Pitch axis trim indicator

[lalnaes]

I'm flying straight and level with the elevator trimmed without any forward or backward pressure on the stick. When I turn on the autopilot pitch axis (altitude hold) the trim indicator wants me to trim down. Even when I trim down as far as the trim will go it will sometimes indicate a yellow "trim down". Is this a known phenomenon?

 

[thibault]

Not trying to be silly, but what did the aircraft do in the pitch axis while this was going on? Did it change altitude? If you had the altitude bug set to something other than the current altitude, the aircraft would try to go to that altitude and might not have had enough "authority" without a trim change.

F/W Ver 2.5 seems to be a lot better in pitch control than before, so I seem to see less request for trim and less slippage. Haven't even tweaked the new knobs yet, the default settings just seem to work better.

 

[lalnaes]

The AP is maintaining the airplane at level altitude, but the yellow arrow is still pointing down, indicating that it would like additional trim.

 

[dedgemon]

My RV8 does this also. Its a pretty minor amount of down trim. Not enough to cause any issue when you disconnect. I would guess(I do mean guess) that the altitude loop may be using a little trim bias to ensure that the control linkage slop is removed.

I just flew the AP this afternoon (ver 2.5) in some pretty good bumps. Altitude hold was working really well. Really the AP was flying the plane about as well as I could (i tried it for comparison).

 

[dynonsupport]

There's a small chance there's something up with the servo. If you engage the AP on the ground in alt mode, with everything centered and slack, do you get the trim annunciation?

 

[lalnaes]

I will check next week and let you know.