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Aviation History
1942
1942 - 0516.PDF
204 FLIGHT MARCH 5TH, 1942 i TWO-SPEED BLOWER DRIVES uoo ing member to point (K) in the driven member, pushing oil at point (L) in the driven member back into the driving member at point (M), and continues to circulate about the core (N) from one member to the other. While in the driving runner the oil picks up considerable angular momen tum. This energy is transferred to the driven member by the impact of the oil on the vanes of the fluid cells. The slip of this coupling, for any given load and engine speed, is deter mined by the quantity and tempera ture of the oil in the coupling: Two pumps supply oil to the coupling. Pump (F) operates at full capacity at all times. At rated power and speed the coupling will drive the impeller at a ratio of about 7.3 :1 with oil from this pump only. For higher ratios additional oil is supplied by the second pump (Q). A balanced plunger valve (R), actuated by an aneroid capsule [S), regulates this flow ; allowing the full capacity of the pump to enter the coupling for the maximum ratio of 10.2: 1 for operation at high altitude, and diminishing.it for lower ratios, to zero at 7.3:1, for operation at low altitudes. A jet (H) allows the oil to flow out of the coupling con tinuously, permitting the oil level, and hence the ratio, to be controlled 'by regulation of the rate of the oil flow into DRAIN TO SUMP S3 se '25 0 20 15 z _^, ./NOIL f PRESSURE 1. 1 | I "'X0IL jFLOVv 1 IQD00 ALTITUDE IN FEET 14,000 10.000 4.000 aooo 12.000 • 16.000 2.000 6.000 IQ0O0 14,000 ALTITUDE IN FEET Fig. 12.—The Mercedes-Benz variable-speed supercharger drive utilises a fluid coupling in the supercharger impeller shaft. Fig. 13.—Characteristics of Mercedes-Benz hydraulic coupling. The full lines show characteristics at 2,400 engine r.p.m. and the dotted lines the performance at take off, or 2,500 engine r.p.m. the coupling. Another important function- of this flow is to cool the coupling. Probably the greatest disadvantage of this drive is the large amount of heat wasted in the churning of the oil in the coupling. At "take-off" power the heat rejection to the oil approaches 1,000 B.T U. per minute. As the slip decreases with altitude, the heat rejection diminishes rapidly to a negligible value. This would not be serious in a pursuit plane installation, as the ship would usually take-off'' with a cold engine and rapidly climb to an altitude requiring operation in the high ratio, minimum slip, condition. However, the performance of a transport or patrol plane, flying at altitudes of 5,000ft. or less, might be seriously affected by an oil-cooler installation of sufficient capacity *or an engine with this type of drive. Conclusions The DB-601 design has stimulated interest in this country in the fluid coupling. A great many studies will be made of it, and it is possible that it will be adapted to our requirements. Certainly, we have benefited greatly by a knowledge of its design. With the exception of the Mercedes-Benz fluid drive, the construction of the European two-speed drives appears to be heavier than most American drives. A conspicuous example is the use of thick riveted friction faces on the clutch discs instead of the cemented facing used in this v-v country. The moderate altitude performance of the two-speed single-stage engine is not impressive compared with the performance required for this war. Greater emphasis is now placed on modifications of two-speed drives adapting them for use with two-stage geared superchargers with mtercoolers. An increasing number of installations with the now firmly established exhaust gas-driven turbo supercharger will also tend to decrease the interest in two- speed superchargers. MARCH NUMBER OF "AIRCRAFT PRODUCTION" OEVERAL articles of special interest to the industry are w-' contained in the March issue of our associated journal, Aircraft Production, which is now on sale. There is, for example, a particularly helpful article on diamond tools—the first of a series of two, written by an authority on the subject. Very little information on cut ting angles and the choice of tool has hitherto been avail able for publication. Andther article in the same special ised category deals with coolant and washing systems— an important matter in view of the high qualitv of surface finish demanded by the aircraft industry, while the second , instalment of the article on the manufacture of the Bristol^ Hercules engine covers such aspects as the production of the master connecting-rod, airscrew shaft, cvlinder head, and the sleeve ball and its housing. Yet another article of outstanding interest is compiled from notes from the journal, Luftivissen, on German spot- welding equipment.
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