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Threadlocker versus Torque Seal?

claycookiemonster

Well Known Member
When one and when the other? For example, rod end bearings? The bolts that hold the lead counterweights for elevators and rudder? The bolts that hold the central VA-146 elevator bearing?

When would you want to permanently lock threads so that they never move, and when would you want to MARK them so you could notice that they had moved?
 
Be careful...

Follow the plans and you will be ok.

Torque seal shows absolutely NOTHING except that it has been applied. I have run across many torque sealed fasteners that were apparently NOT properly torqued before application of the marker. Once the torque seal is applied, the security of the fastener is "no longer in question" so long as the marker is intact. If the fastener hasn't been torqued, well...

Also, be careful using thread lock products. There is really no reason to use thread lock products on fasteners that have a mechanical thread lock, ie nyloc, metal lock nut, fasteners with lock washers, locking nut plates, etc. Also, be aware that some of the thread lock products will attack plastics.
 
Thread locker (LocTite) is rarely used in aviation because you can’t reliably inspect a component or assembly to verify that it was actually used when it was assembled - an inspector can see safety wire or a cotter pin, or that a lock nut was used - but he can’t see down into the threads to see if the LocTite was applied. So you’ll find very little mention of its use in aviation maintenance documentation.

That said, if a service instruction, assembly manual, etc specifically tells you to use LocTite in a spot, then use it!

Paul
 
I understand what you're both saying. Yes, Torque Seal has no mechanical effect on the fastener - it only shows whether things have moved or not.

Here's my concern. On an older style RV8 HS, the elevator counterweights are two rectangular lead weights bolted onto both sides of of a rib web. The bolts called for only fit when the bolt head is on the inner side of the spar web: adjacent to the end of the HS itself.

I'm envisioning a failure mode where the bolt loosens, and is able to back out and block the movement of the elevator. I'm wondering whether this is why the counterweight design changed? Unless there is some improved manner of attaching the lead weights, I'm thinking thread-lock on the bolts holding the lead might be a good idea to prevent that bolt from ever backing out?
 
Don't make the assumption that torque seal or other inspection marking compounds are used for monitoring fasteners for loosening or tightening in use. Folks I have talked in the aerospace industry will tell you torque seal is generally not used to show rotation of a bolt head or nut in the field and this is a misimpression. It is merely used as an inspection checkoff tool to make sure no fastener is left un-torqued. Its use ends after quality control checking at the time of installation and isn't intended to have any further value after the aicraft leaves the shop or factory. Not saying there are times that paints, nail polish or permanent marker lines aren't used in some special alimited applications where movement is monitored. But that is not the intent of inspection putties or other QC checkoff markers like torque seal.

The folks I cite above were fellow employees at one of the largest aircraft manufacturers in the world where I was a detail design engineer specializing in airframe structures and mechanical fastening systems.
 
I understand what you're both saying. Yes, Torque Seal has no mechanical effect on the fastener - it only shows whether things have moved or not.

Here's my concern. On an older style RV8 HS, the elevator counterweights are two rectangular lead weights bolted onto both sides of of a rib web. The bolts called for only fit when the bolt head is on the inner side of the spar web: adjacent to the end of the HS itself.

I'm envisioning a failure mode where the bolt loosens, and is able to back out and block the movement of the elevator. I'm wondering whether this is why the counterweight design changed? Unless there is some improved manner of attaching the lead weights, I'm thinking thread-lock on the bolts holding the lead might be a good idea to prevent that bolt from ever backing out?

Clay - my R-8 was from the 2003 timeframe, so I don't; know if there was an earlier design, but mine has two bolts with fiber lock nuts holding the weight in place, so no other locking method is needed. I’d see if there was a way to use a lock nut if yours is different. If yours has nuts threading into the lead itself, I’d not be sure that thread locker would even hold in lead!
 
Reading this I think all the comments are great but would say

Seal or marking is a QC method. I could in theory show rotation but it is more likely it will just fall off. If in doubt retorque it.

