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Aviation History
1919
1919 - 0401.PDF
MARCH 27, ioro approaching normal pre-combustion pressure. For while it is obvious that the exhaust valves must be held open for the air-flushing, it is equally clear that while they remain open, no charging with mixture above atmospheric pressure can be effected, as any such charge would escape. Again, there is JLILJS^S- Detail view of valve gear, front end, right hand cylinder group. On the left, omnibus induction plate. In front, water-inlet and outlet. Central, inlet cam shaft on left, starting gear with T depressors and pull- rod in middle ; exhaust camshaft on right. the equaliser, suggesting its own function, as apparently to establish an equal charge-pressure in all cylinders alike. Both the impression and suggestion are all the more plausible that in a vertical or even a V-type, however mechan ically balanced or roller-borne as to its crankshaft, some such arrangement, with charging at three atmospheres or so, would probably be essential. Nevertheless—none of them happen to apply! The facts, on the contrary, in this case are, first, that apait from the com plication of having—as the only practicable method in the circumstances—to lift the equaliser cut-off sleeve to some position in which it cut out all four connections, its equalising function does not apply at all for the operation of charging, but solely—and essentially, in default of such a total cut out—for subsequent running. In brief, it acts as a junction- point for a kind of perpetual triplicate connection con stituted by the three pipings, precisely like the far end of a three-way " shorehaul " induction. Secondly, the grouping of the cylinders being, not even at a V„ but at the greater fanwise angle, the connecting-rod thrust angle upon the shaft is so much greater, and bears as from so many more radii at a time, that what with the reciprocatory-weight mechanical balance and the roller-borne crankshaft suspension in further aid, the series of slight explosion efforts of charges ignited at merely atmospheric pressure have been found sufficient for starting. Consequently to effect a start, it is merely necessary to hold back the control lever as far as it will go. Then the cylinder groups, one after another, are flushed with air : next—by the operation of the two-way cock—they are charged with mixture impelled from the pump, and merely filled with it; the lever is let go and the valves closed ; and finally, the equaliser lever is set in the equalising position for all subsequent running-induction, and the motor is ready to be started on the hand-operated magneto. Internally, the chief features of the Lion motor are the crankshaft, with the special method of fitting roller bearings on the three intermediate journals; the connecting rod fitting ; and the internal sump-scavenged lubrication for which all these parts and the valve-gear generally act as conduits ; the only external piping being the two rearward scavenging connections from the sump to the pump, an up ward connection to the valve-gear, and a third one forward to the propeller reduction gear. The crankshaft has its pins and journals hollowed, and closed again by bolt-connected, valve-like plugs to form oil- cells, and its webs drilled diagonally to form a continuous or serial-feed oil conduit from cell to cell. The problem of getting roller bearings on the intermediate journals has been solved—albeit at the compromise of paring the web-faces somewhat heavily, above and below—in what is understood to be the R.A.F. fashion of slipping the races of outsized bearings over the webs, and packing up to them with halved steel bushes, shouldered on one side and stopped on the other with a little butt-screw in the foot of the adjacent web ; one half of the bush being keyed to the journal to enable it to turn solid, and in a driving fit under the roller race. Theo retically the power-saving gain from the use of line-contact, all-but-frictionless bearings, is obviously enormous. Prac tically, owing to the diameter of the peripheral circle of the rollers, in this construction, the peripheral speed seems high. . . Soit-elle brutale, ca marche I The end-journals of course, present no such difficulties, and owing to the reduction spur-gearing at the end, no thrust- races are needed ; the roller-bearings being simply housed in the crank-chamber ends ; their inner races threaded on the shaft; the inner faces butted by the webs ; and their outer ones, held rearwardly by a keeper plate, and forward by the oil-thrower ring which is stud attached to the driving spur gear. The extremity of the crankshaft is mounted in a plain bearing housed in the metal of the reduction gear drum. Being hollow, it serves as the entry from beneath of the for ward oil-pressure lead, as brought through the base-chamber from the other end ; and is merely closed with a removable plate to facilitate the flushing of the whole circulatory system with kerosene after every 50 hours flying. The pistons, cast from a certain aluminum alloy, carry four rings on their very short trunks. These are chamfered and bored through beneath the two lower rings—which are scrapers —so as to return all lubricant in the slightest excess into the base-chamber. The gudgeon pins are hollow, and thus form the final oil-conduits to the cylinder walls. As they are pinned in the lugs with a taper ended split-pinned set-screw in each case, they do not oscillate in their steel bushes. Thus the oil-feed is necessarily intermittent, but only slightly so, owing to the slight angularity of the rod-head oscillation. On the other hand, it is frequently argued that the oil con sumption is rather greater with a gudgeon pin thus fixed than in one that oscillates with the rod-head. The connecting rod group in each case consists of a central I-sectioned—ail-but sectioned—master-rod, the big end of which houses a bronze bearing, white-metal-lined, CWNKSHAFT ExrwsiON On. PUMP DRIVE £/_ OIL PUMP DRIVE. General arrangement of distribution gear for Lion motor. and has its shoe—likewise fined—united in a scarf joint and attached by four-studs ; while the side-rods are tubular, and anchored to lugs on the big-end by hollow pins, so locked by end nuts that they cannot move endwise, and so held by snugs that they cannot rotate. Thus these pins con stitute oil-cells, intermediate to the crank-pin oil-cells on the one hand, and the gudgeon pins on the other. Their oil supply, although direct enough through the bearings, by way of bored leads, is, of course, rendered intermittent by the crank-pin rotation. But their upward feed', like that of the master rod, is effected by external oil-pipes, returned against and into the rod-heads, and thence goes intermittently, into the gudgeon-pins. 40I
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