Trutrak autopilot erroneous trim indication

[Captain Avgas]

I have a Trutrak Digiflight 11 in my RV7A. I have manual pitch trim.

On the Digiflight there is a scrolling bar in the middle of the display to let you know if the plane is out of pitch trim while the autopilot is engaged. If the bar is scrolling up it means you need to manually trim up until the bar stops scrolling.

The problem with my Digiflight is that it always indicates that upward trim is required...even when the aircraft is perfectly in trim. If I trim the aircraft perfectly in level flight and then turn on the autopilot it will indicate that upward trim is required. If I then trim the aircraft until the upward scrolling stops it puts the aircraft into a nose high pitch.

I have read through the Trutrak User Manual but cannot find any way to adjust this scrolling error. Does anyone have any ideas or similar experience????

[Bill Rossmann]

I have the same problem in my Lancair and called Trutrak, They wanted me to send the pitch servo back for calibration

[rleffler]

Originally Posted by Bill Rossmann

I have the same problem in my Lancair and called Trutrak, They wanted me to send the pitch servo back for calibration

That would be my guess too. There is a feedback circuit that the servos provide position data back to the AP head.

[Ironflight]

Has it ever worked correctly? If it has, and then it stopped, I'd suspect something went wrong in the pitch servo. If it has never worked right, then I'd suspect a wiring/installation error. I remember upgrading from an early TT servo that didn't have the feedback to the newer style, and having to do some retiring, so it could be that there's an error in your harness.