No Back Spring Update

[Fly Boomer]

5 hours ago, toto said:

No worries. Yeah - it seems crazy that there wasn’t some kind of mechanism in the original design that would give you one manual extension in the event of a spring failure. I don’t care if it’s safety wire or a zip tie - just something that doesn’t require calling the insurance company if the tiny spring fails. 

It’s a reasonable question.  Apparently if the Piper gear actuator fails, there is a stubby little handle similar to a J-bar, and the gear basically just falls out.

[Pinecone]

7 hours ago, toto said:

No worries. Yeah - it seems crazy that there wasn’t some kind of mechanism in the original design that would give you one manual extension in the event of a spring failure. I don’t care if it’s safety wire or a zip tie - just something that doesn’t require calling the insurance company if the tiny spring fails. 

Single point failure modes are NOT good.

[toto]

4 hours ago, Fly Boomer said:

It’s a reasonable question.  Apparently if the Piper gear actuator fails, there is a stubby little handle similar to a J-bar, and the gear basically just falls out.

Yep. From my limited experience flying Piper retracts, it's also possible to get the gear to extend with some simple light-G maneuvering. 

[Fly Boomer]

The data plate on the gear actuator in my K says Condec/Consolidated Controls.  Looks like they were bought by Eaton at some point.  Does this actuator have potential problems with the NBS?

[GeeBee]

Ultimately, any problem with the supply of gear actuators can easily be solved with either an STC (linear actuators are manufactured by a number of people) or do like the Beechcrafts and covert to hydraulic which is easy. Just the FAA part is hard. I'm actually surprised nobody has done a hydraulic conversion for the Mooney with a CO2 blow down.

 

[PT20J]

27 minutes ago, Fly Boomer said:

The data plate on the gear actuator in my K says Condec/Consolidated Controls.  Looks like they were bought by Eaton at some point.  Does this actuator have potential problems with the NBS?

Yes

[Fly Boomer]

2 minutes ago, PT20J said:

Yes

So, when someone refers to "Eaton" they are really referring to the Condec/Consolidate Controls product bought by Eaton -- not something Eaton designed?

[PT20J]

Arrows and Seminoles (maybe other Pipers) have no uplocks; the gear is held up by hydraulic pressure. If the electrical system or the reversible motor in the hydraulic pump fails, then pulling the small lever on the console releases hydraulic pressure and the gear extends by gravity and maybe some mild g loading to lock the nose gear. Likewise, the gear will extend if hydraulic pressure is lost. 

It’s good unless you are a ferry pilot concerned about a hydraulic leak causing the gear to extend over the ocean which would ruin you trip.

Skip

[PT20J]

6 minutes ago, Fly Boomer said:

So, when someone refers to "Eaton" they are really referring to the Condec/Consolidate Controls product bought by Eaton -- not something Eaton designed?

Hard to tell who actually designed something 50 years ago. The important point is that Eaton currently owns the design except for the Plessey units that no one seems to maintain.

[EricJ]

6 hours ago, Fly Boomer said:

It’s a reasonable question.  Apparently if the Piper gear actuator fails, there is a stubby little handle similar to a J-bar, and the gear basically just falls out.

That's on the Comanche, which has electro-mechanical gear like a Mooney.    Arrows and Seminoles have electro-hydraulic gear where you just release all the hydraulic pressure and the gear falls down.   Usually. 

[EricJ]

I don't think there's a requirement on GA airplanes to have completely fail-safe gear that has a backup for every failure that can be anticipated.   Cessna 210 gear is fairly notorious for that.   The backup is a manual hydraulic pump that does little good if the failure mode is hydraulic, and the electro-hydraulic "power packs" are also notorious for being finicky.

The primary failure mechanism in Mooney gear is electrical, either the motor or switches or relays, and the mechanical backups work well in those cases.   I think we don't know how often that happens because successful deployments are often not reported anywhere.

 

[1980Mooney]

6 hours ago, Fly Boomer said:

It’s a reasonable question.  Apparently if the Piper gear actuator fails, there is a stubby little handle similar to a J-bar, and the gear basically just falls out.

However, in some failure modes the Piper manual emergency landing gear extension system doesn’t work properly- just like Mooney.  No backup system is 100% perfect fail safe in all possible failure modes over decades of use, many thousands of cycles and maintenance by many different parties.

https://www.atsb.gov.au/publications/occurrence-briefs/2018/aviation/ab-2018-024
 

Edited February 5, 2023 by 1980Mooney

[PT20J]

Well, if the gear were fixed…oh, never mind 

[GeeBee]

1 hour ago, EricJ said:

I don't think there's a requirement on GA airplanes to have completely fail-safe gear that has a backup for every failure that can be anticipated.   Cessna 210 gear is fairly notorious for that.   The backup is a manual hydraulic pump that does little good if the failure mode is hydraulic, and the electro-hydraulic "power packs" are also notorious for being finicky.

The primary failure mechanism in Mooney gear is electrical, either the motor or switches or relays, and the mechanical backups work well in those cases.   I think we don't know how often that happens because successful deployments are often not reported anywhere.

 

I once pee'd into a cup and poured it into the power pack on a T-210. Between three bladders, it worked!

[EricJ]

2 hours ago, GeeBee said:

I once pee'd into a cup and poured it into the power pack on a T-210. Between three bladders, it worked!

