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Push/pull tube rod end safety wire

Strasnuts

Well Known Member
I have been doing my second conditional inspection with 300 hours on the RV-10. I noticed my safety wire was broken on the elevator push/pull tube rod end. I had it installed per plans. I believe the edge of the weldment ear rubbed against the safety wire until it broke. My jam nut did not move as you can see from the torque seal. Recent subject so thought I would share. This is the rod end that can back all the way out if the tube rotates.

ims1t5.png
 
So, the nut that is backed off on the pivot bolt-------did you do that, or was it like that when you did the inspection?????
 
This is the rod end that can back all the way out if the tube rotates.
ims1t5.png

I'm not a 10 builder so cut me some slack on this question.

I'm curious if there is something that prevents the tube from being made long enough to prevent the disaster failure mode of the rod end coming out.

This longer length would be similar to the rod length design on the 7 and 9 and I assume others.
 
I'm not a 10 builder so cut me some slack on this question.

I'm curious if there is something that prevents the tube from being made long enough to prevent the disaster failure mode of the rod end coming out.

This longer length would be similar to the rod length design on the 7 and 9 and I assume others.

Not a bad question, but there is a reason: clearance. The aileron push rod that connects the 2 sticks together runs just above the space shown in the photo. If the elevator pushrod was longer then the aileron and elevator pushrods would hit each other when the stick is pulled aft.
 
I had the same problem when I connected the elevator control rod to the horn on my current project. I had a local machinist make a new plug with an extended nose. Works great. My question on the above picture was, "Does that rod end bearing have half of its threads left in the the plug?".

Jim
 
No, which is why the plans call for the use of safety wire. Now the question I had but never expressed when I was at this point of the build was why didn't Van's use as rod-end bearing with a longer shaft instead of going the safety wire route. My guess is they went with the best part that they already had in inventory and came up with a low cost way to make it work.
 
I had the same problem when I connected the elevator control rod to the horn on my current project. I had a local machinist make a new plug with an extended nose. Works great. My question on the above picture was, "Does that rod end bearing have half of its threads left in the the plug?".

Jim

Knowing Sean and how anal he is with safety, I would assume the answer is yes. Sean has develop several products that improve RV-10 safety and are sold on planearound.com.

Although I do admit that the amount of exposed threads in that photo look a little long from what I remember on mine. I'll have to review mine again tomorrow.

bob
 
Perhaps the safety wire would be best installed if it crossed over the bearing threads?

That would tend to keep it away from the sharp edges of the weldment.
 
Or do like you can do with the propeller bolts and use a plastic sleeve and insert the twisted safety wire inside the clear plastic tube and prevent abrasion?
 
The area is already crowded, and the additional thickness of the tube may be problematic.

If the stainless wire got cut, what are the odds that a plastic tube will be tough enough to protect anything?
 
It may help if it was getting caught on the control horn or snagged on something. The lower friction and lack of edges may help. Wouldn't hurt for sure as long as it was thing enough to fit.
 
Not a bad question, but there is a reason: clearance. The aileron push rod that connects the 2 sticks together runs just above the space shown in the photo. If the elevator pushrod was longer then the aileron and elevator pushrods would hit each other when the stick is pulled aft.

Hmm... Maybe its time for a geometry change on the lathe cut tube end fitting by adding a cylindrical section to the "nose" such that it covers more of the thread (for maybe 3/4"), but is small enough in diameter to prevent interferance.

Alan Nimmo, I take royalty fees on a biannual basis :D
 
Rod End

I started taking the nut off and thought I could get a better pic after removing the aileron pushrod, so I left it like that in the picture.
The jam nut did its job and stayed tight. The safety wire is a second means of catching it from rotating. I do like the idea of making a longer conical piece for the pushrod end. That way it would accept a lot more threads and the safety wire would not be needed. I looked at all the other rod ends on the plane and none of them have turned.
I will have to look and see how much room is in there for modification.

I thought of different areas to attach the safety wire but none of them were any good. Anywhere but around the bolt will cause the safety wire to relax and then tighten depending on the position of the elevator. I would suspect that would eventually break the wire too.
 
Good catch

Thanks for posting Sean. I suspect a lot of us have been wondering what our push tube/rod end security looks like after the last couple weeks. I'll be starting my first annual in a week or so, and that'll be the first thing I check.
 
