Aileron Auto Trim Question

[sglynn]

I?m flying Dynon HDX and autopilot. Everything works. After 30 minutes or so enroute I notice my aileron trim has moved over to the left by the AP auto trim function. Why? What is it telling me? I feel the stick and can?t really feel the need to have trimmed left. Plus I think it is flying right wing slightly higher. Might the springs on the servo not be balanced exactly equal? Or might I have a heavy wing do to fuel unbalance? I move the trim back to center and I think the right wing lowered a little. The trim stays there for awhile. I haven?t noticed when it auto trims left again. If you?ve seen this before what do you think is causing aileron auto trim to move? With AP off my RV-7A is pretty hands off stable. So I thought it was trimmed out but ?.. AP auto trim is moving stick left I wonder why?

[leok]

If you turn the Autopilot off is the aircraft in trim?

[sglynn]

Originally Posted by leok

If you turn the Autopilot off is the aircraft in trim?

Great obvious question that I will have to check out on next cross country. It doesn't do it on short lunch runs. I'll be back.

[Raymo]

Likely compensating for a cross wind. I almost never touch my roll trim but find I need to after the AP has adjusted it during XC.

[Bob Martin]

Most likely uncordinated flight. Ball not centered.
I have 2 axis TT auto pilot and no auto-trim....but when when in track or nav mode, if I push on the rudder the ap will roll the wings to compensate.
Very much like altitude hold will raise or lower the nose with updrafts and downdrafts.
So most likey your foot is resting on the rudder pedal and the ap is compensating.
Just a guess.

[sglynn]

Okay, here are more observations and conclusion on what's going on with Autopilot auto trim aileron. I've been testing it.

1. After the autopilot auto trims the aileron to one side or the other when I turn the AP off my RV is not trimmed. I have to bring it back to near center to be trimmed.

2. The AP auto trim moves the aileron when in NAV mode tracking a specific desired track. It doesn't do it in HEADING mode just following the heading bug.

So I think the AP uses the auto trim on aileron to help with cross wind when tracking a desired track. This seems especially true tracking inbound on approaches. The fastest way I've found to see the AP use auto trim on aileron is to shoot an approach. The AP is very fast at figuring out the heading with a few degrees offset to compensate for cross wind when tracking inbound on a specific track. And the aileron trim moves then to help keep the needle center.

That's what I think. I don't think it has anything to do with trimming the airplane for hands off flight, nor anything about a centered ball. I think it is for assisting with the crab to track a desired track. So I'm no longer concerned I may have something goofed up like wheel pants, or VS.

thanks

[BobTurner]

This is not right. Any chance the aileron trim wires are hooked up backwards?

[MCA]

What does Dynon support say? I'm curious and saw this in a friend's RV as well.

[sglynn]

Correction to this. It does auto trim in HDG mode also. I flew again today and tested this aileron auto trim. After disengaging AP today when it had auto-trimmed to left, I think it was in trim. I'm starting to think my right spring just needs to be slightly tighter.

How did you others get the springs adjusted to the same tension on both sides of the stick for the electric aileron trim?

thanks

Originally Posted by sglynn

Okay, here are more observations and conclusion on what's going on with Autopilot auto trim aileron. I've been testing it.

1. After the autopilot auto trims the aileron to one side or the other when I turn the AP off my RV is not trimmed. I have to bring it back to near center to be trimmed.

2. The AP auto trim moves the aileron when in NAV mode tracking a specific desired track. It doesn't do it in HEADING mode just following the heading bug.

So I think the AP uses the auto trim on aileron to help with cross wind when tracking a desired track. This seems especially true tracking inbound on approaches. The fastest way I've found to see the AP use auto trim on aileron is to shoot an approach. The AP is very fast at figuring out the heading with a few degrees offset to compensate for cross wind when tracking inbound on a specific track. And the aileron trim moves then to help keep the needle center.

That's what I think. I don't think it has anything to do with trimming the airplane for hands off flight, nor anything about a centered ball. I think it is for assisting with the crab to track a desired track. So I'm no longer concerned I may have something goofed up like wheel pants, or VS.

thanks

[RickSolana]

Fuel imbalance seems like a good guess. Have you tried starting a flight on the other tank and seeing if it trims in the other direction?