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Aviation History
1955
1955 - 1154.PDF
268 FLIGHT, 19 August 1955 DOUGLAS MILITARY DESIGN... morale factor was escape, and here it was considered that the cscapc-chute or ejector seat were feasible up to from Mach 1.0 at sea level to Mach 2.0 at 45,000ft. At all higher speeds a capsule was necessary. A great deal of work was being done on control- lever arrangement and shaping, harness, seats and other cockpit equipment to ease the pilot's task. Before ending, the speaker touched on the all-important problem of equipment reliability, which, he said, had been found by U.S.A.F. surveys to decrease at established rates in proportion to the reliability and number of component parts, as shown in Fig. 6. Mr. Heinemann concluded by saying that his lecture had out- lined some of the problems and limitations concerned in the design of some successful military aircraft. The outstanding rule, regard- less of the aircraft's purpose, should be "keep it light, simple and reliable." This precept clearly lies behind the speaker's success in designing such widely differing aircraft as the F4D Skyray and A4D Skyhawk. THE DISCUSSION Dr. G. V. Lachmann (director of research, Handley-Page, Ltd.), saidthat it was gratifying to hear Mr. Heinemann praise the slot, particu- larly as he was renowned for cutting down parasitic weight.One might ask why there were no slats on the Victor. Such devices had, in fact, been considered when the H.P.80 was projected in 1946-7,but, in view of the thickness/chord ratio of the outer wings—no more than 4i to 5 per cent—it was then found difficult to install them in theprofile. He asked Mr. Heinernann what was the minimum wing thick- ness for slat installation. Their own solution, nose flaps, were adequateaerodynamically and rather lighter, structurally, than slats; but the hydraulic system—particularly that required for "instantaneous" opera-tion had no mean weight, whereas slats could be made to work themselves. He was surprised at Mr. Heinemann's flight envelope showing theupper limit of turbojet operation as 600 kt (with an afterburner required at higher speeds); perhaps through a different philosophy, Britainbelieved that the basic turbojet limits were much higher. As regards yaw dampers, Victor experience certainly confirmed Mr. Heinemann'sconclusions regarding their great usefulness. Boundary-layer control methods, by blowing or sucking, were controversial. A single blowing-slot was effective but the engine power was otherwise required at take-off. At Handley-Page they had great hopes of schemes based on attachingthe flow by suction. Mr. Heinemann, replying, confirmed that his thinnest wings were of4i to S per cent t/c ratio, and that slats had been quite readily installed. I 10 20 30 40 SO 60 NUMBER OF PARTS IN COMPLETE UNIT Fig. 6. U.S.A.F. surveys in the field have shown these reliability factors in equipment composed of varying numbers of com- ponents, each of a known individual reliability. His engine performance curves had been based on the most optimisticdata obtained from engine manufacturers. Mr. Wood* (aeroplane design consultant, Bell Aircraft Corpn.) notedthat firms with actual supersonic flight experience approached high- speed design problems with more caution than did other companies.Guided-missile experience had preceded, and to a limited extent had formed a guide for, supersonic manned-aircraft design, but the missilerequired no subsonic characteristics and did not have to perform as an armament platform. Only full-scale flight-testing, of subsonic,transonic and supersonic behaviour, could provide a sure guide to the correct wing configurations required. Mr. R. G. Fowler (chief aerodynamicist, Folland Aircraft) commentedon the absence of remarks by Mr. Heinemann on wing loading. He also inquired whether or not the Douglas yaw-dampers were of the simpleviscous (as distinct from the electrical) type. Mr. Heinemann, replying, said that the requirements of carrieroperation imposed definite restrictions on the order of wing loading which could be accepted. A low wing-loading gave a double advantagein permitting greater manoeuvrability and a higher ceiling. The maxi- mum lift-coefficient of the bat-winged F4D was actually roughly halfthat of the A3D Skywarrior, and it could be deduced that the latter machine had, in consequence, roughly twice the wing loading ofthe fighter. BUILDING THE R.A.E, TEST TANK PHOTOGRAPHS of the Bristol Britannia "specimen" under-going