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Aviation History
1959
1959 - 0990.PDF
FLIGHT, if April 1959 493 Valkyrie Wing: THE WORLD'S BIGGEST AND HOTTEST DELTA IN a recent advertisement the Los Angeles Division of NorthAmerican Aviation Inc. said of their B-70 Valkyrie inter-continental bomber, "The B-70 will skirt the edge of space to any target on earth—flying every mile of the way at more than2,000 m.p.h. It will carry the most advanced weapons, including missiles it can launch hundreds of miles from ground defensesor primary targets, plus countermeasures against enemy attack." The problems of designing a reliable vehicle to accomplish thistask are greater than any previously faced by an aircraft con- structor. Even the immense engineering and scientific strengthof North American Aviation is insufficient to meet so colossal a challenge; and, following a practice long established in the aero-nautical field, much of the work has been farmed out to sub- contractors. So great is the task, in fact, that many of thesesub-contractors are themselves the giants of the American aircraft industry. The largest company of all—Boeing—has been assignedthe task of designing and manufacturing the complete mainplane. An accompanying sketch gives a rough indication of the sizeand shape of this remarkable wing. Since the gross weight of the aircraft will be of the order of half a million pounds, the wingwill have to be very large indeed to permit operation from existing Strategic Air Command runways and to confer the announcedoperating height of "above 70,000ft" with full operational load. The Valkyrie will be a canard, control in the pitching plane beingachieved by a delta foreplane, the wing being provided with elevons and carrying the six General Electric J93 turbojets inunder-slung triple packages. Originally the Weapon System 110A (as the overall project wasthen termed) was to be a subsonic-cruise bomber with a dash performance of about Mach 2. During 1956-57, however, therequirement was changed to the far more challenging one of an all-supersonic machine, as noted in the North American statement.The wings may therefore be expected to reach skin temperatures of well over 500 deg F, and to soak at these temperatures for morethan three hours. The form of construction chosen has been out- lined in an article by Don Brannon of the Boeing Airplane Co.in the current issue of his firm's house magazine. The following is a slightly abridged form of his ankle. "The Air Force's future Valkyrie bombers will arrow through thesky on the largest delta wings ever built—wings designed and manu- factured by Boeing's Seattle Division. These wings will have greaterresistance to heat and sonic vibration than the wings of present large aircraft. Fuel-carrying wing bays will be insulated from surfaceair-friction heat. "The Valkyrie will be America's first bomber using stainless-steelhoneycomb-sandwich panels for outer wing covering. Panels will be constructed primarily of PH 15-7 Mo stainless steel. The panels willrange from about the size of a large flapjack to 8 by 20 feet, and will This sketch gives an indication of the size and shape of the stainless- steel-honeycomb wing of the B-70 Valkyrie. Superimposed upon it is a half-wing of the Vulcan 6.2 to approximately the same scale be an inch thick. To do their job, panel cores and outer sheets must be brazed together—a tricky process with stainless steel. "Two existing Boeing hangars are being connected to form a building of 77,000 sq ft where the wing panels will be made. This construction and new equipment will cost more than $3m. Additional equipment amounting to almost $2m will be installed in existing factory areas to support the wing-building job. Assembly and joining operations will be accomplished in the high-bay area of the main factory assembly building at Boeing plant II. "From start to finish, stainless-steel-honeycomb brazing requires utmost care. Although the finished panel is tough and strong, by itself the honeycomb core is little stronger than the bee-built variety. Even finger pressure can damage the paper-thin core. Machining to the required 0.002in tolerance will be accomplished with the finest grinding and cutting tools. Core and outer sheets will be prentted to assure perfect alignment, then disassembled for final cleaning. So critical is the brazing process that panel components will be handled only with clean white gloves by men working in special, dust-free rooms. "Th'n brazing-alloy sheets will be placed between core and outer skin, and will be composed principally of silver, but will contain 7.3 per cent copper and 0.2 per cent lithium. After careful tack-biazing to hold core, alloy and outer sheets together, the sandwich will be pre- pared for insertion in a specially designed retort. A metal framework will be constructed to confine the flow of molten alloys to desired areas. "Extreme care will have to be taken with construction of the retorts. They will be built of stainless steel 0.04in thick. Each retort will be used only about foui times before being replaced. Within the retort, a tack-brazed panel will be laid on a finely tooled graphite base shaped to support it. Graphite combines the advantages of physical stability and good thermal conductivity. When all material is properly aligned inside, the retort will be welded air-tight with the exception of an important pair of pipes. "These pipes will extend from inside the retort through a second air-tight outer shell called a muffle When a panel is ready for firing, both inner retort and muffle will be purged and their air replaced with argon gas. Argon, being inert, will not combine with or form impurities in honeycomb-panel components during the high temperatures necessary for brazing. "The four-stage processing cycle will begin with the placing of a furnace hood over the retort setup. The firing cycle will last for several hours, during which the panel will be heated to 1,750 deg F. A controlled cooling to room temperature will take place within a speci- ally designed cooling head. The panel next will receive a deep-freeze treatment, spending several hours in a refrigerator room at 100 deg below zero. Then temperatures will be raised again to near 1,000 deg in a draw furnace, and the panel will be allowed to cool once more to room temperature. "To make sure that panels are perfect, each will be inspected by one or more of three methods—X-ray, fluoroscopic, ultrasonic. This will complete the manufacturing process, which will ensure fullest possible strength and reliability. "By July Boeing's new facility is expected to be ready for research and development work. Production will begin early next year. New equipment will include contour-machining equipment to shape the graphite base blocks, and a low-temperature curing oven for joining these base blocks. Other major equipment to be installed will include a skin mill for honeycomb-core machining, inspection instruments, 10 cleaning and pickling tanks and overhead handling facilities. Some 30 pieces of existing equipment will be relocated to the new factory in addition to new facilities being procured. "Boeing engineers are studying the wing-brazing method with the hope of speeding production and reducing costs. Considerable refine- ment of the method described above may be made, possibly even before the factory goes into operation." Since the above was written, a news release from the UnionCarbide International Company of New York has commented upon the size of the graphite blocks which are required to brazesuch immense panels. After reiterating the fact that graphite has a very low coefficient of thermal expansion and can be preciselymachined to the intricate contours required, Union Carbide state that production techniques have now been developed to increasethe size of graphite reference form stock from 20x46.5x62in (shown in the background of the photograph) to a length of 84inand, most recently, to a record-breaking llOin (foreground). A number of such forms joined together will permit the fabricationof honeycomb panels as large as 10 X 20ft. The Valkyrie will require some 19,000 sq ft of honeycomb sections, many of themfar larger than any previously attempted. In order to hold the honeycomb panels daring the brazing operation very large blocks of graphite will be required. In the foreground of this photograph is a form block 20 X 46.5 x 7 Win, the largest in the world
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