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Aviation History
1949
1949 - 1516.PDF
8 Sept., 1949 281 end, is in turn splined to the bore of the main input shaft of the reduction gear. A compound plain and epicyclic reduction gear is used in the Dart, the high-speed train employing helical tooth forms, whilst the low-speed (epicyclicj train has teeth of plain spur form. The main input shaft is, in fact, integral with the sun-gear that drives three planetary layshaft pinions, the satellites of which commonly mesh with an internally toothed annular gear. This latter is of drum form, and em- bodies an additional ring of internal teeth in its forward mouth for engagement with the large-dia- meter driving gear formed integrally with the air- screw shaft. Auxiliary drives into and from the reduction gear, respectively for the starter and the oil pumps, are through bevel gears. The starter is mounted on top of the reduction-gear / oil-tank casing, and slightly offset to starboard of the oil cooler, the bevel wheel at the foot of the starter shaft engaging a comple- mentary pinion carried on a sleeve coaxial with, and coupled to, the main input shaft of the sun-gear. On the tail of the lowermost planetary layshaft is splined a bevel gear from which the vertically sloping shaft down to the oil pumps is driven, the scavenge pumps and pressure pump being built into a single housing. As already noted, the lubrication system is com- pletely self-contained. The integral oil tank is divided into two compartments, one of which has a capacity of three gallons for engine lubrication, whilst the other holds one gallon of oil for airscrew feathering. Gear-type pumps are used for pressure feed and scavenging purposes, the pressure pump supplying oil to all bearings and reduction gear jets at a nominal pressure of 30 lb/sq in, and at a nominal flow rate of 460 gall/hr. Oil draining from the turbine bearing and compressor thrust-bearing is scavenged by separate pumps, whilst a third pump scavenges the reduction gear and compressor inter- stage bearing drains. The combined delivery from the three scavenge pumps is returned to the tank via the oil cooler on the casing crown. Drive for an accessory gearbox is provided imme- diately behind the compressor. The transfer coup- ling between the turbine and compressor shafts em- bodies a pinion from which drive is given to a spur wheel splined to a bevel shaft. From this latter torque is transmitted to a vertical shaft bevel- coupled at the head to a short output member ter- minating in a universal coupling for final drive to the accessory gearbox. Flying experience with the Dart has been amassed with a diversity of airframes: the unit first flew in- stalled in the nose of a Lancaster in October, 1947 ; then early last year two Darts were installed in a Wellington, and much valuable information was gained relative to the subsequent Viscount applica- tion ; apart from these, the unit has also been oper- ated in the Avro Athena advanced trainer. It is of considerable point to emphasize that, although the Dart earlier completed its full civil A.R.B. type test at 1,250 s.h.p., plus 300 lb thrust, the latest RDa.3 version has a maximum output of 1,400 s.h.p. + 295 lb thrust.
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