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Aviation History
1942
1942 - 1586.PDF
n6 FLIGHT JULY 30TH, 1942 STEAM IN THE AIR STEAM GENERATOR. A light steel casing enclosed the tubing in order to prevent hot gases in the combustion chamber from entering the air jacket, and the latter had an outer wall of thin sheet aluminium between which and the inner wall was a space of lour inches through which the air passed. This method of heat insu lation proved exceedingly effective and little heat was radiated to the atmosphere. In the ultimate design, it was accepted that a fuel pump would IK- included in the same housing with the water feed pump, and both pumps together with the fan blower would be driven by a tur bine mounted on the pump hous ing so that the plant as a whole would be self-contained. The boiler proved to be a very efficient and flexible steam generator. It was designed to evaporate 9,000 lb. of water per hour at 300 to 500 lb. pressure, and at a tem perature of 800 to 900 deg. F. It proved to be capable of evaporating much more water than this and to main tain an efficiency of 80 per cent, under these full load conditions. On one test with a throttle pressure of 325 lb. gauge and a throttle temperature of 772 deg. F., burning 1.2 lb. of oil per sq. ft. of heating surface, it evaporated 9,450 lb. of water per hour, with an 80 per cent, efficiency. The capacity of the water pump was reached at this flow and this prevented ascertaining the maximum capacity for evaporation of the boiler. Unusual Control System A type of throttle»was adopted which was so arranged that whatever might be the rate of steam produced up to full capacity, the throttle allowed its outflow to the engine but at the same time maintained the predetermined pres sure within the generator. Manual regulation was fur nished to permit control of the amount of fuel and water at will. In other words, manual control was to be only over what was going into the system, instead of what was coming out of it. This system not only insured a constant CYLINDERS A steam power plant for aircraft designed by Besler. steam pressure under all rates o[ steaming, but also dispensed with the necessity of a blow-off safety valve. For the tests kerosene was used as a fuel and there is, of course, a wide difference, as the American re port pointed out, between the use of a volatile fuel and that of a fuel which has to be sprayed under pressure and to which air must be » supplied under forced draught from a blower. As a result of experiments, a generator was developed from which it was estimated that the finished weight of the generator, including pumps, fans and all other auxiliaries, could be reduced below 2,000 lb., which would give a generator weight of less than 2 lb./h.p. It was felt that a generator had been de**"*|P veloped with high thermal efficiency as compared with other boilers, which could, if further developed, have a capacity for producing steam at any desired rate of super heat and which had large steaming capacity per unit of weight and space occupied, adequate steadiness of steam ing rate under fixed conditions, and adequate heat insula tion without the use of fire brick or refractory lining. It was safe from disastrous explosions without the use of a blow-off safety valve; it gave excellent automatic distri bution of water through the heating coils, thus preventing overheating of any coil; it had an efficient automatic throttle system maintaining constant pressure without regard to sudden changes in the demand for steam with the engine ; and it had an efficient and easy method of controlling manually the rate of combustion and corre sponding water supply. It was also capable of raising steam quickly from cold water, and would be free from scaling or cracking. Some Positive Results The investigators felt that there had not been developed adequate control of steam temperature upon sudden manual changes in the steaming rate, nor was the problem of outside rusting of steel tubing solved. With special reference to aircraft propulsion, the generator had a number of favourable points:— 1. 2. 3- The steam aircraft engine of the Great Lakes Aircraft Corp. : (I) Turbine, (a) Valves, [s) Condenser, (4) Gearing, (5] Air Scoop, (6) Ejector, (7) Biower,-(8) Steam Collector, (9) Feed Water, (10) Steam Generator, (ti) Fuel Supply, (12) Collector. Reliability and probably durability as compared with internal combustion engines. The use of fuel oil in place of gasoline. Adaptability for large powers without increase in complexity and with reduced weight per unit of power. 4. Retention of or possible increase in efficiency at high altitudes. 5. Ease of operation and control. The anticipated fuel consumption was also about twice that of a corresponding Otto-cycle engine. Tests showed a reduction in consumption to approximately 250gr. h.p. /hr. but such reduction in specific fuel consumption was con sidered to involve substantial and almost impossible difficulties. Besler's Steam Power Plant (U.S.A.). Besler fitted his steam power plant to the "Standard Travelair" biplane 2,000 in Emeryville, Cal. The pro pelling machinery consisted of a two-cylinder compound V-type steam engine of 90 h.p. The steam generator was a coil-tube boiler fired by oil fuel. The feed water was delivered at one end of the coil by a high-pressure pump., and left the other end in the form of superheated steam. The steam left the boiler with 77 atm. pressure at fr
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