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Aviation History
1918
1918 - 1061.PDF
SEPTEMBER 19, 1918. [• - 1* * IP a* I- i \x ^1 1 1*- ML n F 6 8 •50 fMROTTUE FOUI.OPBM " H rM«»TTue Aer «T - V isa CUBUDEU HOBSOH II —- —• wo AIR - CUB. Pr MRVBOCM A *-* II / 1 —• (SO 20O 2SO -MIH Fig. 39.—Diagram of comparative tests of carburettor. control interconnected, any required throttle curve could be obtained, but it makes an unnecessarily complicated instru- ment. In this particular carburettor there are four ball universal joints and two sliding blocks. (6) Power curves.—The power curves are satisfactory, the mixture being practically constant over a large air speed range. Resistance Test.—The resistance is very high compared with carburettors of ordinary design. For purposes of comparison, the resistance of the H.C.8 Claudel - Hobson carburettor is plotted on the same curve. The two carburet- tors are for engines of about the same horse-power, and it will be seen that the resistance of the Maybach is about nine times that of the Claudel-Hobson. Atomisation Test.— Deposit Air Air, °/o of tempera- cub. ft. Petrol, Deposit, petrol ture. min. pts./hr. cc./min. flow. Maybach .. 58°F 192 50 23 4.85 H.C.8 Claudel- 58°F. 195 51 32 6.62 Hobson The atomisation of the Maybach is rather better than the Claudel-Hobson, but this is obtained by a high depression and high loss •through the carburettor. Conclusion.—The carburettor seems satisfactory on throttle and power curves and atomisation, but the resistance is very high and the weight excessive. The throttle curve is obtained by a complicated mechanical system which would need careful first adjustment and constant adjustment for wear. The air is taken in through the moving parts, and if any dust is present ths mechanism is very liable to stick or to render the control very hard to operate. Petrol Supply System.—Petrol is supplied to the two car- burettors by a small double-acting duplex petrol pump, which is attached to the rear end of the bottom half of the oil base, and is driven at half engine speed directly off the rear end of the main oil pump spindle, the petrol pump driving shaft being coupled to the oil pump spindle by a dog clutch. The installation of the petrol pump is clearly shown in the general arrangement drawing of the engine, and the details of the petrol supply system are shown in the diagrammatic drawing (Fig. 27). Regarding the installation of the petrol supply system to the petrol pump in the machine, it is assumed that the main petrol tank is provided with the ordinary float regulator, which has always been fitted inside the petrol tanks for regulating the supply through the petrol pumps ; but owing to the fact that the machines from which these new Maybach engines were taken are complely destroyed no information regarding the construction and installation of the petrol tanks is available. In the Rumpler machines fitted with the 260 h.p. Mercedes engines two petrol tanks are fitted. The main tank is in the centre of the fuselage behind the pilot's seat, and the auxiliary tank is situated under the pilot's seat. Petrol Pump.—The design of the compound petrol pump is shown in the sectional drawing (Fig. 43) and also in the sectional perspective sketch (Fig. 42). The petrol pump consists of two opposed cylinders, in which a reciprocating plunger works, the ends of which operate as single acting pumps. The pump plunger carries a yoke fitted with a sliding bush, which forms the crank-pin Fig. 40.—Sectional arrangement of carburettor. bearing of the small pump crankshaft, driven, as already described, off the rear end of the oil pump spindle at half engine speed. The bore of the petrol pump plunger is 15 mm. and the stroke is 17 mm. The outer ends of the pump barrels are as shown, and are fitted with screwed plugs, which form compression chambers. The small non-return suction valves are situated directly above and below the two compression chambers, and the two petrol delivery valves are fitted above the compression chambers. The valves communicate with the compression chambers through small ports drilled in the pump barrel. Both the suction and delivery valves are of the poppet type. 1061
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