Topics

Nordlocks on Prop Bolts (Hijacked from Matco Brake Maintenance)


Joel Ventura
 



On Wed, May 27, 2020 at 8:10 PM Keith Spreuer <kspreuer@...> wrote:
I would not use the for prop bolts. Issue there is expansion and shrink in would not slippage of the bolts
I agree that the primary problem is the expansion and contraction of the wood prop with changes in temperature and humidity, but there is also a perceived problem of slippage of the bolts.  If that were not true, then why does everyone safety wire their prop bolts?  I am interested in the Nordlocks not because they cure the expansion problem, but because they may offer a better solution to the slippage problem than safety wire (see below).


On Wed, May 27, 2020 at 8:41 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
...
However, since with bellevilles, we only need to check the prop bolt torque once/year, at the CI, rather than every 10 or 25 hours, or four times per year at the change of seasons, the reduction in maintenance needs is already a large positive factor, and well worth the installation even if it prevents the use of nordlocks to replace the safety wire.

A few years ago we discussed at length the advantages and disadvantages of using  Nordlock washers on prop bolts as opposed to belleville washers, and you did a good job of summarizing your arguments in your response to my last post.   However, you completely omitted the reasons I was interested in testing Nordlocks on prop bolts. So now I will refresh your memory.

First of all, I agree with everything you said in your summary.   I believe that using bellevilles reduces maintenance and significantly increases safety, and is well worth the additional expense, complexity, and weight that it entails, especially if you fly long distances and the airplane is in areas with very different relative humidity for long periods of time.  (In fact, I know a guy who foolishly flew his airplane from the humid Northeast, into the arid west, and lost a prop and a piece of one wing along the way, because he was not using bellevilles.)  And furthermore, we all appreciate the engineering you did to find a solution to this problem, and publicize it.  I am sure you saved some pilots a lot of money, and may have prevented a few injuries and lost lives as well.

But not everyone agrees it is worth the trouble and expense, or perhaps they cannot be bothered to make this change.  Only about half the canards I have seen have bellevilles fitted, and I don't think I have ever seen a non-canard with bellevilles, though I am sure they are out there.  In addition, many non-belleville owners do not check their prop bolt tension often enough.  I believe a big reason for this is because  of the perceived PITA to remove, and then reinstall the safety wire.  That is where the Nordlocks come in.
They have the following advantages:
1.  Without having to deal with the safety wire, without a spinner, checking the prop bolt tension would probably take less than 1/10 of the time, and owners would be much more likely to do this more frequently.
2.  Tests by Craig Catto.several years ago indicated that even if the bolts are properly secured with safety wire, that does not guarantee that the bolts can not back out enough to prevent significant friction loss and result in prop loss.  Nordlocks should prevent that.

My concerns about using Nordlocks are:
1.  Will they in fact prevent the prop bolts from backing out. In theory they should, but that has never been tested as far as I know.   That is why I was so interested in why there was that problem with their use in Matco brakes.  In theory, they should prevent the loosing of those bolts as well, unless  another factor is involved which I am not aware of.
2.  Is there any problem with repeatedly loosening and tightening Nordlock washers?

I do plan to test this, if and when I ever get my airplane flying again, first on two of the  prop bolts, then on all six.  
--Joel

PS:  I claim victory in this discussion, because my response is even longer than yours.
  


Greg Norman
 

Joel,
I understand your theory and will wait to see your experiment results but you do understand the idea the bolts get loose (or tight) by the thickness of the prop expanding and contracting and not the actual "backing out" of the bolts right?

Greg Norman


On Thu, May 28, 2020, 2:07 AM Joel Ventura <ventura@...> wrote:


On Wed, May 27, 2020 at 8:10 PM Keith Spreuer <kspreuer@...> wrote:
I would not use the for prop bolts. Issue there is expansion and shrink in would not slippage of the bolts
I agree that the primary problem is the expansion and contraction of the wood prop with changes in temperature and humidity, but there is also a perceived problem of slippage of the bolts.  If that were not true, then why does everyone safety wire their prop bolts?  I am interested in the Nordlocks not because they cure the expansion problem, but because they may offer a better solution to the slippage problem than safety wire (see below).


