Month in the Patent Office

A Hollow propeller blade comprises a thrust member having an aerofoil portion with an external aerofoil thrust surface and a root portion which comprises two united sections, and a camber member united to the thrust member and having an external aerofoil camber surface. The root portion may comprise two united sections and the aerofoil section a third portion united to or integral with one of the sections. The root portion is formed in two sections 34, 36 welded together and each integral with a set of marginal ribs 18, 20 and intermediate ribs 22, 24, 26 which are complementary, the marginal ribs 18, 20 on the lower section 36 being stepped at 38, 40 to receive shorter marginal ribs on the section 34. Continuation ribs on the blade portion 42 are welded transversely to the ribs on the root portions, preferably using triangular inserts at the joins. The root portions 34, 36 may be of unequal size, the division being on a plane spaced from the neutral axis of the blade, the ribs of the upper portion being short and stub‐like, and the aerofoil part 42 may be integral with the lower root portion 36.