GB207949A - Improvements in or relating to screw propellers, windmills and the like - Google Patents

Abstract

207,949. Ireland, A. J. T. Oct. 19, 1922. Screw propellers.-In the manufacture of metal air screws the blades are formed from a tube of convenient cross-section which increases in size from root to tip, and at the tip triangular pieces are cut out, the tube being then pressed or moulded into its aerofoil section and the edges at the tip being welded or otherwise united. The tube is preferably of tapering thickness. The former on which the tube is shaped is constructed of three or more pieces which can be successively withdrawn at the root. The tube may be seamless or made from a plate with one seam. Stiffening distance-pieces may connect the inner surfaces of the blade faces. A seamless tube of diminishing thickness and increasing diameter has triangular pieces 17, Fig. 8, removed, the parts being drawn together and welded, Fig. 7, or triangular pieces instead of being cut out are folded in Fig. 8. In place of a graduated thick. ness in one tube, a laminated construction may be used with a larger number of laminations at the root. The blades are shaped on a three-piece former 18, 19, 20, Figs. 11 and 12, the centre part 19 having parallel sides and being capable of removable at the butt end, after which the remaining parts 18 and 20 can be withdrawn. Hollow distance-pieces 21 are inserted into the blades when formed and are loosely heM in position opposite holes in the blade faces. The pieces are finally secured by turning in the edges 29, Fig. 15, of the holes and inserting a rivet 25 which is headed at 26. Alternatively the rivet is screwed at both ends and tapered nuts screwed thereon into the flared opening formed by turning in the edges. Additional diaphragm stiffeners may also be used.