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 (16, 17), wherein said stator vanes (16, 17) are angularly modulated such that the interferences between the rotor blades and the stator vanes (16, 17) are limited by avoiding that any angular difference between two rotor blades corresponds to any of the angular differences between two stator vanes (16, 17) or between any of the stator vanes (16, 17) 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, and - 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, characterized in that, - 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 (29, 30) of the the stator vanes (16, 17) 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 (29, 30) of the stator vanes (16, 17), a maximized distance for any points on the trailing edges of the stator vanes (16, 17) being defined by the width of the shroud, namely said trailing edges of the stator vanes (16, 17) are limited within a silhouette defined by said shroud, and - the drive shaft and the control rod are sheathed with an aerodynamic fairing. - 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 (16, 17), wherein said stator vanes (16, 17) are angularly modulated such that the interferences between the rotor blades and the stator vanes (16, 17) are limited by avoiding that any angular difference between two rotor blades corresponds to any of the angular differences between two stator vanes (16, 17) or between any of the stator vanes (16, 17) 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, and - 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, characterized in that, - 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 (29, 30) of the the stator vanes (16, 17) 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 (29, 30) of the stator vanes (16, 17), a maximized distance for any points on the trailing edges of the stator vanes (16, 17) being defined by the width of the shroud, namely said trailing edges of the stator vanes (16, 17) are limited within a silhouette defined by said shroud, and - the drive shaft and the control rod are sheathed with an aerodynamic fairing.