Trim servo issues?

[redbaron1982]

Hi all,

I continue with my in-depth status check of my new Mooney. On the flight back to it's new home we notice that the trim up command from the switch in the joke was not working.

Today I went to the airport, sprayed some contact cleaner in the switch and now it's working, so that problem is solved now.

What I noticed now is that although the trim down moves fine, the trim up, although you can hear the motor be engaged it barely moves (I take the trim wheel as reference). Also I notice that when triming down, the joke moves like in steps rather than a continuous smooth movement.

Two questions: First, ideas on why this could be happening? Second, in the flight school where I did my training some times if the joke was "sticking" they would spray some lubricant in the joke shaft. Is this a correct procedure? Which kind of lubricant should I use?

[N201MKTurbo]

20 minutes ago, redbaron1982 said:

Hi all,

I continue with my in-depth status check of my new Mooney. On the flight back to it's new home we notice that the trim up command from the switch in the joke was not working.

Today I went to the airport, sprayed some contact cleaner in the switch and now it's working, so that problem is solved now.

What I noticed now is that although the trim down moves fine, the trim up, although you can hear the motor be engaged it barely moves (I take the trim wheel as reference). Also I notice that when triming down, the joke moves like in steps rather than a continuous smooth movement.

Two questions: First, ideas on why this could be happening? Second, in the flight school where I did my training some times if the joke was "sticking" they would spray some lubricant in the joke shaft. Is this a correct procedure? Which kind of lubricant should I use?

Both of those issues are caused by a lack of lubrication. The clutch in the trim servo is slipping because it takes too much effort to move the trim. The yoke is jerking because as the trim changes the tail angle it puts pressure on the elevator bungees. this pressure should smoothly move the elevator control rods, but because of the lack of lubrication, it is slip sticking. The pressure on the elevator controls has to overcome the friction, then it moves and waits until it overcomes the friction again, then moves again.

I ferried a Mooney last weekend that needed to be lubed. It was kind of a pain to fly. You will be amazed how much easier the plane is to fly when properly lubed.

A greasy Mooney is a happy mooney...

[alextstone]

26 minutes ago, redbaron1982 said:

Hi all,

I continue with my in-depth status check of my new Mooney. On the flight back to it's new home we notice that the trim up command from the switch in the joke was not working.

Today I went to the airport, sprayed some contact cleaner in the switch and now it's working, so that problem is solved now.

What I noticed now is that although the trim down moves fine, the trim up, although you can hear the motor be engaged it barely moves (I take the trim wheel as reference). Also I notice that when triming down, the joke moves like in steps rather than a continuous smooth movement.

Two questions: First, ideas on why this could be happening? Second, in the flight school where I did my training some times if the joke was "sticking" they would spray some lubricant in the joke shaft. Is this a correct procedure? Which kind of lubricant should I use?

A thorough cleaning and re lube of all of the control pushrod linkages will help but it's a job that requires ideally that the aircraft is jacked up, belly panels and other inspection panels removed and lots of patience.  

There are other items too like the trim wheel actuator etc that could need attention.

In my case, I installed a brand new four servo Garmin autopilot and I had a persistent issue of the Yaw damper servo kicking off.  The root cause turned out to be a missing bushing that acts as a sleeve for a retaining bolt for a control horn that is a component of the rudder / elevator interconnect.  It's buried inside the tail section.  I assume this was not installed properly way back in the mid 2000's when the plane was repainted.  My point of this story is,  a myriad of things could be the cause.

 

[N201MKTurbo]

Have you trimmed it with the wheel? does it move easily? A properly lubed trim system will actually continuously trim down in turbulence all by itself, which is why they put a little friction device on the trim wheel. 

[PT20J]

What autopilot do you have? King pitch servos have more torque than GFC 500’s because of the gearing. 

When you trim down, the whole empennage is moving down with gravity putting the rear jackscrew in compression. If the jackscrew is not well lubricated, it will sometimes be jerky as the friction changes during rotation in this condition. So, I would first clean and lubricate the jack screw per the Service and Maintenance Manual.

