Helicopter rotor

Claim 2

A helicopter rotor comprising: a plurality of fully articulated rotor blades; each of said blades having a fully cambered airfoil surface, a relatively stiff inboard portion and a relatively flexible outboard portion; each of said blades having an angle of twist which provides the outboard portions of the blades with a lower angle of attack than the inboard portions of the blades; each of said blades having a tip and a trailing edge with the trailing edge including a reflexed outer portion positioned at said tip; each said reflexed outer portion having a length along the axis of the blade ranging up to about one chord length of the blade; each said reflexed outer portion having a curvature which imparts a moment to the blade about its aerodynamic center that counteracts negative aerodynamic pitching moments imparted to the blade by air flowing over its fully cambered airfoil surface; the area of each of said reflexed outer portions being approximately sufficient to generate a moment about the aerodynamic center of the blade which balances negative aerodynamic pitching moments generated in the outboard portion of the blade by the flow of air over the fully cambered airfoil surface of the outboard portion; the inboard portion of each of said blades being sufficiently stiff to resist negative aerodynamic pitching moments generated in the inboard portion without excessive twisting of the inboard portion; the relatively stiff inboard portion of each of said blades having a length of about 70 to 80 percent of the length of the blade, and the relatively flexible outboard portion of each of said blades having a length of about 20 to 30 percent of the length of the blade, whereby cyclical twisting of the flexibie outboard portions of the blades is minimized during rotation of the helicopter rotor without a material reduction in the lift-to-drag ratio of the fully cambered airfoil surfaces of the rotor blades.

Claim 3

The helicopter rotor of claim 1 wherein each of said blades have an angle of twist ranging up to about eight degrees.

Claim 4

The helicopter rotor of claim 2 wherein the airfoil surfaces of the rotor blades are contoured to generate lift when the rotor is rotated in a counterclockwise direction.

Claim 5

The helicopter rotor of claim 2 wherein the airfoil surfaces of the rotor blades are contoured to generate lift when the rotor is rotated in a clockwise direction.

Claim 6

The helicopter rotor of claim 1 wherein each reflexed outer portion has a length of about one-half to about one chord length.

Claim 7

The helicopter rotor of claim 1 wherein each reflexed outer portion has a length of about one-half chord length or less.

Claim 8

In a helicopter having a helicopter rotor, driving means for the rotor, a rotor hub, and a plurality of fully articulated rotor blades hingedly connected to the rotor hub for cyclical pitch control of the rotor blades to equalize lifting moments on the blades during rotation of the hub by the driving means, the improvement comprising: each of said rotor blades having a fully cambered airfoil surface, a relatively stiff inboard portion and a relatively flexible outboard portion; each of said blades having an angle of twist which provides the outboard portions of the blade with a lower angle of attack than the inboard portions of the blade; each of said blades having a tip and a trailing edge with the trailing edge including a reflexed outer portion positioned at said tip; each said reflexed outer portion having a length along the axis of the blade ranging up to about one chord length of the blade; each said reflexed outer portion having a curvature which imparts a moment to the blade about its aerodynamic center that counteracts negative aerodynamic pitching moments imparted to the blade by air flowing over its fully cambered airfoil surface; the area of each of the reflexed outer portions being approximately sufficient to generate a moment about the aerodynamic center of the blade which balances the negative aerodynamic pitching moments generated in the outboard portions of the blade by the flow of air over the fully cambered airfoil surface of the outboard portions; the inboard portion of each of said blades being sufficiently stiff to resist the negative aerodynamic pitching moments generated in the inboard portions of the blade without excessive twisting of the inboard portion; the relatively stiff inboard portion of each of said blades having a length which is about 70 to 80 percent of the length of the blade, and the relatively flexible outboard portion of each of said blades having a length which is about 20 to 30 percent of the length of the blade, whereby cyclical twisting of the flexible outboard portions of the rotor blades is minimized during rotation of the helicopter rotor without any material reduction in the lift-to-drag ratios of the fully cambered airfoil surfaces of the helicopter blades and with the pitch of the blades being cyclically controlled to maintain stability of the helicopter.

Claim 9

In a helicopter having a helicopter rotor, driving means for the rotor, a rotor hub, and a plurality of fully articulated rotor blades hingedly connected to the rotor hub for cyclical pitch control of the rotor blades to equalize lifting moments on the blades during rotation of the hub by the driving means, the improvement comprising: each of said rotor blades having a fully cambered airfoil surface, a relatively stiff inboard portion and a relatively flexible outboard portion; each of said blades having an angle of twist which provides the outboard portions of the blade with a lower angle of attack than the inboard portions of the blade; each of said blades having a tip and a trailing edge with the trailing edge including a reflexed outer portion positioned at said tip; each said reflexed outer portion having a length along the axis of the blade ranging up to about one chord length of the blade; each said reflexed outer portion having a curvature which imparts a moment to the blade about its aerodynamic center that counteracts negative aerodynamic pitching moments imparted to the blade by air flowing over its fully cambered airfoil surface; the area of each of the reflexed outer portions being approximately sufficient to generate a moment about the aerodynamic center of the blade which balances the negative aerodynamic pitching moments generated in the outboard portions of the blade by the flow of air over the fully cambered airfoil surface of the outboard portions; the inboard portion of each of said blades being sufficiently stiff to resist the negative aerodynamic pitching moments generated in the inboard portions of the blade without excessive twisting of the inboard portion; the relatively stiff inboard portion of each of said blades having a length which is about 70 to 80 percent of the length of the blade, and the relatively flexible outboard portion of each of said blades having a length which is about 20 to 30 percent of the length of the blade, whereby cyclical twisting of the flexible outboard portions of the rotor blades is minimized during rotation of the helicopter rotor without any material reduction in the lift-to-drag ratios of the fully cambered airfoil surfaces of the helicopter blades and with the pitch of the blades being cyclically controlled to maintain stability of the helicopter.

