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Aviation History
1918
1918 - 1082.PDF
SEPTEMBER~26, 1918. AERO MOTORS AT KING'S COLLEGE SOME TECHNICAL IMPRESSIONS. The Forward View.IT is more in view of the development of the commercial side of aviation after the war than its present military aspect, thatthe indications of the few aeromotors displayed at the recent London University Exhibition are interesting and important.Also in a way, significant ; although one may be well aware that they represent but few of the types actively projected,or even actually available. Indeed, the motor section of an aero show we could produce, were conditions normal, wouldastonish even the insiders of flight. Such a forward view then is the standpoint and pretext of thepresent article. To-day, so long as a given aeromotor can definitely achieve a certain task, mostly within tacticalrather than strategic ranges of travel, and with the main- taining labour available to any amount, at a trifle over ashilling a day, prime cost, consumption, durability and upkeep trouble matter but little, apparently. When it comesto commercial development, they certainly are going to matter a great deal. For they not only all spell Efficiency,but much more than they even did in automobilism, they are going to make up the factor of sheer safety.Few as the exhibits are, there is much that for obvious reasons cannot be disclosed. On the other hand there is stillenough left to show not only the " state of the art " in aero- motor engineering, but also to prove that the British product—here ODe does not refer to the mere reproduction of foreign models—remains well advanced. Safely enough, too, thereseems to be much that can be usefully written, as of any motor, as a mere abstract of visible practice. A Great Continental Example .k MFor example, there is one very notable model of the 8-cylinder V-type, of Continental origin and much fame;inasmuch as it represents that school of construction in which aluminium cylinder-bodies, with steel liners screwedinto them throughout their length, are the chief feature. Externally, there is admittedly no more handsome design.Not only does the monobloc formation of each cylinder-tier render it very clean—even the cruciform induction manifoldhardly seems to encumber the middle space—but the crank chamber moulding is exquisitely curved in every direction toresist the probable stresses. What little there is of accessory detail is designed for quick dismounting ; and there arevarious little points that display much ingenuity. It is only wlien the sections are examined that the make-upof the motor, rather than its basic construction, declares itself faulty. The water-spaces are as ample as they shouldbe : but cast as they are in one piece, the thicknesses of the cylinder bodies and water jackets are all anyhow ; much toothick—the latter excessively so—and uneven. That does not make for reliability. It is all the worse that it does not showin the ordinary way. Worst of all in this model, the occur- rence of the slightest interior defect—to say nothing of theneed to re-grind a valve—means dismounting the entire block. And Its British Analogue., Of the same general system of construction is the largest and most prominent exhibit, all-British. Nevertheless, itaffords a striking contrast, not only because it is a 6-cylinder vertical, but because its constructive design avoids nearly-all these defects, and with but two or three slight detail alterations involving no change of dimension, would eliminateevery one of them. Indeed, one imagines that it would then represent as commercial a production as need be, apart fromthe immediate accessibility imparted. This motor has its cylinders mounted as two triads : andtheir heads, with their jacketing also thus formed, in two aluminium castings; these latter including the combustionchambers only, which appear to be of ample thickness, and are slightly " minaretted " on the exhaust side. Into thesethe steel cylinders, which are a useful ^ of an inch thicker than in the first example, are screwed, but only to a depthof 2 ins., thus leaving all thicknesses even, for the main jacketing. This, also of aluminium, cast separately as atriad, is consequently even in all dimensions, and desirably thin. At the bottom it has inward flanges enclosing rubbergaskets, which make a water-tight joint with rings into which the cylinder tubes are screwed. But at the top it makes alarge and difficult flange-joint with the head-casting, secured with a great number o± little bolts. Some Points of Advanced Practice.One may therefore suggest that sinGe the cold water is pumped direct into the head jacketing from the rear end, Maybach fashion, and the two triads form a central waterjoint, in the Spyker-Maybach manner, the cylinder jackets might as well have been formed in singles, and had theirtops screwed into extensions of the head-casting, as the cylinders are. For they could have been just as well unitedfor continuous circulation below, with ring-unions, in the manner of the Benz cylinders.Even distribution of the cold water to all heads simul- taneously is secured by a thin slotted tubular formationrunning from the inlet directly forward through the mid-line of the head castings. One has seen this feature before, inthe Hall-Scott design, but it is no less effective. Otherwise it might be said that the water spaces around the twin exhaustvalves were a trifle scanty. Piping and jointing is freely eliminated, and the construc-tion given the neatest appearance, by embodying the induc- tion manifolds with the head castings ; each triad having itscarburettor suspended by a short trunk-piece. Here again one recognises gratefully a previous suggestion.The hollow overhead cam-shaft is enclosed, very neatly, in a long rectangular casing, oil-tight for free cam-shaft dis-tributed lubrication. Also very accessibly, the sides being freely panelled. The cams act direct on the spring plates ofthe exhaust valves—which have watch-type helical springs— but opposite the single inlet valves through short rockerspivoted in lugs from the top of the casing. This arrange- ment disencumbers the construction, and enables the valve-gear encasement to be brought at least 2 ins. lower than usual. And Some Suggestions. ..."•' ."--'? Thus so far conditions, wholly unaltered, favour a furtherpossible improvement. The bell-type hollow-stemmed valves are all three seated in bronze rings, pressed into the metalof the head castings. If the factors of expansion under heat be equal, as one assumes, all may be well. But there appearsto be such ample room for these ring seatings that it is clear that detachable box-seatings of the Maudslay or Green typewould have served far better. Then any valve and its seat- ing might have been lifted clear through the valve-gearcasing. As it is, the whole triad, cylinders and all, must be lifted : although the dog-claw or yoke attachments of thecylinders to the crank chamber facilitate such dismounting, the said yokes being mounted on the through-bolts thatapparently suspend the crank-shaft bearings from the top in the approved manner. : . - Minor Details. ' The relative timing of the inlet and exhaust valves—thefigures for which cannot obviously be given—promises that the fullest power indicated by the cylinder dimensions willbe developed. That this is likely to be considerable is also indicated from the exceptional dimensions of the crank shaft,which is lightened, nevertheless, by the freest hollowing ; that also serves for the main lubrication-conduit to all work-ing parts. A very dainty detail, on the other hand, is the way in which the otherwise free gudgeon-pins are kept frommoving endways by little rings of wire sprung into grooves in the piston-lugs. These cannot shift in work, yet a pull ofthe finger can dislodge them. With the main oil-pump driven below the water pump,and on the same spindle—all from the main bevel on the crank- shaft tail—the lubrication is apparently of the dry sump kindmost approved. Only, although located so low, one imagines it might go wholly dry in a long vol-plane. One may there-fore suggest that a tubular formation, cast lengthwise, keel- fashion, externally of the base chamber, yet with openings todraw from it in the middle and at the tront end, and non- return valves at these two points, would overcome such apossibility. This pump, however, apparently connects, though the union is absent, with a second smaller pump act-ing as a non-return valve, delivering into the open end of the crank-shaft. As a final detail of a really exemplary Britishaeromotor, dual ignition is fitted, from a Fellows magneto to all the plugs on the starboard side, and from a Remy coilto those on port; the distributor in the latter case being mounted on the tail-end of the cam-shaft. The air-starterdevice specified was not mounted. ;. Other Notable Exhibits. A^sinall, but no less interesting exhibit, was a single cylinder—evidently from a V-motor—of a Midland make that has done great war service. In this, one feature was the freepanelling of the water jacket, so much so as to afford the IO82
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