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Aviation History
1924
1924 - 0496.PDF
1 sbows^a connecting rod, with the zig-zag oil pipe. 2, A "Zephyr" piston, control valve. 3, Details of the altitude can be carried outside in such a way as to make them self- draining, thus reducing fire risk to a minimum. The reduction gear is entirely different from that of the " Eagle," which latter is of the epicyclic type. In the " Condor " a single-spur gear reduction is fitted, bringing the centre of the airscrew upwards to a point almost exactly in the centre of the frontal area of the engine. Thus a very neat cowling can be employed. The gear reduction ratio has been chosen after very carefully going into the question of airscrew speed, and the ratio decided upon is 0-477, giving an air screw speed at normal revolutions of 907 r.p.m. It has been arranged to use metal airscrews, and a very simplcand light flange fixing has been arranged. An efficient airscrew for an engine of this size is about 16 ft. diameter, and if made of wood would obviously be difficult to handle, and even more so to transport. The metal airscrew, with its Cylinder, piston and connecting rod assembly of Series III engine. detachable blades, offers a very considerable advantage in this respect. Last, but by no means least, the " Condor " is very economical in fuel consumption, the average during the 50 hours of the Air Ministry type tests being below 0-49 lb./ b.h.p./hour. The weight works out at just a fraction over 2 lbs./b.h.p. at normal speed and power, and at even less if the estimate is based on full-power conditions. Like all previous Rolls-Royce aero engines the " Condor " is at the 12-cylinder water-cooled " vee " type, with the cylinder banks placed at an angle of 60 degrees, and with overhead valves operated by overhead camshafts driven by inclined tubular driving shafts from the rear end of the crank shaft. The cylinders are separately mounted on the crank- case, and are of built-up all-steel construction. They are machined from 0.6 per cent, carbon steel forgings, with the heads integral with the cylinder barrels. The water jackets are die-pressed steel, acety lene welded at the joints. There are four valves per cylinder, two inlet and two exhaust, and two sparking plugs per cylinder. The valves are of the " trum pet " type, and are made from special high chro mium steel forgings. The valve seatings are machined in the cylinder heads, and the valve stems are divergent and require a special rocker mechanism. The special rocker mechanism is shown in some of the accompanying sketches. It will be seen that to operate the diver gent valves tappets are interposed between the cams and rockers, the latter being arranged to swing in a plane coincident with or parallel to the plane in which the valve of each lies. There are, it should be pointed out, but three cams for each four valves, the central cam and its tappets oper ating the two inlet valves, while the remaining the Rolls-Royce " Condor 496
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