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Aviation History
1916
1916 - 0042.PDF
\fiML there is no means o( telling, but in all proba bility many months may be accounted for in this way. At all events it may be taken as certain that the design was that existing at a time subsequent to the commencement of the present hostilities. It is at any rate open to question, too, whether the practical performances of the Mercedes engines—excel lent as they certainly are—are yet superior to those obtainable from the engines with which our own military machines are fitted. A connecting rod of the Mercedes engine. — The perforated floattng sleeve shown rides between the small end and the gudgeon pin. "Flight" Copyright The two-piece piston of the Mercedes engine, the crown and bosses being one part, and the cylindrical wall the other. We have heard it said time after time that never by any chance does a Mercedes engine let a German aviator down inside our lines from failure in the air. This may be true, but, even if so, the reason may be that German pilots, either for their own protection or acting under orders, make about 12 miles their limit of flight over our lines. Under these circumstances it is easy for Mercedes-engined aeroplanes to be flown at such a height as to be at all times within gliding distance of their own lines, and this we think is—with very rare exceptions—the common practice adopted by their pilots. On the other hand, our own men take far greater risks, often penetrating very great distances behind the German lines, in new of which it is inevitable that sometimes an engine failure should occur that prevents our own lines being regained. If we are not altogether enamoured of the design, however, the workmanship and finish embodied in the Mercedes are, on the other hand, such as to excite admiration, for they are certainly of the very finest. Moreover, as we said on the occasion of our first notice of the engine referred to above, it is very evident that reliability almost to the exclusion of all else has been the object sought after. This is revealed by the " heftiness " of every internal working part j even in the reciprocating members little or no effort seems to have been made to cut down weight to an extent likely to influence reliability. On the contrary, it is clear the designers have, as we suggested above, been content to & ® The Light* of Paris. IN the House of Commons on January 6th, Sir William Byles addressed a question to the Home Secretary as to the lighting of Paris. Mr. Brace said he was authorised to reply that no information had reached him that the restrictions on lighting in Paris had been relaxed. JANUARY 13, 1916. limit revolutions, and by doing so take the advantage permitted to increase the factor of safety, the result being that the Mercedes—as it undoubtedly is—is an engine comparable with an ordinary car engine in the matter of infrequent need for attention and overhaul, long life, and unfailing service except for accident. It must not be thought from this, however, that the question of weight reduction has not received any con sideration whatever. On the contrary, it has evidently been carefully studied, although this is a fact that is not by any means obvious from the exterior. It is in respect to the parts that may be considered as the framework rather than the working parts of the engine that the endeavours in this direction have been directed, especially the crankcase and the cylinders, though nowhere has the achievement of the object been allowed to interfere with the rigidity of the engine as a whole,, and therefore with its smooth running potentialities. That the crankshaft, pistons, connecting rods, valve gear, bearings, &c, are of robust proportions will be confirmed by the figures we shall produce in due sequence. It is by careful and scientific disposition of the metal that the remarkable result obtained has been made possible in the case of the crank-chamber. The shell itself is extremely thin, but in spite of its length is made rigid, one might say absolutely rigid, by the manner in which it is braced. In the lower half there is a double bottom running nearly the whole length, the space enclosed by it forming the oil sump. A series of exterior longitudinal fins below the casting not only give stiffness but also serve as radiators for cooling the oil, and while making mention of this fact it may not be out of place to call attention to a further and more interesting dupli cation of duties that apparently arises in a similar connection, and that is the manner in which the air to the carburettor is.also made to cool the oil, and in doing so to become itself warmed as an aid to good carburation. To this end, the sump does not occupy the full length of the casting, but really forms two compartments in the double bottom, one in front and one in rear connected together by a large diameter tube. Around this tube and between the adjacent end walls of the two compartments, all the air to the carburettor has to pass, there being apertures cut in the side of the crankcase, that lead to the carburettor situated on the other side of the engine. From practical considerations, however, the last-named feature is certainly one that will not commend itself to the pilot, for it condemns him to serious risk from fire, since the transverse air passage forms a ready receptacle for the accumulation of petrol drippings and also for oil leaks. Should a backfire occur in the carburettor—a prevalent symptom when from any cause the fuel supply begins to fail—the vapour in the passage is liable to become ignited, and to set fire to the oil and not un likely to the machine itself. That this is a very real danger is evidenced by the fact that designs this side provide for the conduct of the incoming air to the carburettor from a place that is entirely exterior to the cockpit, or sump or housing, a point that is well marked for example in R.A.F. engine design. (To be continued?) ® ® More Aeroplanes from India. RECENT contributions to the Punjab aeroplane fund, which now exceeds ^35,000, includes £$,0°° each from the Nawab of Bahawalpur and the Nawab Malik Ata Mahomed Khan of Ala Bagh. The shareholders of the Bombay Cotton Trades Association have subscribed .£1,500 for an ambulance or an airplane. 42
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