You'll find that 2-3deg is the AoB that will give you zero slip. Anymore than that will have the a/c flying not quite aligned with the relative airflow, increasing drag.
5 deg bank is a certification limit, set so that the a/c manufacturer can't specify an very low Vmc that would require unreasonable handling methods. It's not a performance related number in of itself. The more bank the manufacturer can use to determine Vmc the slower the a/c can fly before loss of heading control (I'm any other limiting factor eg Vs). The manufacturer wants a low Vmc because some of the other limiting certification V's can be affected by it.
The ball will be out because it's only a simple inclinometer. No different to the bubble on a builder's spirit level. If you fly with one wing low AND don't have some other horizontal force acting on the a/c (such as occurs in a turn) to push the ball a bit sideways then the ball has to fall to the lowest part of the tube. Tube is bent into a curve so the lowest part of it isn't at one end as would be the case if a straight tubed spirit level was used.
Last edited by Tinstaafl; 26th November 2003 at 09:15.