I've heard that was a not unusual technique in the bombers during WWII.   Whatever works in a pinch!

[Pinecone]

No, no system is 100% fail safe, but it is still bad engineering to have a single point of failure that causes both your normal and your emergency back to not work.

[1980Mooney]

On 2/5/2023 at 6:00 AM, Pinecone said:

Single point failure modes are NOT good.

Like wing failure, engine stoppage (for any of many single point failures- a single connecting rod or piston, a single fuel line break, single fuel line blockage, single crankshaft break, single camshaft break, etc), single propeller blade break/detachment,etc). 
 

Anyone that thinks that the few no-back spring induced gear-ups in 30-50 year old actuators represent poor engineering and an unacceptable risk are living in denial of the overall risk of flying. 

The incidence of engine stoppage and wing separation (other brands) is far higher despite the best efforts of engineers, manufacturers and mechanics. 

[1980Mooney]

3 hours ago, Pinecone said:

No, no system is 100% fail safe, but it is still bad engineering to have a single point of failure that causes both your normal and your emergency back to not work.

What exactly is “the emergency backup”  system on a Mooney when the “single point” crankshaft or camshaft fails(breaks)?  Oh that’s right - Mooney doesn’t have one. But Cirrus does- a CAPS/BRS parachute. 
 

So you are making the point that Mooney is an example of bad engineering. Many would agree. 

[EricJ]

There are plenty of examples on our airplanes where single point failures are Very Bad.    The fuel servo is a good example.   That's a critical function with no backup.   There are many more examples.   From an engineering perspective it just means that those things have to be designed with sufficient robustness to have a low probability of failure.

In the event of stuck gear, it's not nearly as catastrophic as something like a sudden engine failure.    You still get to pick when and where you're gonna land, it's just gonna cost more that time.   So it's not worth the cost/weight/engineering to make it completely redundant.

[slowflyin]

I read @Pincone  's post as a comment on the "backup" system having a common, single point of failure with the primary system as opposed to an opinion on single point of failure items in general.  I tend to agree with the thought process.  My F model's emergency gear mechanism didn't have the vulnerability my M model has and that's unfortunate.  Not the end of the world; all things in proper perspective.  

[EricJ]

22 minutes ago, slowflyin said:

I read @Pincone  's post as a comment on the "backup" system having a common, single point of failure with the primary system as opposed to an opinion on single point of failure items in general.  I tend to agree with the thought process.  My F model's emergency gear mechanism didn't have the vulnerability my M model has and that's unfortunate.  Not the end of the world; all things in proper perspective.  

If your F model had electric gear it had similar issues that were single-point failure locations that would disable the manual and electric deployment at the same time, and there were also failures that could defeat the manual deployment that you might not know about until you needed it.

The clutch spring should be, and evidently almost always is, a high reliability item.  It is possible to assess and engineer around all anticipatable failure modes, no matter how unlikely, but you wind up with a product that is too expensive and or heavy or complex to be useful.   Also, if you keep adding hardware to back up other hardware, you sometimes just add new failure modes and unecessary complexity.    Part of good engineering is knowing when to stop.

[PT20J]

From an engineering standpoint, the requirements dictate the design. If Mooney only specified that the emergency extension system protect against electrical malfunction, then the actuator meets the requirements. 

Skip

[Ragsf15e]

On 2/4/2023 at 8:30 PM, PT20J said:

It was beefier than the Dukes it replaced.

https://www.donmaxwell.com/ad-75-23-04-sb-m20-190

 

I think those of us with the Dukes actuators are going to have significant issues soon too… the gears wear (even the 40:1 gears) and require special grease (which is available but maybe not always used?).  There was someone looking for a set of gears recently on here who couldn’t find them.  I suspect that’s going to be a tough part to source and possibly grounding.  Maybe we convert back to J bar?

[EricJ]

15 minutes ago, PT20J said:

From an engineering standpoint, the requirements dictate the design. If Mooney only specified that the emergency extension system protect against electrical malfunction, then the actuator meets the requirements. 

Skip

FAR 23.729 specifies the legal requirements for gear extension.   If there is no manual extension method (I don't know if the crank or pull handle counts); 

c) Emergency operation. For a landplane having retractable landing gear that cannot be extended manually, there must be means to extend the landing gear in the event of either—

(1) Any reasonably probable failure in the normal landing gear operation system; or

(2) Any reasonably probable failure in a power source that would prevent the operation of the normal landing gear operation system.

I don't know if "reasonably probably failure" is defined anywhere, or it's left up to the manufacturer, but it's clear that single point failure items just need to be "reasonably high reliability" or at least above the threshold of "reasonably probable failure".

 

[1980Mooney]

6 minutes ago, EricJ said:

there must be means to extend the landing gear in the event of either—

(1) Any reasonably probable failure in the normal landing gear operation system; or

(2) Any reasonably probable failure in a power source that would prevent the operation of the normal landing gear operation system.

I don't know if "reasonably probably failure" is defined anywhere, or it's left up to the manufacturer, but it's clear that single point failure items just need to be "reasonably high reliability" or at least above the threshold of "reasonably probable failure".

That sounds reasonable…….

 

Edited February 6, 2023 by 1980Mooney