On Wed, May 27, 2020 at 8:41 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
...
However, since with bellevilles, we only need to check the prop bolt torque once/year, at the CI, rather than every 10 or 25 hours, or four times per year at the change of seasons, the reduction in maintenance needs is already a large positive factor, and well worth the installation even if it prevents the use of nordlocks to replace the safety wire.

A few years ago we discussed at length the advantages and disadvantages of using  Nordlock washers on prop bolts as opposed to belleville washers, and you did a good job of summarizing your arguments in your response to my last post.   However, you completely omitted the reasons I was interested in testing Nordlocks on prop bolts. So now I will refresh your memory.

First of all, I agree with everything you said in your summary.   I believe that using bellevilles reduces maintenance and significantly increases safety, and is well worth the additional expense, complexity, and weight that it entails, especially if you fly long distances and the airplane is in areas with very different relative humidity for long periods of time.  (In fact, I know a guy who foolishly flew his airplane from the humid Northeast, into the arid west, and lost a prop and a piece of one wing along the way, because he was not using bellevilles.)  And furthermore, we all appreciate the engineering you did to find a solution to this problem, and publicize it.  I am sure you saved some pilots a lot of money, and may have prevented a few injuries and lost lives as well.

But not everyone agrees it is worth the trouble and expense, or perhaps they cannot be bothered to make this change.  Only about half the canards I have seen have bellevilles fitted, and I don't think I have ever seen a non-canard with bellevilles, though I am sure they are out there.  In addition, many non-belleville owners do not check their prop bolt tension often enough.  I believe a big reason for this is because  of the perceived PITA to remove, and then reinstall the safety wire.  That is where the Nordlocks come in.
They have the following advantages:
1.  Without having to deal with the safety wire, without a spinner, checking the prop bolt tension would probably take less than 1/10 of the time, and owners would be much more likely to do this more frequently.
2.  Tests by Craig Catto.several years ago indicated that even if the bolts are properly secured with safety wire, that does not guarantee that the bolts can not back out enough to prevent significant friction loss and result in prop loss.  Nordlocks should prevent that.

My concerns about using Nordlocks are:
1.  Will they in fact prevent the prop bolts from backing out. In theory they should, but that has never been tested as far as I know.   That is why I was so interested in why there was that problem with their use in Matco brakes.  In theory, they should prevent the loosing of those bolts as well, unless  another factor is involved which I am not aware of.
2.  Is there any problem with repeatedly loosening and tightening Nordlock washers?

I do plan to test this, if and when I ever get my airplane flying again, first on two of the  prop bolts, then on all six.  
--Joel

PS:  I claim victory in this discussion, because my response is even longer than yours.
  


I. N. Briggs
 

You can screw up the installation of safety wire and it will still provide some protection. Plus it’s cheap and proven. I’ve heard that Nordlocks are expensive and can easily be installed incorrectly. Not something I wasn’t to be thinking about when i feel a new sudden vibration while bombing along overhead. They are a solution in search of a problem. 

Izzy


On May 28, 2020, at 02:07, Joel Ventura <ventura@...> wrote:




On Wed, May 27, 2020 at 8:10 PM Keith Spreuer <kspreuer@...> wrote:
I would not use the for prop bolts. Issue there is expansion and shrink in would not slippage of the bolts
I agree that the primary problem is the expansion and contraction of the wood prop with changes in temperature and humidity, but there is also a perceived problem of slippage of the bolts.  If that were not true, then why does everyone safety wire their prop bolts?  I am interested in the Nordlocks not because they cure the expansion problem, but because they may offer a better solution to the slippage problem than safety wire (see below).


On Wed, May 27, 2020 at 8:41 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
...
However, since with bellevilles, we only need to check the prop bolt torque once/year, at the CI, rather than every 10 or 25 hours, or four times per year at the change of seasons, the reduction in maintenance needs is already a large positive factor, and well worth the installation even if it prevents the use of nordlocks to replace the safety wire.

