GFC 500 elevator trim servo torque

[PT20J]

One thing I've noticed about my GFC 500 is that the trim servo seems a little wimpy. The manual trim works fine with no excessive friction. The old KAP 150 servo would easily power the trim from stop to stop on the ground and if I grabbed the trim wheel I could feel the clutch slipping and the servo continuing to apply torque. The GSA 28 servo on the other hand struggles to get the trim full up slowing noticeably (up is harder because the jackscrew has to lift the weight of the tail), and if I put any pressure on the trim wheel at all it just stops moving. Per the STC, the torque is set at 100% so that's all it's got. I think the problem is that the servo doesn't turn fast enough to run the Mooney trim system without a high gear ratio on the chain drive and this reduces torque available at the trim torque tube. My installer has installed several GFC 500s in other airplanes but this was his first Mooney and he commented on the size of the sprocket. During the annual inspection immediately after the installation my IA also commented on it and said he'd never seen a sprocket that big either. It flies fine but I'm wondering how it will hold up over time.

The old KAP 150 servo was geared about 1:1

For comparison, here's the GSA 28 chain drive.

Skip

[201Mooniac]

Skip, I checked mine and there is no problem at all with the trim servo driving the trim full nose up.  I can certainly stop it but it does fine on its own.  Do you have any friction in the mechanism when you turn it manually?

[PT20J]

47 minutes ago, 201Mooniac said:

Skip, I checked mine and there is no problem at all with the trim servo driving the trim full nose up.  I can certainly stop it but it does fine on its own.  Do you have any friction in the mechanism when you turn it manually?

I went through the whole system a while back and the friction is pretty low. It passes all the post installation tests and it does reach the up stop, but it slows during perhaps the last quarter travel approaching the up stop and has noticeably less torque than the old B-K servo. Perhaps “struggles” overstated it. In flight, it’s not an issue.

The other thing I noticed about the GSA 28 servos is that the force required to overpower them in pitch and roll is pretty high since they don't have slip clutches. 

Skip

[201Mooniac]

I find the force to overpower is about the same as my previous S-Tec servos.  I don't have that much time with BK APs so I can't compare.

[Baker Avionics]

4 hours ago, PT20J said:

I went through the whole system a while back and the friction is pretty low. It passes all the post installation tests and it does reach the up stop, but it slows during perhaps the last quarter travel approaching the up stop and has noticeably less torque than the old B-K servo. Perhaps “struggles” overstated it. In flight, it’s not an issue.

The other thing I noticed about the GSA 28 servos is that the force required to overpower them in pitch and roll is pretty high since they don't have slip clutches. 

Skip

Skip, do you want to bring it here for us to take a quick look at it?  We wouldn't charge you to see if we can find something.  We have done a lot of these and haven't had any issues as well.  We are just in Oregon.  Also, did you look at the setups in the controlling G5, 275 or G3x to be sure the settings are all correct?  Sorry, just had to ask.

[PT20J]

29 minutes ago, Baker Avionics said:

Skip, do you want to bring it here for us to take a quick look at it?  We wouldn't charge you to see if we can find something.  We have done a lot of these and haven't had any issues as well.  We are just in Oregon.  Also, did you look at the setups in the controlling G5, 275 or G3x to be sure the settings are all correct?  Sorry, just had to ask.

Thanks, Greg. 

I may stop by next time I'm down your way. Never hurts to get a second look .  But it does work OK and meets the Garmin specs. My point was mainly that it is not nearly as robust as the old KS 179 servo. I see posts here and on Beechtalk about servo failures. There was a recall in early 2020, but some are complaining about failures after that event. I ran a little poll here and out of 22 respondents with GFC 500 installations at least 6 months old, 5 had found it necessary to replace one or more servos.

Have you seen any failures?

Skip

[icurnmedic]

I’ve noticed when mine has allot of nose down trim in, it has a difficult time applying nose up.
The other day the g3x actually told me to apply nose up trim. 
I too wonder how long this will hold up. 
Thomas

[Seymour]

  

On 11/15/2021 at 12:17 AM, icurnmedic said:

I’ve noticed when mine has allot of nose down trim in, it has a difficult time applying nose up.
The other day the g3x actually told me to apply nose up trim. 
I too wonder how long this will hold up. 

We're skipping the trim servo / controller for now on our GFC-500 install for both budget and parts availability reasons...

Has anyone else skipped the trim when installing the AP on a short body?    Does the AP ever disconnect at inopportune moments (eg. approach) because you didn't respond to a trim request?

[N201MKTurbo]

I would assume they are limiting torque by limiting motor current. Weather it is a stepper motor or a servo motor, the motor will never overheat from exceeding its torque capability because the current is limited. This will not put any excessive electrical, mechanical or thermal stress on the motor. 
 

It should be just as wimpy 50 years from now as it is today.