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Loctite on pushrod end bearings

lostpilot28

lostpilot28

Well Known Member
Just a quick question about this subject...I've been reading the other posts on how to prevent the aileron pushrods from unthreading and falling off. I know that they should have over half the threads engaged on each end of the pushrod, but I think mine are maybe 1 thread more than half. Not much!

Obviously, if the pushrod vibrated and twisted it's way to unthread one end, I'd be in trouble. Although, with a single jam-nut on each end, I should have 4 or 5 threads engaged at the least because it will prevent the pushrod from backing all the way out.

So my question is this - why not just use a healthy dose of blue locktite on the threads? Wouldn't this prevent the pushrod from rotating at all? I could go with 2 jam-nuts on each end, but I thought the loctite may be a worthy solution.
 
would like to dig out this old question that has never been answered. didn't find a general consensus on the use of Loctite on pushrods. i'm about to use the blue (less permanent) Loctite on the final rigged aileron pushrods etc., so the same question came up...
 
I agree with Walt... give it a go. Keep in mind that Loctite can loose its effectiveness over time (over years), so using a second form of locking is a good idea.
 
Apply Carefully

I recommend it be applied very carefully to avoid wicking into the actual bearing. Had this problem a lot on large scale RC aircraft.
 
pulsar said:
I agree with Walt... give it a go. Keep in mind that Loctite can loose its effectiveness over time (over years), so using a second form of locking is a good idea.
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Ok, so I agree, a jam nut is the way to go (installed properly - as in snug with a hand wrench) and that blue loctite won't hurt (although I would not use it, simply because it's not needed and something else to annoy me if adjustment was needed).

However, your statement that Loctite loses (you said "loose", but I think mean "lose" - although contextually, both words could apply) it's effectiveness over time gave me pause. This statement isn't supported by either the manufacturer or by my own experience. As a matter of fact, the use of red Loctite is considered a permanent thread locking solution - as in forever, and requires the use of about 500ºF to remove it. And while blue loctite is removable with hand tools, it will retain it's thread locking tension indefinitely.

What is your basis for saying Loctite will lose its effectiveness?
 
The effectiveness loss just comes from my experience with it. No white paper or other specific data on the topic. I?ve spent a bunch of years working as an engineer in the R&D world. There have been a number of times when the loctite we installed has lost a sizable percentage of its initial breakaway torque. It could have been contaminated joints or other unrelated failures.... we were never sure. A little contamination can go a long way to messing things up. Grease, oil, gremlin spit, they can all do bad things to thread lock. These joints were assembled by knowledgeable folks (pros with wrenches) and we still found the occasional loss of breakaway torque. This happened over years on in-service equipment that was living out in the sun. The lesson for me was sometimes even what you think is a properly assembled joint, things can can still go bad and it?s worth the occasional look. I probably should have been more clear on that. Loctite is great stuff and I use it when the application is right.


Loose... lose... ya you are right, I should reread what I type so early in the morning.
 
For anyone under construction I would suggest not using loctite until after flying and rigged to satisfaction. The jam nuts require a specific torque, which would be checked each year during condition inspection presumably.
 
Wunderon said:
For anyone under construction I would suggest not using loctite until after flying and rigged to satisfaction. The jam nuts require a specific torque, which would be checked each year during condition inspection presumably.
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Now I'm curious - what is the required torque, and (dumber question) how do you measure if if you can't put a socket on it?
 
Crowsfoot

rdamazio said:
Now I'm curious - what is the required torque, and (dumber question) how do you measure if if you can't put a socket on it?
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Torque from the table. Varies with size.
Use a crowsfoot and adjust torque for the additiinal length of the crowsfoot.
 
I think this is being overthought a bit - there is no need to use thread locker on jam nuts.

If you watch Vic Syracuse's recent RV maintenance EAA webinar (also recapped in the January 2020 EAA magazine), the issue with jam nuts is simply that they don't get tightened up to begin with.

