Abstract: A base wing 11, as attached at its root end portion to the rotor head of a rotational drive unit, is provided with a front wing 12 and a rear wing 13 having substantially equal spans. The vortex, as generated at the wing tip, is divided into relatively weak tip vortexes of a front wing vortex 12c generated at the tip of the front wing and a rear wing vortex 13c generated at the tip of the rear wing 13. Since the front wing 12 and the rear wing 13 have equal spans, on the other hand, the front wing vortex 12c and the rear wing vortex 13c are close to each other so that they interact positively with each other and are weakened and diffused. As a result, while the helicopter is hovering, the interactions between the retreating rotor blade of the rotor and the tip vortex generated by the tip of the advancing rotor blade are drastically reduced to suppress the occurrence of the BVI noises.

Abstract: A base wing 11, as attached at its root end portion to the rotor head of a rotational drive unit, is provided with a front wing 12 and a rear wing 13 having substantially equal spans. The vortex, as generated at the wing tip, is divided into relatively weak tip vortexes of a front wing vortex 12c generated at the tip of the front wing and a rear wing vortex 13c generated at the tip of the rear wing 13. Since the front wing 12 and the rear wing 13 have equal spans, on the other hand, the front wing vortex 12c and the rear wing vortex 13c are close to each other so that they interact positively with each other and are weakened and diffused. As a result, while the helicopter is hovering, the interactions between the retreating rotor blade of the rotor and the tip vortex generated by the tip of the advancing rotor blade are drastically reduced to suppress the occurrence of the BVI noises.

Abstract: A rotor blade for a rotary-wing aircraft, of an airfoil section has a basic blade thickness at 12% chord length, a portion of an increased blade thickness between the leading edge and a point corresponding to about 90% chord length, a maximum blade thickness at a position shifted backward, a curvature distribution concentrated on the middle portion thereof, and a portion contiguous with the trailing edge and cambered. The drag coefficient of the airfoil section is small when the Mach number is about 0.6 and the lift coefficient is about 0.6, and the airfoil section has a large maximum lift coefficient and a large zero-lift drag divergence Mach number, and generates a small pitching moment.

Abstract: A rotary-wing blade of a rotary-wing aircraft has an airfoil section which has an asymmetrical region of positive camber from its leading edge to its approximately 30-percent chord length point and an essentially symmetrical airfoil region from its 30-percent chord point to approximately its 90-percent chord length point. The region aft of the 90-percent chord point can be optionally curved or reflexed upward or downward to a limited degree. This blade has a large lift coefficient and a small pitching moment and is readily adaptable to meet various design conditions of lift coefficient and pitching moment.