Abstract: A flow-straightening stator is fixed into the duct downstream of the rotor mounted so that it rotates in this duct, and includes vanes with aerodynamic profile which straightens out the airflow downstream of the rotor substantially along the axis of the duct, and are each inclined to the radial direction, from the axis of the duct towards its periphery, and in the opposite direction from the direction of rotation of the rotor, and/or inclined at a slant, from the center of the duct to its periphery and from upstream to downstream of the duct.

Abstract: A method of manufacturing a vane for a counter torque device includes extruding a hollow metal section of cross-section corresponding to the aerodynamic profile of the vane, in cutting off a section portion of length not substantially less than the span of the vane, and in arranging each end of the section portion as an end fitting with at least one fastening tab, either by machining and deformation of the ends of the section portion, or by fitting end fittings attached to its ends.

Abstract: A flow-straightener with stationary vanes and aerodynamic profile is mounted downstream of the rotor with blades in the transverse duct passing through the fairing at the tail of the helicopter. The blades of the rotor are distributed angularly about the axis of the rotor with uneven azimuth modulation, such that any angle between two arbitrary blades of the rotor is different from any angle between two arbitrary vanes of the flow-straightener.

Abstract: The blades of the rotor which can rotate in the transverse duct have an angular distribution according to an uneven azimuth modulation given by the following sinusoidal law:.THETA.n=n.times.360.degree./b+.DELTA..THETA. sin(m.times.n.times.360.degree./b)where .THETA.n is the angular position of the nth of the blades counted in series from an arbitrary origin, b is the number of blades, m is a whole number chosen from 1 to 4, which is not prime with the number b of blades, chosen from 6 to 12, and .DELTA..THETA. is chosen to be greater than or equal to a minimum value .DELTA..THETA. min, which is such that the product .DELTA..THETA. min.times.b is chosen within a range of values extending from 1.5 radian to 1 radian.