ORIGINAL: B.L.E.
The amount of rudder needed for a coordinated turn depends on the bank angle. A 90 degree bank is all elevator. A 45 degree bank is half elevator and half rudder. A 30 degree bank is 86% rudder and 50% elevator.
I use the ailerons to set the bank angle and then I use a mix of elevator and rudder to carve the turn. The ailerons should be neutral during the turn. If you have to hold ailerons to stay banked, you are not using enough rudder. If you have to hold opposite ailerons to keep the bank from increasing, you are using too much rudder.
To add a minor detail to (and completely obfuscate
) the discussion, an airplane will maintain a "neutral aileron" bank of around 17ish degrees depending on its configuration (wingspan, dihedral, high/low wing, etc).
At bank angles less than the "neutral aileron bank", the airplane will tend to shallow out due to inherent lateral stability.
At bank angles steeper than the "neutral aileron bank", the airplane will tend to increase the bank angle (overbank) requiring opposite aileron to maintain a steeper bank angle. Overbanking is caused by the different turn radii of the two wings. How this works is that a steeper bank angle means a smaller turn radius, and the radial difference between the inboard and outboard wing panels is larger as a percentage of the turn radius... Outboard wing is now flying faster, more lift, overbanking...
This probably has limited practical application for model aviaiton but I can go back to my Merlot now...
Cheers!
Jim