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Trim Malfunction M20k 252


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On final yesterday I could not get the nose to come up with the electric trim right at the runway threshold. Pulling back on the yoke was not fun and i used the manual trim wheel. All of this threw a wrench into my approach and i went around. I completed a lap and landed using manual trim (trim wheel functioned properly) and the electric nose up trim did nothing again. After landing i noticed the number two alternator circuit breaker popped. and the indicator light on. The trim and autopilot worked fine during takeoff and the one hour flight. I don't have access to an electrical schematic, if someone has one I'd appreciate a copy. Anyone dealt with this before?  Ideas? BTW when operating the manual trim wheel the jack screw felt un encumbered in flight and ran end to end without binding via the manual trim wheel on the ground.

Mike

Edited by mike261
clarification
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So, how about some clarification.

Is there a problem with the electric trim? Did it fail to run the trim up?

Or, Is there some issue where you run the trim all the way nose up and it isn't having any effect?

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Sounds like a trim system malfunction. Was the trim annunciator on the KC192 illuminated after the failure? Did the trim switch/breaker trip? Try reseting the breaker and pressing test. TRIM light should flash 4 times and then stay out and then there are several beeps. 

Which breaker popped: the alternator output or the alternator Field?

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1 hour ago, mike261 said:

80 amp alternator breaker. I assume that's the output breaker.

Hmmm. That breaker (except in the unlikely event it’s faulty) can only be tripped by a fault within the alternator or the alternator output wiring as the alternator cannot supply enough current to trip it. Not sure how that would be related to the trim issue. I would troubleshoot that first and then go on to the trim if that doesn’t fix it.

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Apparently you only have one alternator on your 252. When the alternator went offline, and bus voltage dropped to battery voltage, the electric trim is often the first thing to go and suspect there is nothing wrong with the trim. But the alternator shouldn't be putting out anywhere near enough current to pop the output CB - this deserves investigation if its repeatable.  

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The electric trim uses the same servo as that AP auto trim.  If the auto trim is working with the AP engaged, but the electric trim is not working with the AP disengaged, there is some issue from the trim disconnect relay to the switch on the yoke.

My electric trim is INOP and it's down the list of things to fix while bringing 2VF out of hibernation.  But if the auto trim works, and the disconnect relay is working, as evidenced by the fact that your manual trim wheel turns easily, there's only so many things to check between the relay and the yoke.

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This happened to me last week as I was doing work in the pattern at KTAN. For me it turned out to be that I simply forgot to flip the Electric Trim switch on my panel. This is my first plane with electric trim so I was clueless. I landed and went through the checklist that I have and BAM there it was and what a relief. Hope your able to trace the issue down.

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congealed grease on the jackscrew it turns out. i searched the site but couldnt find the type of grease specified. it gets cold here in winter, need a better grease maybe.

mike

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4 minutes ago, mike261 said:

congealed grease on the jackscrew it turns out. i searched the site but couldnt find the type of grease specified. it gets cold here in winter, need a better grease maybe.

mike

This happened to me as well - AP behaving crazy, AP disconnect and the plane pitches up. Hand fly the rest of the way with no trim, interesting landing with pretty much all of my upper body strength hauling back on the yoke to flare. 

It took the shop less than an hour to re-grease the jack screw and I haven't had a moment's trouble in about two years since then. 

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2 hours ago, mike261 said:

congealed grease on the jackscrew it turns out. i searched the site but couldnt find the type of grease specified. it gets cold here in winter, need a better grease maybe.

mike

It's in the Service and Maintenance Manual: Aeroshell 7. Should be cleaned and lubed during the annual inspection. The trim carrier bearing also if you have a King autopilot. 

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AP says this is a common issue here in new england in february. so damn cold, and planes sit more. Im not the first case this winter either.

Mike

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1 hour ago, mike261 said:

AP says this is a common issue here in new england in february. so damn cold, and planes sit more. Im not the first case this winter either.

Mike

-73C cold?

1175199168_AeroshellAviationGreaseAircraftGreaseShellGlobal.thumb.png.4171e00805db69e0725de8454da50366.png

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Mike,

Look deeper into this issue...

Sure NH is pretty cold on the ground in winter... don’t use this for a reason to stop looking for the answer...

The real issue with the grease used in the trim system... it solidifies into rocks over the years... whether you are in NH or FL...


runaway or stuck trim can be very difficult for some people to physically overcome...  lots of force, similar to doing 75# arm curls...

There is plenty written about cleaning and regreasing the whole trim system...

Some times... a sure note that the trim system is locking up... it no longer operates from full up to full down...

Some MSers were surprised how wide the operating range is supposed to be...

Inviting @Amelia to the discussion... She has experience with trim issues in an M20K...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

 

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ok, im out. this place is no different than anywhere else. i come looking for help, and now im on defense to you two. the grease is old, the grease is dirty, and it failed in the cold....probably the last straw. jesus.

 

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No one is trying to give you a hard time. It's just that for some reason the trim system on Mooneys gets overlooked a lot and it does need routine lubrication. Often times pilots use the electric trim exclusively and don't know it's getting stiff until it gets so bad that the trim servo gives up. 

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