Two actually:
Set trim command by typing a .<----dot
And center rudder, s, command.
The 2nd doesn't seem to do anything. E.g. turning a buff or fighter using j or l and releasing has the same result as hitting "s." That is the rudder doesn't snap into center at once.
The first, I've not figured out its usefulness.
Englighten the benighted please.
All the best,
hap