At my next inspection I will look at this area. I have 2 ideas to try:

1. "braid" the safety wire around the threaded area of the rod end, to hold it in close to the rod end and away from the steel fitting that chaffs.
or
2. Get a bolt with a drilled hole in the end, change it 180 degree to your photo, and run the safety wire thru the hole. This would keep the push tube from rotating, and also keep the nut from ever falling off.
 
Good point

I'd be interested to know from any of the A&Ps out there (Sean is an A&P, so chime in), could you drill the threaded shaft of the rod end bearing so you could just safety from the push/pull tube to a hole in the rod-end bearing shaft? Or maybe a drilled jam nut? I like the idea of a drilled bolt head and safetying to it also. Are any of these ideas legit in the A&P world?


At my next inspection I will look at this area. I have 2 ideas to try:

1. "braid" the safety wire around the threaded area of the rod end, to hold it in close to the rod end and away from the steel fitting that chaffs.
or
2. Get a bolt with a drilled hole in the end, change it 180 degree to your photo, and run the safety wire thru the hole. This would keep the push tube from rotating, and also keep the nut from ever falling off.
 
I like the idea of plastic sleeve

Slide plastic sleeve (thin wall nylon bushing or even poly pipe, heat shrink)over the remaining rod end threads.....protects the threads from the wire and if the nut does backoff, a secondary "stop" to only allow the nut to back off a few threads. Still follow the plans from Vans.....just added security. Problem is if the nut loosens, the risk over time of rolling the threads completely out of female socket due to the nature of the "push pull" motion. We use locktite when in doubt. We see this happen on ag equipment but only after things have been overlooked for some time. Good thing ag equipment doesn't ever leave the ground though cause NTSB would be busy!
Just a thought coming from a new guy.
 
Pro Seal

I think I will just put a good dab of pro seal around the counter nut on both sides and be done with it.
Of course I'll leave the mechanical measures in place but when those fail, pro seal will do the job.
 
I happened to be working on that area and I re-inspected mine and all was OK. Incidents like this get you second guessing yourself. This attachment really deserves a more elegant solution.
 
2. Get a bolt with a drilled hole in the end, change it 180 degree to your photo, and run the safety wire thru the hole. This would keep the push tube from rotating, and also keep the nut from ever falling off.

Bad idea, I think.

The bolt should be tight enough to make the ball fixed to the weldment, and therefore the bolt will not be moving in relation to it.

But, the push rod does move in relation to the weldment, so the safety wire will be flexed with each elevator stick input.

Probably be pretty hard on the safety wire.
 
Checked mine today

I am in the middle of my annual and mine was still OK.
For those wondering, that extension is how the plans tell you to make it for clearance.
 
Wouldn't this be the simplest fix? I don't recall the size of the jam nut, but surely there's one out there somewhere?

http://aircraftproducts.wicksaircra...-6?&plpver=10&origin=keyword&by=prod&filter=0

Drilled-Jam-Nut.jpg


Especially if you machined a groove in the pushrod end and used one of these...

http://aircraftproducts.wicksaircra...ver=10&categid=100&prodid=2412&origin=keyword

NAS513.png


If there is a Mil-Spec equivalent to the Vans rod end, it will be called a "keyway option" to get it with the groove. Aurora uses a "K" in the part number for this option.
 
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Lockwire the rest of the rod-ends

I believe that if we are worried about this rod-end, we should safety wire the other rod ends. If any one of the rod ends got loose enough to move a couple threads, it should be lockwired. I plan to drill a hole in the shaft of the rod end and lockwire it to the cone of the rod with a similar hole as the one in this discussion.
 
I believe that if we are worried about this rod-end, we should safety wire the other rod ends. If any one of the rod ends got loose enough to move a couple threads, it should be lockwired. I plan to drill a hole in the shaft of the rod end and lockwire it to the cone of the rod with a similar hole as the one in this discussion.

If built according to plans the other push rods don't need safety wire as you're supposed cut the tubes to such a length that the rod end bearings will have more than half of their threads engaged making it impossible for the rod ends to back out once pinned.

This rod as previously discussed is the exception. Personally, I think the safety wire solution is just fine, but it illustrates the importance of thorough condition inspections.
 
.... could you drill the threaded shaft of the rod end bearing so you could just safety from the push/pull tube to a hole in the rod-end bearing shaft?

Heim and Aurora do not offer a cross-drilled shank as regular production option for rod ends. The standard approach is a keyway.

Rod ends specified to have a lubricator get a reduced capacity rating because of the hole.

