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Aviation History
1942
1942 - 0813.PDF
APRIL I6TH, 1942 FLIGHT 369 MERCEDES-BENZ D.B.601 N (Left) The cylinder block is secured to the crankcase by a geared locking ring on each cylinder liner. (Below) Section of the fuel injector fitted to each cylin der. A 3 mm. bore pipe feeds fuel into the labyrinth filter, from whence the fuel passes a non return valve to the nozzle provided with six small jets. The lagging is em ployed to prevent vaporization of the fuel by local heat. LAGGING GEARED LOCKING RING LABYRINTH FILTER genious mechanism allows for increased boost and power for take-off for the duratioruof one minute. When opening up, the pilot gives an increased movement to his throttle lever, which also operates a clockwork gear in the control mechanism. This clockwork device keeps the throttle at its extra opening until a small slipstream-operated wind mill retards the opening at the end of a minute, and the engine then returns to its normal full-throttle power. There is also another mechanism on the engine, interconnected with the throttle and the oil-pressure system, by which the spark plugs are cleaned by temporary advancement of the ignition when the engine has been started up from cold ,.^p\Jjen the plugs tend to oil up), retardation of ignition to normal being restored shortly afterwards. Engine Auxiliaries At the rear of the engine, and driven by gears from the crankshaft, are the gun-interrupter mechanisms (for Me log), Bosch dual magneto, and electric generator. Electric or hand starters can be bolted to the casing at the rear end of the crankcase below the magneto and driven direct through a dog coupling to the crankshaft. Below the cannon mounting are located the throttle mechanism and main oil filter and fuel pumps, and all external fuel and oil pipes are wire wound and flexible, with banjo connection fittings. The twin delivery centrifugal coolant pump and main oil-pressure pumps are located between the cylinder blocks and in front of the main oil filter. Net dry weight is 1,400 lb., but with all accessories, coolant header tank, piping and airscrew control gear, etc., (Above) The Bosch twelve - plunger injection pump and a few of its parts. The camshaft with twelve cams for operating the plungers is of special interest. the weight is 1,540 lb. Thus, at 1,270 maxi mum b.h.p. at 2,600 r.p.m., a figure of 1.20 lb./h.p. is obtained. A feature of German design is quick inter- changeability. The D.B. engine designed for rapid detachment and replacement in the air craft is complete with auxiliaries. It has electron cantilever bearers of sturdy section supported by four rubber-metal reinforced mountings—two high up at the forward end of the crankcase and two at a lower position at the rear. Garburation Features In comparing the major features of the Merlin, Allison and Daimler-Benz, it is interesting to note that the three engines have entirely different systems of introducing air and fuel into the cylinders. Whereas carburettors of nor mal design are fitted to the Merlin, and air-fuel mixture passes as a homogeneous stream through the supercharger, the Allison has a triple venturi carburettor which passes air only to a point in the supercharger intake elbow where it meets a metered flow of fuel issuing from a single jet and supplied under pressure from the fuel pump in the engine, the jet supplying fuel for the 12 cylinders. In the case of the D.B., air only is conveyed direct to the com bustion chambers, where it meets the fuel sprayed from the injector nozzles just before the ignition point. A short curved intake on the port side of the engine cowling conducts air through a wire mesh grid to the supercharger impellor. V.D.M. propellers are used, the motor with its pitch- limit control and filter unit being carried on a bracket sup ported by the engine crankcase. As the controlling energy is separate from the engine, the airscrew can be feathered with "the engine stopped. The blades are interchangeable, and a blade can be removed for inspection and replaced in about 20 minutes. The total weight of the airscrew is 304 lb., including the motor bracket and wiring. LIQUID-COOLED IN-LINE ENGINES . ;"" Merlin XX Allison C.15 Mercedes-Benz D.B.601 N Bore Inches 5.4 5.5 5.9 Stroke Inches 6.0 6.0 6.29 Capacity Litres 27.0 28.1 33.9 Comp. Ratio - 6:1 6.66 : 1 7.9 :1 Horse-power 1,175 at 2.850 r.p.m. at 17,500ft. 1,240 at 2,850 r.p.m. at 10,000ft. 1,090 at 3,000 r.p.m. at ' 13.200ft. 1,270 at 2,600 r.p.m. at 16.2:50ft. Weight Lb. 1.450 1.340 1.540 Lb. per h.p. 1.13 1.23 1.20 Companion articles in this series of descrip tions of prominent aircraft engines of the war appeared in the following issues :— BRISTOL HERCULES— November 27th, 1941. ROLLS-ROYCE MERLIN XX- February 26th, 1942. ALLISON—March 26th, 1942.
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