Blade provided with a resonator to reduce the drag movements of said blade, and a method implemented by said blade

1. A blade ( 10 ) extending longitudinally from a root ( 11 ) of the blade ( 10 ) to a free end ( 12 ) of said blade ( 10 ), the blade ( 10 ) being provided with an incorporated resonator ( 20 ) for reducing the drag movements (F 1 , F 2 ) of said blade ( 10 ), said resonator ( 20 ) being provided with a closed tank ( 30 ) that is partially filled with a liquid ( 50 ), wherein said resonator ( 20 ) includes a central tube ( 40 ) immersed inside said tank ( 30 ), the tank ( 30 ) and the central tube ( 40 ) being arranged in a longitudinal direction (Y) of the blade ( 10 ), said central tube ( 40 ) having first and second ends ( 41 , 42 ) that communicate with said tank ( 30 ) so that said liquid ( 50 ) can move from the tank ( 30 ) into the central tube ( 40 ), and vice versa.

2. A blade according to claim 1 , wherein said tank ( 30 ) includes fastener means ( 33 ) for fastening said central tube ( 40 ) to an inside wall ( 38 ) of said tank ( 30 ).

3. A blade according to claim 1 , wherein said first and second ends ( 41 , 42 ) of the central tube ( 40 ) are open and open out into the inside of said tank ( 30 ).

4. A blade according to claim 1 , wherein said tank ( 30 ) presents symmetry of revolution about a first axis of symmetry (AX 1 ).

5. A blade according to claim 1 , wherein said central tube ( 40 ) presents symmetry of revolution about a second axis of symmetry (AX 2 ).

6. A blade according to claim 4 , wherein said tank ( 30 ) and said central tube ( 40 ) have respective first and second axes of symmetry (AX 1 , AX 2 ), and said first and second axes of symmetry (AX 1 , AX 2 ) coincide.

7. A blade according to claim 6 , wherein said first and second axes of symmetry (AX 1 , AX 2 ) coincide with a longitudinal axis (AXL) of said blade extending along said longitudinal direction (Y).

8. A blade according to claim 1 , wherein said tank ( 30 ) is provided in succession going from the root ( 11 ) of the blade ( 10 ) towards its free end ( 12 ) with first and second end zones ( 31 , 32 ) having respective first and second dimensions (DIM 1 , DIM 2 ) in a transverse direction (X) of said blade ( 10 ) perpendicularly to said longitudinal direction (Y), said first dimension (DIM 1 ) being greater than the second dimension (DIM 2 ).

9. A blade according to claim 1 , wherein said fluid possesses a maximum viscosity of 2000 centistokes.

10. A rotorcraft rotor provided with a hub ( 1 ) suitable for rotating about an axis of rotation ( 1 ′), at least one blade ( 10 ) being fastened to said hub ( 1 ) via a drag hinge ( 2 ), wherein said blade ( 10 ) is a blade according to claim 1 that is provided with a resonator ( 20 ) comprising a tank ( 30 ) and a central tube ( 40 ), each presenting symmetry of revolution, said tank ( 30 ) being provided with first and second end zones ( 41 , 42 ) in succession going from the root ( 11 ) of the blade ( 10 ) towards its free end ( 12 ), the angular frequency (ω) of said resonator ( 20 ) being determined by the following relationship:

ω

=

Ω

×

R

0

[

1

+

(

R

1

R

2

)

2

]

×

(

R

0

′

-

R

0

)

where:

× represents the multiplication sign;

ω represents the angular frequency of the blade resonator in radians per second;

Ω represents the speed of rotation of the rotor;

R 0 represents the spacing between said axis of rotation and the liquid when the blade is in a mean position;

R 1 represents the first radius of the first end zone;

R 2 represents the second radius of said central tube; and

R′ 0 represents the spacing between said axis of rotation from a face of the second end zone further away from the root of the blade.

11. A method for limiting the drag movements (F 1 , F 2 ) of a blade ( 10 ) extending longitudinally from a root ( 11 ) of the blade ( 10 ) to a free end ( 12 ) of the blade ( 10 ), wherein said resonator ( 20 ) comprises a tank ( 30 ) having a central tube ( 40 ) immersed therein, and a liquid element ( 50 ) of a resonator ( 20 ) incorporated in the blade ( 10 ) is shifted in a longitudinal direction (Y) of said blade ( 10 ) so as to create secondary Coriolis forces (C 1 , C 2 ) opposing the drag movement (F 1 , F 2 ) of the blade ( 10 ) by causing at least some of said liquid ( 50 ) to pass from the tank ( 30 ) towards the central tube ( 40 ) or from the central tube ( 40 ) towards the tank.

12. A method according to claim 11 , wherein the method is performed by a blade ( 10 ) extending longitudinally from a root ( 11 ) of the blade ( 10 ) to a free end ( 12 ) of said blade ( 10 ), the blade ( 10 ) being provided with an incorporated resonator ( 20 ) for reducing the drag movements (F 1 , F 2 ) of said blade ( 10 ), said resonator ( 20 ) being provided with a closed tank ( 30 ) that is partially filled with a liquid ( 50 ), wherein said resonator ( 20 ) includes a central tube ( 40 ) immersed inside said tank ( 30 ), the tank ( 30 ) and the central tube ( 40 ) being arranged in a longitudinal direction (Y) of the blade ( 10 ), said central tube ( 40 ) having first and second ends ( 41 , 42 ) that communicate with said tank ( 30 ) so that said liquid ( 50 ) can move from the tank ( 30 ) into the central tube ( 40 ), and vice versa.