# A Problem for the Membership to Consider

By **Bruce Rule** - Dec 4, 2013

Wikipedia provides the following:

In aeronautics and marine hydrodynamics, the advance ratio at which a propeller is operating is the ratio between the distance the propeller moves forward through the fluid during one revolution, and the diameter of the propeller. When a propeller-driven vehicle is moving at high speed relative to the fluid the advance ratio of its propeller(s) is a high number; and when it is moving at low speed the advance ratio is a low number. The advance ratio of a propeller is analogous to the angle of attack of an airfoil.

The fluid velocity relative to the propeller blade increases with distance from the hub, due to the rotational velocity of the propeller. Therefore, the direction of the flow relative to the propeller blade is equal to the vector sum of the speed of advance and the rotational speed of the propeller.

Comment:

It would appear that imagery of a propeller from which the diameter and the "angle of attack" can be determined

can be used to determine a turns-per knot (TPK) value, and, conversely, if the TPK and the diameter are known, the

angle of attack (pitch?) can be derived.

If these relationships can be so exploited, it may - repeat may - be possible to estimate TPK values from imagery alone.

Have fun.