Abstract: Overlapping twisted radial aerofoil blades or vanes are formed on a compressor rotor or turbine disk or the like (102) by electro-discharge machining with a curved tool electrode which is in the form of an elongate and substantially rigid element other than a wire (150) which is turned by a tool holder (130) as it is advanced on a helical path to form the inner surface of each blade or vane with the outer curve of the electrode, or the outer surface of each blade or vane with the inner curve of the electrode, the disk being indexed to a next rotary position after each blade surface is machined.

Abstract: A gas turbine engine comprises a rotary compressor (6) which is subject to forward thrust forces and is mounted on an axial shaft (50) which has a forward facing surface (67) located in a thrust bearing (52). A bleed of air under pressure (70, 74, 78) is provided from the compressor to the thrust bearing to form an air cushion (66, 68) opposing the forward thrust of the compressor transmitted by the shaft. The air cushion pressure automatically increases with engine speed. Other air cushion bearings (54, 56) are also provided along the shaft.