FBW A320 - rudder trim inputs ?

[jcomm 5,939]

I've been noticing that from time to time, and without the presence of asymmetric thrust, the rudder trim is set by the AP  and shows in the pedestal scale display.

Pressing the "nil" button doesn't produce any effects.

Any idea why it's being programmed that way ?

[RaptyrOne 1,413]

I have seen it react to cross winds and trim for those. The trim deflection is so marginal that it might appear to be doing nothing. I have only ever reset it on the ground though.

[jcomm 5,939]

3 minutes ago, RaptyrOne said:

I have seen it react to cross winds and trim for those. The trim deflection is so marginal that it might appear to be doing nothing. I have only ever reset it on the ground though.

Good point, but if it's that, I believe it's not as per the real aircraft ( ? ). Well, it's a NEO, so, I really am not sure...

[GearUp180 55]

5 minutes ago, jcomm said:

Good point, but if it's that, I believe it's not as per the real aircraft ( ? ). Well, it's a NEO, so, I really am not sure...

By design, in the real aircraft, the rudder trim reset button has no effect if the autopilot is engaged.

[jcomm 5,939]

14 minutes ago, GearUp180 said:

By design, in the real aircraft, the rudder trim reset button has no effect if the autopilot is engaged.

Yes, but I believe that other than due to asymmetric or other non-normal situations under which it gets used and displayed in the pedestal display, rudders are actually used instead.

Rudder trim input by the AP can't be cancelled unless the AP is disconnected - that's ok.

Edited September 8, 2021 by jcomm

[GearUp180 55]

Another way to see it is: trimming the aircraft is within the autopilot scope so resetting it (asking for a 0 position) defeats the purpose.

[GearUp180 55]

2 minutes ago, jcomm said:

Yes, but I believe that other than due to asymmetric or other non-normal situations it gets shown in the pedestal display, or actually used... ( rudders are ).

Rudder trim input by the AP can't be cancelled unless the AP is disconnected - that's o.

Gotcha.

I need to dive back to the books.

[jcomm 5,939]

Well, my bad it appears...

The following thread suggests AP can use rudder trim even out of non-normal situs:

https://www.pprune.org/tech-log/519811-a320-rudder-trim-short-final.html