Originally Posted by
Big Pistons Forever
So here is a tip. If you are a new copilot and are preflighting an aircraft that just came in from a revenue flight like this guy was, and you find the rudder trim at 1.5 units right and the aileron trim at 1 unit left wing down, there was probably a good reason for it and maybe you don't want to mess with it.
This is all very well, provided you don't subsequently discover that the aircraft flies wings level, but with the balance ball displaced to the left because of crossed controls as a result of trim set improperly by the previous incumbent.
Personally, therefore, I would favour resetting trims to zero on the pre-flight, after making a note of the setting(s) found, and then making any necessary adjustments as soon as stable in the cruise. The only exception would be if there was an existing Tech Log entry to the effect that trim had been found to be required to fly straight and level, in which case I would accept the recommended trim setting but confirm it myself by inspection in flight.
Incidentally, I agree with
Big Pistons Forever about the order of 3-axis trimming. After trimming the elevator, hold the wings level with the ailerons and trim off any tendency to yaw (i.e. centre the ball) with the rudder trim; then (and only then) remove any roll tendency with aileron trim. If you trim in a different order, you are quite likely to end up with crossed-controls - such as in the situation posed in the quote above.
JD
