How exactly does the trim on the A320-200 work?

[G-NADS]

Would be grateful for any help.

[yaverona]

Fly by wire system makes horizantal and vertical trim automatic.

But when some computer fails, you can make vertical trim by trim wheel.

There is no aileron trim control in the cocpit

[Flap 5]

There is, however, a rudder trim. But this does not work with the autpilot engaged.

[Frederic]

Ah, the FBW flight control systems, my favorite subject!
I don't have a 320 type rating, but I'm getting the FCOMs from somebody who has. As soon as I get them I'll find out for you. Do you want to know how the trim works on the A320-200 specifically or how it works on any Airbus FBW type?
This is what I found out upto now:
In normal law pitch stick input results in a G-force demand that is proportional to the input. Stick full back is +2.5G, neutral +1G, full forward is -1G. Elevator deflection gain is changed to account for config/CG/Speed changes. G feedback is given through the ADIRS and is compensated for bank and pitch angle. So stick neutral the aircraft will always keep 1"earth G" (1G relative to earth horizontal. That is why it keeps its flight path angle in climbs, descends and turns (upto 30 degrees bank) with stick neutral. To get to the point, the way I understand it,
the trim system works with a slight delay, then it tries to align the THS with the elevator. For 1G flightpaths it trims so as to keep the flightpath without the elevators being deflected.
In alternate law, pretty much the same thing.
In direct law you're flying a conventional aircraft. So you need to trim to maintain a certain angle of attack(ie speed @1G) and you need to change the thrust tochange the flight path angle (assisted by stick input for the temporary G-force change. Am I getting to technical? Think about this, I'll get back to you!

[F/O Junior]

Automatic Pitch Trim:
Pitch trim is automatic in both manual control and with AP engaged. There is no need to trim with speed, thrust or configuration changes (you get a 500'/min balloonig when setting flaps 2, but that's a different story).
In normal turns (up to 33° bank) no pitch correction is needed once the turn is established.
Automatic pitch trim is inhibited in the following cases:
-Manual trim order
-Radio height below 50ft (100ft with AP engaged.)
-Load factor below 0.5g.
-In high speed/Mach protection (except in the event of L/R ELEV FAULT).
Automatic pitch trim is limited between the actual THS setting and 3.5° nose down to inhibit further nose up trim in the following cases:
-If angle of attack protection is activated
-If 33° bank angle is exceeded.
-If 1.25 g load factor is exceeded.

[G-NADS]

Thats very helpful guys.

So all in all it is a very big step from those (Hawker) trim, trim, trim, (Siddely) trim, trim, trim, (Trident) trim, trim, trim days!

Many thanks.

[Frederic]

NADS, you flew the Trident? What was that like? I flew the Trident sim with that farmer just south of London. It was, how can I put it,... "special"?.