Claim 10

The helicopter of claim 7 wherein the length of the reflexed portion of each blade is about one-half to about one chord length of the blade.

Claim 11

The helicopter of claim 7 wherein each of said blades has an angle of twist ranging up to about eight degrees.

Claim 12

The helicopter of claim 7 wherein the helicopter rotor is rotated in a counterclockwise direction during flight of the helicopter.

Claim 13

The helicopter of claim 7 wherein the helicopter rotor is rotated in a clockwise direction during flight of the helicopter.

Claim 14

The helicopter of claim 7 wherein a rotor blade is an advancing blade and a rotor blade is a retreating blade at any given point in time during rotation of the helicopter rotor in flight of the helicopter; said retreating blade having a positive angle of attack with the reflexed outer portion of the retreating blade immersed in a tip vortex; said advancing blade having a lower angle of attack than said retreating blade, and the outboard portion of the advancing blade having a sufficiently low angle of attack to produce negligible lift, and the reflexed outer portion of the advancing blade positioned on the outboard portion of the advancing blade which produces negligible lift.

Claim 15

The helicopter of claim 7 wherein the length of the reflexed portion of each blade is about one-half chord length or less.

Claim 16

In a helicopter blade having a root, a tip, an airfoil surface with a leading edge and a trailing edge, and a twist of the blade between its root and tip which provides the leading edge adjacent the tip with a lower angle of attack than the leading edge adjacent the root, the improvement comprising: said airfoil surface being fully cambered; said blade having an inboard portion which is relatively stiff and an outboard portion which is relatively flexible; said blade having a tip with a portion of the trailing edge of said outboard portion being reflexed at said tip; said reflexed trailing edge extending inwardly from the blade tip for a length of up to about one chord length of the blade; said reflexed trailing edge having a curvature which imparts a moment to the blade about its aerodynamic center which counteracts negative aerodynamic pitching moments imparted to the blade by air flowing over said fully cambered airfoil surface; the area of the reflexed trailing edge being approximately sufficient to generate a moment about the aerodynamic center of the blade which balances negative aerodynamic pitching moments generated in the outboard portion of the blade; the inboard portion of the blade being sufficiently stiff to resist negative aerodynamic pitching moments generated in the fully cambered airfoil surface of the inboard portion without excessive twisting of said inboard portion; the relatively stiff inboard portion of the blade having a length of about 70 to 80 percent of the length of the blade, and the relatively flexible outboard portion of the blade having a length of about 20 to 30 percent of the length of the blade.

Claim 17

In a helicopter blade having a root, a tip, an airfoil surface with a leading edge and a trailing edge, and a twist of the blade between its root and tip which provides the leading edge adjacent the tip with a lower angle of attack than the leading edge adjacent the root, the improvement comprising: said airfoil surface being fully cambered; said blade having an inboard portion which is relatively stiff and an outboard portion which is relatively flexible; said blade having a tip with a portion of the trailing edge of said outboard portion being reflexed at said tip; said reflexed trailing edge extending inwardly from the blade tip for a length of up to about one chord length of the blade; said reflexed trailing edge having a curvature which imparts a moment to the blade about its aerodynamic center which counteracts negative aerodynamic pitching moments imparted to the blade by air flowing over said fully cambered airfoil surface; the area of the reflexed trailing edge being approximately sufficient to generate a moment about the aerodynamic center of the blade which balances negative aerodynamic pitching moments generated in the outboard portion of the blade; the inboard portion of the blade being sufficiently stiff to resist negative aerodynamic pitching moments generated in the fully cambered airfoil surface of the inboard portion without excessive twisting of said inboard portion; the relatively stiff inboard portion of the blade having a length of about 70 to 80 percent of the length of the blade, and the relatively flexible outboard portion of the blade having a length of about 20 to 30 percent of the length of the blade.

Claim 18

The helicopter blade of claim 14 wherein said reflexed trailing edge extends inwardly from the blade tip for a length of about one-half to about one chord length of the blade.

Claim 19

The helicopter blade of claim 14 wherein the angle of twist of the blade between its root and its tip ranges up to about eight degrees.

Claim 20

The helicoPter blade of claim 14 wherein the airfoil surface of the blade is contoured to generate lift when the blade is rotated in a counterclockwise direction.

Claim 21

The helicopter blade of claim 14 wherein the airfoil surface of the blade is contoured to generate lift when the blade is rotated in a clockwise direction.

Claim 22

The helicopter blade of claim 14 wherein said reflexed trailing edge extends inwardly from the blade tip for a length of about one-half chord length or less.