Tail rotor of a  <a href="https://en.wikipedia.org/wiki/A%C3%A9rospatiale_Alouette_III" class="extiw" title="en:Aérospatiale Alouette III">Aérospatiale Alouette III</a> from <a href="https://en.wikipedia.org/wiki/Austrian_Air_Force" class="extiw" title="en:Austrian Air Force">Austrian Air Force</a>
<a href="//commons.wikimedia.org/wiki/User:P_e_z_i" title="User:P e z i">Peter Haas</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>