Gear up due to broken no back spring question

[A64Pilot]

Does anyone know of how many gear up’s there have been due to the spring failure?

I’ve talked to a few, not really all that many Mooney drivers and have yet to find one that has ever heard of a no back clutch spring, and to be honest if it weren’t for this forum I woudnt have either.

Makes me think that there’s quite a few aircraft flying around without the spring having been replaced, but of course I’ve only talked to a couple of pilots, not any kind of representative sample.

Of course as with every thing else I have tried to order, there are no springs to be had, even at the over $1,000 price, and won’t be for at least a month

[ArtVandelay]

According to the SB 282A, Eaton was notified it happened at least once, maybe a manufacturing defect?

[A64Pilot]

I’ve done a little bit of reading on it and asking etc. A little bit of knowledge can ne a dangerous thing though.

Searching this website it seems some believe that there were a batch that were first heat treated, then after heat treating the tangs were bent, which of courses likely to stress it and start a crack. The breaks are from this improperly heat treated batch. That seems logical.

Assumption is normally the tang is made with the metal in the annealed condition, then heat treated. It’s important to realize that nothing I’m saying here is supported by known facts, it’s ALL supposition, and could be completely wrong, that's why I’m asking, it seems someone is compiling statistics here and I’m wondering if there are any for no back springs gear ups.

‘Some seemed adamant that they weren’t changing their springs, but that may have just been an initial knee jerk reaction? 

Talking to someone at LASAR he seemed to indicate that the few that he knew of that broke, broke when the gear were down fully, and you don’t know it’s broken until the next takeoff and they won’t retract, but no gear up as they are down.

That makes sense to me as the time of greatest stress is likely when they are fully down and the bungee springs are being compressed, I assume compressing the springs is when the actuator is at its highest load.

Maybe some of the load is transmitted to the spring?

[toto]

I'm very interested in this topic. I, too, had never heard of the NBS and probably would never have heard of it if not for this forum. I learned a great deal from the various threads and really appreciated the efforts from Don Kaye and Andrew to document the spring and its replacement. 

I have the original NBS in my a/c, and my sense has long been that it's far less likely to fail than a bunch of other things that require less specialized knowledge to replace. I'll definitely replace my NBS one of these days, but I sure don't want a random shop pulling the gear actuator (much less tearing it apart). So it will be a "travel to Don Maxwell" event and I'll defer 100% to them on the correct approach to replacement. 

 

[GeeBee]

At least on mine, I knew when it was going bad. The noise will be distinct to your ears.

 

[PT20J]

It’s listed in the M20J Service Manual and Service Bulletins.

[carusoam]

The cracks in the springs are interesting...

@Hyett6420 Andrew took a few pics of the system and posted them...

You may want to have a look at your spring...

It would be interesting to put those pics in front of MS’s resident metallurgist...

Best regards,

-a-

[ArtVandelay]

I don’t like the hours requirement, if used for training it could have 5000 cycles or more but if used as normal it could have a 1000.

[A64Pilot]

Couple of statements.

No one tracks landings in the US that I know of, maybe your logbook I guess, other Countries do, they have a log book entry for every flight the aircraft makes in the aircraft logbook, so I believe we are stuck with hours as opposed to landing gear cycles

Secondly I know from both wing main spar caps and tail landing gear springs that fatigue in high strength steel is nearly impossible to detect prior to failure, you can’t detect cracks visually as they are internal, so dye pen is out, mag particle isn’t very good either, so that leaves X-ray and eddy current, for a tiny spring?

Secondly crack propagation once it begins is so rapid that you have to have a short inspection interval, many times replacement is cheaper than multiple inspections.

So in most cases you establish a replacement interval based on worst case and add in a rather large scatter factor, as an example the scatter factor on our wing spars was 7 meaning of course the life limit was actually 1/7 of actual life limit. Wing main spar cap failure of course means the wing comes off, so who wants to play with that? You would be surprised.

‘So if they are failing from fatigue, we need to replace them prior to failure, if it’s damage then inspection ought to work as you can see damage as it’s external.

‘I’ve never seen one, but I think I know what it is and what it looks like, and a price of a little over $1,000 is well, maybe more than it should be.

Makes one wonder what Eaton charges Mooney, because someone is guilty of price gouging in my opinion.

‘Then of course there is the argument that if that’s what it takes to keep Mooney alive and kicking so that parts are available, well then I guess we need to pony up.

Problem is of the half dozen parts I have tried to order from Mooney, backspring included, there are none available.

‘If the spring is what I think it is and operates the way that I think it does, then it ought to have a nearly infinite life, as it’s outside of the fatigue cycle, or should be.

Where is Don Maxwell’s shop located?

I plan on sending mine to LASAR as I believe even if the spring will last forever, it’s likely that after 41 years the grease has dried out and the whole thing needs to be disassemblied, cleaned inspected and repacked etc. and while I’m legal to tear it apart, it may be better if someone who has done it a few times does it.

‘Some repack wheel bearings every year 

Edited May 26, 2021 by A64Pilot

[PT20J]

 

 

M20-282A_m76xlr7v.pdf

[carusoam]

DMax is in KGGG Texas.... (check my accuracy)

The cracks are visually evident at the surface mostly near the bent ends...  from the pics I almost remember seeing...

Best regards,

-a-

https://www.airnav.com/airport/KGGG

[A64Pilot]

I believe without looking it up that the SB calls out for inspecting new springs for cracks and or maybe springs of a certain manufacture date?

If so then that seems to add credence to the improperly heat treated and or formed springs theory that I’ve read.

‘If you try to bend say a higher T rated piece of aluminum to a tight end radius, you will get cracks on the external part of the metal.

‘But I believe fatigue often occurs from the inside out, meaning of course that you may not be able to determine fatigue from either a visual or dye pen inspection.

‘So I think by having a visual inspection, your looking for improperly manufactured parts, not fatigued.

[A64Pilot]

But anyway, does anyone know how many gear ups were there, that the smoking gun was a broken spring?

I’m curious as to the risk, as currently replacement is not an option, and surely this is not a part you get salvaged

[A64Pilot]

On 5/25/2021 at 7:50 PM, GeeBee said:

At least on mine, I knew when it was going bad. The noise will be distinct to your ears.

 

It’s not just a sudden failure with no warning?

[GeeBee]

I cannot say for sure. Those in the know say it will give you warning. Mine made no noise, then all of the sudden on a couple gear swings while up on jacks made that "stretchy springy noise" that lets you know that a spring is not really enjoying the tension.

 

[LANCECASPER]

8 hours ago, A64Pilot said:

I’m curious as to the risk, as currently replacement is not an option, and surely this is not a part you get salvaged

Mooney orders them in batches to fill orders, they don't seem to stock them. They always end up supplying them, just usually a few week wait.

[toto]

5 hours ago, GeeBee said:

I cannot say for sure. Those in the know say it will give you warning. Mine made no noise, then all of the sudden on a couple gear swings while up on jacks made that "stretchy springy noise" that lets you know that a spring is not really enjoying the tension.

 

Out of curiosity, did you put it on jacks because you had heard the strange noise, or was it just a regular gear swing at annual? 

[GeeBee]

Regular swing