PROBLEM TO BE SOLVED: To effectively reduce BVI (blade vortex interaction) noises of a helicopter.;SOLUTION: For reducing BVI noises of a rotor blade of the helicopter, a tab 3 capable of moving back and forth for the rear in rotational direction of the rotor blade between a position protruding from a trailing edge of the rotor blade and a position not protruding, and an actuator 4 moving the tab 3 back and forth are fixed on the rotor blade 2. The actuator 4 is operated so as for the tab 3 to move back and forth corresponding to rotation timing of the rotor blade 2.;COPYRIGHT: (C)2004,JPO
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