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Old 09-12-2020, 04:31 PM
Chattin35's Avatar
Chattin35 Chattin35 is offline
Join Date: Jul 2014
Location: Boise, ID
Posts: 274
Default Autopilot servo control drag

Just installed GRT pitch and roll servos on my RV-7 and it changed the control feel of the aircraft significantly. I love love LOVE the way my light and simple -7 handles. But, I fly a bunch of long cross countries – which can get fatiguing. So, I figured installing an autopilot was a good idea. After the install, the control response significantly heavier. Much of the magic handling is gone – to the point I'm considering removing and selling the servos. Granted, I've only done one test flight with the new servos to date. So, maybe I'll get used to it. But, I'm pretty disappointed in the effect so far...

Is this just the cost of business for having an autopilot?

Do you get used to the heavier control feel?

Are there alternate servos that don't drag on the controls?

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Old 09-12-2020, 04:46 PM
BobTurner BobTurner is online now
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,177

Trio servos use a clutch, so they are ‘out of the loop’ when off, e.g., no drag. Of course you’d need a Trio control unit to drive them (which can be, in turn, controlled by a grt efis). I have a Trio Pro on my -10 and the performance is top rate. Now, I would say, that most others using a stepper motor type servo say that they notice it on the ground, but not in the air. You might take a good look at yours, make sure they are really off when you think they’re off, any binding in the mechanical installation, etc.
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Old 09-13-2020, 10:25 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,768

I had a similar experience a few years ago and discussed it with GRT. GRT told me they had some issues early on with slop in the bushing, so they started making them tighter out of the factory, with an expectation of wear from use. They indicated that they will wear in to a comfortable drag level without slop. Over time, mine were no where near as tight as when new. I have no issues with mine, but I also don't have a super light aircraft.

Both Garmin at Trio have servos with zero drag.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 09-13-2020 at 10:27 AM.
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Old 09-13-2020, 10:39 AM
jbDC9 jbDC9 is offline
Join Date: Jan 2005
Location: Houston, TX
Posts: 879

My Trutrak Vizion 385 was similar, I could feel the servos in the stick and didn’t really like it... but it wasn’t enough to make me want to yank the system and go without, was mostly just a bit annoying. But, when I upgraded my panel with new Garmin stuff, I replaced the a/p with a Garmin head and servos. No drag at all, can’t feel a thing.
John Bixby
RV-8 QB sn 82030 - 1800 hrs
Houston, TX
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Old 09-14-2020, 10:18 AM
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Chattin35 Chattin35 is offline
Join Date: Jul 2014
Location: Boise, ID
Posts: 274
Default More test flying

Thanks for the info. I did some more flying and it's feeling a little better. I can't tell if it's me or the servos . So, I think I'll leave them in for the time being and see if they loosen up.

Interestingly, there was a -9 at the fuel pump with a Trio installed. So, I had the chance to feel the difference. I think the clutch drive is definitely the way to go. Van's airplanes handle too nicely to mess with the light/positive control feel. They really are special airplanes in that regard.

Good to hear the Garmin servos don't drag on the controls either. I was just about to ask after reading that they were a clutch drive too.
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Old 09-16-2020, 08:22 PM
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Chattin35 Chattin35 is offline
Join Date: Jul 2014
Location: Boise, ID
Posts: 274
Default Support Reply

Just got a reply from GRT support...

The servos are set up with very little play and are a bit tight at the start. Flying the airplane will free them up, give it 20 hrs or so. After this time they will be fine.
I'll leave them in for a while and report back.

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Old 01-15-2021, 12:09 PM
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Chattin35 Chattin35 is offline
Join Date: Jul 2014
Location: Boise, ID
Posts: 274
Default PIREP time!

Ok, got about 50 hours on them now. They've definitely loosened up like they said they would – probably about 50% less drag. I can still feel them, though, which is not ideal. But, I'm accustomed to it. And, it's super nice to have the autopilot capability for longer x/c's. Gonna leave them in.
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