PURPOSE: To improve the hovering performance and reduce vibration and noise by installing vanes and small blades which can be easily projected and retracted, at the upper part of the body of a helicopter.

CONSTITUTION: The electric signal is transmitted to a hydraulic device or an electric motor 16 as driving device, passing through a wiring 17, by the switch 18 operation of a pilot 19, during a helicopter is in the hovering (stop in air) flight, and the hydraulic device or the electric motor 16 operates to shift 20 a vane 14 through a rod 15. When the vane 14 is set in the upper part of the helicopter, a rotor blow-down 21 flows along around a body 5 between the vane 14 and the body 5, and the exfoliation region reduces, and the downward force due to the rotor blow-down reduces, and the hovering performance of the helicopter is improved, and also the vibration and noise of the helocopter are reduced, and the drive feelings of passengers and pilot can be improved.