The arrangement of gears serves to change the rotational axis by 90° as well as reducing the rotational speed of the input drive.

This model uses gearing similar to that found in the Airbus H125 helicopter transmission gearbox. The helical gear design produces less vibration and noise than a conventional gear with straight teeth.

An animation showing how a pair of spiral bevel gears interact. Notice that the blue arrow is rotating more slowly than the orange arrow.