A few years ago we discussed at length the advantages and disadvantages of using  Nordlock washers on prop bolts as opposed to belleville washers, and you did a good job of summarizing your arguments in your response to my last post.   However, you completely omitted the reasons I was interested in testing Nordlocks on prop bolts. So now I will refresh your memory.

First of all, I agree with everything you said in your summary.   I believe that using bellevilles reduces maintenance and significantly increases safety, and is well worth the additional expense, complexity, and weight that it entails, especially if you fly long distances and the airplane is in areas with very different relative humidity for long periods of time.  (In fact, I know a guy who foolishly flew his airplane from the humid Northeast, into the arid west, and lost a prop and a piece of one wing along the way, because he was not using bellevilles.)  And furthermore, we all appreciate the engineering you did to find a solution to this problem, and publicize it.  I am sure you saved some pilots a lot of money, and may have prevented a few injuries and lost lives as well.

But not everyone agrees it is worth the trouble and expense, or perhaps they cannot be bothered to make this change.  Only about half the canards I have seen have bellevilles fitted, and I don't think I have ever seen a non-canard with bellevilles, though I am sure they are out there.  In addition, many non-belleville owners do not check their prop bolt tension often enough.  I believe a big reason for this is because  of the perceived PITA to remove, and then reinstall the safety wire.  That is where the Nordlocks come in.
They have the following advantages:
1.  Without having to deal with the safety wire, without a spinner, checking the prop bolt tension would probably take less than 1/10 of the time, and owners would be much more likely to do this more frequently.
2.  Tests by Craig Catto.several years ago indicated that even if the bolts are properly secured with safety wire, that does not guarantee that the bolts can not back out enough to prevent significant friction loss and result in prop loss.  Nordlocks should prevent that.

My concerns about using Nordlocks are:
1.  Will they in fact prevent the prop bolts from backing out. In theory they should, but that has never been tested as far as I know.   That is why I was so interested in why there was that problem with their use in Matco brakes.  In theory, they should prevent the loosing of those bolts as well, unless  another factor is involved which I am not aware of.
2.  Is there any problem with repeatedly loosening and tightening Nordlock washers?

I do plan to test this, if and when I ever get my airplane flying again, first on two of the  prop bolts, then on all six.  
--Joel

PS:  I claim victory in this discussion, because my response is even longer than yours.
  


Marc J. Zeitlin
 

Joel Ventura wrote:
 
I am interested in the Nordlocks not because they cure the expansion problem, but because they may offer a better solution to the slippage problem than safety wire (see below).

Without bellevilles, I agree with you - Nord-locks would be simpler than safety wire and would prevent the bolt rotation that safety wire can still allow, which, without bellevilles, can be an issue if it occurs.

Only about half the canards I have seen have bellevilles fitted...

Geez, I'd be ecstatic if I thought the percentage of users was that high.

and I don't think I have ever seen a non-canard with bellevilles...

There are a few. Less prevalent though, as almost ALL canards use wood core props, where many tractor planes have metal props and don't need bellevilles.

In addition, many non-belleville owners do not check their prop bolt tension often enough.

Geez, you think? :-).
 
1.  Without having to deal with the safety wire, without a spinner, checking the prop bolt tension would probably take less than 1/10 of the time, and owners would be much more likely to do this more frequently.

Agreed - I explicitly stated that they'd reduce maintenance time in the case of non-belleville usage.
 
2.  Tests by Craig Catto.several years ago indicated that even if the bolts are properly secured with safety wire, that does not guarantee that the bolts can not back out enough to prevent significant friction loss and result in prop loss.  Nordlocks should prevent that.

Agreed as well - I have had discussions with Craig regarding the tests he did. However, Craig still recommends bellevilles due to the lower frequency of checking prop bolt torque, and the fact that the small amount of bolt rotation that the safety wire can allow becomes a moot point with the bellevilles, rather than a safety issue without.

I don't disagree that Nord-locks without bellevilles COULD be a good 2nd choice, after bellevilles with safety wire, assuming someone does some safety testing in flight to ensure that there's not something we're missing about the Nord-lock behavior on prop bolts. My first choice is still the bellevilles though, and I don't think we're in disagreement here.
 
