing).

It's not the fanciest RV-6a in the world -- in fact it was a fixer-upper -- but it's been flying well.

DJASideView.jpg


Much obliged,

Dave
 
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