Bent retract rod

[David Perry]

Found this bent retract rod at annual. No one seems to know the cause. 

79 J

[takair]

I once saw this on an aircraft that was misrigged.  

I can also also imagine it occurring if the gear is actuated while in the ground or not yet down and locked when landing.  More likely gross  mis-rigging.

[Yetti]

I think that is the front gear rod.  Running over a chock?

[Marcopolo]

On 5/9/2018 at 9:08 PM, David Perry said:

Found this bent retract rod at annual. No one seems to know the cause.

That's the right main gear extend/retract/control tube.  Extreme bind on the pre-load spring, or the gear hung up while in transition coming down or the right gear took enough side load to unlock and almost collapse before righting itself.  Yikes!

 

Ron

[N201MKTurbo]

That happens when the preloads are set too high or something jams the gear.

[Vance Harral]

Could be a malfunctioning (even temporarily) or mis-adjusted down-limit switch.  The down-limit switch is what "tells" the gear motor to stop running when the gear reaches the down-and-locked position.  If the switch malfunctions, or the tab that is supposed to actuate it slips, I think the motor will keep driving the system until it encounters enough resistance to pop the gear motor breaker.  Presumably this should happen before anything bends, but I've always wondered what actually happens in practice.  Any chance you had the gear motor breaker pop at least once since you last had it opened up?

[David Perry]

This is my second annual. The only gear related issue I have had is a nose tire went flat while taxing. The tire came off the rim ant the nose shook badly. I wasn't going very fast but it stopped the plane almost immediately. 

Still I did not suspect damage. 

[TerryDubYa]

Had that same tube bend during my last annual.  The mechanic blipped the gear up until it unlocked in order to swing it by hand to ensure the reinstalled gear door would fit.  I guess it wasn’t fully unlocked when he tried to push the right main into the gear well and the FBO had to eat the $450 part and the shop time to replace it.

[DJ67]

On 5/10/2018 at 3:22 PM, Vance Harral said:

Could be a malfunctioning (even temporarily) or mis-adjusted down-limit switch.  The down-limit switch is what "tells" the gear motor to stop running when the gear reaches the down-and-locked position.  If the switch malfunctions, or the tab that is supposed to actuate it slips, I think the motor will keep driving the system until it encounters enough resistance to pop the gear motor breaker.  Presumably this should happen before anything bends, but I've always wondered what actually happens in practice.  Any chance you had the gear motor breaker pop at least once since you last had it opened up?

I am in annual now and have one of these.  But my gear is J-bar, so I would be the motor, and I don't recall any jamming while deploying the gear.

[Ragsf15e]

2 hours ago, DJ67 said:

I am in annual now and have one of these.  But my gear is J-bar, so I would be the motor, and I don't recall any jamming while deploying the gear.

Wowza! Glad it didn’t collapse on you!

[Elijah]

The fact that the other one is not bent to me suggests it pretty much has to be mis-rigging. Or, like TerryDubYa said someone pushed the gear up into the well while it was on jacks. When properly rigged, there's an arm near each gear leg that goes "over center" and at that point no matter what you hit or run into, it's not going to put any additional force on these pushrods....  it would be interesting to see a pic of the right main gear linkage (see pic) now when the gear is fully extended. Is the preload spring compressed at all? 

[MB65E]

Great looking wheel well and Gear I must say. I’m impressed.

-Matt

[1980Mooney]

9 hours ago, Elijah said:

The fact that the other one is not bent to me suggests it pretty much has to be mis-rigging. Or, like TerryDubYa said someone pushed the gear up into the well while it was on jacks. When properly rigged, there's an arm near each gear leg that goes "over center" and at that point no matter what you hit or run into, it's not going to put any additional force on these pushrods....  it would be interesting to see a pic of the right main gear linkage (see pic) now when the gear is fully extended. Is the preload spring compressed at all? 

Watch both of these videos. See the second one at 3:30 min and 5:00 min  

 

 

[Shadrach]

On 5/10/2018 at 1:27 PM, Marcopolo said:

That's the right main gear extend/retract/control tube.  Extreme bind on the pre-load spring, or the gear hung up while in transition coming down or the right gear took enough side load to unlock and almost collapse before righting itself.  Yikes!

 

Ron

I don't think side load could do something like that unless the gear hit something stationary.  In my experience, properly rigged gear is extremely robust and resistant to loads from any direction.

[A64Pilot]

1 hour ago, Shadrach said:

I don't think side load could do something like that unless the gear hit something stationary.  In my experience, properly rigged gear is extremely robust and resistant to loads from any direction.

Still I tip toe around corners and don’t take them at speed because long ago I was told because there are no down locks that we were susceptible to side loads possibly collapsing a gear.

Likely BS, but I figure what do I have to lose by slowing down to turn?

 

[Shadrach]

26 minutes ago, A64Pilot said:

Still I tip toe around corners and don’t take them at speed because long ago I was told because there are no down locks that we were susceptible to side loads possibly collapsing a gear.

Likely BS, but I figure what do I have to lose by slowing down to turn?

 

Manual has a down lock, electric does not. But it hardly matters because all three gear mechanisms lock over center.  I don' take turns fast either but I have landed in crosswinds strong enough to cause the mains to skip/skid laterally. Terrible sound and feeling.  Even though I was confident the upwind main would not fold, it still made me nervous.

