In 1915, when dealing with various problems connected with Lifting Screws, the author desired to obtain a general idea as to the performance of a propeller when it was moved at various speeds forwards and backwards along its axis of rotation, and to express this information in some simple way, so that the approximate performance of any similar propeller working in a fluid medium of any density might readily be deduced.
If, when comparing the performance of similar propellers working at the same slip ratio, the resistances due to skin friction and viscosity are assumed to follow the velocity squared law, and change of density in the neighbourhood of the propeller is neglected, there are six main factors to be considered.