Abstract: A cowl comprising, inter alia, a stationary part formed by a diffuser (10) which exhibits a fastening base (11), a nozzle-funnel (12), a connection zone (13), a cylindrical skirt (14), and a moving part (20) able to rotate about an axis (200), which moving part (21) exhibits a peripheral profiled annular hoop (20) which is intended to be rigidly connected to the blade (22) tips (221) of a helix and which is mounted coaxially in this skirt (14) so as to be able to rotate therein, is characterised in that, taking as references the direction of flow and the axis (200), this hoop (21) is delimited by an inner wall (2101), an outer wall (2102) and a rear section (2103), this connection zone (13) is delimited in particular by an inner surface (131) with an upstream limit (1310), and in that this rear section (2103) of the hoop (21) is situated in a plane (P) which is perpendicular to the axis (200) and which passes practically through the upstream limit (1310) of the inner surface (131) of the connection zone (13).

Abstract: The profiled annular hoop for a fan helix blade tip exhibits a curved inlet collar whose convexity is directed towards the axis (100), and is characterized in that this collar (11) has a given axial length (l) and a meridian section (110) shaped approximately as a quarter ellipse whose eccentricity is of the order of 1.5 and whose major half-axis (a) lies between approximately one third and one half of this given axial length (l).Application to cooling motorized fans of vehicle radiators.

Abstract: The blade has an axis (.GAMMA.) which is the locus of the thrust centers (C) of its cross-sections parallel to its foot (13) which has a connecting point (I) between an abyssal arc (.gamma..sub.1) whose concavity faces toward the leading edge (11) and a summit arc (.gamma..sub.2) whose concavity faces toward the trailing edge (12) of the blade.