The recommendation I have is to make a list of every jam nut on your airplane, then use it as a checklist to verify they're all tight. Torque on RV's is simply the standard torque for the AN thread being used for the rod being jammed. In reality, if you just use a hand wrench and go about 1/4 turn past finger tight - it will be tightened sufficient not to come loose until you want it to do so.
 
Why not use Torque Seal. It shows if there has been any movement. Also confirms that it has been torqued. I purchased a new Waco YMF lately from the factory and every nut that was not a castle nut had torque seal on it. It comes in different colours to show who torqued it when several different people are working on the same aircraft.

DYKEM? Cross-Check? provides a convenient visual method for identification of vibratory loosening or tampering in nuts, bolts, fasteners, and assemblies. Provides warranty protection against tampering. Marks will be easily broken if parts are tampered with or become loose. Highly visible under ambient light. Excellent adhesion to metal and other substrates.

https://www.aircraftspruce.ca/catalog/cspages/crosschecktorqueseal.php
 
I think the problem with using Loctite would be the inability to adjust the rod end after applying the Loctite. You really wouldn't want to move it after the Loctite has set up. I really don't know how long you would have...
 
I really wouldn?t recommend the use of Loctite on the jamnuts. If they are tightened properly they shouldn?t come loose. As someone else mentioned, do use torque seal, now Cross check, as a visual indicator.

Over the course of owning your airplane, if you keep it long enough, you will need to remove some of the jamnuts, either to replace the bearings or the parts that they are attached to, like throttle/mixture arms, autopilot servos, etc, or due to modifications, maintenance, or upgrades. The loctite will make it somewhat difficult to move the jamnut easily on the rod.

BTW, there was so much response to the webinar that I am going to do a follow-up one in February 19th. I plan to answer questions that were sent in from the first webinar, go into detail on some items and talk about some other maintenance areas on the RV?s.

Vic
 
As usual, I’m with Vic on this - LocTite can make it hard to do further maintenance on any item because it gets in the thread (duh!) and gums things up.

People that come into aviation maintenance from other worlds often wonder why LocTite isn’t generally used in aircraft, and the reason iOS that you can’t assure yourself that it has been applied properly. Safety wire, cotter pins, locknuts, (unmodified) nutplates....they all are positive locking methods for hardware that can be visually checked, or are locking by nature. LocTitie is hidden, and you can’t tell if it has ben applied or not once the assembly has been done. In aviation applications, we want to be able to VERIFY (in the filed, long after it has ben assembled) that a fastener is locked, and you just can’t do that with LocTite.

As an example, the VW conversion engine for our motor glider project has a prop hub that is keyed on to the end of the crankshaft, and held on with an interference fit and a big bolt that is LocTited and torqued. We installed that bolt, so I know that the LocTiote is there....but what about some second or third owner (or mechanic) - they can never know if we did it right....

Paul
 
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wirejock said:
Torque from the table. Varies with size.
Use a crowsfoot and adjust torque for the additiinal length of the crowsfoot.
Click to expand...

Nice. I was just about to ask how to torque the hinge stop hardware on the RV-12 stabilator. I think a crowfoot adapter should work. Off to Amazon I go.

One tip - if you can rotate the crowfoot 90 degrees to the wrench you don't have to worry about adjusting the torque as the moment arm is identical to using the wrench with no adapter/extension.
Good demonstration of the effect here: https://www.youtube.com/watch?v=tv_KHH55qdQ&list=RDfBjr9-FDWYw

I'm using a torque wrench with a 7" moment arm, so if I can't rotate the crowfoot to 90 degrees my torque could be as much as ~20% low (assuming 1.5" additional length from crowfoot)
And for those that are wondering how to adjust the torque, the formula for a non-90-degree angle can be found here: https://en.wikipedia.org/wiki/Torque_wrench towards the bottom.
 
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rv9builder said:
Why not use a torque wrench with a socket on the bolt and a regular wrench on the nut to torque the hinge stops?
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Rivets prevent socket access:
IMG-1700-small.jpg


Ok, I see my error now. D'oh! Time to remove a few rivets. Ugh

Nope, now I'm confused again... will post in RV-12 forum...

