A320 Rudder Trim PB / Nose Gear ?

[321XLR]

Gents

My understanding is the rudder trim is a "FAC thing" and has no physical relationship/linkage to the nose landing gear. However during an after-start flow the other day, a Captain told me to "hold on, rudder trim until tow bar is disconnected, as we don't want the nose wheel to move at all." I said yes sir but it got me to thinking about this. (after start flow being requested while tow bar still attached is another conversation...)

I have looked back into our training materials and FCOM stuff and cannot located any information that the rudder trim PB can cause the nose gear to move. I respect everyone's experience so maybe it is buried somewhere. Possibly on other aircraft it is and this was "leftover" from the Captain's thousands of hours in other airplanes.

Thank you

[hans brinker]

Gents

My understanding is the rudder trim is a "FAC thing" and has no physical relationship/linkage to the nose landing gear. However during an after-start flow the other day, a Captain told me to "hold on, rudder trim until tow bar is disconnected, as we don't want the nose wheel to move at all." I said yes sir but it got me to thinking about this. (after start flow being requested while tow bar still attached is another conversation...)

I have looked back into our training materials and FCOM stuff and cannot located any information that the rudder trim PB can cause the nose gear to move. I respect everyone's experience so maybe it is buried somewhere. Possibly on other aircraft it is and this was "leftover" from the Captain's thousands of hours in other airplanes.

Thank you

With the NWS disconnect the nose wheel will (should) not move regardless where the input comes from. During taxi you can steer the airplane using the rudder trim, it definitely moves the nose wheel and the pedals as well as the tail, and centering leftover trim will cause nws movement too..
I don't put my feet on the pedals or hand on the tiller until push is complete and tug is gone, but I have never had an issue with the rudder trim centering pb being pushed during the after start flow while the tug is still attached.

[giggitygiggity]

Take a look at the architecture diagrams in FCOM 27-10-20 Yaw Control and FCOM 32-20-10: Nose Wheel Steering Description.

Rudder Trim controls the rudder through the trim switch or autopilot via the FACs. It's not linked to the NWS system. So adding rudder trim results in a rudder deflection to keep you straight on the taxiway if you're testing it to confirm an offset.

NWS is actuated via the Steering Servo Valve commanded by the BCSU through the Y HYD system (or the green on very old aircraft). That's only controlled by the tiller, else the rudder pedals or the autopilot via the ELACs.

[iggy]

Take a look at the architecture diagrams in FCOM 27-10-20 Yaw Control and FCOM 32-20-10: Nose Wheel Steering Description.

Rudder Trim controls the rudder through the trim switch or autopilot via the FACs. It's not linked to the NWS system. So adding rudder trim results in a rudder deflection to keep you straight on the taxiway if you're testing it to confirm an offset.

NWS is actuated via the Steering Servo Valve commanded by the BCSU through the Y HYD system (or the green on very old aircraft). That's only controlled by the tiller, else the rudder pedals or the autopilot via the ELACs.

I don't have any doubt that what you say is correct, but I have one question, if you don't mind: the rudder is effective enough to change the direction of the airplane with only 5 kts of airspeed? I always assumed that the rudder trim was linked to the nose wheel because the rudder is only effective above a certain speed...

[AerocatS2A]

Take a look at the architecture diagrams in FCOM 27-10-20 Yaw Control and FCOM 32-20-10: Nose Wheel Steering Description.

Rudder Trim controls the rudder through the trim switch or autopilot via the FACs. It's not linked to the NWS system. So adding rudder trim results in a rudder deflection to keep you straight on the taxiway if you're testing it to confirm an offset.

NWS is actuated via the Steering Servo Valve commanded by the BCSU through the Y HYD system (or the green on very old aircraft). That's only controlled by the tiller, else the rudder pedals or the autopilot via the ELACs.
Yaw Control architecture shows the rudder trim moves the rudder pedals via the feedback circuit and the rudder pedals move the NWS via the ELACs so wouldn’t that suggest the rudder trim will move the NWS via the rudder pedals?

[lurkio]

That’s how I saw it when I looked it up.

[sonicbum]

Gents

My understanding is the rudder trim is a "FAC thing" and has no physical relationship/linkage to the nose landing gear. However during an after-start flow the other day, a Captain told me to "hold on, rudder trim until tow bar is disconnected, as we don't want the nose wheel to move at all." I said yes sir but it got me to thinking about this. (after start flow being requested while tow bar still attached is another conversation...)

I have looked back into our training materials and FCOM stuff and cannot located any information that the rudder trim PB can cause the nose gear to move. I respect everyone's experience so maybe it is buried somewhere. Possibly on other aircraft it is and this was "leftover" from the Captain's thousands of hours in other airplanes.

Thank you

FCOM Tasksharing applies, so your Capt. tried to be unnecessarily smart. Did this guy really want to be addressed as sir? 😅

[HOVIS]

As has been said, if the tow bar is still connected, the steering lockout pin should still be fitted. The nose wheels will not move until that pin is removed. The only thing I can think your Capt was getting at was the possibility of the nose wheel not being centered after the push. When the pin is removed, with hyd system pressurised it will try to centre itself. This could, to an inexperienced ground crew, cause some alarm, injury or inconvenience if they insist on chocking the nose wheel after the pushback.