One of these 2 thoughts might help:
Step on the ball
The the ball is not in the centre you should increase pressure on the rudder pedal on the same side as the ball is (or reduce pressure on the opposite side - depending on what your feet are doing at the time.
Starting with this we get:
- You are turning left
- You need more right rudder / less left rudder
meaning you are turning the aircraft using the rudder - i.e. it will be skidding out of the turn. (Think about the case where you turn left using rudder alone).
The slip ball can be looked at like a pendulum.
- If you have too much pro-turn rudder it will move out of the turn (towards the top wing) - you are skidding.
- If you don't have enough pro-turn rudder it will move towards the inside of the turn (towards the lower wing) - you will be slipping into the turn.
It's so much easier to explain with a couple of diagrams
Does this help at all?
OC619