Thank you Nick, that question has been banging around my head for quite some time now, I have been slightly confused by this energy possibility after reading about the DH Mosquito which had Merlins that turned the propellers in opposite directions so as to allow the A/c to take of in a straight line, unlike the Bristol Beaufighter whose Hercules engines turned the props in the same direction and caused the pilots allsorts of problems especially when landing .