G3X Manual Trimming not functinal if autopilot is powered

[maus92]

Interesting thread. I have my electric trim (2-axis) system running through the VP-X Pro, which has a "runaway trim" disable function. Inflight with the AP servos powered, the autotrim system keeps the aircraft in proper trim, whether or not the AP is actively steering the aircraft. I don't believe that I can alter the trim manually when the AP servos are powered. My before landing procedure is to depower the AP servos, which allows me to dial in more nose up trim on final than the autotrim usually applies (if the AP servos were powered) - just my preference.

[MCA]

Don,

I had a Trutrak AP with autotrim module (which I assume is similar in functionality to the Garmin system). When you engage the AP, it uses the autotrim module to maintain proper trim and specifically turns off manual input which is not needed.

AP on = autotrim
AP off = manual trim

So if you have auto trim that may be the "culprit."

[Walt]

Originally Posted by maus92

Interesting thread. I have my electric trim (2-axis) system running through the VP-X Pro, which has a "runaway trim" disable function. Inflight with the AP servos powered, the autotrim system keeps the aircraft in proper trim, whether or not the AP is actively steering the aircraft. I don't believe that I can alter the trim manually when the AP servos are powered. My before landing procedure is to depower the AP servos, which allows me to dial in more nose up trim on final than the autotrim usually applies (if the AP servos were powered) - just my preference.

That operation seem really weird to me, on the standard Garmin system:

The auto trim (no VPX) auto trims only when the AP is engaged.
If the AP is engaged and you manually trim the AP disconnects.
When the AP is not engaged the manual trim works normally.
Trim speed is based on airspeed and is always active when the servos are powered.

[alcladrv]

Do you really want electronic flight control inputs when you're near the ground like in takeoff or landing where the good 'ol "meat servo" usually does a very good job?

I like the way my G3X disconnects the AP whenever I manually trigger the electric pitch trim. That's the same way it works on every higher performance plane I've flown like King Airs, corporate jets, large airliner turboprops and regional jets.

[Ezburton]

First off, I found the settings in the G3X and disabled the trim servo functionality, which it seems disables the GSA28 from being the trim servo and enables the trim actuators I have installed. This cleared the red TRIM fail annunciation. I didn't have much time to test the functionality of the trim due to having a short flight with lots of traffic in the area.

When it worked intermittently, it was nice to have the AP trim while flying. It did throw up an annunciation when it was doing it (not sure I would have made it a caution... cyan or white would have been better IMO since it is a normal function). When I disconnected the autopilot the plane was trimmed just fine like the right seater just transferred controls to me.

WRT electronic inputs near the ground, I would use the AP to fly an approach to the missed approach point and perform the go-around. Given the speed changes, why would you not let it trim?

Thanks for helping me get this straightened out. The lesson learned here was to not change software in the middle of troubleshooting the problem. This was the last problem to solve with the glass upgrade.