The “Fenestron,” Shrouded Tail Rotor of the SA. 341 Gazelle

The shrouded tail rotor developed by the Socie´te´ Nationale Industrielle Ae´rospatiale for the SA. 341 “Gazelle” eliminates most of the drawbacks of the conventional tail rotor of mechanically‐driven helicopters, Protected by the tail fin, in which it is enclosed there is no risk of the tail rotor touching the ground during approach and landing, and impact with any object becomes practically impossible. Total aircraft power required in hovering is 3–4% higher than in the case of a conventional tail rotor, but slightly less power is needed in forward flight. Also, sincc the tail fin is designed with a cambered airfoil to furnish antitorque thrust in forward flight, all the tail rotor transmission system is alleviated of this load and if, for any reason, the antitorque rotor should become inoperative, the aircraft can return to base instead of having to make an immediate autorotational landing. Considering the low values of alternating stresses in the blades and control components, this system is particularly attractive for high‐speed rotary wing aircraft.