FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1949
1949 - 1429.PDF
August 18th, 1949 193 (Above) Arrangement of the torquemeter pistons and ring gear. (Right) The airscrew reduction gear is of the compound epicydic type. the usual screwed or bolted joints of the combustion equip- ment. Fuel is supplied by a Lucas variable-displacement pump delivering at a pressure of 750 lb / sq in. Atomization of the fuel is effected by Lucas Simplex-type burners mounted centrally in the flame-tube. Control equipment— barometric pressure-control unit, accumulator and throttle cock—is also of Lucas design. Combustion gases are expanded in three turbine stages: two provide the power necessary to rotate the compressor system and the third furnishes an independent drive for the airscrew. All three wheels are of Jessop G.18B steel and carry blades of Nimonic 80A alloy with fir-tree roots. The first wheel has a short integral shaft on which is secured the outer member of the toothed coupling to drive the com- pressor rotor. First and second wheels are clamped to- gether by a sleeve passing through their bores and torque is transmitted by interengaging radial serrations on the abutting disc faces. This compressor turbine-wheel assembly is overhung from two bearings housed in the hub of the mounting spider. Thrust from the turbine is taken by the rearwardly located ball bearing while the other bearing is of the roller type. The toothed coupling permits independent axial expansion of turbine and compressor components. Turbine nozzles are built up of multi-blade segments, precision-cast in Nimonic 80 alloy by the lost-wax process. The independent single wheel driving the airscrew is the third stage of the turbine assembly. The segments are bolted to the diaphragm located forward of each turbine disc and carrying labyrinth seals. On account of the substantial pressure drop through the tur- bines the nozzle area is increased conriderably from entrance to exit at the second and third stages. To avoid a too-rapid expansion of the gases the nozzle blades, therefore, are of relatively long section. . As the gases expand through the stages their temperature is lowered and, as a consequence, the turbine components can safely withstand higher mechanical stressing. Advan- tage is taken of this factor in the third stage to run the air- screw turbine-wheel at 10,700 r.p.m. instead of the 10,000 r.p!m. of the compressor wheels. Thrust from this wheel is taken on a ball bearing located in the rear casing, and the tubular shaft, flanged to the disc, extends through the sleeve clamping the first-"and second-stage wheels and carries the male member of the toothed coupling connecting to the drive shaft. This tubular shaft passes right through the axial compressor rotor, the centrifugal impeller and the accessories drive casing and terminates in a second toothed coupling by which the drive is transmitted to the reduction gear. Ball and roller bearings, at front and rear respec- tively, support the shaft in the compressor rotating assembly. . Turbine—disc cooling Three supplies of air at different pressures are tapped from the compressor to cool the turbine discs. For the first- stage turbine, at which the gases are at high pressure, air is piped from the centrifugal compressor casing in the vicinity of the impeller periphery to two arms of the turbine spider. From one of these a flow passes through drillings and holes in the diaphragm to the shroud and thence up the forward face of the first disc. The supply to the second arm passes through drillings in the hollow turbine shaft and longitudinal grooves in the exterior of the sleeve inside the shaft to the rear face of the first disc and, after passing through a labyrinth seal on the diaphragm, to the forward • face of the second disc. Air at somewhat lower pressure, also tapped from the centrifugal-compressor casing, is led down a third arm of the spider to a space in the centre of a labyrinth seal on the turbine shaft. By way of drillings in shaft and sleeve it reaches the annular space between the sleeve and the airscrew shaft and thence passes up the rear face of the second disc. For the airscrew turbine, the third disc, air is piped from the seventh and sixth stages of the axial compressor to the rear of the turbine casing and thence to the housing of the bearing for the rear stub shaft of the disc. That from the seventh-stage tapping is passed by a drilling to the centre of a labyrinth seal and thence by a drilling in the stub shaft
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
