Use of rudder trim

[cornwallis]

One of the aircraft that I fly requires an increasing amount of rudder trim to keep the wings level during the climb.Despite matching N1 the rudder trim has to be increased to 1,0 units by top of climb and maintained during the cruise and needs to be removed during the descent to keep wings level.What is causing this phenomenon?It is always in the same direction.

[spannersatcx]

Had something similar on a 747 many years ago and it was a spoiler panel delaminated causing extra drag on one side which needed rudder trim to get it to go straight and level.

[cornwallis]

It is interesting that you give this reason as i had a dead heading pilot in the back and he thought one spoiler panel was slightly proud .

[spannersatcx]

Sometimes I even impress myself;)

[Bolty McBolt]

Rudder trim on climb then nulled then trimmed the other way on descent.

This phenomenon happens on the 767-300 regularly. I think you are allowed up to 2 units trim before we engineering types have to look at it.
The reason givin to me was due to different expansion rates of the fuselage versus the rudder cables. I know there are cable tensioners/compensators in these cable system but that is what I was told..:ok:

Another thing we regularly find is when a trim defect comes in. 744 or 763 The trim position indicator is a ribbon with an ^ on it. Most often the ribbon has stretched and no longer reads 0 trim when the rudder is centered and the EICAS position indication isn't fine enough to show up the fault to tech crew.
I have seen tech log write ups where crew have chased this trim indication error with aileron trim and had the A/C crossed up.

[cornwallis]

The aircraft concerned is an old toulouse turkey.It is not an indication problem-perhaps the old girl is just badly bent,but it only seems to start at about FL200.

[hikoushi]

We had an old Dash-8 that took aprroximately 2.0 degrees of LEFT aileron trim and 2.5 of RIGHT rudder to stay wings-level in cruise; stayed in almost the same configuration through cruise and descent (give or take a little rudder with power changes) until bringing the props up to max RPM during the landing checklist, whereupon the plane asked you very firmly to neutralize it's aileron trim. No spoiler problems, trim indication was fine. Best we could figure it was just bent to snot, but it passed all the airframe tests they could put it through. Never did figure that one out.