Abstract: A method of laser-drilling a hole through a workpiece, such as an injector nozzle (40), into a cavity comprising drilling a hole (41) through the workpiece (40) with a laser (50), providing a fluid having laser-barrier properties in the cavity so that, when the hole (41) is open to the cavity, laserlight passing through the hole (41) is incident upon the fluid whereby the workpiece (40) across the cavity from the hole (41) is protected from the laserlight, and arranging that the fluid does not enter the laser-drillled hole (41) during the drilling process. Apparatus for performing the method is also described.

Abstract: A ducted fan gas turbine has a fan shaft which is supported at its upstream end by a bearing. In the event of damage to the engine's fan, frangible bolts fracture to permit radial movement of the shaft. That movement is limited by the sequential engagement of the outer race of the bearing with first and second movement limiting portions on fixed structure of the engine. This alters the natural frequency of vibration of the fan, so permitting the fan to windmill without excessive vibration.

Abstract: A gas turbine engine has an assembly of circumferentially spaced rotor blades each having a radial tip. A plurality of seal segments mounted for radial movement circumscribe the rotor blades. Each segment is connected to the casing through a seal carrier provided with a flexible membrane which divides high pressure air from low pressure into two channels.

Abstract: A ducted fan gas turbine engine is provided with a fan which is carried by a shaft. A frangible fuse ring maintains the shaft carrying the fan coaxial with the engine longitudinal axis. In the event of severe fan damage, the fuse ring (28) fractures and the fan shaft orbits about the engine longitudinal axis. A pair of threaded members (39, 41), one of which is of generally frusto-conical configuration, cooperate as a result of the orbiting motion to restore the coaxial relationship between the fan shaft and the engine longitudinal axis.

Abstract: A bladed rotor has blades fitted in grooves around its rim. The blades are prevented from making significant movement lengthways of their grooves by abutment members which are so formed as to enable fitting and removal without the use of special tooling.

Abstract: A rotor disc which is suitable for carrying the fan blades of a ducted fan gas turbine engine is constituted by two sub-discs which are maintained in axially spaced apart relationship by a plurality of spacer members. The spacer members are generally axially extending and at least partially define the operational air flow path over the disc.

Abstract: A stage of fan blades in a ducted fan gas turbine engine have the spaces between them filled by a rotary annulus wall filler which has a leading portion made from metal and a trailing portion made from a composite material. The metal portion resists the impact damage from the ingress of foreign bodies and the trailing portion provides a lighter structure.

Abstract: In an accessory drive unit e.g. as used in a gas turbine engine, some of the gears in a gear train are provided with pockets 20 in which drainage oil is collected on engine shut down. On re-starting of the engine, the collected oil is acted upon by ribs 16 and is flung onto the teeth of the gears so as to provide immediate lubrication, rather than experience a delay until main lubricant supply pressure is increased. Friction and wear on start up is reduced.

Abstract: A propeller module for a gas turbine engine comprising two contra-rotating propellers has a reduction gear positioned axially between the propellers. Pitch change mechanisms are provided to change the pitch of the blades of both propellers independent of the differential speed of the propellers.