[EricJ]

48 minutes ago, Shadrach said:

Manual has a down lock, electric does not. 

The jack screw is difficult to back drive and I believe the Mooney gear actuator is designed to not backdrive.    This provides the actuation lock.    I've not heard of one failing, while the manual downlocks have failed.

And +1 that the overcenter mechanisms prevent gear collapse.   This is why it's important to check their preloads.

[N201MKTurbo]

51 minutes ago, EricJ said:

The jack screw is difficult to back drive and I believe the Mooney gear actuator is designed to not backdrive.    This provides the actuation lock.    I've not heard of one failing, while the manual downlocks have failed.

And +1 that the overcenter mechanisms prevent gear collapse.   This is why it's important to check their preloads.

FWIW, the jackscrew back drives very easily. The ring and pinion gears in the Dukes cannot be back driven and the other actuators have a brake (I think).  Either way, if the gear comes off the down limit switch, the actuator will turn on and drive it back.

The only force on the actuator after the gear is down is the preload, which isn’t very much. 

[PT20J]

The common acme thread jackscrew (such as the trim screw in the tail) is not easily back driven under load due to friction. This is why screw jacks can lift and hold a load with no locking mechanism. (They are susceptible to slipping under vibration which has the effect of reducing friction.)

To reduce operating friction, the landing gear actuators utilize a ball screw with ball bearings between the screw and nut threads. Such screws are easily back driven. As @N201MKTurbo said, the gear train in the Dukes prevents back driving. In the Eaton and Plessey actuators, the infamous noback spring acts as a wrap spring brake to prevent back driving (hence the spring’s descriptive name.)

If the weight of the landing gear were able to back drive the actuator, the wheels would not stay in the retracted podition.

[A64Pilot]

On the Mooney, if we accept both electric and manual systems have something that functions similarly to down locks, the difference is that instead of being at the gears they are at the actuating end, meaning of course that there are flexible tubes between the lock and the gear. IF there was an excessive force acting on the gear, and the down lock didn’t fail, then the tube is going to bend. 

That’s pure speculation with nothing but speculation to back it up, but I’ve heard of a couple of mysterious bent actuating rods on this forum. I say mysterious as there isn’t any smoking gun, but something is causing it. Another speculation is that rigging wise, it would have to be grossly out of rig to get bent, flexing sure, but a bend of that magnitude?

I think one indicator may be what is the position of the springs? If there isn’t excessive clearance, meaning that the gear is in proper position with the bent tube, then in my mind that points to rigging? If it was properly rigged with a straight tube, then it would have to be loose now with a bent tube?

Edited September 12, 2024 by A64Pilot

[A64Pilot]

Another thought, IF there were occasional shock loads feeding back into the system, like say crosswind landings as @Shadrach has brought up, and the no back spring is what’s absorbing those shocks, that may eventually lead to a no back spring failure? That force is going somewhere.

[Fly Boomer]

6 minutes ago, A64Pilot said:

Another thought, IF there were occasional shock loads feeding back into the system, like say crosswind landings as @Shadrach has brought up, and the no back spring is what’s absorbing those shocks, that may eventually lead to a no back spring failure? That force is going somewhere.

Does the "no back spring" lock the gear down as well as up?

[A64Pilot]

3 minutes ago, Fly Boomer said:

Does the "no back spring" lock the gear down as well as up?

I don’t know, good question. It may be a one way clutch like a sprag clutch, allowing free movement in one direction.

I’m guessing that the manual gear system and electric system differ primarily in that one is manual and the other has a linear actuator.

The manual requires a down lock of the gear can collapse, we know that, so I’m postulating that the electric system requires a similar lock, but ALL this is pure speculation on my part.

 

[Shadrach]

1 hour ago, Fly Boomer said:

Does the "no back spring" lock the gear down as well as up?

My rudimentary understanding of the Mooney gear system is limited to the J-Bar models. If I apply my understanding of the manual system to the electric gear system, I would say that the actuator and the up limit switch are what hold the gear in the up position in the same way they hold the gear in the over center down position.

I’ve never seen a detailed explanation of precisely how the “no back spring” incorporates into the system. I was under the impression it was part of a clutch mechanism. 

[A64Pilot]

31 minutes ago, Shadrach said:

I’ve never seen a detailed explanation of precisely how the “no back spring” incorporates into the system. I was under the impression it was part of a clutch mechanism. 

That’s been my understanding too, sort of a mechanical Chinese finger trap, free running in one direction, but maybe that’s incorrect?

But IF the rest of the retract system is very similar and the J bar requires a down lock to keep from collapsing, wouldn’t the electrical system also require one? If not, why not?

I’m not disregarding the overcenter mechanism / springs in this, I think they play a large part as the tubing itself clearly isn’t up to the task in compression all by itself, but it seems that you need both, the overcenter plus something that locks the movement of the tubing. The gear need that spring pressure to keep from collapsing it seems. IF the actuator didn’t have something that locked it in place then that spring pressure could be lost?

Again, I’m not stating this as fact, many times I’ve come up with what seems to be logical theories only to find they were way off base because I didn't have all the data, an assumption got me.