# 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:

$J = \frac{V}{nD}$

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

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