Feeling humbled, I just learnt something
I'd never really thought about situations where the aircraft could have the ball (or your bum) centred but be sideslipping before but yes... wings level, aircraft tracking straight but the longitudinal axis not dead on to the airflow
eg with propellor P factor trying to yaw nose one way, compensating for that with rudder and keeping wings level so tracking straight - straight and wings level would mean ball in the middle.
In that situation - is it in balance? Buggered if I know!
Thanks a lot zzuf
I can no longer say "keep it balanced". Bugger.
Thinking something like a glider's yaw string would indicate difference from a balance ball in that situation...