Method and device for driving an aircraft during the ground run thereof

1. A method for driving an aircraft during run over ground, said aircraft including a steerable nose gear and a rudder disposed at a rear of said aircraft, the method comprising:

controlling yaw in said aircraft using a rudder bar at a disposal of a pilot of the aircraft, configured to address a combined control command to said steerable nose gear and to said rudder;

equipping at least two undercarriage legs with brakes, the at least two undercarriage legs symmetric with one another with respect to a longitudinal vertical mid-plane of the aircraft; and

producing a braking command to control the wheel brakes of a corresponding one of the at least two undercarriage legs using two braking control members which are at the disposal of said pilot, respectively, associated with said corresponding one of the at least two undercarriage legs, wherein:

a difference between said braking commands is formed;

said difference in the braking commands is transformed into an additional control command for said rudder and for said steerable nose gear; and

said additional control command is applied to said rudder and to said steerable nose gear, on the dual condition that:

said difference in the braking commands is greater than a first threshold; and

said combined control command addressed by said rudder bar to said rudder and to said steerable nose gear is less than a second threshold, and wherein:

a maximum travel of each of said braking members lies between a neutral position and a maximum braking position, wherein said first threshold corresponds to a fraction of said maximum travel lying between one third and two-thirds.

2. The method as claimed in claim 1 , wherein said first threshold corresponds at least approximately to half of said maximum travel of said braking members.

3. The method as claimed in claim 1 , wherein, prior to said transformation into an additional control command, said difference in the braking commands is converted into a first function taking a value zero up to said first threshold and increasing onward of said first threshold, up to a maximum value attained for the maximum value of said difference in the braking commands.

4. The method as claimed in claim 3 , wherein said first function increases linearly between said first threshold and said maximum value of said difference in the braking commands.

5. The method as claimed in claim 3 , wherein said maximum value of said function is at least approximately equal to said maximum value of said difference in the braking commands.

6. The method as claimed in claim 3 , wherein the transformation of the difference in the braking commands into an additional control command for the rudder is obtained by multiplying said first function by a coefficient equal to a ratio of said maximum travel of levers of the rudder bar to said maximum travel of said braking control members.

7. The method as claimed in claim 6 , wherein said additional control command is subjected, before addition to said combined control command, to a limitation defining, with aid of said second threshold, a domain outside which said additional control command is zero and inside which authority of said additional control command has a limited authority on said rudder and on said steerable nose gear.

8. The method as claimed in claim 7 , wherein a contour of said domain corresponds to a function which is zero, when said combined control command is equal to said second threshold, and which is equal to said second threshold, when said combined control command is zero.

9. The method as claimed in claim 8 , wherein said function varies at least approximately linearly between zero value and value equal to said second threshold.

10. The method as claimed in claim 7 , wherein said second threshold corresponds to a fraction of the maximum travel of the levers of the rudder bar.

11. The method as claimed in claim 10 , wherein said second threshold corresponds to two-thirds of the maximum travel of the levers of the rudder bar.

12. The method as claimed in claim 7 , wherein a sum of said combined control command and of said limited additional control command is subjected to a limitation before application to said rudder and to said steerable nose gear.

13. The method as claimed in of claim 1 , wherein each of said braking commands undergoes a limitation before formation of their difference.

14. A device for driving an aircraft during a run over ground, said aircraft comprising:

a steerable nose gear;

a rudder, disposed at a rear of said aircraft;

a rudder bar at a disposal of a pilot of the aircraft, configured to address a combined control command to said steerable nose gear and to said rudder, to control said aircraft in yaw;

at least two undercarriage legs, symmetric with one another with respect to the longitudinal vertical mid-plane of the aircraft, wheels of said undercarriage legs being equipped with brakes; and

two braking control members at the disposal of said pilot, respectively associated with said undercarriage legs and each producing a braking command to control the wheel brakes of the associated undercarriage leg, wherein the device further comprises:

a subtracter forming a difference value between said braking commands;

a function generator transforming said difference value into a function taking the difference value of zero up to a first threshold and increasing, onward of said first threshold, up to a maximum value attained for the maximum value of said difference value in the braking commands;

a converter for transforming said function into an additional control command for said rudder and for said steerable nose gear;

a limiter to limit said additional control command and defining, between said first threshold and a second threshold, a domain outside which said additional control command is zero and inside which the authority of said additional control command has an authority on said rudder and on said steerable nose gear;

a summator forming the sum of said combined control command and of said additional control command limited by said limiter limitation; and

first and second actuation devices applying said sum to said rudder and to said steerable nose gear, wherein

a maximum travel of each of said braking members lies between a neutral position and a maximum braking position, wherein said first threshold corresponds to a fraction of said maximum travel lying between one third and two-thirds.