PURPOSE: To delay the generation of a stall by installing a flap at the rear edge in the vicinity of the top edge of a rotor blade and carrying out control so that the corrective pitch may become optimum as a rotor blade according to the revolution and air speed of the rotor blade by a control means.

CONSTITUTION: As for the rotor blade of a helicopter, an actuator housing 2 is installed at the position for reducing the blade vibration force to the min. in the vicinity of 1/10r from the top edge of a blade spur 1, and a flap which is divided into an inside flap 3 and an outside flap 4 in the housing 2 is installed at the rear edge of the rotor blade. The opening degree of the flap is set by the mechanism of the actuator so as to increase on the outside flap 4. The actuator is of a motor-driven type, and the driving electric power, control signal, flap angle signal, etc. are inputted into the actuator through a slip ring 6, and each signal is generated by receiving the blade direction angular signal, speed signal for air, and the corrective pitch signal by a control amplifier 5.