As I understand it, the P factor only comes in when the prop is advancing in a direction different than it's axis.  Like a tail wheeld airplane with it's tail still on the ground or any airplane at a high angle of attack.  That is not a factor on a tri geared aircraft on innitial role.

 

An engine properly trimed for a counter-clockwise prop (1 or 2 degrees left thrust) would have a large effect when changing to a standard (American direction) prop.  A lot of left turning reaction tendencies plus left thrust would require lots of right rudder.  A major force is torque.  More HP, more torgue. The swerl effect is mild in comparison.

 

As an example, the SA-16 (large twin amphibion) drivers start their max take-off run from the left side of the runway, pointed about 45 toward the center line.   Said that there was no way, when quickly adding full power that they could keep it from turning-so they just planned for the turn.  No swerl effect here.

 

FWIW

 

Bob Darrah

 

(I know, but my spell checker said it was ok)