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Aviation History
1941
1941 - 1965.PDF
FLIGHT, August 28th, 1941. ALTITUDE EQUIPMENT into tiny bubbles in the blood-vessels, bringing on the discomfort of aeroembolism. First used some years ago in developing equipment for the Boeing 307 Stratoliner, the strato-chamber can reproduce flight conditions at altitudes up to 40,000ft., and can accommodate three trainees and their equipment at one time. Vacuum pumps reduce the inside pressure to the equivalent of any desired altitude. Observers outside can watch the progress of the flight through thick windows and communicate with those inside by telephone. Once denitrogenised, and wearing complete flying equip- ment to become used to the encumbrances, trainees enter the chamber, which has complete oxygen equip- ment installed. The door is sealed tight, pumps start, and the flyers "ascend" to 35,000ft. The Turbo-Supercharger Like most other devices in aeronautics, the exhaust- driven turbo-supercharger is not new, for in 1920 Major R. W. Schroeder flew a biplane so equipped to an altitude of 33,000ft. in U.S.A. This turbo-supercharger had been developed by Dr. Sanford A. Moss, and was successfully tested in September, 1918, on the 14,000ft. summit of Pike's Peak. Mr. E. H. Sherbondy was also another American worker in this field of research and development, and some success was obtained with these superchargers fitted to Liberty engines. Prof. Rateau, in Paris, was simultaneously at work, for the whole scientific world knew of the advantages of the exhaust-driven supercharger—but the trouble was to make it work—at about 700 deg. C.! Now, thanks largely to metallurgical advances, trie turbo-supercharger is in production and is fitted to the Wright Cyclones of the Boeing Fortresses. Fittingly, Dr. Moss is still connected with its development as consulting engineer for the General Electric Company. Retiring from the company in 1938 after 36 years of work, he has now returned at the age of 68 to continue his research. These three denitrogenised trainees are in the chamber.They practise handling their masks, parachutes and other equipment as they " ascend.'' Suction pumps can reducethe pressure to less than one-quarter of that at sea level and solid carbon dioxide is used in the cooling system tolower the temperature to minus 50 or 60 deg. C. DIAGRAM OF EXHAUST-DRIVEN SUPERCHARGER.A, exhaust gases from engine to turbine ; B, exhaust valve ; C, intake valve ; D, carburettor ; E, air cooler ; F, compressed air on way to carburettor. It is the desire for military aircraft which can operate at higher and ever higher altitudes that has forced the development of this type of supercharger for, as altitude increases, so does the advantage of the exhaust super- charger over the gear-driven increase. Though it is not possible to draw hard-and-fast dividing lines between the respective fields of the various types, it seems that for engines with rated altitudes up to about 15,000ft., the gear-driven two-speed supercharger is best because of its installation simplicity. Above a rated altitude of 25,000ft. the exhaust supercharger has no competitor, while between these heights the gear-driven two-stage type with an inter- cooler fights it out with the exhaust type. If it were possible to make an infinitely variable gear box, the usefulness of the gear-driven type would probably be raised. Its inefficiency lies in the fact that, if it is designed to give maximum unthrottled power at a high altitude, then the manifold pressure which it delivers to the engine at sea level if unthrottled would be so great that the engine could not '' take it'' and would at least detonate or might even crack the cylinder head by exces- sive explosion pressure. So at sea level, throttling is necessary and this means loss of power.
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