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Aviation History
1949
1949 - 1884.PDF
650 FLIGHT, 17 November 1949 AIR DEFENCE AT THE CROSS ROADS . . . for day fighters, it is of sufficient importance to rule outthe use of rocked fighters for perimeter defence. It will be remembered that the Germans produced several designs,one of which was used operationally, for a rocket fighter, but these were intended specifically for the defence of keytargets. The policy of target defence is obviously incom- patible with the atomic bomb, unless, of course, the targetwas sufficiently important and situated so that a near-miss of perhaps several miles would not affect it. Rocketfighters are also impracticable for the obvious reason that, to maintain the strength of a fighter force, the turn-aroundtime between sorties must be as short as possible. With a powered endurance of a few minutes, the chances of arocket fighter being able to land back at its base are remote. A study of the question leads one to conclude that therecan be no purely rocket-propelled aircraft between the com- posite-powered interceptor and the guided missile which isthe defence and ultimate offensive weapon of the future. A fighter design is, of course, the means to an end, whichis to transport the human element and its armament to such a position in the air to assure the certain destructionof the target. While it is not possible to speculate on the airborne interception equipment which will enable contactto be made, the means of destruction will bear review. British fighter armament has standardized on the fourBritish Hispano cannon of 20 mm calibre, firing ball, tracer and explosive ammunition at up to about 700 rounds perminute. With a concentrated mounting, these weapons are effective up to about 800 yards' range, and have proved their worth over the past tew years. Increasing speeds, how- ever, have reduced the time factor available for strikes on the target, which means that either the mass of the pro- jectiles has to be increased to maintain the weight of fire, or the number of guns increased. Larger calibres and in- creased numbers is probably the most promising combina- tion, and the 30 mm cannon developed by the Germans and fitted to their interceptors at the closing stages of the war in Europe is a pointer in the right direction. Fire can be opened at longer range with these heavier-calibre guns, and their punch is formidable. While it may at first seem odd to q.uote repeatedly the developments of the Germans, who after all were the defeated nation, it must be remembered that they were probably the most experienced nation in the world, be it unsuccessfully, in defence against an overwhelming air offensive. Significance should therefore be given to their experiments with small rocket-projectiles, which were to be fired in salvos of as many as thirty at a time. What a target the B-36 would make for these projectiles, fitted with proximity or other electronic fuses! Although much progress has. still to be made with re- search and development of guided missiles, effective de- fence will undoubtedly evolve the combination of the piloted fighter and the ground-aimed rocket anti-aircraft gun. The ideal missile, fitted with homing devices and a selection of electronic fuses, and propelled by liquid rockets, will probably be capable of air or ground launching—being, in the latter case, independent of the weather—and will be the panacea for interception. Strategy, however, must be taken into account together with technical progress, and absolute air defence may well prove to be obtainable only simultaneously with offensive air superiority. IN SEARCH OF PROOF (Continued from page 635) ground particles (0.005/0.00 ioin) ofPerspex suspended in the water. With the light mounted on top of the work-ing section and shining downwards through a narrow slit parallel with thsstream, the characteristics of the flow across the model in any one plane atany spanwise station—according to the spanwise location of the slit of light—can readily be observed. For flow across the underside of the specimen, the lightis placed beneath the working section with the slit beam projecting upwards. The tunnel is filled from a header tankand is bled at the two highest points of the circuit. In the return circuit andunderneath the working section, a four- blade, single-stage water screw, or im-peller, is driven from a 40 h.p. D.C. in- duction motor at a speed of 570 r.p.m.The impeller was designed and built by the company to preclude cavitation,but if the pressure at the vent of the tunnel is lowered, cavitation will occuron the model where shock waves would form in flight. A tunnel such as this is, therefore, of consider-able value in developing, among other things, wing entries and ducts for jet units. The structural test frame at Warton comprises five 15ft bayswith a transverse dimension of 24ft and a vertical dimension of 15ft; the six bridges are of 20-25 tons capacity. In orderto cater for loading cases combining vertical, lateral and tor- sion loads, each vertical member of the side-frame bracingand the transverse plan bracing-member at the same station have been incorporated in a U-frame. The design of theside frames and plan bracing is conventional except that bolted joints are used throughout so that the bracing may be modifiedquickly at any section to accommodate unusual shapes, For reasons of simplicity and flexibility, the loading unitswere designed round electrically driven straining gear and medium-pressure hydraulic load-measuring capsules. Eachloading unit comprises a box-section weighbeam which, pivoted near one end on a plain bearing, carries at the other end thestraining gear and is supported between this and the pivot 'on a hydraulic load-measuring capsule. A two-speed motor SECTION THROUGH ENGINE NACELLE Schematic perspective of the jet-induced-flow high-speed tunnel. The inset section shows the disposition of the Nene nacelle in the tunnel and the engine intake and by-passed airflow-paths. A, settling chamber ; B, intake flare ; C, working-section ; D, first d iff user ; E, mixing chamber ; F, engine section ; G, mixing length ; H, main tunnel air J, heat-control valve ; K, second d iff user ; " L, hot-air return ; M, gauze filter box ; intake ; N, control and observation roont; O, workshop ; P, tunnel air exit. mounted on the base near the pivot drives a gearbox withthree output shafts running at varying speeds, which can be connected to the straining unit through a torsion shaft. The straining rods are raised and lowered by capstan nutssimultaneously rotated by left- and right-hand worm-gears keyed to the driving shaft. These parts, together with thethrust bearings for the nuts, are assembled in a massive steel block supported mid-way between the straining rods on large,_self-aligning taper roller bearings. The load applied at each loading unit is distributed on tothe specimens in the requisite manner by a conventional link and lever system of predetermined proportions. To keep theratio between the loads on the individual units constant, the capsules are positioned so that their distances from the weigh-beam pivots are in the same ratios as the loads. In this way the pressures in all capsules are equal when the loads bearthe correct relation one to another. Hence, provided all cap- sules are connected to the same hydraulic circuit and they canall be kept floating, the required load distribution can be ; maintained. B 18
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