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Aviation History
1941
1941 - 2109.PDF
SEPTEMBER IITH, 194r. FLIGHT JET PROPULSION of AIRCRAFT PART II.—More Designs of Aircraft Units Employing Rotary and Reciprocating Compressors : The Work of British, Swedish and Swiss Engineers By G. GEOFFREY SMITHT HE discussion in Flight of August 28th of the possi- bilities of jet propulsion for aircraft and the foreign examples illustrated have served to draw attention to progress in an entirely new field of research. New, that is, to the vast majority of aircraft technicians whose whole attention would appear to have been concentrated upon the improvement of accepted types of aircraft. It is, indeed, strange that so revolutionary a technique as the propulsion of aircraft by the reaction of a high-velocity jet of gas from a nozzle should have come into prominence at this particular juncture and be engaging the atten- tion of the scientists and the Governments of many coun- tries. The immense im- provement in the efficiency of airscrews, which until comparatively recent times had tended to exercise a retarding influence upon engine development, the wonderful advancement in aero engines, with two-speed, two-stage or exhaust-turbo superchargers, would seem to have implied that the tech- nical excellence of aircraft propulsive units would admit of no challenge from a fundamentally different angle of development. Yet it is a natural process, with a parallel in other spheres. Consider wheels, for instance. From the crude wooden disc to the spoked type, later the wheel shod with an iron rim, and, finally, the beautifully de- veloped rubber-tyred carriage wheel. Then came the revo- lutionary pneumatic tyre, which allowed speeds to be raised enormously, and was developed, in its high-pressure form, to have reliability and long-wearing qualities until it secured universal adoption. A virtual perfection seemed to have been achieved when, like a bolt from the blue, the low-pressure balloon tyre appeared. This provided a degree of comfort that no previous form of spring suspension device had been able to attain. It literally marked a new motor- ing era, and rapidly superseded the high-pressure type. The introduction of the Parsons steam turbine is an example of the sudden appearance of a new system of pro- pulsion, which was destined to oust a form of power unit that had held unchallenged sway for,a very long period. Jet propulsion may or may not emulate the examples quoted in point of time, but what is clear is that the con- I'N a former article ("Flight," August 28th) the possibilities of jet propulsion for aircraft were discussed and progress in a new field of development revealed for the first time. Italian and German schemes were described and illustrated. In these notes the review is continued and examples shown of jet impulse reaction projects of British, Swedish and Swiss engineers. A furthei article on the subject will follow centrated attention of the world's research scientists and engineers has brought various jet reaction systems to such an advanced state that successful flight is well within the bounds of possibility. This apart from the brief flight reported to have been made in Italy last year by the Cam- pini machine illustrated in the first article of this series. It should here be interpolated that the jet propulsion *now under consideration has little relation to the applica- tion of the reaction principle as exemplified in rocket propulsion. Certain newspaper writers have confused the issue when taking up the discussion. The aims of both may, in general, be identical: high speed, high- altitude flight, rapid climb and elimination of many problems of stratosphere flying, by converting liabili- ties into assets. There is, however, a fundamental dif- ference. In rocket propul- sion the oxygen necessary for combustion is embodied in the explosive substance employed. For thermal-jet propulsion the oxygen required for the combustion of the fuel is taken in from the sur- rounding atmosphere. The Germans employ an omnibus title for the principle of jet propulsion: "' Heissluftstrahltriebwerke." The French term for jet propulsion units is " Thermopropul- seurs." At the Paris Salon in 1938 a French conception of the future aeroplane was exhibited in model form. It was r mid-wing monoplane with a highly streamlined fuselage inside which the propulsive organs were to be carried. Its ambitious specification included: Speed, 1,000 k.p.h. ; h.p., 14,000; ceiling, 30 km.; wing area, 16 m2 ; weight, 2,000 kg. As I intimated in former notes, British engineers have been in the forefront of progress with jet propulsion for aircraft, a number of patents having been granted during the last twenty years or so. The names most prominent in this field of development are H. S. Harris, as early as 1917, and F. Whittle. In the following notes we continue a review of the main features of promising jet-propulsion layouts, this time oi British, Swedish and Swiss origin. Attention is- particu- larly drawn to the Schurter scheme, in which the distribu- A projected twin-unit Milo installation for high-altitude taJprf « from each compressor aggregate air is foT .. ,° raise the Pressure in the cabin and also Provide heat. This supply is, of course, controlled from the cabin. The streamlined Milo unit is intended for wing installation. Allthe air compressed by the multi-stage blower is passed to the combustion chamber and, with added fuel, is expanded through themulti-stage gas turbine. The final conduit is a diminishing area to increase the velocity of the discharge.
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