Patent ID: 8974189
Filing Date: 2015-03-10
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 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: and where k is a radius of the root section, R