its water test in the new Farnborough tank have already appeared in Flight (page 750, June 3rd and page 820, June 17th), and it is now possible to add some notes on the construction of the tank itself. The information has been provided by Horseley Bridge and Thos. Piggott, Ltd., of Tipton, Staffs, who were responsible for its manufacture. Briefly, the tank may be described as consisting of three separ- ate parts: (a) the forward end, constructed from standard 4ft tank plates and half-plates, with a top tier of specially pressed plates; (b) the wing box—a mild-steel section to accommodate the water seals affixed to the base of the wings; and (c) the rear end, again constructed from standard plates, half-plates and special pressings. The entire floor consists of standard plates and carries rails to take the aircraft on bogies. Overall dimensions of the tank are 160ft long x 20ft wide X20ft high. For any normal water-storage application, a tank of comparable size (but which in any case would be unlikely to exceed 16ft in height) would have internal stays to brace the walls against the outward pressure. The very nature of the test pur- pose, however, demanded that the test tank should have an interior completely free of obstruction. This requirement was met by the fitting of external frames consisting of 9inx7in rolled-steel joists for the base and 18inX6in R.S.J.s for the verticals, with top ties, at 4ft centres throughout the length of both pressed- steel-plate sections. The sides of the lower half of the wing box were constructed from mild-steel plate 84in wide by iin thick, butt-welded to a continuous web carrying horizontal stiffeners and reinforced with internal vertical stiffeners of 10inX4|in split "I" section, welded to. the web. There is also external staying. Surmounting the wing-box diaphragm plates on each side of the tank are heavy welded plate girders in the form of an inverted "T," constructed from |in plate. The base member, designed to counteract horizontal water pressure, is reinforced longitudin- ally with 6inX3in billets, increased to 5in thick above the wing apertures. The vertical section, strengthened by internal and external web stiffeners, carries the dead weight of this base. In order to support this weight and to maintain it against the extremely high internal pressure, end frames were incorporated, built up from fabricated box girders. The verticals, suitably stif- fened, were made to a special shape,, proportionately increasing in breadth from 2ft at the top and bottom to 3ft 2in at the point of greatest stress, ten feet above the junction with the base mem- ber. Eight 2in diam. H.T. steel dowels resist any tendency to twisting under stress. In addition to undergoing the normal loading tests, special cross-members above the tank were also subjected to fatigue loading tests, since they carry some of the equipment necessary to create fatigue stresses in the aircraft on test and thus come under similar stresses themselves. A photograph of the tank during initial erection at the makers' works appears oh p. 271. EXHAUST AUGMENTERS FOR DOVES T"HE American agents for de Havilland Doves, Buder Airplane -* Sales of Dallas, Texas, are offering exhaust augmenter instal- lations for standard Doves. The system was developed joindy by diis company and Dallas Aero Service, who tested six different aircraft with various refinements aimed at increasing the cruising speed. The best of those tried proved to be the exhaust augmenter, which (it is stated) for a cost of $2,780 (about £990), adds between 8 m.p.h. and 16 m.p.h. to die Dove's cruising speed, raising it above the 200 m.p.h. mark. The principal effect of the augmenter is to smooth out the airflow around the standard exhaust stacks, close to the wing leading edge, but it is also said to lower by half die back-pressure in the cylinders, and to save some ten pounds of weight. The modification is claimed to be worth some three to four inches of manifold pressure at 8,000ft. At present the augmenters are being offered to potential cus- tomers on a trial basis, one pipe only being fitted, and removed again free of charge should no increase in cruising speed be noticed. Test climbs, carried out widi 42in boost and 2,700 r.p.m. at 105 m.p.h., showed diat the augmenters gave better cooling in these conditions than the original stacks. Augmenters are fitted as standard equipment to most of the American light-twin executive aircraft.
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