Thanks John_T for pulling me up. While I stand by my reasoning I accept the response could have been better worded so here goes. Lets assume a failure of the left engine at takeoff thrust without any nice yaw damping technology to ease the task.
A healthy measure of right rudder is needed to stop the significant yaw toward the dead (drag producing) engine. The yaw is produced by the thrust drag couple from the live and dead engine the yaw is balanced by right rudder producing a strong correcting force to the left at the tail.
The yaw is stopped but, the couple and correcting force are both to the left so the left drift (skid) which results will result in the relative airflow approaching from the left side. The balance of turning effects - Force against a couple - is just like tail-rotor drift in a helicopter. Designed lateral stability and dihedral effects will encourage a roll to the live engine.
In reality this is just what you require up to 5 degrees anyway, but I have often seen (and been guilty of) the results of poorly worded training that over emphasises the matter of yaw to the exclusion of the important understanding of the part of roll. At night, or in IMC flight, you are very dependent on the Attitude Indicator and this even strengthens the instinct to lock the wings level on the horizon and hold a magnetic heading (stop yaw) with rudder. This will result in crossed controls as we oppose the aircrafts need and desire to roll toward the live engine. The displacement on the slip indicator is another source of distraction.
There isn't any fat left in a Vmca certification exercise - generally the published figure is for 5 degrees favourable bank. Perhaps you might explain a bit further ?
I agree that certification leaves no fat. My point that;"The bank places the controls where we maintain greater available deflection so it is reasonable that once achieved the minimum speed may actually be lower. But only after the failure and initial set-up, or during a staged demonstration from the shallow banked condition."
This is confirmation that the stable demonstration of Vmca may give a lower airspeed than the Dynamic Vmca. This is a point acknowledged by the testing requirements of FAR 23.149. The benefit of the bank is that it produces a small sideslip which counters the skid in wings level flight. This will reduce overall drag on the fuselage and improve control margins as we are less cross controlled as a result.
In short stop the yaw with rudder, bank slightly toward the applied rudder, and slowly replace some applied rudder with a careful return of the roll control somewhere toward centre. Should we have got ourselves a bit cross controlled in our initial dynamic response to the emergency.