Paul - M20C

M20C Landing Gear kickback

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My landing gear springs back about 1/4" after full down. Anyone seen this and know what causes it? My A&P brought in an expert and they re-rigged everything but it still does it. The current thought is that the actuator may need replacing or the gears. Looking for your experiences.  Thanks.

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Does this C have electric gear? And I'm naturally suspicious of the "expert".

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I'm not sure if this will help you, but here is a gear swing video on youtube.  There are many others to chose from as well.    Best of luck with it, I hope it works out for the better.

 

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45 minutes ago, Tcraft938 said:

I'm not sure if this will help you, but here is a gear swing video on youtube.  There are many others to chose from as well.    Best of luck with it, I hope it works out for the better.

 

Yep, that's mine from 2 years ago. My now retired IA is short and had a hard time reaching the switch from outside.

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2 minutes ago, Hank said:

Yep, that's mine from 2 years ago. My now retired IA is short and had a hard time reaching the switch from outside.

The manual bar would have been a killer for him.  LOL

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The video below shows the gear retraction and extension.  It's kind of hard to see in this video but it's a lot more pronounced than the videos above.  I will post a video of the gear motor next and you'll really see what I mean.  It's that last second where the gear motor actually reverses.

https://youtu.be/nw9rYPy7LZo

Edited by Paul - M20C

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I would check the down limit switch for proper functionality, there is normal close and normally open terminals, make sure both are working as designed, and make sure switch is properly secure.

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Going by memory as I'm now a lurker versus a MSer. I would strongly suspect, at a minimum, the actuation paddle for the down cycle is incorrectly set. This essentially means that everything on the down cycle is incorrect.  In the videos. the motor re-energizes momentarily after the gear is supposedly locked. This should not happen. The gear motor should de-energize (Green light on) at the specified over-center torque and vice versa.  The subsequent motor/actuator overrun should stop before the spring cans are fully collapsed. You are within some degree of having a gear collapse. 

Additionally, "spring back" is impossible with a worm gear (assuming you have the typical which should be with the 20:1 fast gear). Forces cannot be transmitted backward to the drive end and they fail in-place. That's why many landing gear and almost all flap systems utilize them. They're loud AF on Airbus's. You've probably noticed.

Before reading any other comments:

Read the Service Manual section specific to gear rigging. Afterwards, read it again.  Everyone makes mistakes, even supposed experts. That is your investment, no one else's. Protect it

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On 1/12/2020 at 12:26 PM, Paul - M20C said:

My landing gear springs back about 1/4" after full down. Anyone seen this and know what causes it? My A&P brought in an expert and they re-rigged everything but it still does it. The current thought is that the actuator may need replacing or the gears. Looking for your experiences.  Thanks.

There are a number of crucial service bulletins on your gear transmission.  They are free on www.mooney.com Best to familiarize your self with them.

The 20:1 gears in your transmission are subject to wear when not greased properly.


Clarence

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In the video it is back driving the actuator. How are your preloads after it back drives? How do your spring compressions look? I have a feeling you are overdriving the gear, but I can't tell unless I'm there. 

If you use the crank until the light comes on does it want to back drive? Does it get hard at the end?

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Wish I had all the data or you lived nearby. As mentioned, a worm gear cannot apply a force back through the drive end. Decent chance your coupling (rubber donut with embedded steel plates) between the motor and gearbox is getting torsional strain (wound up) and/or some part of the mechanism is yielding; strongly suggesting the mechanism has hit a mechanical limit. Here you'd guess spring cans are collapsed. These cans limit the mechanical force/strain of the mechanism during down actuation; linkage columns being the critical member. Forces rise dramatically if the springs are collapsed to solid height at any time during the actuation. The outlier in the data is why the breaker never tripped.  Maybe the very short re-enegize cycle prevents that.  Keep us informed. It's a good one.

Read the SM and SBs.  Its your aircraft and your bank account. If it's experiencing higher than design forces, it's costing you money. The weak link in the entire system gear box. At least they're plentiful and almost free.

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This almost kind of reminds me of an issue I had 25 years ago with my first M20C with electric gear.  I called up Dugosh and spoke with the owner at that time, Ronnie.  He said that the tensioner/friction springs inside the motor were old and no longer holding the motor from spinning when the motor wasn't energized.  

I took my motor to him, he disassembled it and installed 2 standard AN 960-10 washers as shims to make up for the springs that had lost some of their tension.  Worked great.  And he wouldn't let me pay him.  He was a great guy, hope the new Dugosh owners are similar.

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