View Full Version : Autopilot servo control drag
09-12-2020, 04:31 PM
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?
09-12-2020, 04:46 PM
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.
09-13-2020, 10:25 AM
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.
09-13-2020, 10:39 AM
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.
09-14-2020, 10:18 AM
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 :D. 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.
09-16-2020, 08:22 PM
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.