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Aviation History
1954
1954 - 1577.PDF
698 FLIGHT 28 May 1954 STRATOTANKER . type aircraft capable of fulfilling the combined requirements of a tanker for the Strategic Air Command, a cargo and passenger transport for the Military Air Transport Service and a medium to long range high-capacity civil airliner. Into this design was put all the relevant results of 5,000 hours of multi-jet research flying, 21,000 hours of project tunnel testing and the immense experience acquired during the manufacture and operation of several hundred jet bombers and large tanker aircraft. It is now just two years since the end of the C-97 assembly hall in the company's Renton plant was walled off to form a private and self-contained bay in which the construction of a prototype was quietly begun at a short ceremony at which representatives of all branches of the company watched the driving of the first rivet. Construction was completed ahead of schedule a few weeks ago, and the finished aircraft was ceremonially rolled out on May 14th of this year. The general layout of the new aircraft—which has the Boeing type number 367-80, and has also become known as Model 707 —is clearly shown in the accompanying photographs. The engineering features of this aircraft are discussed below under a number of sub-headings. fact that the smooth oval cross section eliminates the re-entrant portion seen on the C-97 and Stratocruiser. As the Stratotanker is an all-purpose demonstrator, large cargo doors are fitted on the upper deck. As these doors hinge outwards and upwards, and each have an area of at least 75 sq ft, they are a remarkable engineering achievement when it is borne in mind that the pressure differential is of the order of 9 lb/sq in. This means that the in-flight load on each door must be about 44 tons and the problems of obtaining a door frame of reasonable weight can possibly be imagined; furthermore, the doors must transmit flight loads just as though no doors were there. Power Plant.—The Pratt and Whitney J57 is a high-com pression, all-steel, two-spool, turbojet with a rated static thrust of 10,000 lb; it has been discussed in several past issues of Flight including that of May 14th last. The engine is in large scale production for military aircraft and can be regarded as fully developed and highly successful. The civil variant, styled JT3-L, is slighdy different but is not yet available. The engines are mounted in single pods, the configuration of which is the outcome of immense research. Each pod strut resembles a two-spar wing, each spar having an attachment at the lower end picking up the main mounting points at the top of the engines. When attached to the airframe via these pylons, the nose fairing is bolted to the intake of the engine itself and the On the left, Mrs. William £. Boeing breaks the champagne bottle, with William M. Allen, the Boeing president, looking on. The "roll-out" picture above provides some pod and undercarriage details. Airframe.—Boeing have followed conventional stressed-skin, flush-riveted practice, carried to an extremely high pitch of development. Although the basic structure is generally of light alloy, most of the skin is in 75 ST, while the lightly stressed portions are almost entirely of magnesium alloy. Some of the skin is very thick by present airliner standards, the wing skin being seven-sixteenths of an inch between the spars, tapering to one-eighth inch at the tip. As a result, jigging and tooling is very extensive, every rivet and bolt hole being sunk to a tolerance of within a very few thousandths of an inch. The 128ft fuselage is almost entirely pressurized and the wing passes through it just beneath the main floor. The fuselage structure is very similar to that of the C-97 with closely spaced hoop frames leaving the interior quite unobstructed. The rear end of die pressure hull is covered with a convex dome and the external skin is applied in large sheets taking advantage of the Taken in April, this photograph shows the prototype shortly before leaving the experimental bay in which it was built. Spoilers, cowlings and cargo doors are prominent. pod is men completed by fitting two huge shell doors which form the skin of the pod itself. These doors are hinged along their upper edges and are clipped togemer along the lower centre line of the nacelle, so that the pod can be opened up to reveal the entire engine for maintenance purposes. The structure of the pod is in stainless steel and titanium alloy. The bottom of each inner engine is no more than 28in from the ground, and the outers are at head height. The installa tion is fully protected against ice by hot air tapped from the rear engine compressor. Fire prevention is achieved by division of the pod into a number of sealed bays, each with its own extinguishing system; in addition the entire nacelle can be isolated from the wing by valves and shutters, the engine itself having an anti-windmilling brake as an additional safety measure. The Boeing thrust reverser (Flight, April 30m, 1954) is not fitted to the Stratotanker prototype but should be on production aircraft. Fuel System.—Owing to the considerable sweep angle of 35 degrees the Stratotanker wing has a useful thickness, especially at the root. As a result, it has been possible to accommodate a truly immense fuel capacity between the spars; in Imperial gallons, the tankage is as follows: outboard of the outer engines, 392 gal in each wing; between the pods, 1,808 gal; between the inner pod and the fuselage, 1,958 gal plus 1,540 gal. With a 3,500-gal overload tank in the centre section (actually in that pan of the wing lying under the cabin floor), the total tankage is 14,896 gal; at 7.8 lb/gal this weighs some 116,000 lb. All tankage is integral with the wing structure, the sealing being of a new type specially developed for this aircraft. All tanks are linked to permit pressure fuelling at rates of at least 400 gal/min, from a single point below each wing. A special high-capacity venting system is employed to accommodate the large vapour-release expected during rapid climbs to high alti tude. No details can be given regarding tank purging, but— if Boeing practice with bombers is any guide—a form of inert- gas purging will be provided. The present J57 engines are, of course, purely military. As a result, the specified fuel is JP-4 wide-cut gasoline or AvTAG; this is the only fuel so far cleared for use in the J57. It is possible that, were circumstances to require such a step, the
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