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Aviation History
1943
1943 - 1565.PDF
JUNE 17TH, 1943 FLIGHT 629 The. Dive Bomber Reasons for Dive Brakes : Some Engine Problems : History of Qerman Development By "HELLDIVER" Continued from page 605, June 10th) THE dive bomber's power plant has alwaysdemanded special study. Although ofcomparatively crude aerodynamic de- sign early diving aircraft reached such high speeds that their engines, which drove fixed- pitch airscrews, were subjected to undesirably high r.p.m. Refinement in aerodynamic design and consequent higher diving speeds aggravated the situation, and the formidable inertia forces gave rise to difficult strength problems con- cerning the engine and airscrew. This difficulty was en- countered by the Junkers concern during the development of the Ju 87. Attempts were made to remedy this situation by diving at full throttle in order to balance the inertia forces in the engine by the gas forces, but the excessively high r.p.m. ,;• soon demanded a better solution, and, since diving with •;*' closed throttle led to racing of the engine, variable-pitch airscrews were adopted to keep the engine r.p.m. within permissible limits. Although this eliminated over-stressing, it led to a further increase in diving speed due to the loss of the braking effect of the engine, which is similar to that in the engine of a car travel- •'ling downhill. For this reason a v.p. airscrew is set for diving at maximum permissible r.p.m. During the pull-out after a dive '• gyroscopic moments occur in the airscrew and introduce additional stresses on the airscrew ., itself, on its shaft, and on the engine mounting. The possibility of the engine being overcooled during the dive has also to be contended with. With an engine running '' light'' the amount of heat to be dissipated is small and the lubricating oil and coolant may become un- duly cold and interfere with the proper working of the engine when full power is demanded immediately following the dive. Flaps on the oil and coolant radiators must, therefore, be closed before a dive is started, and, if neces- sary, special precautions, such as the blanking of the radiator intakes, be taken to prevent overcooling. Diving with a closed throttle results in a comparatively high suction in the cylinders of the engine, and a consider- able quantity of oil may be drawn into the combustion Grerman dive-bomber design may be said to have started in Sweden with this Swedish-built Junkers-designed K.47 with Bristol Pegasus engine. chamber and escape through the exhaust ports. This pre- sents a risk of oiling up of the sparking plugs which can, however, be avoided by suitable combustion chamber de- sign and positioning of the plugs. Regarding the fuel system, special piping and ventilation arrangements must be incorporated to ensure adequate supply, not only in the dive, but in the subsequent zoom. Special arrangements must also be made to ensure the correct functioning of the lubricating system. An incidental difficulty is the great strain imposed by the abrupt change of height on barometric aneroids of various instruments and controls. Such devices are being adopted in increasing numbers on modern aircraft. On the Junkers Jumo engine as in- stalled in Germany's standard dive bombers they are used not only for automatic boost control but for the automatic blower speed-changing gear. Other complications may be introduced, if a liquid-cooled engine is used, by vapour locks. These : : can be avoided by the adoption of pressure cooling, which is, in fact,used on the latest Junkers Jumo engines. Lost week's article dealt with the principles and practice of dive bombing. This week some special precautions which have to be taken with power plant installations are out- lined, and development in Germany is described.. Next week a review of the work done by other nations will be published. The prototype of the Junkers Ju 87 was registered as a "civil " aircraft. 'The engine was a Junkers Jumo 210 of 600 n.p. Germany £ For several years before the outbreak of the present war German designers were studying American dive-bomber design. Their interest, and that of the German Air Min- istry, was readily apparent from a perusal of the German technical Press, but, although dive-bomber development in Germany undoubtedly owed much to research in the U.S.A., it cannot be denied that some of the early German prototype aircraft displayed great originality. It is known that technical research was initiated in Sweden and was continued there until such time as condi- tions in Germany made it possible to proceed with it at the Junkers Dessau works. The forerunner of the Ju 87 may be con- sidered to have been a Swedish-built aircraft of Junkers design, the K 47. This was a radial- engined strut-braced monoplane with fixed undercarriage, and was originally intended for use as a two-seater fighter. A Bristol radial engine was fitted and the bombs were car- ried externally on flie bracing struts. It seems that results were sufficiently encour- aging for development orders to be placed for the Ju 87, which had the basic airframe of the modern Ju8/, but had an engine of about half the present power (600 h.p. Jumo 210). It differed in cockpit and undercarriage design and in certain structural details. The designer was Dipl. Ing. Pohlman. It has lately become known that an early prototype of the Ju 87 had twin fins and rudders, following in this
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