Gear Down annunciation in J

[midlifeflyer]

I was asked this question by a new Mooney J owner the other day and didn't have an answer.

In systems with "3 green" each light represents one wheel, so if one gear hangs you know it.

How is the J set up? Is the single light and the visual indicator associated with only one gear? Are they interconnected in some way? Or is it merely indicating a single wheel and might not indicate all three are down?

[jetdriven]

There is a switch on the right side main landing gear push rod in the belly. There’s a metal tab bolted to the pushrod, and when the tab reaches  a certain point, it contacts a limit  switch attached to the plane.  This switch turns off the gear motor and illuminates the gear down  light. The motor overruns slightly which creates some additional down pre-load from the values that you measure every year at annual.  . basically as long as everything is rigged  properly and everything is tight and there are no loose Heim bearings and that sort of thing, if one gear is down theyre all down. 

[midlifeflyer]

Thanks @jetdriven for the explanation of the setup.

I guess "that sort of thing" is exactly the concern. For example, recently an Arrow pilot had one of the landing wheels "hang" - that sort of thing. The pilot was alerted by the lack of a third green.  

[Vance Harral]

While there are always corner cases, it would be rare for only one wheel to have a problem.  It would be vanishingly rare - impossible I'd argue - for one wheel to have a problem you could actually do something about in flight except make a normal landing on a normal runway and hope for the best.  The Arrow and other aircraft like it have three indicators because their hydraulic gear systems are arguably three independent mechanisms, each of which could fail independent of others.  Yes, one wheel can "hang" in those systems, and you might jar it loose with some positive G maneuvers, etc.  Not so in a Mooney.

If you're really concerned about it and think it would change your piloting in a positive manner to have three indicators, suggest you just mount a camera on the tail tie-down, and look for all three gear to be down on your phone/tablet/whatever.  Cheap and easy.

[EricJ]

Because the gear on the Mooney are mechanically interconnected and actuated by a single actuator, the gear aren't independent.   The only way one gear would not be down and locked if the others were would be if there was a significant mechanical fault of a passive component.   That can defeat any kind of warning system, so independent lights on Mooney gears would just be unnecessary duplication.

[midlifeflyer]

2 hours ago, Vance Harral said:

While there are always corner cases, it would be rare for only one wheel to have a problem.  It would be vanishingly rare - impossible I'd argue - for one wheel to have a problem you could actually do something about in flight except make a normal landing on a normal runway and hope for the best.  The Arrow and other aircraft like it have three indicators because their hydraulic gear systems are arguably three independent mechanisms, each of which could fail independent of others.  Yes, one wheel can "hang" in those systems, and you might jar it loose with some positive G maneuvers, etc.  Not so in a Mooney.

If you're really concerned about it and think it would change your piloting in a positive manner to have three indicators, suggest you just mount a camera on the tail tie-down, and look for all three gear to be down on your phone/tablet/whatever.  Cheap and easy.

I'm not and it would not. Sometimes questions are just a search for knowledge.

[midlifeflyer]

1 hour ago, EricJ said:

Because the gear on the Mooney are mechanically interconnected and actuated by a single actuator, the gear aren't independent.   The only way one gear would not be down and locked if the others were would be if there was a significant mechanical fault of a passive component.   That can defeat any kind of warning system, so independent lights on Mooney gears would just be unnecessary duplication.

Thank you, Eric. I think that's what I am looking for.

[kortopates]

As Eric and Byron summarized above, the way the Mooney gear, both manual and electric versions are entirely inter-connected is genius. The Piper and Bonanza versions are nothing like the Mooney. And this is why the floor window and bulb are primary, not the annunciator in the panel (even though the bulb is on the same circuit as the floor bulb) you want to see the green foot ball position.


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[midlifeflyer]

Thank you, @kortopates. 
 

edit. Silly word anticipation.

Edited November 10, 2019 by midlifeflyer

[bradp]

All the electric gear moonies are just Johnson bar moonies minus the bar and plus an actuator motor.   All three gear are interconnected.

[midlifeflyer]

Thank you all for the responses. I have merged them into this answer to the pilot who asked me:

If you look at a schematic of the Arrow landing gear system, you see three separate actuators. Essentially, each wheel is an independent system so each  can fail when the others are working. So each has its own gear light.

In the Mooney,  the three wheels are mechanically interconnected. Single actuator. If one is down, all are down. One wheel "hanging" while the other two are down should not happen.The way the system operates is also the reason that the floor window is primary for ensuring gear down.

Of course, no system is completely foolproof. But the types of issues which would lead to a one-wheel failure in a Mooney while gear down is indicated would also likely bypass a three gear light system.