A theorem on swirl loss in propeller wakes

It is noted that if the longitudinal component of velocity for a high speed aircraft propeller is uniform across the propeller's wake, the swirl energy in the wake is commensurate with the work accomplished by wake suction. In the case of a lightly loaded propeller rotor, whose longitudinal velocity is characteristically uniform, the present relation between swirl energy and wake suction is a good approximation. Either swirl energy or wake suction may be used to measure swirl losses, but not both, since this value cannot be their sum.