The eyeballs that pass through the instrument panel for the yoke shafts are supposed to be self lubricating and Mooney’s instruction for later models is to keep them dry. Unfortunately, the M20J manual still says to lubricate them with Triflow. Doing this attracts dirt and causes them to get sticky. It might be possible to flush them out with solvent, but the real solution when they get too bad is to replace them which is a real pain. Sometimes it helps to apply some silicone spray to the shaft and then wipe it off.

Skip

 

[redbaron1982]

1 hour ago, PT20J said:

What autopilot do you have? King pitch servos have more torque than GFC 500’s because of the gearing. 

I have a King KFC150.

1 hour ago, N201MKTurbo said:

Have you trimmed it with the wheel? does it move easily?

I will double check, I just flew it only once, but as far as I remember it didn't look bad trimming from the wheel.

Funny thing is that the airplane just came out of annual, so I would expect everything to be lubricated.

I will try to get the service manual check as far as I can myself, if problem is not solved I think I'll take it to a shop to take a look.

Question, it would better not to operate the trim like this, correct? I imagine that the clutch slipping would cause premature wear.

 

[N201MKTurbo]

8 minutes ago, redbaron1982 said:

I have a King KFC150.

I will double check, I just flew it only once, but as far as I remember it didn't look bad trimming from the wheel.

Funny thing is that the airplane just came out of annual, so I would expect everything to be lubricated.

I will try to get the service manual check as far as I can myself, if problem is not solved I think I'll take it to a shop to take a look.

Question, it would better not to operate the trim like this, correct? I imagine that the clutch slipping would cause premature wear.

 

Those clutches are pretty robust, but if it slipped too much for too long, it will wear it out. just help it with the wheel and you will be OK.

[N201MKTurbo]

You should talk to Don and tell him what is happening and see if he will take care of it.

[redbaron1982]

2 minutes ago, N201MKTurbo said:

You should talk to Don and tell him what is happening and see if he will take care of it.

will do.

One point, that I didn't mention, is that this test was done on the ground. I'm mention this just in case on the ground it is expected to be harder. Anyway it would explain the jerking movement.

[redbaron1982]

One related additional question. I noticed that the controls in my Mooney tend to spring back into a more or less neutral position if pressure is released, this is both for elevator and ailerons. I'm talking here about deflecting the controls while in the ground. This also happens when testing the AP. I set the AP to HDG and select a bearing that required left aileron and if I hit the AP Disconnect while the ailerons were deflected they will snap back into a more or less neutral position.

In the airplanes I used to fly in the flight school that was not the case, meaning that controls would stay in the same position when released.

Is the behavior I get in my Mooney normal?

[carusoam]

Keep in mind…

There is a gear box for the trim system in the tail…

If you have difficulty with the trim system’s lubrication….

There are two sources of grease turning to rocks over time….

One is in the gear box, the other is the Jack screw…

One is much easier to clean than the other…

PP thoughts only, not a mechanic…

Best regards,

-a-

[N201MKTurbo]

5 hours ago, redbaron1982 said:

One related additional question. I noticed that the controls in my Mooney tend to spring back into a more or less neutral position if pressure is released, this is both for elevator and ailerons. I'm talking here about deflecting the controls while in the ground. This also happens when testing the AP. I set the AP to HDG and select a bearing that required left aileron and if I hit the AP Disconnect while the ailerons were deflected they will snap back into a more or less neutral position.

In the airplanes I used to fly in the flight school that was not the case, meaning that controls would stay in the same position when released.

Is the behavior I get in my Mooney normal?

The Mooney has a rudder - aileron interconnect under the floor that tends to center the rudder and ailerons. The elevator has spring bungees in the tail that tends to bring the yoke back to the trimmed position. They are both spring loaded, so yes it is normal for your airplane to do that. 
 

Not all Mooneys have the elevator bungees, but yours does.

[Emmet]

Keep in mind…
There is a gear box for the trim system in the tail…
If you have difficulty with the trim system’s lubrication….
There are two sources of grease turning to rocks over time….
One is in the gear box, the other is the Jack screw…
One is much easier to clean than the other…
PP thoughts only, not a mechanic…
Best regards,
-a-

There is a third one that is often overseen (ask me how I learnt about it) : There is a bearing just below the trim servo where the torque tube runs through. That is supposed to be lubed regularly but probably doesn‘ t get the attention it deserves…