About the FOC Calculator

By entering arrow data as required above and clicking on 'calculate' an estimate is made of the arrow FOC and two values the 'Response Coefficient'' and the 'Drift Coefficient' presented.

All the requested information re fletchings relates to a single fletching (three fletchings are assumed).

The 'Fletch Length inch:' is the length of the base of the fletching in inches.
'Fletch Distance From Front inch:' is the distance from the front of the shaft to the front of the fletching in inches.

The Response Coefficient represents the angular acceleration of the arrow (i.e. how fast it will straighten up) when flying at an angle for some reason (bad tuning, wind gust etc.). The higher this value the better as far as arrow flight goes.

The Drift Coefficient represents the arrow angular acceleration (Response Coefficient) divided by the sideways acceleration when flyng at an angle for some reason. This coefficient represents the drag drift sensitivity of the arrow. The higher this value then the faster an arrow will stabilise, probably leading to a more 'forgiving' arrow and reduced group size.

FOC remains the best overall 'evaluator' for assessing arrow flight performance. The idea of the Response and Drift coefficients is principally to compare the performance of different arrows with the same FOC.

Last Revision 1 July 2009