Helicopter antitorque tail rotor

1. A helicopter antitorque tail rotor ( 3 ), comprising a shaft ( 5 ) rotating about a rotation axis (A), at least two blades ( 6 ) extending along relative longitudinal axes (B) crosswise to said rotation axis (A), and a hub ( 7 ) for connecting said shaft ( 5 ) to said blades ( 6 );

each blade ( 6 ) comprising, in turn,:

a leading edge ( 8 ) and a trailing edge ( 9 ) opposite each other and elongated along relative longitudinal axis (B); said trailing edge ( 9 ), in use, interacting with the air current after said leading edge ( 8 );

a first and a second surface ( 12 , 13 ) opposite each other and extending between said leading edge ( 8 ) and said trailing edge ( 9 );

a radially inner first end ( 10 ) with respect to a rotation axis (A) of said blade ( 6 );

a radially outer second end ( 11 ) opposite to said radially inner first end ( 10 ); and

a root portion ( 14 a ) comprising said radially inner first end ( 10 ) and spaced from said outer second end ( 11 ) along said longitudinal direction (B);

said root portion ( 14 a ), when sectioned in a plane perpendicular to said leading edge ( 8 ) or said trailing edge ( 9 ), comprising a profile (G) asymmetrical with respect to a chord (P) joining said leading edge and said trailing edge ( 8 , 9 ) in said plane;

characterized in that the points of first ends ( 10 ) of said blades ( 6 ) are located at a distance from said rotation axis (A) ranging between 10 and 25% of the maximum distance between said rotation axis (A) and the points of said second ends ( 11 ) of said blades ( 6 ).

2. A rotor as claimed in claim 1 , characterized in that said hub ( 7 ) defines control means ( 25 , 20 , 35 , 36 ) for rotating said blades ( 6 ) about respective said longitudinal axes (B) to vary the angles of attack of said blades ( 6 ) with respect to the air current; said control means ( 25 , 20 , 35 , 36 ) being at least partly ( 36 ) housed in respective said root portions ( 14 a ) of said blades ( 6 ).

3. A rotor as claimed in claim 2 , characterized in that said control means ( 25 , 20 , 35 , 36 ) comprise at least:

an actuator ( 25 ) movable parallel to said rotation axis (A);

at least two pairs of plates ( 20 ) integral with respective blades ( 6 ) and connected functionally to said actuator ( 25 ) to rotate about the respective longitudinal axes (B); and

two pins ( 35 ) which rotate about respective said longitudinal axes (B), are integral with respective pairs of plates ( 20 ), and each have a respective portion ( 36 ) extending inside a respective said root portion ( 14 a ).

4. A rotor as claimed in claim 1 , characterized in that, at said root portion ( 14 a ), said first and second surface ( 12 , 13 ) of each blade ( 6 ) are blended at said leading edge ( 8 ).

5. A rotor as claimed in claim 1 , characterized in that, at said root portion ( 14 a ), said first and second surface ( 12 , 13 ) of each blade ( 6 ) are sharply joined at said trailing edge ( 9 ).

6. A rotor as claimed in claim 1 , characterized in that said second surface ( 13 ) of each blade ( 6 ) is convex at said root portion ( 14 a ).

7. A rotor as claimed in claim 1 , characterized in that said first surface ( 12 ) of each blade ( 6 ) is partly concave and partly convex at said root portion ( 14 a ).

8. A rotor as claimed in claim 7 , characterized in that, from said trailing edge ( 9 ) to said leading edge ( 8 ), said first surface ( 12 ) of each blade ( 6 ) comprises, at said root portion ( 14 a ), a concave portion ( 41 ) followed by a convex portion ( 42 ).

9. A rotor as claimed in claim 1 , characterized in that said chord (P) of each blade ( 6 ) comprises a main portion (P 1 ) interposed between said first and second surface ( 12 , 13 ); and in that one ( 12 ) of said first and second surface ( 12 , 13 ) is interposed between an end portion (P 2 ) of said chord (P) and the other ( 13 ) of said first and second surface ( 12 , 13 ).

10. A rotor as claimed in claim 9 , characterized in that said end portion (P 2 ) of said chord (P) of each blade ( 6 ) is located on said trailing edge ( 9 ) side.

11. A rotor as claimed in claim 9 , characterized in that an end portion of said first surface ( 12 ) of each blade ( 6 ), located on said trailing edge ( 9 ) side, is interposed between said end portion (P 2 ) of said chord (P) and said second surface ( 13 ).

12. A rotor as claimed in claim 1 , characterized in that the points of said profile (G) defining said first surface ( 12 ) of each blade ( 6 ) are further away from said chord (P) than the corresponding points defining said second surface ( 13 ).

13. A rotor as claimed in claim 1 , characterized in that each said blade ( 6 ) comprises:

an end portion ( 14 c ) comprising, in turn, said radially outer second end ( 11 ); and

an intermediate portion ( 14 b ) interposed, along said longitudinal axis (B), between said root portion ( 14 a ) and said end portion ( 14 c );

said intermediate portion ( 14 b ) of each blade ( 6 ) being spaced from said first and second end ( 10 , 11 ); the distance between said leading edge ( 8 ) and said trailing edge ( 9 ) at said intermediate portion ( 14 b ) being constant, and the length of said chord (P) at said intermediate portion ( 14 b ) being constant.

14. A rotor as claimed in claim 1 , characterized in that, from said leading edge ( 8 ) to said trailing edge ( 9 ) at said first end ( 10 ), said first and second surface ( 12 , 13 ) of each blade ( 6 ) comprise:

respective first portions ( 45 ) lying in the same plane sloping with respect to said trailing edge ( 9 );

respective curved second portions ( 46 ); and

respective third portions ( 47 ) lying in the same plane sloping with respect to the plane of said first portions ( 45 ).

15. A helicopter comprising a tail rotor ( 3 ) as claimed in claim 1 and a tail fin; characterized in that that said second surface ( 13 ) is interposed between said tail fin and said first surface ( 12 ).