THE ADVANCE RATIO
Much of the foregoing may be expressed in a single figure, the advance ratio, represented by the letter J. The formula is:
Advance ratio = J =
where D is the diameter and V the flight speed. As shown above, the angle of attack of the blade, for a constant pitch propeller, depends on the flight speed and rate of rotation. The
remaining variable is the diameter which, at a given RPM, determines the actual speed through the air of the propeller tips and, at a given pitch, has a dominant effect on the power required to drive die propeller at the stated RPM.