Helicopter with a transverse duct

1. A helicopter with a longitudinal axis and with a tail portion with a transverse duct and a drive shaft inside a drive shaft fairing for a counter-torque device supported within said transverse duct, said counter-torque device including:

a rotor rotatable mounted within said transverse duct, said rotor including: a rotor hub having a rotor axis, and rotor blades extending from said rotor hub, said rotor blades having a modulated angular distribution about said rotor axis,

a stator fixedly mounted within said transverse duct offset along said rotor axis from said rotor, said stator including a plurality of stator vanes, wherein said stator vanes are angularly modulated such that the interferences between the rotor blades and the stator vanes are limited by avoiding that any angular difference between two rotor blades corresponds to any of the angular differences between two stator vanes or between any of the stator vanes and the drive shaft fairing,

the drive shaft originating from a main gear box and ending in a gear box in the transverse duct to drivingly engage with the rotor, and

a control rod to control pitch angles of the rotor blades wherein:

the rotor is rotational about a rotor axis, tilted in the range between −20° to +45° around a rotation axis parallel offset to the longitudinal axis of the helicopter or the drive shaft, said rotation axis going through the center of the rotor and being directed to the tail of the helicopter,

the distances between the plane of the rotor and points between a root and a tip at the transverse duct on leading or trailing edges of the stator vanes are greater than the distances between the plane of the transverse duct rotor and any points on a straight line between said root and said tip at the transverse duct of the leading or trailing edges of the stator vanes, a maximized distance for any points on the trailing edges of the stator vanes being defined by the width of the shroud, namely said trailing edges of the stator vanes are limited within a silhouette defined by said shroud, and

the drive shaft and the control rod are sheathed with an aerodynamic fairing.

2. The helicopter according to claim 1 , wherein the maximum number of stator vanes equals six.

3. The helicopter according to claim 1 , wherein the rotor axis is tilted about 1°.

4. The helicopter according to claim 1 , wherein the distances between the plane of the rotor and the points between a root and a tip on leading or trailing edges of the stator vanes are defined by parabolic functions.

5. The helicopter according to claim 1 , wherein the stator vanes are configured to carry both: tension and compression.

6. The helicopter according to claim 2 , wherein the azimuthal positions and the incline of said two stator vanes are respectively given by θ v-01 =140°, ν 1-01 =25° and θ v-02 =255°, ν 1-02 =25°.

7. The helicopter according to claim 4 , wherein the parabolic shaped leading edge is defined using three points, a first point being defined at the root of the respective stator vane, a second point at the stator vane tip depending on the first point and an angle ν 2 and a third point defined in between the first and the second point.

8. The helicopter according to claim 1 , wherein the stator vanes are tilted with an angle ν 2 =5°±2° relative to the rotor plane.

9. The helicopter according to claim 7 , wherein the first point is closer to the rotor plane than the second point.

10. The helicopter according to claim 1 , wherein the aerodynamic fairing is provided with at least one rounded edge.

11. The helicopter according to claim 6 , wherein the azimuthal position relative to the rotation axis of the first and second stator vanes can vary in the range of θ v =±40°.

12. The helicopter according to claim 6 , wherein the inclination of the first and second stator vanes relative to the radial direction from the gearbox fairing towards the transverse duct can vary in the range of ν 1 =±20°.

13. The helicopter according to claim 1 , wherein positive values of ν 1 are defined in the opposite direction from the direction of rotation of the rotor or in direction of rotation of the rotor.

14. The helicopter according to claim 1 , wherein the drive shaft fairing has a reduced volume and/or a reduced cross section rejuvenating from the central gearbox fairing to an inner circumference of the transverse duct.

15. The helicopter according to claim 14 , wherein the cross section of the drive shaft fairing rejuvenates with a constant rate of 1% within a distance of 20 to 55 mm from the root at the central gearbox fairing to the inner circumference of the transverse duct.

16. The helicopter according to claim 1 , wherein the maximum number of stator vanes equals four.

17. The helicopter according to claim 1 , wherein the maximum number of stator vanes equals two.

18. The helicopter according to claim 7 , wherein the third point is defined in the middle section of the respective stator vane.

19. The helicopter according to claim 14 , wherein the cross section of the drive shaft fairing rejuvenates with a constant rate of 1% within a distance of 35 to 40 mm from the root at the central gearbox fairing to the inner circumference of the transverse duct.

20. The helicopter according to claim 14 , wherein the cross section of the drive shaft fairing rejuvenates with a constant rate of 1% within a distance of 38 mm from the root at the central gearbox fairing to the inner circumference of the transverse duct.