1.  Will they in fact prevent the prop bolts from backing out. In theory they should, but that has never been tested as far as I know. That is why I was so interested in why there was that problem with their use in Matco brakes. In theory, they should prevent the loosing of those bolts as well, unless  another factor is involved which I am not aware of.

We have one anecdotal story of Nord-locks not keeping bolts tight in brakes. We know nothing about the installation history, nor how many times they might have been used, or whether they were correctly installed (reverse 1/2 of the washer and they won't do squat). It's certainly possible that they were installed perfectly and somehow backed out, but it seems unlikely.

It's also possible that MATCO has not designed their system using the guidelines available here:


and with inappropriate design, maybe the MATCO system isn't as robust as it could/should be. I have no knowledge of whether this is the case or not, but it could be a contributor to the single bolt loosening episode that was once described.

If you're going to be the designer of the Nord-lock Prop Bolt retention system, then you'd want to ensure that you followed all of their guidelines and insights so as to make the system as robust as possible.

2.  Is there any problem with repeatedly loosening and tightening Nordlock washers?

There is nothing in the Nord-lock usage documentation that indicates a single-use design, nor a fixed # of tighten/loosen cycles.

I do plan to test this, if and when I ever get my airplane flying again, first on two of the  prop bolts, then on all six.

Sounds like an appropriate path. First two, then four, then all six.

PS:  I claim victory in this discussion, because my response is even longer than yours.

Quantity over quality, eh, Joel? :-). 

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2020                     Burnside Aerospace


Bob Holliston
 

I have bellviews (bellevilles) and being the pessimistic sort I still check the torque at least once a month. Never found anything amiss. I never take the safety wire off either. It only takes 60 seconds. Okay, closer to 30 seconds.  


On Thu, May 28, 2020 at 9:00 AM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Joel Ventura wrote:
 
I am interested in the Nordlocks not because they cure the expansion problem, but because they may offer a better solution to the slippage problem than safety wire (see below).

Without bellevilles, I agree with you - Nord-locks would be simpler than safety wire and would prevent the bolt rotation that safety wire can still allow, which, without bellevilles, can be an issue if it occurs.

Only about half the canards I have seen have bellevilles fitted...

Geez, I'd be ecstatic if I thought the percentage of users was that high.

and I don't think I have ever seen a non-canard with bellevilles...

There are a few. Less prevalent though, as almost ALL canards use wood core props, where many tractor planes have metal props and don't need bellevilles.

In addition, many non-belleville owners do not check their prop bolt tension often enough.

Geez, you think? :-).
 
1.  Without having to deal with the safety wire, without a spinner, checking the prop bolt tension would probably take less than 1/10 of the time, and owners would be much more likely to do this more frequently.

Agreed - I explicitly stated that they'd reduce maintenance time in the case of non-belleville usage.
 
2.  Tests by Craig Catto.several years ago indicated that even if the bolts are properly secured with safety wire, that does not guarantee that the bolts can not back out enough to prevent significant friction loss and result in prop loss.  Nordlocks should prevent that.

Agreed as well - I have had discussions with Craig regarding the tests he did. However, Craig still recommends bellevilles due to the lower frequency of checking prop bolt torque, and the fact that the small amount of bolt rotation that the safety wire can allow becomes a moot point with the bellevilles, rather than a safety issue without.

I don't disagree that Nord-locks without bellevilles COULD be a good 2nd choice, after bellevilles with safety wire, assuming someone does some safety testing in flight to ensure that there's not something we're missing about the Nord-lock behavior on prop bolts. My first choice is still the bellevilles though, and I don't think we're in disagreement here.
 
1.  Will they in fact prevent the prop bolts from backing out. In theory they should, but that has never been tested as far as I know. That is why I was so interested in why there was that problem with their use in Matco brakes. In theory, they should prevent the loosing of those bolts as well, unless  another factor is involved which I am not aware of.

We have one anecdotal story of Nord-locks not keeping bolts tight in brakes. We know nothing about the installation history, nor how many times they might have been used, or whether they were correctly installed (reverse 1/2 of the washer and they won't do squat). It's certainly possible that they were installed perfectly and somehow backed out, but it seems unlikely.

