To provide a helicopter ducted fan provided at the tail structure of a helicopter, capable of preventing a torque generated on the helicopter, used for operation of yawing and polarity, and capable of eliminating such defects that an efficiency is low because a clearance between the blade end of a rotor blade and a duct inner peripheral surface cannot be reduced and the diameter of a hub is increased and the operating space for the rotor blade is reduced because a rotor blade drive device and a pitch control device are incorporated in the hub.

This helicopter ducted fan comprises bearings connecting the blade end of a rotor blade, provided between the inner peripheral surfaces of a ring rotating in a duct and a duct and the outer peripheral surface of the ring, and reducing a clearance between the blade end of the rotor blade and the inner peripheral surface of the duct with the rotor blade is rotated so that the rotor blade can be rotated at high speeds 11. Thus, a trouble that the clearance produced between the blade end and the inner peripheral surface of the duct is increased can be eliminated.