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G3X Auto Trim Informal Poll

J

JLuckey

Member
Installing G3X in RV-14 and trying to decide whether or not to use the Auto-trim function of the G3X autopilot.

To all you G3Xers out there:

1. do you like auto trim?

2. I have read several threads where there was difficulty with configuration and getting it to fly approaches. Did you have trouble getting yours configured?

3. I (think) I read in the Garmin docs that if you want airspeed-sensitive-trim speed, that you must wire for auto-trim. Is that correct?

TIA
 
I like auto-trim

Works well and flies approaches very smooth. I had to slow mine trims down (except for yaw) to keep from getting a slight bounce in cruise but approaches have been fine all along.
 
High performance

My rv9a is a high performance airplane. Not a spam can 172. As such, it needs to be flown differently. In cruise, the plane is fast an a momentarily nudge on the stick will cause a rapid change in attitude and response. So i tend to fly the plane on autopilot most of the time.
Without auto trim, the plane would have a large trim change and or pitch up when i come off autopilot for landing. Unlike 172, it cruises quite a bit above maneuvering speed, so trimming is important.
Like I said, it is not a 172 and needs to be flown differently. And this difference is a lot easier to manage with auto trim. JMHO YMMV
 
I am completely comfortable manually responding to G3X flags to “trim up or down”. No auto trim for me.
 
Works great. Easy to incorporate. Don't know why you wouldn't want it (everything in the bigger airplane world has it) but it can easily be disabled in configuration of you choose.
 
MED said:
I am completely comfortable manually responding to G3X flags to “trim up or down”. No auto trim for me.
Click to expand...


I don’t have auto trim and follow the “up/down” flags also. However, I wish there was a “left/right” trim flag also. Anyone know why this isn’t incorporated?
 
I am back to using auto trim however roll trim change requirements occur very slowly. I am in the habit of knocking off the autopilot occasionally on long cross-country flights to check trim. Not a big deal. This is a carryover of flying older high performance airplanes with uneven fuel burn.
 
Auto trim

I don't see the down side and it's a nice plus that every time you turn the autopilot off, the airplane is in trim.
 
Love autotrim

No issues whatsoever with autotrim and flying approaches and let me tell you I have flown a **** ton of coupled approaches with autotrim and the G3x Touch system.

To get airspeed sensitive trim, something has to manipulate the voltage going to the trim motor. A simple manual trim switch can't do that by itself. That means you have to wire some sort of controller in series with the manual switch. Pretty sure if my memory serves me correctly, you can have airspeed sensitive trim without autotrim enabled on the G3X Touch system but you still have to wire it appropriately.
 
I forgot about it because it works so well. I have a thread here somewhere with the changes I made to the trim rate because mine oscillated until I slowed it down from the Vans numbers.
 
I believe an auto trim runaway was a contributing factor in a crash of a Cirrus. Immediately after this crash Garmin came out a Service Alert having us disable the auto pitch trim function. Had to be turned off until they came out with a software update. I just recently turned mine back on. I didn't want to be an early adopter of Garmin's software testing.

https://support.garmin.com/en-CA/?faq=60VrEe33C53rCIuF4KUIt7
 
Service Alert 22109

Jetmart said:
I believe an auto trim runaway was a contributing factor in a crash of a Cirrus. Immediately after this crash Garmin came out a Service Alert having us disable the auto pitch trim function. Had to be turned off until they came out with a software update. I just recently turned mine back on. I didn't want to be an early adopter of Garmin's software testing.

https://support.garmin.com/en-CA/?faq=60VrEe33C53rCIuF4KUIt7
Click to expand...

The linked service document is related to the information we provided in this VAF Post. The pilot who experienced this failure event quickly recognized the problem and successfully took corrective action. We then analyzed the failure event, resolved the problem and released the necessary guidance to prevent the problem from occurring again in other fielded installations.

Thanks,

Justin
 
AutoTrim

There's an easy solution to have your cake and eat it too: I have a three position switch on the panel for the trim that picks the mode:

AP, which is autotrim
Stick (which I have on a voltage regulator to reduce trim speed, which applies to AP mode too)
Panel, which uses the trim servo included switch (which is on 12V.)

And there's a left/right stick select switch.

That way you can have it your way, and in AP mode, you still have trim on the stick if the AP is not engaged. If it is engaged, and you activate the stick trim, the AP disconnects.
 
It is straight forward to turn autotrim on and off in configuration mode, my approach has been to wire for autotrim - not any dig deal - and fly initially with auto trim off. Also not any big deal, not much trimming required (RV-6). Then enable autotrim, equally no big deal.

Very few downsides, auto trim failure is a very unlikely occurrence, I have a trim off-on-reverse switch so can isolate trim motor quickly.
Upside is aircraft is in trim when autopilot is disconnected.

I would definitely wire your system for autotrim.
 
JLuckey said:
Installing G3X in RV-14 and trying to decide whether or not to use the Auto-trim function of the G3X autopilot.

To all you G3Xers out there:

1. do you like auto trim?

2. I have read several threads where there was difficulty with configuration and getting it to fly approaches. Did you have trouble getting yours configured?

3. I (think) I read in the Garmin docs that if you want airspeed-sensitive-trim speed, that you must wire for auto-trim. Is that correct?

TIA
Click to expand...

1. ABSOLUTELY! The whole point of autotrim is that when the autopilot disconnects, the airplane is in trim. There are failure cases where this won't happen, but so what.

There are numerous situations in multiple disciplines where it only makes sense to be 100% in or 100% out. Autopilot without autotrim is one of those. As Mr. Miagi said in the Karate Kid, "Walk on road, hm? Walk left side, safe. Walk right side, safe. Walk middle, sooner or later… [makes squish gesture] get squish just like grape. Here, karate, same thing. Either you karate do 'yes' or karate do 'no'. "

2. Makes no sense to me. The autopilot has to be trimmed for your airplane, but this is not a function of autotrim.

3. The speed sensitive trim is so wonderful that it would be worth doing anyway.
 
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