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Aviation History
1942
1942 - 0526.PDF
2IO FLIGHT MARCH 5TH, 1942 WORLD PRESS SUMMARY RESUME OF TECHNICAL ARTICLES DEALING WITH AIRCRAFT AND ASSOCIATED SUBJECTS For ihe summaries and translations from aircraft and technical journals of the world, we are indebted to Vie \ Directorate of Scientific Research and Technical Development, Ministry of Aircraft Production. ' j '' Safe '' Altitudes IF a parachutist opens his parachute immediately after leav ing the aircraft at 12,000 m., his rate of descent will gradually diminish from about 13 m/sec. to 7 m/sec. as he approaches the ground. The total time of descent will be of the order of 21 minutes, an altitude of 6,000 m. being reached after about 9 minutes. When dropping freely, on the other hand, the same altitude is reached in about 1 minute, the rat* of descent varying from about 100 m/sec. at 12 km. to 57 m/sec. near the ground. It is clear, therefore, that if the parachute is opened imme diately at great altitude, the parachutist is exposed to dele terious physiological effects over a considerable period of time during the drop. These effects, at any rate as far as concerns oxygen concen tration, were reproduced in a high altitude chamber on specially picked personnel. It appears that a delayed rate of descent, i.e., parachute opened immediately, was accompanied in each case with collapse of the experimental subject; grave injury and possible death could only be avoided by the immediate supply of additional oxygen. On the other hand, the physio logical effects of a free drop from 12,000 to 6,000 m. were generally withstood without serious disturbance of the organism, and the author, therefore, strongly recommends that if high altitude jumps have to be carried out without special oxygen equipment carried by the parachutist, the parachute should not be opened until a." safe " altitude of the order of 5,000- 6,000 m. has been reached. This procedure is all the more to be recommended since it cuts down the time of exposure to great cold and also reduces the amount of ground drift before landing. The latter may be very important in wartime. It is thought that with delayed opening of the chute the carrying of special oxygen equipment would be rendered unnecessary. Of the 9 experimenters, only 3 experienced serious incon venience when dropping freely from 12 to 6 km. All would have died if, the rate of descent had been that corresponding to the open parachute. Parachute Descent from Great Altitudes.—(H. W. Romberg, Lujtwissen.) (Germany.) Tip Interference THE periodic changes of the air forces acting on an airscrew blade element that passes by the flanks of a fuselage nose are theoretically investigated. This forcing function, known to excite vibrations of airscrews and airplane structure, is har monically analysed. The strength of the fundamental harmonic and the relative strengths of the higher harmonics are found to be greatly dependent upon the location of the airscrew plane downstream from the fuselage nose and upon the ratio of fuselage diameter to airscrew diameter. The farther downstream the propeller is located behind the fuselage tip and the greater the fuselage diameter compared to the propeller diameter, the smaller is the intensity of the fundamental harmonic and the smaller is the relative import ance of the higher harmonics ot these propeiler-tip excitations. The clearance between propeller-tip and fuselage flank is found to have comparatively little beneficial effect within the usual limits at the designer's disposal. The simplifying assumptions of this analysis restrict the validity of the results to fuselage shapes corresponding to a Rankine point-source half-body in flow of axial symmetry and propeller locations one fuselage diameter or more down stream from the fuselage bow. Experimental verifications of this analysis and an investigation of oblique flow about the fuselage are desirable. On Propeller Tip Interference Due to ihe Proximity 'of a Fuselage.—~(A. Gail and H. G. Lee, /. Aeron, Sei.) (U.S.A.) Spitfire and Me 109 T HE German fighter Me 109 has been designed mainly for speed and high rate of climb, whilst the British Spittire represents a compromise, speed and rate of climb being to some extent sacrificed with the object of increasing the manoeuvrability and achieving a low landing speed. Broa'Hly^, speaking these differences are directly due to the smaller relative wing area of the German design, i.e., the wing loading of the Me 109 is greater than that of the Spitfire. It is true that at very high altitudes, the induced drag becomes of increasing importance and the small-wing machine is thus handicapped. Up to 20,000 feet, however, the highly loaded Me rog has the higher speed and rate of climb, and with this advantage its performance enables it generally to choose the instant and position of attack, with the added ad vantage of a possible surprise. It is true that in a dog-fight, the sharp turns of the Spitfire might prove of advantage, but there is nothing to force the German pilot to adopt such tactics for long, since his higher speed will enable him to break off the engagement at any time and renew it at will. It must also be remembered that the main object of the fighter is to work in co-operation with the bomber. Here dog- fighting tactics necessarily lead to the escort losing touch with its bombers. The fighter with the higher speed, even if he does not shoot down his opponent, will have already achieved part of his object, since he will be the first to catch up the bomber formation. In short, speed is the characteristic of attack, manoeuvrability that of defence, and in a war experience has shown that attack generally scores. Why are the German Fighters Superior?—(Luflwissen.) (Germany.) *#- Tank Armour THE thickness of the armour plating of the British tanks in the 1914-18 war was of the order of 15 mm. in front, 10 mm. on the side and 6 mm. on top. Modern medium tanks of 20 tons have a turret armour of about 25 mm., whilst Russian heavy tanks go to 35 mm. and super heavies (Type Klim Woroschilov) are said to possess armour up to 70 mm. thick. According to the author, the armour-piercing shell of a 20 mm. aircraft cannon will pierce the soft armour plate favoured by the Russians. The German tanks use hardened steel plates, which, although offering more resistance to heavy calibre shells, are stated to be more likely to crack. The Germans claim to have destroyed a considerable number *;! Russian medium tanks by this means, the fighter attackifif; from the rear at low level. A rear attack is favoured, since the tank armour is weakest in this section due to weight of the engine, always installed at the back. Of course, tanks can also be attacked by dive bombers. In this case a near miss may incapacitate the tank by the effect of blast, jamming the gun turret or dismantling the creeper track. The cannon attack has the advantage that the aircraft can fly over the target a number of times until its ammunition is depleted. A dive bomber after it has dropped its load must return to its base. High-level bombing attack may achieve outstanding successes, if the tanks can be surprised whilst refuelling, with the attendant danger of fire. The author is of the opinion that attacks by aircraft either with cannon or bomb are at least as effective as those carried out with special anti-tank guns, assuming that the latter are available hi the positions required, and that this is reflected in the German claims of successes. At the moment, most tanks do not incorporate anti-aircraft guns in their armament. Until this is remedied, the attack of aircraft will continue to be effective. Aircraft Attach on Tanks, witJf special reference to the Russo-German War.—(T. Weber, Flugwehr und Technik.) (Switzerland.)
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