A helicopter with - a fuselage and a vertical midplane in an x-z plane through said fuselage, said fuselage having a width (W fus) > 1 m in a y-direction transversal to said x-z plane between parallel left hand and right hand surfaces of the fuselage, - a main rotor mounted on top of said fuselage, - a tail boom mounted on a rear end of said fuselage, - a tail rotor in a rotor duct of a shroud mounted to a rear end of said tail boom, - a vertical fin projecting from an upper transition region of said shroud essentially along the x-z plane towards the top, said upper transition region having a left hand and a right hand upper transition edge between respectively a left hand and a right hand annular surface around the rotor duct of the shroud and the vertical fin, - a bumper projecting from a lower transition region of said shroud essentially along the x-z plane opposite to the top, said lower transition region having a left hand and a right hand lower transition edge between respectively the left hand and the right hand annular surface around the rotor duct of the shroud and the bumper, and - upper leading edges (12, 32) of said vertical fin and of said shroud and - left hand and right hand trailing edges (13, 17) of said shroud, - characterized in that a diameter D of the rotor duct is 62% +/- 30% of the fuselage's width (W fus), a radial dimension D sh of the annular surface is 110% with tolerances of - 9,5% to +20% of the diameter D, a projection of the upper transition edge to the x-z plane is defined by a spline curve through points Pi (i=1..5) defined by their coordinates (xi, zi) relative to a Fenestron-Rotor's centre according to the following table: Point P of curve Horizontal X distance (range of variation) Vertical Z distance (range of variation) 1 11a x1 -1.7 D (-1;0.7) z1 D (-1.71;+0.5) x D 2 11a x2 -0.85 D (-0.15;+0.35) xD z2 0.25 D (-0.25;+0.5) x D 3 11a x3 0 (±0.5 D) z3 0.71 D (-0.11;+0.29) x D 4 11a x4 D (-0.5;+0.4) z4 0.4 D (-0.2;+0.3) x D 5 11a x5 1.7 D (-0.3;+0.7) z5 0.1 D (±0.5 D) where for all the points Pi (i=1..5) the following constraints must be fulfilled: • x1 < x2 < x3 < x4 < x5; • z1 ≤ z2 ≤z3; and • z5 ≤ z4 ≤ z3. - a fuselage and a vertical midplane in an x-z plane through said fuselage, said fuselage having a width (W fus) > 1 m in a y-direction transversal to said x-z plane between parallel left hand and right hand surfaces of the fuselage, - a main rotor mounted on top of said fuselage, - a tail boom mounted on a rear end of said fuselage, - a tail rotor in a rotor duct of a shroud mounted to a rear end of said tail boom, - a vertical fin projecting from an upper transition region of said shroud essentially along the x-z plane towards the top, said upper transition region having a left hand and a right hand upper transition edge between respectively a left hand and a right hand annular surface around the rotor duct of the shroud and the vertical fin, - a bumper projecting from a lower transition region of said shroud essentially along the x-z plane opposite to the top, said lower transition region having a left hand and a right hand lower transition edge between respectively the left hand and the right hand annular surface around the rotor duct of the shroud and the bumper, and - upper leading edges (12, 32) of said vertical fin and of said shroud and - left hand and right hand trailing edges (13, 17) of said shroud, - characterized in that a diameter D of the rotor duct is 62% +/- 30% of the fuselage's width (W fus), a radial dimension D sh of the annular surface is 110% with tolerances of - 9,5% to +20% of the diameter D, a projection of the upper transition edge to the x-z plane is defined by a spline curve through points Pi (i=1..5) defined by their coordinates (xi, zi) relative to a Fenestron-Rotor's centre according to the following table: Point P of curve Horizontal X distance (range of variation) Vertical Z distance (range of variation) 1 11a x1 -1.7 D (-1;0.7) z1 D (-1.71;+0.5) x D 2 11a x2 -0.85 D (-0.15;+0.35) xD z2 0.25 D (-0.25;+0.5) x D 3 11a x3 0 (±0.5 D) z3 0.71 D (-0.11;+0.29) x D 4 11a x4 D (-0.5;+0.4) z4 0.4 D (-0.2;+0.3) x D 5 11a x5 1.7 D (-0.3;+0.7) z5 0.1 D (±0.5 D) where for all the points Pi (i=1..5) the following constraints must be fulfilled: • x1 < x2 < x3 < x4 < x5; • z1 ≤ z2 ≤z3; and • z5 ≤ z4 ≤ z3. a diameter D of the rotor duct is 62% +/- 30% of the fuselage's width (W fus), a radial dimension D sh of the annular surface is 110% with tolerances of - 9,5% to +20% of the diameter D, a projection of the upper transition edge to the x-z plane is defined by a spline curve through points Pi (i=1..5) defined by their coordinates (xi, zi) relative to a Fenestron-Rotor's centre according to the following table: Point P of curve Horizontal X distance (range of variation) Vertical Z distance (range of variation) 1 11a x1 -1.7 D (-1;0.7) z1 D (-1.71;+0.5) x D 2 11a x2 -0.85 D (-0.15;+0.35) xD z2 0.25 D (-0.25;+0.5) x D 3 11a x3 0 (±0.5 D) z3 0.71 D (-0.11;+0.29) x D 4 11a x4 D (-0.5;+0.4) z4 0.4 D (-0.2;+0.3) x D 5 11a x5 1.7 D (-0.3;+0.7) z5 0.1 D (±0.5 D) where for all the points Pi (i=1..5) the following constraints must be fulfilled: • x1 < x2 < x3 < x4 < x5; • z1 ≤ z2 ≤z3; and • z5 ≤ z4 ≤ z3. • x1 < x2 < x3 < x4 < x5; • z1 ≤ z2 ≤z3; and • z5 ≤ z4 ≤ z3.