Blade for a helicopter anti-torque device

摘要

A blade (1) for a tail anti-torque device of a helicopter, said device comprising a ducted rotor (13). The blade (1) has an assembly of sections, a leading edge (2) and a trailing edge (3); a stacking line (4) of the profiles extending at a distance lying in the range 25% to 50% of the chord (C). The stacking line (4) presents a shape that is curved having successively from the root (5) to the end (6) of the blade a back sweep, a forward sweep, and a last back sweep; and a chord (C) that becomes larger going towards the end (6) of the blade (1) over at least the end profile (1a).

主权项

1. A blade for a tail anti-torque device of a rotorcraft, the device comprising a ducted rotor, the blade having a three-dimensional geometrical shape defined by different airfoil profile sections extending between a leading edge and a trailing edge of the blade and defined radially by a root section and by an end section of the blade; at least two of the airfoil profile sections having different chord values along a stacking line extending from the root section to the end section, the blade being twisted, the stacking line, prior to twisting, defining a plane extension surface defined radially from the root section to the end section, and a twisting line of the plane extension surface that is defined by a predetermined twisting relationship, the stacking line extending at a distance lying in a range 25% to 50% of a respective chord (C) for each of the airfoil profile sections from the leading edge and presenting a curve on the plane extension surface comprising in succession from the root section: a first back sweep; a forward sweep; and finally a last back sweep going to the end section; the end section having an end chord (cmax) and the root section having a root chord (Cref) less than the end chord (cmax), the end chord (cmax) being the largest of the respective chords, and the end chord (Cmax) being equal to or less than 1.6 times the root chord (Cref) of the root section, wherein the stacking line is a curve traced relative to a radial direction of the tail anti-torque device and given by a polynomial such that:
YAC/Cref=ae×Q3+be×Q2+ce×Q with 0≦Q≦1where:Q=r-kRmax-kis a non-dimensional number;YAC is a position of the stacking line of the respective airfoil profile sections for a radius r; k is a radius of the root section, Rmax designates a maximum radius of the end section, and ae, be and ce are first, second, and third predetermined values,
wherein the respective chords (C) are defined by a variable relationship such that a chord value C(r) for a radius r of a respective section of the airfoil profile sections, is given by:⁢C⁡(r)=Cref,if⁢⁢k≤r≤bc×Rmax⁢andC⁡(r)=Cref+[Cmax-Cref]×[r-(bc×Rmax)]n{Rmax-(bc×Rmax)]n⁢⁢if⁢⁢r≥bc×Rmaxwhere k is the radius of the root section, Rmax designates the maximum radius of the end section, Cmax designates the chord of the end section and is equal to ac×Cref, where ac is a factor, x designates the multiplication sign and bc and n designate first and second predetermined constants, and
wherein the first predetermined constant bc lies in a range 0 to 1.