Air impellor

Method according to any one of the preceeding claims, wherein the local angle of inclination increases progressively over at least 50% of the radial length of each vane segment.

Method according to any one of the preceeding claims and comprising forming at least four said cuts which extend radially.

Method according to any one of the preceeding claims, wherein said cuts are form by a stamping operation.

Method according to any one of the preceeding claims, wherein edges of the vanes are undercut at least at the inner and base region of each cut thereby to form the sheet material with a smooth curved profile.

Method according to any one of the preceeding claims, wherein a central zone of the sheet material is removed.

An air impellor manufactured by the method according to any one of the preceding claims.

An air impellor comprising a sheet of plastically deformable material having a plurality of cuts which each extend radially outwards from a central position defined by the intersection between said sheet of material and an axis about which, in use, the impellor is intended to rotate, each cut extending to an outer boundary edge of the sheet material from an inner end base region which lies at a position spaced radially outwards from said central position, each vane segment thereby defined by the sheet material lying between each successive pair of cuts having a twisted profile in which the local angle of inclination of a circumferentially extending line on said vane segment, as considered relative to a plane perpendicular to said axis of rotation, increases with increasing radial distance of the circumferentially extending line from said axis of rotation.