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Aviation History
1942
1942 - 0418.PDF
i64 FLIGHT . FEBRUARY igra, 1942 Correspondence The Editor does not hold himself responsible Jor the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. THE TANK BUSTER Difficult to Improve on Dive-bombing A.A. guns must use a very high velocity not only to defeat the avoiding action of aircraft but also to reach the required height. A 6 lb. shell shot out at 4,000 f .p.s. possesses twice the energy of a 12 lb. shell at 2,000 f.p.s., but both will be accompanied by the same recoil. This energy equals force x shift and governs the rise against gravity or, in the case of anti-tank and naval guns, the piercing of armour. A shell exploding on the outer surface of armour does comparatively little damage. Your correspondent, " Letusdo It First" (and do let us hit hist), may like to be-reminded of a lecture before the Royal Aeronautical Society on April 19th, 1940, in which S. Rogalski suggested the mounting of shell-guns in aircraft of a calibre comparable with A.A. guns and taking their place. The Battle of Britain showed later, however, that existing aircraft arma ment and A.A. barrages provided effective defence when used together. The recoil mechanism of a gun only reduces the load on the mounting by spreading out the time during which the recoil momentum is sustained. This momentum equals force x time find must be transferred entirely to the aircraft carrying the* gun and directly affects its movement. (I believe it is true that an early experiment with a shell-gun on a flying-boat reduced its speed to the stall every time a burst was fired forwards.) This problem engaged the attention of inventors even during the last war, and in 1940 the French Air Ministry published some very interesting information in "Publications Scienti- fiques et Techniques du Ministere de l'Air—No. 157," describ ing devices ranging from rocket-propelled aerial torpedoes to a gun which threw off a weight backwards for every bullet fired forwards. The high-velocity shells from existing aircraft shell- guns are not to be despised against light tanks. The only case of an external explosion effective against thick armour is a marine torpedo (naval or aircraft) when the sur rounding water concentrates the force against the side of the ship. For " tank-busting" it seems difficult to improve on dive-bombing, which provides some of the desired speed for aiming, with bombs heavy enough to deal almost bodily with a tank. R. C. ABEL. NO NATIONAL MONOPOLY " Carping Spirit " Must be Checked IT is fortunate that Edward P. Warner's well-balanced views appear in your issue (February 6th) at the same time as the quotations extracted from trie American Press, particu larly when the '' Man in the Street'' is reading in our daily Tress that the Buffaloes and other American aircraft are being out-manceuvred in Singapore, and note we were outclassed until the Hurricanes arrived. He also reads, moreover, that mechanised equipment supplied from the U.S.A. which is being used in Libya is sharply criticised as l>eing nut-gunned and out of date. These "rough-neck" Isolationist-inspired writers, unless checked, will completely upset the spirit of the Atlantic Charter and the co-operative efforts inaugurated by the Churchill- Roosevelt conferences; these same writers will slowly learn that announcements of "umpteen" million dollars for something to be made "sometime, never" does not kill Japs or Nazis. I recently read in a Detroit newspaper, sent by an American friend, that the Rolls engines (now in production at the Packard plant) fitted to certain American fighters, have "boosted" up their performance at least 50 m.p.h. (actually, this important news was tucked away in the local items). Having visited America since 1940, round about the "Battle of Britain" period, I am at a loss to understand the mentality of many of the writers,, who have deprecated any thing British and called them "yellow" in 1938 (Munich period). Dying to the last Frenchman in 1939-40; Australians and New Zealanders (1940-41) doing all the African fighting; dying to the last Russian (late 1941)—do these scribes realise that the best blood of our race, our airmen, the fittest men in the world, have beaten the enemy in every case- where they had anything like a sporting chance, often with the odds against them, and that we have and are losing them still by hundreds each week? When over the "Pond," I met socially some oi their "best factory pilots, such as Major Dolittle, with whom I flew oyer a wide area and thousands of miles in their airliners, receiving kind consideration everywhere. But when outsiders, often of enemy origin or pro-Fascist, came in my path, they received better than was given at any .time. I have the impression that too many of our English officials and essential business visitors do not "bare their teeth" when the occasion arises, but $0? the impression that we are a '' done for'' race; the real Yank likes " guts." Every one of the R.A.F. laddies I have met who have been to the U.S.A. training schools have been well received, but this carping spirit of the few must be fought by others, who, like the writer, are not interested in the aviation business other than to see its ultimate travel-benefit for the human race in the new world to be. W. J. LORD. CAMERA CURIOSITY Yet Another Theory Advanced IN reply to your correspondent, R. H. Warring, ingenious though his suggestion is as to the cause of distortion of the lower blade in photographs of revolving propellers, the theory is based on a fallacy. If Mr. Warring were to place a thin sheet of frosted glass or tissue paper in his camera where the film is normally situated, direct the camera towards an illuminated object, such as a candle flame, with the shutter open, he will observe an inverted image of the candle flame on the frosted glass or paper. If he then holds a thin pencil horizontally in front of and above the camera lens, close to the camera, and slowly lowers it, he will observe that the image of the candle flame on the frosted glass or tissue paper is merely lessened in intensity by the passage of the pencil. If Mr. Warring's theory were correct the image would be partially obliterated and a shadow would pass from one end of the image to the other. The dimming of the image is due to the fact that an optical image will be formed complete even though the lens be par tially covered. The intensity of brightness of the image will vary directly according to the area of the lens surface exposed. Now considering this last dictum, we may assume that the image on the camera film will first be dim, secondly bright and thirdly dim as the aperture of the shutter closes down, but in each case the image will be complete. Each end Ww propeller is moving equally fast, therefore the "drawn-out" effect shown in the illustrations will be seen at both ends. This disposes of the reason suggested for differences of appearance of the two ends of the airscrews, but I can advance an alternative theory for the appearance. The source of illumination for the photographs is either direct sunshine or light diffused from the sky, therefore some surfaces will be in shadow and others lighted, since the two blades of the airscrew are not in the same plane. (I use the word in its mathematical sense.) Now, if the lighted side of the airscrew is photographed against a light background (e.g., sky) it will come out comparatively invisible on the photo graph while the dark side of the airscrew will stand out in silhouette against a light background. WILLIAM CLEGG. ISOLATED A.T.C. UNITS SQUADRONS of the A.T.C. in the more isolated parts of the country invariably lack most of the amenities enjoyed by those in the big towns, and our attention has been called to a case in point by a letter from the O.C. of No. 77 Squadrjp. Redruth, Cornwall, which was started as long ago as Ma3#) 1939, as a unit of the Air Defence Cadet'Corps. This squadron is trying to build up a library, and would be grateful for old copies of Flight and other aviation journals, and for copies of books on flying, both technical and otherwise. Its address is County School, Redruth. \
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