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Aviation History
1919
1919 - 1396.PDF
THE ALTITUDE LABORATORY FOR THE TESTING OF AIRCRAFT ENGINES BY H. C. DICKINSON AND H. G. BOUTELL (Concluded from page 1380) The Air Cooling Systems THE air cooling system may be divided into three parts— the refrigerating plant, the cooling system for the carburettor air, and the cooling system for the interior of the altitude chamber. The refrigerating plant is installed in the left hand portion of the building, as seen in Figs. 1 and 11. The ammonia compressor is a 9 by 9 in., double cylinder, vertical, enclosed machine, with a refrigerating capacity of 25 tons in 24 hours, and was built by the York Manufacturing Co., York, Pa. It is belt-driven from a 50 h.p. electric motor. The plant operates on the direct-expansion system, the ammonia condenser being placed against the outside of the west wall of the building, with the ammonia receiver along the north wall, back of the compressor. The cooling system for the carburettor air consists of a bank of ammonia coils mounted on top of the altitude chamber. The coils are made up of 2,000 ft. of ij-in. pipe, enclosed in a box and insulated with 4 ins. of sawdust. The air is made to pass through this box in a tortuous path, and is then led through an insulated pipe provided with a set of electric heating grids and a regulating valve to the test- chamber through opening 18. From this inlet it passes through the air meter to the carburettor. In this way warm or cold air may be supplied to the intake as required. The system for cooling the air within the chamber is made up of a bank of 800 ft. of 1 J-in. ammonia coils, placed in the left hand portion of the altitude chamber, as shown in Figs. 1 and 3. Four motor-driven fans are provided to force the air over these coils, while another fan is installed to circulate the air past the engine itself when desired. By means of the refrigerating plant and cooling system just described, it is possible to reduce the temperature of the air admitted to the carburettor and that within the test- chamber to a point approximating the temperature at any altitude up to about 30,000 to 40,000 ft., depending upon the size of the engine. Owing to the fact that the temperature cannot be readily controlled by means of the refrigerating plant, the air, after cooling and before admission to the carburettor, is passed over a series of electric grids, by means of which the temperature may be again raised and kept at any desired point. The current flowing through these grids is controlled by conveniently placed switches. Some diffi culty has been experienced due to the condensation of moisture which occasionally causes a " snow storm " in the air passage to the carburettor. It is hoped that this difficulty will be entirely overcome in the new laboratory, through the elimina tion of leaks into the refrigerating chamber and the use of what may be termed a " settling chamber," through which the air will pass after being cooled, and in which the air flow will be so sluggish that the snow will be deposited. The Jacket Circulating Water Cooling System The jacket water cooling system is arranged as follows :— Above the altitude chamber is placed a cylindrical iron tank connected to the inlet and outlet pipes of the engine's cir culating system, and with another pipe from the city mains, while an overflow leads to the sewer. A thermostat is placed within the tank, the brass rod of this device controlling a pilot valve which admits or discharges city water from a bellows, which in turn, controls the main valve on the city supply pipe. In case the temperature of the water in the tank rises above a certain point, the expansion of the thermo stat rod causes the pilot valve to open, admitting water to the bellows, and thus allowing cold water from the city supply mains to flow into the tank. When the temperature has again fallen, the contraction of the thermostat rod closes the pilot valve and allows the water to escape slowly from the bellows. Two-coil springs then close the main valve, cutting off the supply. The thermostat is mounted in the fitting through which the water enters the tank from the engine jackets, and also from the city mains. It is, therefore, very sensitive to slight changes in temperature; a very important matter in a laboratory of this sort, since even a comparatively slight variation in the temperature of the circulating water affects the heat distribution in the entire engine. In practice it has been found possible to hold the temperature of the jacket water to a variation of about 50 C. The Exhaust Cooling System The exhaust cooling system is shown diagrammatically in Figs. 3 and 5. The exhaust pipes connected to the engine are water-jacketed, the inner pipe extending down about 3 ft. from the exhaust port, while the outer pipe or jacket is continued from the exhaust port to the main exhaust manifold in the form of a flexible tube. In this way the whole con nection is flexible. This arrangement is clearly shown in Fig. 9. The water from the annular space mixes with the exhaust gases only at a point a considerable distance from the engine. The water enters the altitude chamber through FIG, 5. "ntOntin « — i WMLttr Ifcnfc Water mum and le d><tphr*ff> oi-V cff**W length of hard r*»b&«r «-«4 lot r***wr* R«3>>i *.t«» m Fi>m «nf mm t I f I UhMftT T« 4mmtm&.1 V 'To wafer Awpplg *f X *—V«ntuM ,4-VaUt To k>«m >S» (rttn.* iwit bL FV»m UlMMtr «398
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