Loctite (a kind of glue) is used in aerospace but not widely. Adhesives, bonds, tapes, glues are used all over planes. The resistance to Loctite may be due to certification World and accepted practices. On your RV you can use Loctite on non critical items and still be able to disassemble it and reassemble easily. It comes in Red, Blue, Green and Purple. If it is a CRITICAL item you will use positive torque retention methods.

If you want to make sure it stays tight drilled fastener and safety wire or cotter pin are the ways to go. It is visually obvious it was torqued and is secured.

The other methods are locking washers, nuts with a crimp or friction or nylon inserts and double nut. The biggest locking mechanism is TORQUE and fiction. If the fastener is critical and in an area that vibrate (which is the whole plane) you may need to inspect and modify your methods if they are getting lose.
 
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use loctite on all jam nuts because the geometry does not allow for enough length and stretch of the threaded member to hold by friction.
 
Just me

With PROPERLY applied torque strip, I have never seen a bolt, nut or screw loosen without breaking the torque stripe. But I would say 95% of the torque stripe I inspect on experimental airplanes is not applied correctly per the Mil Standard, so there. I have been using torque strip since 1978 on aircraft, spacecraft, and race cars and it is effective at showing rotation if properly applied.

But since very few apply it properly, I agree that it should only be used as an inspection aid during assembly to signify things that have had final torque, and things that have not been final'd.

The recent article on torque seal in Kitplanes magazine showed God-awful examples in the pictures (In fact, I dont recall seeing one picture that had acceptable torque stripping). I hope nobody here does it that way.
 
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use loctite on all jam nuts because the geometry does not allow for enough length and stretch of the threaded member to hold by friction.

Do you have an aviation standard / specification you can reference regarding this?
I have never seen one, and I have never seen any come loose if they were properly torqued at installation (which is why the practice is not specified in any of our construction manuals).
 
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I'm wondering whether this is why the counterweight design changed? Unless there is some improved manner of attaching the lead weights,

The only reason for the design change was for weight reduction.

With the new counter weight design, the center of mass is further away from the hinge line. Because of this a lower counter weight mass value can be used and still have the same moment value.
 
Do you have an aviation standard / specification you can reference regarding this?
I have never seen one, and I have never seen any come loose if they were properly torqued at installation (which is why the practice is not specified in any of our construction manuals).

no manual, just physics.
 
no manual, just physics.

If real world experience matched the physics theory, it would have been incorporated into aviation as a standard decades ago...... (since thin jamb nuts have been in aviation for more than a 1/2 century)
 
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If real world experience matched the physics theory, it would have been incorporated into aviation as a standard decades ago...... (since thin jamb nuts have been in aviation for more than a 1/2 century)

and yet cavemen still today run around continually tightening jam nuts.
 
Clarify torque importance ?

Why is torque , beyond tight, important on joints loaded in shear(99% of airframe fasteners)?
The only thing I can conjecture is a plain washer that needs friction to resist nut rotation during thermal expansion cycles ? Where is there a sheared fastener that does not use a locking washer, nut , key or safety wire ?
 
because I said so

Why is torque , beyond tight, important on joints loaded in shear(99% of airframe fasteners)?
The only thing I can conjecture is a plain washer that needs friction to resist nut rotation during thermal expansion cycles ? Where is there a sheared fastener that does not use a locking washer, nut , key or safety wire ?

The bolts in shear need to be torqued because the bolt preload is important to prevent gaping of the bolt/washer from the surfaces. It is this gaping under vibration that causes bolts/nuts to loosen, and surfaces to wear. The aviation lock nuts are designed to force the threads together so the bolt threads and the nut threads do not gap under vibration. Dime store self locking nuts, just add friction but do not necessarily keep the threads engaged. That is why critical self locking fasteners should be aviation grade
 
Thanks for the explanation for the design change on the elevator counterweights.

