Electric trim issue

[Greg Ellis]

I wasn’t sure where to put this topic.  However, I had the GFC 500 installed and the electric trim as well.  I have the up down switch on my yoke.  The electric trim is not working well when the autopilot is off and needs manual assistance when going nose up.  Nose down it seems to be okay.  The auto pilot is working great with no issues and reports no faults at all.

I printed out Garmin’s trouble shooting page on if the electric trim does not run and will go through it this weekend but I was wondering if anyone had any advice on where to look.  I was thinking that maybe the trim system needed lubrication which I think is a big job.  Do the belly panels have to be removed to do this?  But if the autopilot flies well then is it a lubrication issue or something else?

Any advice would be appreciated so I can try to guide the correction of this process with my maintenance shop.  Airplane is a 63 C model.

Thanks.

[PT20J]

It sounds like there is too much friction in your trim system. The trim motor works harder trimming nose up than down on the ground because the jackscrew is lifting the tail. In flight, aerodynamic loads relieve some of this. There is a run time spec for the GFC 500 trim from stop to stop that should have been tested during installation. 

The Mooney trim system should be lubricated every annual inspection, especially the tail jackscrew. Some older models have a friction adjustment on the trim wheel that may be set too tight.

Skip

[Greg Ellis]

28 minutes ago, PT20J said:

It sounds like there is too much friction in your trim system. The trim motor works harder trimming nose up than down on the ground because the jackscrew is lifting the tail. In flight, aerodynamic loads relieve some of this. There is a run time spec for the GFC 500 trim from stop to stop that should have been tested during installation. 

The Mooney trim system should be lubricated every annual inspection, especially the tail jackscrew. Some older models have a friction adjustment on the trim wheel that may be set too tight.

Skip

Thank you for this information.  I will talk to my shop about this.

[Greg Ellis]

So, I went to the plane this weekend.  I opened up the tail area and exposed the jackscrew in the trim system.  It definitely was not gummed up at all.  The threads were clean.  They did seem to have some grease on them because it got on my fingers when I touched the screw.  However, how little grease is too little?  There certainly was not enough to be what I would call greasy or gummy.  I could see the peaks and valleys of all the threads, etc....

I can run the trim manually from stop to stop with really no issue.  It occasionally feels tighter in spots but nothing that I would have even thought twice about before getting the electric trim.  I tried the electric trim again and it ran it nose down and it ran smoothly all the way.  It will not go nose up on its own.  It will for a moment but then stops and needs manual assist.

I spoke to the installer and he thought there may be an issue with the actual installation so he is going to take a look at it when he is able.  But I guess my question is....should the jackscrew be coated in grease or just an extremely thin layer?  I have an extremely thin layer for sure.  It is not dry but certainly not a lot of grease.

[47U]

On 3/27/2023 at 9:02 AM, Greg Ellis said:

I can run the trim manually from stop to stop with really no issue.

Certainly have the installer review the electric trim system for installation/operation.  

But, being able to manually trim from stop to stop ‘with really no issue’ doesn’t lend itself to much confidence.  It really should be smooth as butter.  What friction you feel while manually trimming could be enough to limit effectiveness of the electric trim.

The jackscrew should be cleaned first, then the light layer of grease is appropriate.  This doesn’t sound like your problem to me.  

One thing that doesn’t get any attention during the annual or 100 hr lube schedule is the ‘trim housing’ in the tail.  It is greased and then sealed during manufacture at the factory.  If it’s never been taken out and cleaned, reshimmed, and greased, it very well could create the friction that is giving your electric trim system trouble.  

Good luck…

[Greg Ellis]

7 hours ago, 47U said:

Certainly have the installer review the electric trim system for installation/operation.  

But, being able to manually trim from stop to stop ‘with really no issue’ doesn’t lend itself to much confidence.  It really should be smooth as butter.  What friction you feel while manually trimming could be enough to limit effectiveness of the electric trim.

The jackscrew should be cleaned first, then the light layer of grease is appropriate.  This doesn’t sound like your problem to me.  

One thing that doesn’t get any attention during the annual or 100 hr lube schedule is the ‘trim housing’ in the tail.  It is greased and then sealed during manufacture at the factory.  If it’s never been taken out and cleaned, reshimmed, and greased, it very well could create the friction that is giving your electric trim system trouble.  

Good luck…

Thank you for this response.  I will take to my A&P about this as well.