# Advance ratio

*Image: An illustration describing the advance ratio, the ratio between the distance travelled in one revolution $F$, and the propeller's diameter. [1]*

The advance ratio is a non-dimensional number. It is the ratio between the forward distance travelled by the vehicle forward during one revolution of the propeller and the diameter of the propeller:

where $J$ is the advance ratio, $n$ is the propeller's angular velocity in revolutions per second, and $D$ is the propeller's diameter [2]. It is not quite a description of the blade tip's angle of attack.

[1] An Illustrated Dictionary of Aviation, McGraw-Hill, 2005

[2] wikipedia.org/wiki/Advance_ratio, retrieved March 28th, 2015

Documentation License: