Tail rotor

Its drive system consists of a shaft powered from the main transmission and a gearbox mounted at the end of the tail boom.

The tail rotor and the systems that provide power and control for it are considered critically important for safe flight.

Despite the emphasis on reducing failures, they do occasionally occur, most often due to hard landings and tailstrikes, or foreign object damage.

In cases where the failure occurs due to contact with the ground, the aircraft is already at low altitude, so the pilot may be able to reduce collective pitch of the main rotor and land the helicopter before it spins completely out of control.

The enclosure around the fan reduces tip vortex losses, shields the blades from foreign object damage, protects ground crews from potential hazard of an openly spinning rotor, and produces a much quieter and less turbulent noise profile than a conventional tail rotor.

The ducted fan uses more numerous shorter blades, but otherwise works in very similar thrust principles to a conventional tail rotor.

McDonnell Douglas developed the NOTAR (NO TAil Rotor) system, which eliminates having any rotating parts out in the open.

This creates a boundary layer which causes the downwash from the main rotor to hug the tail boom according to the Coandă effect.