It's also possible that MATCO has not designed their system using the guidelines available here:


and with inappropriate design, maybe the MATCO system isn't as robust as it could/should be. I have no knowledge of whether this is the case or not, but it could be a contributor to the single bolt loosening episode that was once described.

If you're going to be the designer of the Nord-lock Prop Bolt retention system, then you'd want to ensure that you followed all of their guidelines and insights so as to make the system as robust as possible.

2.  Is there any problem with repeatedly loosening and tightening Nordlock washers?

There is nothing in the Nord-lock usage documentation that indicates a single-use design, nor a fixed # of tighten/loosen cycles.

I do plan to test this, if and when I ever get my airplane flying again, first on two of the  prop bolts, then on all six.

Sounds like an appropriate path. First two, then four, then all six.

PS:  I claim victory in this discussion, because my response is even longer than yours.

Quantity over quality, eh, Joel? :-). 

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2020                     Burnside Aerospace



--


Marc J. Zeitlin
 

Bob Holliston wrote:

I have bellviews (bellevilles) and being the pessimistic sort I still check the torque at least once a month. Never found anything amiss. I never take the safety wire off either.
 
I'm glad you're using the belleville washers, but how can you possibly check the bolt torque if you don't remove the safety wire? In order to check the torque correctly, you have to be measuring it dynamically, meaning that the bolt has to be turning under the torque load. This implies that you have to loosen the bolt enough so that when you re-tighten it to the correct torque, it's moving. None of that can be done if the safety wire is on the bolts.

If you just put a wrench on the bolt head (safety wire or not) and push on the torque wrench until you get to the specified torque level, but the bolt does not turn at all, you have no idea if what you're measuring is bolt tightness and compression of the prop hub, or a bolt that's rusted into the lug and could take 100 ft-lb before turning. And if the safety wire is on and the bolt starts turning, how can you get it to the correct torque level?

Ask me how I know that this is an inappropriate and ineffective manner of checking prop bolt torque :-).

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2020                     Burnside Aerospace


Joel Ventura
 

I took a look at the Nord-Lock web site (https://www.nord-lock.com/insights) since Marc was kind enough to include the link in his last post in response to mine.  It has been a few years since I looked at their site, and they have a lot of new information there.  Because I am such a nice guy, I copied the links for a couple videos, and an article for your viewing pleasure:

This first one is a good place to start if you are not familiar with the basic principles of how Nord-Locks work, and it also has several demos showing the superiority of Nord-Locks compared to other bolt locking methods.  WARNING:   You can't unsee this video once you see it, and once you see it, you may lose all confidence that your engine will not fall apart in mid air from vibration.  Keep in mind that the vibration level in these demos is much higher than your engine bolts will experience in normal operation.
https://www.youtube.com/watch?v=IKwWu2w1gGk&feature=emb_rel_end  

Everyone who ever plans to  tighten a prop bolt should read this brief note first.

A question I and others had was is there any problem repeatedly loosening and tightening bolts with Nord-Locks on them.  That is, will it damage the Nord-Locks.  This video addresses that question.  Their recommendation is that these washer sets can be reused, but they should be inspected before reinstallation to make sure the cams have not been damaged.  A partial inspection can be done if the bolts are just loosened, but a complete inspection would require that the bolts and washers be removed.  That kind of inspection would impact my statement that Nord-locks would cut the prop bolt torque check time  by a factor of 10 compared to safety wire.  However, those washers are hardened, and the probability of damage to the cams is very small, because the cam loads in this application are so low, because the prop bolt torques are so low.  

 Initially I will check the cams everytime, but eventually I will probably be convinced that the cams only have to be fully inspected every 5 or 6 adjustment cycles.  Additionally, the washer sets come glued together, so unless you break this bond, the washers can not be installed incorrectly.  Once they are torqued and removed, that bond is broken, so you do have to be careful to install the washers with the cam faces facing each other.

I also took a quick look at costs, and online I found the washer pair sets, including shipping, for $1 to $1.20 each in quantities of 20, depending on the size and source.
--Joel

PS: I am not paid by Nord-Lock.