Ok, never mind, all better again now. Read, re-read, and read again. I missed the AN470AD call-out as there's a big LP4-3 call-out pointed at the other side of the gussets. :rolleyes::D
 
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Jam nuts will become loose

jam nuts will become loose. a nut relies on friction force to keep it tight. friction force is calculated as the friction coefficient x the bolt clamping force. normally bolts can maintain a relatively constant clamping force because they are stretched during the initial torque. the bolt needs to be long enough to allow it to stretch to maintain clamp. the jam nut however does not allow for any significant bolt length between the nut and tie rod end. how much can the bolt stretch between the two members. almost none. that is the root of the problem with jam nuts. the best thing one can do to overcome this archaic mechanical device is to apply loctite to the jam nut. I will eventually win out with this message because it's simple physics. not even Vic can beat physics. Vic, BTW, nice job on the webinar.

49288495306_1ac3ccb8ee_b.jpg
 
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Steve Melton said:
jam nuts will become loose. a nut relies on friction force to keep it tight. friction force is calculated as the friction coefficient x the bolt clamping force. normally bolts can maintain a relatively constant clamping force because they are stretched during the initial torque. the bolt needs to be long enough to allow it to stretch to maintain clamp. the jam nut however does not allow for any significant bolt length between the nut and tie rod end. how much can the bolt stretch between the two members. almost none. that is the root of the problem with jam nuts. the best thing one can do to overcome this archaic mechanical device is to apply loctite to the jam nut. I will eventually win out with this message because it's simple physics. not even Vic can beat physics. Vic, BTW, nice job on the webinar.

49288495306_1ac3ccb8ee_b.jpg
Click to expand...


Too funny, Steve. I've not seen jamnuts come loose that are properly torqued. That includes some that have been on airplanes for over 50 years. :)

Glad you liked the webinar.



Vic
 
Steve Melton said:
jam nuts will become loose. a nut relies on friction force to keep it tight.


I will eventually win out with this message because it's simple physics. not even Vic can beat physics. Vic, BTW, nice job on the webinar.

49288495306_1ac3ccb8ee_b.jpg
Click to expand...

No, a properly tightened jam nut will not. I?ve owned and operated airplanes, in addition to building and operating many power plants with vast numbers of jam nuts existing in very harsh environments - and have never found one to come loose. I have found them not tightened due to poor post maintenance QA.

There are many examples of threaded fasteners that use torque as the sole retention, aka stressed friction, to ensure stiction is maintained. And that is physics. Good examples are the connecting rods and cylinder head bolts on my engine - an aircraft engine no less.
 
This from the original post

Just a quick question about this subject...I've been reading the other posts on how to prevent the aileron pushrods from unthreading and falling off. I know that they should have over half the threads engaged on each end of the pushrod, but I think mine are maybe 1 thread more than half. Not much!

The push tubes need to be replaced with tubes long enough that they can not fall off if the jam nuts come loose. Jam nuts do not require loctite. One thread is certainly not enough, perhaps someone can post the required number of threads remaining should both jam nuts come loose
 
On most rod ends there is a hole in the threaded end of the bearing that goes on the shaft. The threads of the shaft should extend into the bearing so as to plug this hole. A piece of safety wire is a good check---it should not go through the hole.

Vic
 
Loosening

There is far more to loosening of these nuts and bolts than meets the eye. To say it is just simple physics, well, it is physics but not quite what you might call simple.

Do a web search on self loosening of nuts and bolts. you will find articles and engineering analysis of this phenomena. Really, quite interesting, if you are into the engineering of things...
 
rocketman1988 said:
There is far more to loosening of these nuts and bolts than meets the eye. To say it is just simple physics, well, it is physics but not quite what you might call simple.

Do a web search on self loosening of nuts and bolts. you will find articles and engineering analysis of this phenomena. Really, quite interesting, if you are into the engineering of things...
Click to expand...

