Optimized method of controlling yaw for rotary-wing aircraft, and a system for implementing it

1. A method of controlling the pitch of blades of a tail rotor in a rotary-wing aircraft, the method comprising the following operations:

a) generating a main control ( 18 ) for the pitch of the blades of the tail rotor as a function of a first control member ( 4 b ) for controlling the pitch of the blades of the tail rotor that is actuated by a pilot of the aircraft; and

b) generating a collective pitch and yaw decoupling control ( 16 ) as a function of the collective pitch of the rotary wing;

c) generating a bias control ( 17 ) that is variable as a function of the flying speed (V) of the aircraft and as a function of at least one of i) the main control and ii) the position (PP) of the first control member ( 4 b ); and

d) adding ( 111 ) the bias control to said decoupling control and to said main control in order to obtain an overall control ( 10 ) and thereby control the pitch of the blades of the tail rotor.

2. A method according to claim 1 , in which the bias control is also generated as a function of the collective pitch of the main rotor.

3. A method according to claim 1 , in which variation (CL 1 ) of the bias control as a function of the speed (V) takes place from a threshold (SV 1 , SV 2 ).

4. A method according to claim 1 , in which variation (CL 1 ) of the bias control as a function of the speed (V) takes place along a slope that is linear or exponential.

5. A method according to claim 1 , wherein,

the first control member is a yaw control member, and

variation of the bias control as a function of the flying speed, as a function of the main control ( 18 ), as a function of the position of the yaw control member ( 4 b ), and as a function of the collective pitch, comply(ies) with at least one monotonic function.

6. A method according to claim 1 , in which variation (CL 2 ) of the bias control as a function of the at least one of the main control and the position of the control member is asymmetrical.

7. A method according to claim 1 , in which variation (CL 2 ) of the bias control as a function of the position of the first control member is linear between two values (SP 1 , SP 2 ).

8. A method according to claim 1 , in which the bias control is also generated as a function (COL) of the position of a second control member ( 4 a ) actuated by the pilot to control the collective pitch of the main rotor.

9. A method according to claim 8 , in which variation (CL 3 ) of the bias control as a function of the position of the second control member is linear between two values (SC 1 , SC 2 )

10. The method of claim 1 , wherein,

the generating a bias control ( 17 ) is variable as a function of the flying speed (V) of the aircraft and as a function of both the main control and the position (PP) of the first control member ( 4 b ).

11. The method of claim 1 , wherein,

the generating a bias control ( 17 ) is variable as a function of the flying speed (V) of the aircraft and as a function of the main control.

12. The method of claim 1 , wherein,

the generating a bias control ( 17 ) is variable as a function of the flying speed (V) of the aircraft and as a function of the position (PP) of the first control member ( 4 b ).

13. A yaw control system for a rotary-wing aircraft having a main rotor and a tail rotor, the system including decoupling means ( 106 ) provided for delivering a decoupling control ( 16 ), and means ( 108 ) for generating a pilot control and delivering a main control ( 18 ) as a function of the position of a yaw control member ( 4 b ), the system further comprising calculation means ( 107 ) for determining a bias control ( 17 ) as a function of the yaw control and of the speed of the aircraft, and summing means ( 111 ) for adding the bias control to said decoupling control and to said main control in order to obtain an overall control ( 10 ) for the pitch of the blades of the tail rotor.

14. A system according to claim 13 , in which the means ( 107 ) for determining a bias control include means (CL 1 ) for limiting the bias control over ranges of speed values.

15. A system according to claim 13 , in which the means ( 107 ) for determining a bias control include means (CL 2 ) for limiting the bias control over ranges of yaw control values.

16. A system according to claim 13 , in which the means ( 107 ) for determining a bias control include means (CL 3 ) for limiting the bias control over ranges of control values for the collective pitch of the main rotor.

17. A system according to claim 13 , in which the means ( 107 ) for determining a bias control are integrated in an electrical flight control computer ( 1 ).

18. A system according to claim 17 , in which the decoupling means ( 106 ) and the means ( 108 ) for generating a main control are integrated in the electrical flight control computer ( 1 ) which is connected to transducers delivering signals or data concerning the positions of the yaw and collective pitch control members ( 4 a , 4 b ) actuated by the pilot of the aircraft, and also to servo-controls ( 3 ) for adjusting the pitch of the blades of the tail rotor.

19. A system according to claim 13 , which is connected to mechanical flight controls including a specially adapted actuator on the yaw axis.

20. A system according to claim 13 , which is connected to mechanical flight controls including an additional actuator on the yaw axis.