When we install a standard AN bolt cross-drilled for a cotter key, we take great care to ensure that no tensile or torsional load is applied to the bolt outboard of the hole.

Let's be cautious about modifying critical hardware in primary control systems, please.
 
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This discussion had me thinking about this daily. The inspection is due in February so I decided it was close enough. Yesterday I took the entire interior apart and inspected the entire elevator control system. Everything was good including the safety wire.
 
My solution

I re-safetied mine today. I used the same approach but deburred the ears more. They really weren't sharp to begin with but rounder should be better. I moved the pushrod back and forth and figured it was better than the first installment. It wasn't rubbing the threads or the ear. I will be checking this more often this year to make sure it doesn't break. Thanks for all the responses. I believe it is good to bring up any anomalies we find during our inspections.
 
The simple solution

Plus one. This is used on a lot of adjustable ends of hydraulic actuators. The piston with a rod end screwed in can rotate, and this is the safety. Important stuff like landing gear actuators. Could this also work on the flap motor?
Drilled-Jam-Nut.jpg


Especially if you machined a groove in the pushrod end and used one of these...

http://aircraftproducts.wicksaircra...ver=10&categid=100&prodid=2412&origin=keyword

NAS513.png


If there is a Mil-Spec equivalent to the Vans rod end, it will be called a "keyway option" to get it with the groove. Aurora uses a "K" in the part number for this option.
 
Good here

I just opened mine up for my first annual (235 hours). Mine looks fine but I'm going to convert it to the corner-drilled jam nut safety wired to the push tube while it's open - unless someone can convince me there is something wrong with that approach. It sure seems like a better approach, but I'll defer to the experts. Probably put a little locktite on the jam nut for good measure.
 
Well done!

I just opened mine up for my first annual (235 hours). Mine looks fine but I'm going to convert it to the corner-drilled jam nut safety wired to the push tube while it's open - unless someone can convince me there is something wrong with that approach. It sure seems like a better approach, but I'll defer to the experts. Probably put a little locktite on the jam nut for good measure.

235 hours in less then 1 year! Well done sir, well done!
 
I guess if the jam nut was safetied to the pushrod it would stay tight but couldn't the pushrod just rotate with the jam nut until they both ran out of threads?
 
Hmmm

Good point. I assumed that if the nut was tight the rod end wouldn't turn but that may not be correct. However, I could see that if the nut got loose, which it could do even if safety wired, then the rod end could rotate freely in both the push tube end and the nut. Maybe not the way to go.

For clarity, I was planning to safety the drilled nut to the end of the push tube.
 
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This may sound stupid but would Nylok nuts instead of jam nuts at both ends of the pushrod work?

The better equivalent would be a nylok insert in the threaded portion of the rod end.

It is usually a listed option, but my guess is it would be non-stocked and expensive (ie custom made) for a few...
 
Seems like what we want is a simple safety measure to add in the field.

The challenge is how to stop the big pushrod tube from rotating clockwise onto the long rod end shank, which can allow the rod end shank on the other end to become unthreaded.

Try this.

Add another nut to the shank. Spin it all the way onto the shank until it bottoms on the last thread, near the head. Install the pushrod, adjust to length, then measure the length of the threaded shank showing between the new nut and the original jamb nut. Obtain a short length of thinwall steel or aluminum tubing with an inner diameter as necessary for a slip fit on the rod end shank. Cut it to the correct length to fit between the nuts and install it there. Again check pushrod adjustment......control travel as necessary while maintaining enough rod end threads in each end so that even with the jamb nuts loose the pushrod cannot rotate and unthread at either end. Tighten and mark the jam nuts.

If you're the nervous type you can sleeve both rod ends.

213f2mq.jpg
 
Dan - great idea, but couldn't we make it a little simpler and not even install the extra nut?

The added sleeve can just sit loosely in place and do it's job. Even if it allows a turn or two back off of the rod end, it will remain safe.

In some cases the extra nut may interfere with the bellcrank end.
 
Dan - great idea, but couldn't we make it a little simpler and not even install the extra nut?
The added sleeve can just sit loosely in place and do it's job. Even if it allows a turn or two back off of the rod end, it will remain safe.
In some cases the extra nut may interfere with the bellcrank end.

I was thinking about tightening the original locknut, then tightening the new locknut against the tube. Thus the assembly is double locked, the tube can't rattle, and even if it all comes loose the pushrod can't unthread. However, as you say, it doesn't need to be that way.

Can't speak about clearance. I seem to have misplaced my RV-10 ;)
 
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