Mxsmanic wrote:
How much of a movement in the little ball in the turn indicator
corresponds to something you can feel in a real aircraft? And how
much of a movement represents an error large enough to affect flight
safety or proper maneuvering?


The answer is that it depends. It is more important to keep the
plane coordinated at slower airspeeds and/or higher load factors.

It is also important on climbout (high angle of attack & large P
factor) because you want the best climb capability you can get
especially with underpowered aircraft. Needless to say it is well
to keep it coordinated in cruise as well since drag is greatly
incresed thus reducing cruise efficiency.

An experienced pilot can feel it when the aircraft is not
flying coordinated. If you were a passenger with a drink sitting
on a table in the back you would notice un-coordinated flight
because the liquid would not be level in the glass.