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Aviation History
1955
1955 - 0817.PDF
FLIGHT, \Ojime 1955 AIR COOLED MACHINE •—OIL COOLED MACHINE The size reduction ob- tained by using oil cooling is typified by the diagram; at tar right is a schematic diagram of the oil-flow. ENGINEERING DATA ON NEW J & Nominal rating VoltsSpeed (r.p.m.) PhaseFrequency (c.p.s.) . Power factorWeight (pounds) Moment (Ib-in) Length (inches) Diameter (inches) . G51-2 2,500 W S12,000 Ss s30 165 13.0 4.5 G52 9,500 W S 12,000 SS S 70 400 15.0 7.75 H OIL-COOLED GENERATORS G129 100amp 288,000 D.C.S S35 145 10.84 6.5 G190 40 kVA 120/2086,000 3400 0.75 165* 2,250' 27.25' 13.0» G192 20 kVA 120/2088,000 3400 0.75 100' 1,100* 26.0' 9.0* G280 15 kVA 120/20812,000 3400 0.75 50 225 13.25 7.19 MOUNTING-.FLANGE • LIQUIO . INLET ' LIQUID OUTLET r i ii i L ALTERNATOR STATOR ALTERNATOR FIELD EXCITER STATOR -ROTOR ' EXCITER ARMATURE i , 815 OIL-COOLED GENERATORS . . . greatly to reduce hot spots and thermal gradients which, in turn,minimizes numerous problems which previously reduced genera- tor life and reliability. One of the most serious component problems used to be thefailure of bearings. The trend towards the use of only one bear- ing in liquid-cooled machines greatly simplifies the control ofbearing operating conditions. Another advantage is that grease- lubricated bearings can be replaced by more efficient oil lubrica-tion, a modification which is simplified because oil is already circulating through the machine. It is a significant fact that Jack and Heintz foresee the possibilityof establishing a standard generator for each required rating, the service limits of these machines then being governed by modifica-tion to the heat exchanger with which it is associated. Thus, an oil-cooled generator can serve as wide a range of environmentsas the efficiency of the heat exchanger and bulk flow of oil will permit. Generator design, therefore, becomes important only inthe light of electrical requirements. Summing up in the light of present knowledge, the followingconclusions can be drawn. For flight at low altitudes and low airspeeds there is no objection to the use of blast-cooled electricmachinery. For high altitudes and short periods at high speeds blast-coolingis still practicable, provided flight and load cycles are checked against evaluation charts to pick the proper machine. Liquid-cooled machines should certainly be considered whenever inlet- air temperature may exceed 120 deg C at sea-level. For a widerange of supersonic speeds at high altitudes, oil-cooled machines are essential. Here the capacity of the heat-sink must be deter-mined to establish the liquid temperature level that can be main- tained. Together with knowledge of the liquid employed, thiswill determine the operating limits of the machine. At the extremely high flight speeds and altitudes now beingencountered by missiles, thermal lag or vapour-cooled machines may be required. At present, the former type of machine is suit-able only for applications involving short duration. By far the greatest promise for extreme service and long operating periodsare the J. and H. vapour-cooled units already being extensively used in various missiles. There are two such machines in pilotproduction—the G75 (illustrated) and the G188, operating at 12,000 r.p.m. and rated at 12 and 30 kVA respectively.A vapour-cooled machine operates in the following manner. Coolant, usually water, is injected under pressure into the hollowshaft of the generator. The water is flung centrifugally from four ports and scatters as a fine spray over the interior of the machine.As it picks up heat, the water vapourises and escapes through an exhaust port as steam. These vapour-cooled machines areas near environment-free as any yet developed. They appear to be practical for aircraft as soon as the question of coolant require-ments is resolved. The G188 machine uses approximately 9 lb of water per hour at full load. G52 oil-cooled 9.5 kW generator. G280 oil-cooled 15 kVA alternator. G51-1 oil-cooled 2.5 kW generator. * Includes constant-speed drive. S requirements. ^Special characteristics to meet customer G75 vapour - cooled alternator tor mis- siles, delivering 12 kVA at 120 V (0.8 power factor, 3- phase, 400 c.p.s.) at 12,000 r.p.m.
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