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Aviation History
1941
1941 - 1949.PDF
AUGUST 28TH, 1941. FLIGHT POSSIBILITIES of JET PROPULSION :••. Engineers in Many Countries Grapple with fascinating Problem Some r >,,. :. . .»- Original Aircraft Designs and Layouts _ ? ,: " By G. GEOFFREY SMITH THE idea of an aeroplanebeing propelled throughthe air without the aid of an airscrew strikes one at first as fantastic. Yet scientists and engine designers the world over have been at work for years past in an endeavour to evolve a prime mover that will supersede the internal-combustion engine —airscrew combination as we know it—and at the same time achieve progress in directions where at present development work is temporarily checked. Internal combustion turbines and rocket propulsion have been much in the public eye in discussions of late years. Over the last thirty years, too, jet propulsion has been the subject of intense study, many patents and many experi- ments, not to say many disappointments. We have ex- amined the projects of inventors in Great Britain, Sweden, France Germany, Italy, U.S.A. and Switzerland, including material issued from time to time by R. T. P. of the Air Ministry. It is good to know that British engineers quite early began investigations into the possibilities of applying jet propulsion systems to aircraft. It seems clear from the advanced state of these designs and the progress revealed by the passage of time that we are on the eve of successful application of jet impulse reaction to modern aircraft. Jet reaction is probably the oldest method of converting heat into mechanical energy. It is the principle employed in the legendary eolipile of Hero; the hollow sphere rotated on an axle by the reaction of jets of steam issuing from tangential pipes. A wheeled carriage propelled by a fixed sphere with rearwardly-directed nozzles is well known for classroom demonstration. In what is. probably its simplest form of construction PRIME movers alternative to the engine-airscrew combination are the subject of intense study and experiment in various countries. Comparatively little is known of the progress with such aircraft units, but the accompanying article, with drawings by "Flight," indicates the line of development being followed by Germany and Italy in this new field of engineering. Other jet propulsion units will be reviewed :n succeeding articles. the plant comprises a turbo- compressor and a gas turbine on a common shaft. The compres- sor delivers air under pressure to a chamber into which fuel is in- jected. Pressure drop on re- expansion takes place in two stages : at the turbine and at the discharge nozzles. Of course, auxiliary equipment will be necessary for starting, fuel injection and lubrication. There are, however, a number of possible alternative arrangements. A reciprocating engine may be employed to drive the turbo-compressor. In this case one portion of the air delivered by the compressor is used to scavenge and charge the engine cylinders into which the fuel is injected. The other portion of the air cools the engine cylinders, thus absorbing heat, and is mixed with the engine exhaust in a final expansion chamber. Additional fuel could be injected into the final expansion chamber, although its use would be relatively inefficient owing to the lowered pressure. Such a system could possibly be of advantage in providing boost for take-off or for emergency power or speed in the air. A turbo- or centrifugal compressor is not an essential feature. A survey of patent specifications shows that schemes have been evolved utilising combined engines and compressors of reciprocating type. Some are of the air- cushioned, free-piston type having no crankshaft or con- necting rods. It has even been suggested to use the heat of the compressed air, to raise steam in a boiler, possibly with the assistance of a combustible fuel, for a steam turbine driving the compressor. This would scarcely seem to be a practical arrangement for aircraft propulsion, how- ever, as it would be necessary to carry a heavy load of A Campini design of high-altitude craft for operation at either sub- or super-sonic speeds. The control cabin is pressure charged.Weighing 8,8oolb., a Campini type was flown for 10 minutes on August 27, 1940, at the Forlanini Aerodrome, Milan
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