The kit I'm working on is 8-1651, so not a spring chicken. Sadly, the plans that came with it showed construction with the newer counterweights, while I actually have the old style to build with. So, in trying to see how to assemble them, it seemed obvious that the bolts should be inserted from the outside in, so, worst case, only the nuts might come loose alongside the end of the HS. However, given the rest of the geometry, it seems that the bolts are actually intended to be inserted from inside out - and therefore it seemed like the bolts themselves might back out and completely block elevator movement. Yes, there are nuts with fiber centers to hopefully prevent them from backing out. Still, the overall arrangement seemed odd, so I was wondering about a way to REALLY lock those nuts. I can change things up until I put the tips on, at which point I lose access to the outer end of the elevators. Ok. Pondering...
 
Thanks for the explanation for the design change on the elevator counterweights.

The kit I'm working on is 8-1651, so not a spring chicken. Sadly, the plans that came with it showed construction with the newer counterweights, while I actually have the old style to build with. So, in trying to see how to assemble them, it seemed obvious that the bolts should be inserted from the outside in, so, worst case, only the nuts might come loose alongside the end of the HS. However, given the rest of the geometry, it seems that the bolts are actually intended to be inserted from inside out - and therefore it seemed like the bolts themselves might back out and completely block elevator movement. Yes, there are nuts with fiber centers to hopefully prevent them from backing out. Still, the overall arrangement seemed odd, so I was wondering about a way to REALLY lock those nuts. I can change things up until I put the tips on, at which point I lose access to the outer end of the elevators. Ok. Pondering...

Clay - looking at your resume (in your signature) I hope you realize just much of your life you have been dependent on nylon lock nuts…..just saying! ;)

Bottom line - they are everywhere in critical components in all our airplanes. If you think too hard about some things, you’ll never finish….or fly…

Paul
 
I use thread locker in two places on my airplane. Nose gear bolt and all wheel fairings screws. The torque seal on gear bolt is checked and reapplied every condition inspection ( bolt replaced every three years on average)

nose_gear_bolt_-_1.jpeg


nose_gear_bolt_-_1_(1).jpeg


Wheel fairings get the hardest beating and lowest screws are always backing off. Thread locked with blue loctite. Pictured at Ottawa River ice flyin, Canada.

Mos%202016%20-%201%2011.jpg
 
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Wheel fairings get the hardest beating and lowest screws are always backing off. Thread locked with blue loctite. Pictured at Ottawa River ice flyin, Canada.

Mos%202016%20-%201%2011.jpg

At the risk of thread creep... (see what I did there? :rolleyes:)

The, um, evidence of use on the left wheel pant is heartening to me. The construction manuals aren't kidding when they say finished wheelpants live a hard, hard life.

Checking tire pressure last weekend, I found a similar crack in my right rear wheel pant. It was dead nuts on the bottom side. The pant looked undamaged and felt tight on the preceding walkarounds.

I had no clue it was there. No (memorable) hard landings since an infamous off-runway sojourn. Maybe the clearance is a bit tight and a more or less normal tire bulge caught the edge. I'll open it up a bit more as part of the repair. (And it's brother pant on the left side.)

In any event, no matter how tight your airstop tubes might be, take off your pants regularly. You never know what you might find down there.

And I best bring along an inspection mirror on future walk-arounds. Dang, them RV pants are loooow to the ground...
 
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At the risk of thread creep... (see what I did there? :rolleyes:)

The, um, evidence of use on the left wheel pant is heartening to me. The construction manuals aren't kidding when they say finished wheelpants live a hard, hard life.

Checking tire pressure last weekend, I found a similar crack in my right rear wheel pant. It was dead nuts on the bottom side. The pant looked undamaged and felt tight on the preceding walkarounds.

I had no clue it was there. No (memorable) hard landings since an infamous off-runway sojourn. Maybe the clearance is a bit tight and a more or less normal tire bulge caught the edge. I'll open it up a bit more as part of the repair. (And it's brother pant on the left side.)

In any event, no matter how tight your airstop tubes might be, take off your pants regularly. You never know what you might find down there.

And I best bring along an inspection mirror on future walk-arounds. Dang, them RV pants are loooow to the ground...

yes, on finished working airplanes it seems it's all about the engine and gear maintenance. keep those in good shape.
 
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