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Aviation History
1919
1919 - 1398.PDF
opening 14, and is distributed to the different exhaust pipes as shown. The mixture of exhaust gases and water passes through two 5-in. pipes to the auxiliary exhaust tanks, placed just outside the chamber, as shown in Figs, i, 3 and n. Here the water is drained off while the gases pass to the exhauster. The Exhausting System The auxiliary exhaust tanks are both connected to a 6-in. main which leads to the centrifugal exhauster. Another 3-in. pipe is led from the main directly to the altitude chamber and serves to withdraw the air from the latter, thus main taining the barometric pressure on the exhaust and within the chamber approximately equal. By means of a valve communicating with the outside air, placed near the exhauster, the pressures maintained may be easily regulated irrespective of the speed of the pump. The exhauster is of the Nash " Hydroturbine " type, size No. 7, made by the Nash Engineering Co., South Norwalk, Conn., and has a rated capacity of 1,500 cub. ft. per min. at a 12-in. vacuum, at 300 r.p.m. (Fig. 11). It is belt- driven from a 75 h.p. direct current motor, and discharges to a point outside the building. The Dynamometer The connection from the engine to the dynamometer is made through the flexible coupling shown in Fig. 7. The electric dynamometer is mounted on a concrete foundation at the right of the alti tude chamber, as shown in Fig. 1. It was built by the Sprague Works of the General Electric Co., and has a rated capacity of 300 h.p., though it is capable of caring for considerable overloads. The dynamometer consists essentially of a direct current generator, the field ring of which is free to rotate with the armature, except as this rotation is opposed by a connection to a scale beam, which, therefore, measures the torque delivered to the machine. An auxiliary spring balance is also used, inter posed between the torque arm of the dynamo meter and the scale beam, which serves as a handy means for measuring the approxi mate torque. Current from the dynamometer is controlled from a switch-board placed near by. and may either be dissipated in grids placed outside the building, or may be returned to the regular power lines of the Bureau. The dynamometer with its scale beam is shown in Fig. 10. As the plant was originally laid out for the " Liberty " eight aeronautic engine, before the " Liberty 12 " was de cided upon, the 300 h.p. dynamometer selected for the purpose is not capable of carrying continuously the full power of the latter engine. Hence it was necessary to increase the capacity, which was done by the addition of a speciaiiy designed water brake. This brake consists of alternate fixed and rotating perforated steel plates. It is illustrated in Fig. 7. The rotor is mounted on the shaft of the electric dynamo meter, and the stator is mounted on the dynamometer field, so that the two always operate together; yet the water brake, when empty, does not interfere with the operation of the electric dynamometer. The water brake alone can absorb about 400 h.p. at 1,800 r.p.m. An unique feature of this brake, made possible by the fact that it is integral with the electric dynamometer, which cares for the adjustments of load, is that it can be operated Fig. 9 Engine in Chamber 14OO
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