Patent ID: 9162749
Filing Date: 2015-10-20
Classification: B64C,Y10S

Abstract:
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 (c max ) and the root section having a root chord (C ref ) less than the end chord (c max ), the end chord (c max ) being the largest of the respective chords, and the end chord (C max ) being equal to or less than 1.6 times the root chord (C ref ) 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: where: is a non-dimensional number; Y AC 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, R max designates a maximum radius of the end section, and a e , b e and c e 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: where k is the radius of the root section, R max designates the maximum radius of the end section, C max designates the chord of the end section and is equal to a c ×C ref , where a c is a factor, x designates the multiplication sign and b c and n designate first and second predetermined constants, and wherein the first predetermined constant b