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Aviation History
1945
1945 - 1855.PDF
FLIGHT SEPTEMBER 2OTH, 1945 ROLLS-ROYCE GRIFFON (65) MAGNETO the war the Griffon was rather displaced by the Vulture until the latter was discarded, then the Griffon was resurrected as the need for a larger engine than the Merlin was again realised as a necessity. The various marks of Merlin Spitfires were capable of handling enemy aircraft at height, but. when the Fw 190 was de-rated to give maxi- mum performance low down we were somewhat pressed. A quick decision was reached to put the Griffon II into some Spitfire VIII's, which then be- came the mark XII ; these were built in limited numbers, but effectively squashed the opposition. F.A.A. and R.A.F. Requirements '] hese models of the Griffon wer,e all fitted with single-stage, two-speed blowers, and this basic type has progressed for Fleet Air Arm use (vide the Fairey Firefly), whilst the special needs of the R.A.F. have been met by the two-speed, two- -stage engine for high-altitude use. As may be expected, the Grifton owes a fair amount to Merlin development, but what is peculiarly interesting is that various practices initially proved on the Griffon have been incorporated in the later Merlins. Basically the engine is, of course, on the same lines as the Merlin, although the detail design is new pretty well throughout. One of the most important innovations is in taking the cam- and mag-drives from the front. This was decided upon in order to relieve the valve operation from as much variation as possible: by interpolating a semi-floating coupling between the crankshaft and the driving wheel of the reduction gearing and, in addi- tion, by taking the cam drives from the airscrew-driving gear, angular variations in crankshaft speed are greatly reduced in their transmis- sion to the camshafts. Further, air- screw inertia results in a reasonably constant rate of r.p.m., and, to top- off the advantages, the front drive allows a comparatively shorter 'overall length which, in turn, per- mits the larger and more powerful engine to go into existing fighters Whilst on the subject of the cank- shaft, we might as well deal with that interesting component. It is, ol course, machined all over from a forged billet, and is fully counter- balanced, the front throw of No. 1, ENGINE COOLANT OUTLETS TO HEADER TANK MAGNETO INCLINED DRIVE PORT CAMSHAFT DRIVE AIRSCREW REDUCTION WHEEL Detail of frontend showing how • cam drive andmagneto drive are taken from re-duction gear. CAMSHAFT- STELLITE- C8ANKCASE' VAIVE ROCKER ROCKtR SPINDLE .BRIDGE-PIECE I COOLANT CONNECTION1I FROM SKIRT TO HtAO .._ CYLINDER BLOCKSECURING STUD --BUBBERRING -01 BRAIN TOCRANKCASE cection through cylinder and head illustrating simple valve gear and large coolant areas. Three-quarter front view of crankshaft with semi-floating toothed annulus in front coupling. Note the detachable counterweights on crank throws. both throws of No. 4 and the reai throw of No. 6 bearings each hav- ing a separate balance weight bolted to them. Vibratory troubles in the crankshaft have been very few, but a pointer to the Derby standard is that the firing order geography was selected to give optimum crankshaft harmonics. Crankshaft Lubrication Perhaps the most novel feature of the crank assembly is that the main bearings and big ends are all lubricated from the hollow interior of the shaft. This scheme, though novel, is by no means new, Rolls having first tried it years ago ; how- ever, the Griffon is the first Kolls engine in which it has become .prac- tice. Feed is into each end of the shaft and, in addition to the system pressure, shaft rotation provides a "built-in" centrifuge. A great advantage of the system is that the amount of oil supplied to each bear- ing is not influenced by relative shaft / bearing movement. Jn addjr""" tion, each main journal has internal standpipes which act as sludge traps as well as permitting, by a variation in their diameter, a means of metering or controlling the amount of oil supplied to any par- ticular bearing. Another interesting feature of the crankshaft is that it is rigidly connected neither to the front nor the rear driven members. At the front end an internally toothed annulus is bolted on, this meshing with and housing a semi-floating ring which itself is internally splined to a coupling shaft. The latter is splined at its front end to the driving wheel of the reduction gear so that this mechanism is
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