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Aviation History
1942
1942 - 0390.PDF
15-1 FLIGHT FEBRUARY IOTH, 194: MORE ABOUT JET PROPULSION Diagram showing the method of regu lating the propulsive jet and the possible arrangement for swivelling the discharge nozzle to assist manoeuvring. tests at the Guidonia .Research Laboratory. Doubtless the flight had been well publicised in advance, but* as the ex perimental Caproni monoplane passed over cities en route, interest was par ticularly aroused by the unusual char acter of the noise created by the machine. This %vould be largely ex plained by the absence of the usual airscrew whirr. When, as Flight has already re corded, the Campini machine was first flown ill 1940 at the Forlanini airdrome and remained in the air ten minutes, Italian engineers were jubilant at the demonstration of their technical suc cess. This was understandable in view of the experiments known to be pro ceeding in several countries. It was at once proclaimed to the world that this successful flight was the prelude to a revolution in the design of power units and aircraft. Differences in Layout From a close examination of new views of the Caproni-Campini air craft, the first illustration of which appeared in Flight of December 4th, 1941, it is clear that the only opening for the admission of air is a circular duct in the nose, and the only dis charge nozzle is in the tail of the fuse lage. Thus the scheme departs mate rially from the original layout which had a pressure cabin in the nose and admitted air via a peripheral duct at the point of maximum pressure on the fuselage. This feature and the method of ad justing the peripheral duct to meet conditions at sub-sonic and super-sonic speeds may be seen in the line drawing in the issue referred to. Recent pictures of the new design would ap parently confirm that Campini's orig inal suggestion of controlling the characteristics of the jet by means of a longitudinally adjustable, double- conical member mounted coaxially in the discharge nozzle, has been re tained. The diagram shows the general prin ciples of this device. As the conical member, under the control of the pilot, is adjusted axially, the cross- sectional area of the nozzle aperture is Varied in much the same manner as a tapered needle may be employed to alter the effective area of a carburettor jet. Although there is no specific in formation available on this point, it would also seem possible by means of this device to adjust the discharge nozzle to either a convergent or a divergent contour. If this is actually so it would become possible in some degree to regulate the terminal pres sure of the jet and also the terminal velocity. The point of the conical member will be seen actually project ing beyond the discharge orifice in the side elevation of the machine. The original design proposed the use of a universally swivelling discharge nozzle in order to impart direction to the jet, as also shown in the diagram. Externally there is no evidence of this being employed on ths latest design, which is provided with the conven tional elevators and rudder. How ever, within the not inconsiderable girth of the tail end of the fuselage it is conceivable that the swivelling mechanism is completely enclosed by the external skin. At present-day speeds in flight it is doubtful if facility to give direction to the jet is a feature ot importance, but probably it would be of assistance in manoeuvring the machine on the ground. It must be remembered that there is no airscrew slipstream for the rudder on a jet-pro-, pelled machine of this type. In referring to the girth of the fuse lage it would seem that the cross-sec tional dimension would be at least 6ft. diameter, as the engine, which is pre sumed to be a radial type, is approxi mately 4ft. in diameter. In general, the fuselage is of rocket shape and the structure, and also that of the wings and tail planes, is of duralumin. -Wing roots appear to be unusually gener ously proportioned. This may be accounted for by the need for all struc tural attachments to be arranged ex ternally in order to leave the interior of the fuselage unobstructed for the main air duct.* The same reasoning may provide an explanation for the peculiar bulge be low the fuselage from which the tail wheel is supported. Furthermore, this necessity to keep the interior of the fuselage clear may have been the dominant factor leading to the adop tion of the unusually low position of the main wing. It will be seen from the illustrations that the wing passes completely below the fuselage and it is possible that the centre section is utilised to house the main fuel tanks. A New German Design In the meantime some details have reached .us of a further German scheme of jet propulsion, sponsored this time by none other than the firm of Ernst Heinkel. The designer Herr Max Hahn, of Seestadt P.ostock, has A self-contained, all-rotary jet propul-' sion unit recently patented by the German firm of Ernst Heinkel. evolved what appears to be a simple and compact unit embodying a tur bine and compressor in combination. The main feature of the design will be appreciated from the diagram. In a circular casing having an axial air intake at the front and coaxial dis charge orifice at the rear, a shaft is mounted in two bearings supported on spiders. On this shaft is a single rotor which is divided to form a box-type blower impeller A and a boxed turbine wheel B. Air drawn into the unit through the forward central aperture leaves the impeller at its periphery and the stream is here divided by a projecting guide C on the enshroud ing wall of the annular combustion chamber D. The main supply is diverted to the rear to the turbine wheel, whilst a smaller portion passes along passage E between the main casing and the com bustion chamber wall. At the point of smallest diameter, surrounding the intake aperture, this portion of the airstream is again divided. Part enters chamber D into which fuel is injected by nozzles F and burnt to furnish ad ditional heat for the final jet. The remainder continues around the com bustion chamber in space G and joins the initial airstream and the effluent from the combustion chamber to form a common stream which expands through the turbine and furnishes the motive power for rotating the blower. The annular discharge from the tur bine wheel is a high velocity, rear- wardly directed jet, the reaction of which furnishes the propulsive effort. By passing a portion of the air stream completely round the combus tion chamber this is effectively insu lated and heat from the chamber is not completely lost by radiation to the atmosphere but is largelv carried off by the air to perform useful work i_K expansion through the turbine. Previous articles on jet propulsion hare appeared in issues of "Flight" dated Aug. 2SII1, Sept. nth, Sept. 25th, Oct. 9th and Dec. 0i, 1941.
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