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G3XT v.8.71 - Now Wandering Trim Indicator

Mountain Time

Active Member
I upgraded to v. 8.71 and everything seemed to work properly - but then I noticed that my pitch trim position indicator was wandering back and forth with no apparent rhyme or reason. Autopilot checks out and operates properly, as does the autopilot trim function (i.e., GSA 28 controlling the Ray Allen elevator trim servo), and when powered up on the ground the trim indicator is steady and then moves appropriately when trim is actuated.

Once the engine is fired up, though, trim indication begins to move around, and continues to do so in-flight, regardless of autopilot being engaged or what mode it is in.

I have not disturbed the trim system in any way that I can think of, the upgrade to v. 8.71 is the only recent change. The indicator is driven by the GP1 output from the GEA24.

I'm going to head back to the airport this morning and go through all the LRU and configuration settings yet again, just to see if something changed with 8.71 and I need to reconfigure - but I would sure appreciate any insight from the collective mind to help me chase this down!
 
Anyone else having issues ?

I'm a big fan of Garmin and the Garmin Team. These folks are some of the best in the business. Unfortunately it seems like the last couple of software releases have had some corky issues. I generally do an N-1 upgrade to make sure I'm not upgrading to the latest but I'm sitting happily 2 versions behind right now. I was going to upgrade this weekend but having similar setup with Ray Allen trims, I think I'm going to hold off for a bit longer.
This is in no way downgrading the Garmin system or their engineers and developers. I am still a huge fan.... currently working on another Garmin panel for another plane and plan to have a 3rd plane with the G3X system by the end of the year. Just an observation that the last couple of releases have had some issues. I'm sure this will get resolved soon also, if it proves to be the software.

Good luck with it.
 
Switch Fuel Tank Warning

8.70 was an expensive disaster for me. Transponder software reinstall $200. Upgraded to 8.71 and lost my "Switch Fuel Tank" warning.

I have not watched my trim indicator for movement whilst flying. The trim works fine manually and on auto pilot. I assume the reference here is that the trim indicator is swinging up and down with the trim actually not moving. I will closely inspect tomorrow on the next flight, however I suspect I am not having that issue, but I will check.

Just hope Garmin can come up with a way of fixing my Switch Fuel Tank warning to make it operative again.
 
It's not just the last few months. There was one update about 2 years back, version 5.7, that really hosed things up, especially the autopilot. It was terrible. They did get right on it but it was a huge boondoggle. I am still a fan but I learned to never upgrade to the latest Touch software until it has been out for at least a month.
 
The trim indicator on a Ray Allen trim servo is just a built in potentiometer. It doesn?t effect the trim function. This really sounds like a connection somewhere that is causing a fluctuation in the resistance with vibration. I would check connections as was suggested above.
 
Trim relay

My elevator trim position indicator was bouncing up and down like a ping pong ball. Replaced the connector under the empenage fairing with micro pins and that did not help.
So opened up elevator to check the ray allen unit and had forgotten about that connector in the bay area. Connector wire was only holding on by one wire strand at pin, felloff when I touched it. Replaced pin and no problems since.

RV 14A 140507 flying
 
Good Suggestions....

Could just be a coincidence as a few of you have suggested - I did try moving and shaking the plane with the unit powered up, and its rock solid. Its only once the engine is running that the indicator starts to move around, and it gets worse in the air. But it's worth opening up the tail fairing and taking a look at the connections back there.

The other odd thing my CFII and I noticed yesterday was that along with the trim indicator wandering, the attitude indicator on the G3X seemed a little twitchy/jumpy, whereas the G5 next to it was smooth and stable. Maybe just our imaginations but who knows.

I saw on the 8.70 update thread that someone was able to get a download of the old 8.60/8.61, and if I can find that I may just reload that and see if anything changes. My system was stable with that software.

On the plus side, the new fuel tank reminder based on flowrates works nicely - I've always been a "switch every 6 gallons" person and this reminder is helpful.

John
 
John,

As others have mentioned, your trim indication issue is most likely a poor connection somewhere. The wires that come with the ray allen servo are very small and the connectors typically used on these wires are often subject to failing in the way you described. I cannot image how a software upgrade could affect the trim.

On your attitude, you should run the engine vibration test to see if your AHRS is shaking excessively due to engine vibration. Not only can too much vibration cause a little bit of jitter on the display, but it can lead to autopilot performance issue or even a poor attitude solution. Vibration is the enemy of the sensors inside of your AHRS.

Thanks,
Levi
 
I'll take a look at that today, Levi. If this had come up at a time where I hadn't changed anything then for sure I'd be homing in on wiring/connection issues.

I was able to view trim setting on the Garmin logbook online, and compared a flight pre-8.71 with the flight on Saturday. The earlier flight shows stable trim settings in cruise and once established in a climb or descent. Saturday's data show trim moving all over the place in these flight conditions, although the trim tab position itself was clearly not changing. So that could be bad data from the Ray Allen servo due to wire/connection issues, or perhaps something screwy in the processing of that signal thru the GEA24, or ???

Well, as they say, we build and fly these for education, right? :rolleyes:
 
And Levi calls it. Found a bad D-sub connector under the empennage fairing, all looked good from the outside but upon manipulating the connector and wire leads the display began jumping around. This connector is original and has been there for 15 years and 600+ hours. The 5 conductor cable was secured well on each side of the connector but the connector itself had come loose from its adhesive mount, so I suspect tail movement and vibration under high engine power and flight loads moved the connector around enough to fail some of the leads at the pins.

Easy enough to fix, and current materials and practices should make a longer lived solution.

And, goes to confirm that temporal relationship doesn?t equal causation, although it sure can make diagnostics a little murkier.

Hitting the hangar first thing tomorrow to make the repair.
 
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