Bob Holliston
 

Easy answer: There's still enough play with the safety wire on to back it off some. My torque wrench reads both ways. That said, sometimes I do have to remove the wire to get the torque below 25 pounds, but not usually. 


On Thu, May 28, 2020 at 7:15 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Bob Holliston wrote:

I have bellviews (bellevilles) and being the pessimistic sort I still check the torque at least once a month. Never found anything amiss. I never take the safety wire off either.
 
I'm glad you're using the belleville washers, but how can you possibly check the bolt torque if you don't remove the safety wire? In order to check the torque correctly, you have to be measuring it dynamically, meaning that the bolt has to be turning under the torque load. This implies that you have to loosen the bolt enough so that when you re-tighten it to the correct torque, it's moving. None of that can be done if the safety wire is on the bolts.

If you just put a wrench on the bolt head (safety wire or not) and push on the torque wrench until you get to the specified torque level, but the bolt does not turn at all, you have no idea if what you're measuring is bolt tightness and compression of the prop hub, or a bolt that's rusted into the lug and could take 100 ft-lb before turning. And if the safety wire is on and the bolt starts turning, how can you get it to the correct torque level?

Ask me how I know that this is an inappropriate and ineffective manner of checking prop bolt torque :-).

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2020                     Burnside Aerospace



--


Phil Kriley
 

Seems to me that loosening and retightening Nordlocks would wear them out eventually, but if you just leave them alone they should last forever.  I would think Nordlocks on the brakes, where everything is metal, would not need to be checked once properly installed and safetied.  Ditto for Nordlocks on a metal prop.  But I would go with the Bellevilles on a wooden or composite prop.

Does that make sense?

Phil Kriley

On May 29, 2020, at 11:01 AM, Bob Holliston <bob.holliston@...> wrote:

Easy answer: There's still enough play with the safety wire on to back it off some. My torque wrench reads both ways. That said, sometimes I do have to remove the wire to get the torque below 25 pounds, but not usually. 

On Thu, May 28, 2020 at 7:15 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Bob Holliston wrote:

I have bellviews (bellevilles) and being the pessimistic sort I still check the torque at least once a month. Never found anything amiss. I never take the safety wire off either.
 
I'm glad you're using the belleville washers, but how can you possibly check the bolt torque if you don't remove the safety wire? In order to check the torque correctly, you have to be measuring it dynamically, meaning that the bolt has to be turning under the torque load. This implies that you have to loosen the bolt enough so that when you re-tighten it to the correct torque, it's moving. None of that can be done if the safety wire is on the bolts.

If you just put a wrench on the bolt head (safety wire or not) and push on the torque wrench until you get to the specified torque level, but the bolt does not turn at all, you have no idea if what you're measuring is bolt tightness and compression of the prop hub, or a bolt that's rusted into the lug and could take 100 ft-lb before turning. And if the safety wire is on and the bolt starts turning, how can you get it to the correct torque level?

Ask me how I know that this is an inappropriate and ineffective manner of checking prop bolt torque :-).

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2020                     Burnside Aerospace



--


Joel Ventura
 



On Fri, May 29, 2020 at 12:06 PM Phil Kriley via groups.io <greilich=aol.com@groups.io> wrote:
Seems to me that loosening and retightening Nordlocks would wear them out eventually, but if you just leave them alone they should last forever.
The Nord-Locks are very hard, and since they do not use friction as the locking mechanism, they can be lubricated. It seems to me they should last thousands of cycles unless they get chipped or cracked, but we will see.

 
 I would think Nordlocks on the brakes, where everything is metal, would not need to be checked once properly installed and safetied.  Ditto for Nordlocks on a metal prop.
The point is Nord-Locks are potentially better than safety wire, and they don't need to be safetied, unless you are a belt and suspenders kind of guy.

 But I would go with the Bellevilles on a wooden or composite prop.

Does that make sense?
I think we all agree that Bellevilles are a better safer way to go.  I am proposing Nord-Locks as a potentially better safer way to go for those who do not use bellevilles, which is more than half of the fleet. --Joel 


--