ORIGINAL: DarZeelon
Red,
If trim is initially needed in one direction, which then changes to an input need in the other direction, this is an 'effect reversal' (due to attitude change of the plane).
This is what I was referring to.
That is of course one way to put it, but there is no need to reverse the input unless the pilot forgets to reduce the right rudder trim towards neutral. The aircraft were built to require minimal rudder trim at cruising speed, which in the cases mentioned (Merlin Spitfire and P-51) makes right rudder necessary during the whole of the take-off sequence.