Fenestron

A Fenestron (or fantail, sometimes called "fan-in-fin") is a protected tail rotor of a helicopter operating like a ducted fan. Placing the fan within a duct reduces tip vortex losses, shields the tail rotor from damage, is much quieter than a conventional tail rotor, and shields ground crews from the hazard of a spinning rotor. The housing is integral with the tail skin and, like the conventional tail rotor it replaces, is intended to counteract the torque of the main rotor. It was first developed by the French company Sud Aviation (now part of Airbus Helicopters) and is installed on many of their helicopters.