RV10Rob

RV10Rob

Well Known Member
Has anyone considered safety wire on pushrods for preventing them from twisting? Most of mine have not much more than half the threads showing, so I'm afraid that they may twist all the way to the end, leaving only 1-2 threads engaged on the other end.

The RV-10 plans have the following instructions for one of the three elevator pushrods only (presumably since that one has less than half the threads engaged on one end).
pushrodsafety.JPG


Any reason I shouldn't do this on all of them? I'm usually not one to consider an unnecessary "belt and suspenders" approach, but otherwise I don't see much of anything preventing the pushrods from twisting.

-Rob
 
Why not cut a piece of thin wall alum tubing to fit over the exposed threads. It won't allow either end to screw in...........
 
OK, I'm not at this stage either, but after reviewing the plans here's my $.02. Safety wire is not needed on the other rod ends because if built to spec, more than half of the threads on each are engaged making it impossible for them to back out when pinned. Now on the forward elevator push rod end, the bearing (GMM-4M-675) has a longer threaded shaft than the MD3616M bearings used on the opposite end of the forward rod and on the other pushrods. For whatever reason, to make the theorectically correct center-to-center rod length of 37-13/32", you have to have less than half of the threads engaged on that -675 bearing. That means with less than half the threads engaged it can back out even when pinned, hense the safety wire requirement for only that bearing. What I don't get since I'm not at this stage is why Van didn't just make the tube itself a little longer, but I'm sure there's a good reason--interference or something.
 
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GAHco said:
I am using Corner Drilled Jam Nuts on all Rod ends as practical.;)
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Aren't jam nuts going to screw up the threads? I will only use jam nuts if there is no other option. Another solution is put a metal jacket on the exposed threads, both sides of the rod. However, it is dangerous with only less than 2 threads are engaged.
 
Just to clarifiy, all push-rod bearings get installed with jam nuts. Also, there's no way the bearing will have only 1-2 threads engaged. If there is then a measurement has been made wrong in cutting the length of the push-rod tube. The real issue is having less then half (or 1/2) of the threads engaged.

To illustrate the issue, take a pushrod, install the bearings without the jam nuts and so that a little more than half of the threads are engaged. Bolt the bearings to some structure so the length of the push rod is fixed and non-changeable. Now spin the rod. It will eventually bottom out against one of the bearings but it will still be engaged on both no matter which direction you spin the rod. Now repeat but this time install one bearing with more than half the threads engaged and the other with less than half engaged. Now because of the unequal length of threads engaged on each side the rod can fall off one bearing before it bottoms out on the other. That's the reason for the safety wire on this one end of the pushrod.
 
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Jam nuts are required period. If jam nuts are used and tightened properly there is no way for the bearing ends to come off and the jam nuts will not ruin the threads.
 
Norman CYYJ said:
Jam nuts are required period. If jam nuts are used and tightened properly there is no way for the bearing ends to come off and the jam nuts will not ruin the threads.
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I agree with Norman. I would add an external stripe of thread seal for an easy visual way to periodically inspect the assembly and you will be fine. On my Ercoupe, many of these were safety wired, not sure why.
 
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Say whut!

Aviator168 said:
Aren't jam nuts going to screw up the threads? I will only use jam nuts if there is no other option. Another solution is put a metal jacket on the exposed threads, both sides of the rod. However, it is dangerous with only less than 2 threads are engaged.
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If Jam nuts are detrimental to aircraft, we all better think twice about flying. Almost all certified aircraft have jam nuts securing their primary flight control rod ends (thank goodness for that):rolleyes:

I was just helping this poster out by showing him the almost ultimate in Jam Nut / Rod end security.

There are actually rod ends available with slots/grooves parallel to the threaded shank having an anti-rotation key that fits in there and the Jam Nut holds it in place. It would be a little advanced for what we are trying to accomplish, but they are the Ultimate in anti rotation security.
 
Don't jam nuts work by stretching the threads between the nuts? They do work very well. I am just afraid you are not going to be able to disassemble it later.
 
That's how normal nuts work, but the friction needed at the jam nut is way lower than that. You are not torqueing the jam nuts to the same level as the regular nut so there's no danger of thread damage.
 
YIKES !!

Geez, some of this discussion kinda scares me. :eek: Follow the directions.

If you can't have a few threads more than 1/2 of the total threads engaged on both ends of a control tube, then somethin' gotta change. Either get longer threads, or get/fabricate a longer tube. As mentioned, if you hold both ends still, and rotate the control tube fully in both directions, you should not be able to unscrew either end.

Lock nuts are good, they don't cause damage.

Maybe spend some time reading AC 43.13xxx for standard practices. Sorry for the Rant!:eek:

And, PLEEZE don't install a control tube with only a couple of threads engaged!! Or did I misread a post or two?
 
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