Safety Wire on Pushrods?

RV10Rob · #1 04-01-2009, 10:59 PM

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).

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

gasman · #2 04-02-2009, 01:18 AM

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...........

Aviator168 · #3 04-02-2009, 07:04 AM

Quote:

Originally Posted by RV10Rob

only 1-2 threads engaged on the other end.

-Rob

I am far away from that stage. How about adding a lateral support? Either way, it is scary to only have 1-2 threads engaged. Is there a way to adjust the other end of the rod?

Auburntsts · #4 04-02-2009, 12:20 PM

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.

Danny7 · #5 04-02-2009, 12:25 PM

why not use some thread sealant on the threads if you are worried?

loctite?

GAHco · #6 04-02-2009, 01:14 PM

I am using Corner Drilled Jam Nuts on all Rod ends as practical.

NAS1423-6

Tech Page http://www.gen-aircraft-hardware.com...er_drilled.pdf

Purchase or check prices http://www.gen-aircraft-hardware.com...nate=NAS1423-6

Aviator168 · #7 04-02-2009, 01:59 PM

Quote:

Originally Posted by GAHco

I am using Corner Drilled Jam Nuts on all Rod ends as practical.

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.

Auburntsts · #8 04-02-2009, 02:15 PM

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.

Norman CYYJ · #9 04-02-2009, 03:56 PM

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.

N62XS · #10 04-02-2009, 04:16 PM

Quote:

Originally Posted by Norman CYYJ

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.

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.