It's down to the direction of rotation of the prop. In 'US' engined types (Lycoming, Continental) the prop (and therefore the airfow onto the fin/ rudder) favours aeros 'to the left'. It's the same reason you need right boot during take off - at low speed and high power it yaws left (as at top of a stall turn - so go with it - left - and it'll go round). Like wise torque reaction aids rolls to the left.
Chippies, Yaks, and aeroplanes whose engines rotate the 'correct' way favour manouvres to the right for the same reasons. But I always do Barrel trolls to left in chippy 'cause I want the roll rate to nice and slow ;~))
SSD
[ 14 December 2001: Message edited by: Shaggy Sheep Driver ]