GB210841A - Improvements in or relating to screw propellers or the like - Google Patents

Abstract

210,841. Gill, J. H. W., and Gill Propeller Co., Ltd. Nov. 3, 1922. Screw and like propellers.-Relates to screw propellers and the like having a shroud or casing attached to or integral with the blade tips the contour of the inner surface of the casing being such that the nett cross sectional area, after deducting the area of boss and blades, varies irversely as the square root of the axial distance of the particular section from a datum section. The blades C, Fig. 1, are attached to a boss A having a fairing B and carry a casing D. With blades of negligible thickness the inner contour of the casing would be curved as at E. In considering blade thickness, blades and boss are designed so that the contour is mainly that of a conical frustrum F with bevelled front and rear edges G, G<1>, following the shape E. The blades have a maximum thickness at about onetihrd of the width from the leading edge. The axial pitch increases from the leading, to the following edge such that the product of the square root of the cross sectional area and the mean pitch is constant. The radial pitch may also be increased from tip to root. The blade edges may be straight or curved so as to be convex on the inlet side. The length of the casing is one-fifth to one-quarter of the diameter at the inlet, and the angle of the coned part F is between 9‹ and 13‹. The propeller may be placed in a casing between two sets of fixed guide blades when used as an axial-flow impeller. The casing may be made in sections S, T, Fig. 11, each carried integrally by a blade tip, the blade U, V, being secured to the boss W by bolts. The sections terminate in diagonally disposed inwardly arranged flanges x, and are secured together by bolts through the abutting flanges. Specifications 142,713, 175,922, and 177,047 are referred to.