So which side do you subscribe to? Can a properly installed jam nut on a Van's RV come loose though normal use or no? (I phrased it very specifically because I suspect the answer would be different for an off-road land vehicle like a rock crawler, just as an example.)
 
BobbyLucas said:
So which side do you subscribe to? Can a properly installed jam nut on a Van's RV come loose though normal use or no? (I phrased it very specifically because I suspect the answer would be different for an off-road land vehicle like a rock crawler, just as an example.)
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Talk about a loaded question...

You phrased it very specifically; Can a jamb nut come loose? I suppose so. As a Mechanical Engineer, you should know that anything CAN happen in a mechanical system, and you should also be familiar with using the words "always" and "never" when referring to theses systems.

The real question should be, "Is it likely that a properly torqued jamb nut on a Van's RV will come loose through normal use."

I would be in the "not likely" camp. Does that mean that I would not bother visually checking them during condition inspections? No but the likelihood of the nut self loosening, IMO, is very small if they were installed properly...
 
rocketman1988 said:
Talk about a loaded question...

You phrased it very specifically; Can a jamb nut come loose? I suppose so. As a Mechanical Engineer, you should know that anything CAN happen in a mechanical system, and you should also be familiar with using the words "always" and "never" when referring to theses systems.

The real question should be, "Is it likely that a properly torqued jamb nut on a Van's RV will come loose through normal use."

I would be in the "not likely" camp. Does that mean that I would not bother visually checking them during condition inspections? No but the likelihood of the nut self loosening, IMO, is very small if they were installed properly...
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Thanks, I was of the same opinion, but I wanted to hear what the aerospace engineer though as I'm just a lowly automotive engineer. ;) It goes without saying that torque seal is a good idea and inspections are not optional.

And yes, I actually thought about changing that to "likely," but you know what I meant. :rolleyes: Lol
 
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BobbyLucas said:
Thanks, I was of the same opinion, but I wanted to hear what the aerospace engineer thought as I'm just a lowly automotive engineer. ;) It goes without saying that torque seal is a good idea and inspections are not optional.

And yes, I actually thought about changing that to "likely," but you know what I meant. :rolleyes: Lol
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Lowly automotive engineer? Ha! Automotive engineering is lightyears ahead of where aviation is!!!
 
ha

...we may have had autopilots longer but at least we are still using ancient technology for our engines...:rolleyes:

Queue the hysterics in...three...two...one...:D
 
rocketman1988 said:
...we may have had autopilots longer but at least we are still using ancient technology for our engines...:rolleyes:

Queue the hysterics in...three...two...one...:D
Click to expand...

True dat! At least we got rid of the stinkin' carbs with the iS.

(Thread officially hijacked. Squawk 7500)
 
Hard to believe all the posts on a simple question about use of Loctite.

And I love all the engineering replies, makes for great reading material. When at the airlines I used to enjoy bringing the 'pencil pushers' down to the shop floor to show them what happens in the real world, but that's another story...

I use Loctite on jam nuts for one good reason, I've found many of them (along with many other things) loose over the years working as a lowly mechanic, dozens and dozens of loose jam nuts on RV tail feathers to name just a few (I doubt they were all left loose at the factory:D).

So believe what you wish based on either engineering theory, or real world experience.
 
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Well...... My real world experience is that a proper torqued jam nut is not likely to come loose ( not saying absolutely can't because nothing is absolute, which is why I always check them during a condition inspection).

I have never found one loose that I know for sure was properly torqued, which measures in the many hundreds based on the number of airplanes built or currently maintained.

I am convinced that people like Vic and Walt find so many loose is that so many builders fail to properly torque them and then there are so many inspections done where the inspector fails to check them (an entirely different subject for discussion).
 
Torque values

What is the proper torque value for a jam nut? Same as if that hardware is used in other application? Or is ?snug? about right? Rod bearings with a spar web (elevator) and without (push tubes) are the same value, given same nut type? Access seems a real challenge to torque with a reading in many spots. Suppose Crows Foot wrench at 90 degrees offset could often work.

Thanks.
 
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