Tru Trak auto trim

Hey guys,

I have an “older” Tru Trak Digitrak II (circa 2010) with a stand alone auto trim module (again circa 2010). I am having some intermittent issues (loss of all electric trim function) which I think I have nailed down to the auto trim module. Before I call Bendix on Monday, is anyone out there on VAF that really knows this system that I could explain these issues? I’m wondering if the current Bendix folks really know the inner workings of the older TT autopilots/auto trim units. I could be wrong!!

I understand that Honeywell/TruTrak service is now provided by Mid Continent at 316-630-0101 (also 800-821-1212), http://mcico.com. Last time I called, Bruce was their TruTrak guy.

In the case of my TruTrak VSGV, the system came with a plug that can be put in the circuit to circumvent the auto trim function and restore pilot trim control operation if the auto trim fails. If you don't have that plug, it looks to be pretty easy to fabricate a jumper plug to circumvent auto trim during the troubleshooting process (see the attached wiring diagram screen shot).

I'd be interested to hear about your experience getting Honeywell/TruTrak support. I hope it goes well.

Thanks Tim, what has been happening is on occasion the elev trim was completely inop. I though at first there was a connection issue as this only occurred in flight and I could never duplicate on the ground. Wiggled all connections at every possible location and never could duplicate. Two days ago I discovered the auto trim would only operate in one direction and began to wonder if there could be an issue with the auto trim. Then yesterday I flew again and the auto trim worked perfectly fine in both directions. I do have access to the plug you mentioned. I may call Mid Continent and see what they think.

Based on your description of the intermittent failure I would closely look at the wiring on the elevator trim motor.

for reference,

during the test phase, I practiced landings with a trim "runaway" to maximum deflection to either side. although the feeling is quite awkward and maybe more of a problem if unprepared/briefed, the RV remains at all times controllable (a -7A in our case).
So a frozen trim is not nice but manageable. (not tested at cruise speeds, only 100kts roughly and below)

Regarding the autotrim module, after initially not having it in, we fortunately retrofitted it before it became unavailable.
Loving it.
And definitely a safety benefit.
Before, there was a risk to get an untrimmed aircraft upon autopilot disconnect when there had been a power/speed change.
And even more problematic was the fact that the autopilot would not hold altitude or slowly descend below the glide (without alert or disconnecting!) if there was not enough power set. Creepy.

Good luck on getting yours fixed and the wiring sorted out! Also looking forward to hear about your experience with support.

flyvans.com said:

And even more problematic was the fact that the autopilot would not hold altitude or slowly descend below the glide (without alert or disconnecting!) if there was not enough power set. Creepy.
.

Click to expand...

This is a safety feature; the autopilot will lower the nose to maintain a safe margin above stall, even if that means not holding altitude or tracking the GS. Auto trim won’t fix this.

flyvans.com said:

Regarding the autotrim module, after initially not having it in, we fortunately retrofitted it before it became unavailable.

Click to expand...

Is there reason to believe it will become unavailable? The Auto Trim module appears to be in stock at Spruce and other places:

https://www.aircraftspruce.com/catalog/avpages/xcruze_autotrim.php