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Aviation History
1918
1918 - 1060.PDF
SEPTEMBER 19, 1918. A, which is also connected to the main petrol tank by a pipe, G, leading to a hand petrol pump, or may be plugged and not used, as was the case in the Rumpler biplane. The main and pilot jets consist of two holes drilled in the top cover of the lower reservoir D, and are similar in principle to the White and Poppe jets. The area of the jet openings is mechanically controlled by means of a small hole drilled eccentrically in the jet cap H, which, as previously described, is connected by levers to the throttle and air control levers. The function of the top tank A is apparently to deal with the large excess of petrol delivered by the petrol pump at Pig. 37.—An ingenious steel band joint clip, used on the rubber connections of induction pipes and water joints. high speeds, whilst the lower tank, which is gravity fed, provides a constant petrol level for the jets. The mixture strength at any point on the throttle curve is governed by purely mechanical means, there being no venturi or special jet arrangement. The jet depression is obtained by restricting the air flow at what approximates to a sharp- edged orifice, consequently the loss through the carburettor is very high compared with a carburettor using a venturi tube to get the jet depression. Contrary to usual practice, the jet depression actually increases on throttling down, the depression being about four times as great at half-throttle as at full throttle. Control adjustment.—When running-slowly, the throttle is slightly open, the supplementary air port closed, and the air shutter practically closed. In this position the small . or pilot jet only is open. On opening the throttle the supple- mentary air port commences to open in conjunction with the throttle opening. The main air shutter automatically opens in proportion, admitting more air, which passes directly across the top of the jets, and the jet area increases until the main jet orifice is fully open. Owing to the inter-connection of the control levers there comes a point when the supplementary air port area increases out of all proportion to the increase in the jet area, the latter reaching a limit with no further increase by reason of the arrangement of the levers. This point represents the opening for maximum power at ground level. If the throttle is opened beyond this point, the air supply rapidly becomes out of proportion to"*he jet opening and petrol supply. By this arrangement a simple form of altitude control is pro- vided. The various positions for " slow running," " slow speed," " full speed " and " altitude," are marked on the body of the carburettor, and are indicated by a pointer attached to the throttle lever of the rear end carburettor. By means of these markings on the carburettor the correct settings of the throttle lever can be checked when the engine is installed in the machine. The translation of these markings on the carburettor is as follows:— LE — Leer =• running light. V =Voll =full speed. LA — Langsam —slow speed. H =Hohe "-Altitude. The induction pipes are aluminium castings, and are oi exceptionally neat design, being, as shown in Fig. 36, joined together in one straight pipe. A cast aluminium baffle plate drilled in the centre with a 20-mm. hole is provided in the centre of the two induction pipes between the front and rear three cylinders. This baffle is evidently fitted to equalise the gas supply to all cylinders. The design of this equalising baffle is shown in the per- spective sketch Fig. 36, which also shows the method of joining the ends of the induction pipes by rubber connections- and band clips. Details of the six small primer valves fitted into the top of the induction pipe are shown in the sketch. Fig. 37 clearly shows the construction of the interesting type of band clip which is used for making the connections in the induction pipes, and also for most of the water joints on these engines. These clips are now extensively used on all enemy engines. The method of using these clips is herewith reprinted from; the previous report on the 230 h.p. Benz engine. The clips are made of thin strips of annealed spring steel; these are wound twice round the rubber rings and fastened by small steel links and bolts. In starting to make this joint, the end of the steel band is first bent over the bottom bar of the connecting link, and then wound twice round the rubber ring, the free end of the steel band passing through the centre portion of the connecting link on the second winding. The end of the steel band is then fastened to the top end of the link by coiling the end several time* round the small bolt in the head of the link, the end of the*- steel band being bent over for about 2 mm., and inserted into a slot cut in the bolt, so that by turning the bolt in the link the steel band is wound tightly round the ring joints, and, owing to the position and shape of the link, remains- fixed. Carburettor tests.—The Maybach carburettor has been tested separately at R.A.E. The result of these tests is shown graphically in the power and throttle curves (Fig. 41), together with a throttle curve diagram in comparison with • the H.C.8 Claudel-Hobson carburettor (Fig. 39). Characteristic curves.—(a) Throttle curve.—The throttle Fig. 38.—The throttle and jets dismantled ; air- shutter, and sectional views of petrol reservoirs in carburettors. - •_- . curve appears good. There is an excess of petrol at first which should give good acceleration, and there is a fair range,, down from full throttle, of weak mixture suitable for cruising. Obviously, if it is considered desirable to have petrol and air 1060 ; . u v
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