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Aviation History
1956
1956 - 1357.PDF
FLIGHT, 21 September 1956 509 THOUGHTS ON THE HUSTLER . . . suffer fearsome drag rise in the transonic region, and a reductionin the estimated ultimate performance caused the U.S.A.F. to cut the initial order for the type from 30 to 13 aircraft. Applica-tion of the rule more than restored the lost speed and, as a diagram shows, has been done in a most happy manner. In the final configuration the four powerplant nacelles are sodisposed that they exactly fill in the area diagram to give mini- mum transonic drag. The fuselage also has a variable cross-section, which makes allowance for the external stores associated with some of the weapons-systems with which the B-58 isidentified. Undoubtedly the most noteworthy part of the aircraft is ispowerplant system. The basic J79 is a single-spool, variable- stator engine rated at about 11,000 lb thrust (16,000 lb with after-burner). In conformity with the integrated design philosophy the overall thermodynamics of the four engines have been treatedas a single factor, in conjunction with the aerodynamics and thermodynamics of the airframe. The problem of heating thewing under-skin during ground running has already been men- tioned; in flight there was no such problem, although the nacelleincidence for maximum inlet recovery during high-altitude sub- sonic cruise conditions (i.e., at a high angle of attack) aggravatedthe heating and demanded a compromise. In the event the inner engines are mounted at a marked positive angle and the outersat a negative angle (their propelling nozzles being clear of the trailing edge). A schematic diagram (p. 508) outlines the arrangement of air-flow within each nacelle. Air is used for all cooling functions, even that required by the engine-oil system. AH the air is takenin through the main circular intake, which is a variable-geometry assembly with a central spike positioned by a Minneapolis-Honeywell system which also opens and shuts diffuser-bay bleed doors to position the second (normal) shock inside the intake.The Hustler intake has been extensively tested under all condi- tions and is likely to be standardized on other types of aircraft. The main flow is divided up into a supply to the engine (about89 per cent of the total) and secondary cooling flows for the engine, accessories, oil and hydraulic fluid and cabin air. All thebasic engine and airframe accessories are mounted directly on drive pads under the J79. As far as possible each accessory isin the drag shadow of the first so that they form a row of mini- mum frontal area. Cabin air is bled, at very high temperature(certainly over 750 deg F under some conditions), from the J79 compressor and cooled by one of the ram-air flows, the latterbeing boosted by a bleed-air ejector pump as shown in the diagram. In a high-pressure turbojet at Mach 2 the temperatureat the delivery from the compressor is almost as high as that reached at the hot end of the engine. This is one of the factorswhich led Convair and G.E. to dispense with all nacelle firewalls and use instead a veritable hurricane of cooling air between theengine and cowling. Not only does this form a cooling blanket but it isolates the engine from the pylon strut, which also has afirewall at its lower end and a fire curtain where it joins the wing. The strut itself is fully ventilated. Airframe Design Most of the Hustler airframe has probably been a fairlystraightforward, plodding job, but the design of the wing has undoubtedly caused several major headaches. Thickness/chordratio is of the order of four per cent and virtually the whole primary structure forms an integral fuel tank. The aerodynamicsof the wing are essentially similar to those of the much smaller F-102, except that fences are, Convair hope, not needed. A mostinteresting, but classified, system of construction has been evolved which reduces heat transfer. About 15 per cent of the superficialarea of the Hustler is skinned in stainless steel, including the rear of the nacelles, the pylons, and much of the wing undersurfaceand ailerons. Stainless honeycomb has been found to stand up well both to high surface temperature and to intense high-fre-quency vibration from the engines. A problem which is becoming increasingly acute in the designof fast aircraft with integral-tank wings is that, owing to the high ratio of surface area to volume, the fuel temperature is veryquickly raised or lowered by variation in skin temperature— which is, in turn, critically dependent on solar radiation andkinetic heating. For the Hustler new techniques have been evolved to minimize wing temperature. These involve keepingthe aircraft in the shade before take off; climbing quickly to cold atmosphere; minimizing supersonic flying; use of a special finishto reflect more solar radiation (so that the Hustler may have a white top as well as a white bottom); and, in hot ambient con-ditions, use of insulating blankets and ground refrigeration. Clearly there has also been a lot of work on the problems oftemperature-resistant auxiliary services, hydraulic fluids and on cabin conditioning. It is likely that the B-58 programme has required the develop-ment of more completely new accessory equipment than has any PYLON This sketch indicates how the various parts of the basic B-58 fill in the area diagram to give minimum drag (a Sears-Haack profile). The "mission pod" is not allowed for. other aircraft. All this new paraphernalia has become "hardware"in advance of the aircraft itself, and Convair have logged many thousands of hours from Carswell A.F.B.—next to the Fort Worthplant—in testing it under extreme environmental conditions. The work began some 20 months ago with a specially prepared B-36,and has since required the services of another B-36, together with a B-47, an F-86, an F-89 and three C-131B avionic (aviationelectronic) test beds. Avionics are a major item in the B-58; Convair once estimated that, of every dollar spent on the pro-gramme, Convair received 38 cents and the avionics firms 45 cents. In most missions the B-58A production machine—if it isbuilt—will be a bare carrier vehicle which will not become a weapon until something has been added to fit it for a particularfunction. Normally this "something" will be a pod attached under the fuselage over which the aircraft will be towed; andthe size and expected growth of such pods accounts, in part, for the considerable clearance between the Hustler fuselage and theground. One pod will contain nuclear weapons; another will contain cameras; another will contain various types of missile.The intercepter B-58 will act as mother ship to pilodess inter- cepters, named Duck and Goose; the Fairchild Blue Goose,already tested, is the "long-range" portion of this system. The RB-58 will have a camera pod full of closed-circuit TV to actas the viewfinder and to govern the automatic control system of the cameras for pulse and image-motion control. The FairchildCamera and Instrument Corporation recently announced that they had cut the weight of this system from 1,584 to 295 lb, nodoubt by transistorization. Yet another system involves an air- borne countermeasures pod, developed by the Waltham Labora-tories, which will be standard on four out of the first 13 machines. There are even tanker and transport Hustlers on the drawingboards. Advance Prospects Of the basic geometry of the B-58 little need be said, since it isevident from the three-view drawing and from the photograph published last week. It is very largely a case of scaling-up theF-102, and, incidentally, making a better and more thoroughbred aeroplane. Reflection shows that it was inevitable that, short oftaking off from a trolley, the B-58 should have a multi-wheel bogie undercarriage—very similar to those of the Victor andVulcan. The first of the 13 at present being built is currently about tostart taxying trials and could be in the air by October. Convair have a big stake in this aeroplane, for not only are they entirelyresponsible for every bit of it but their Fort Worth plant's future depends on it. For years past many eminent Americans havebeen by no means "sold" on the idea of a supersonic bomber. Among them can be counted a fair proportion of the generalsof Strategic Air Command; and a story is told that even the terrifying LeMay himself once walked out of the B-58 mock-updeclaiming "I don't buy it—it doesn't fit my figure," or words to that effect. A cramped cockpit is, of course, difficult to avoidin such a machine. Now, however, the tide may be turning for Convair. Researchand development funds are becoming harder to obtain, and the new supersonic bomber designs, originally intended as B-58replacements, may be held up in consequence. In fact it is arguable that the visit of Tactical Air Command to the B-58team last February is a portent of increased orders and wider applications for this noteworthy machine. Nevertheless Convairare not going to have things all their own way; and, in particular, the complete dependence of the B-58 upon flight refuelling forstrategic operations is making it difficult for it to win over the recalcitrant S.A.C. generals. More and more is S.A.C. looking to even more advancedmachines. Lockheed are teamed with Pratt and Whitney in the development of a nuclear bomber and Convair are themselvesworking with G.E.—all on U.S.A.F. study contracts. Tangible hardware for these aircraft is already in existence and so it is forthe Boeing Weapons System 110, a Mach 2 bomber running on ethyl borane fuel and with a brochure performance likely to putall other bombers out of business (and this does not except the score of range). One can only wait and see what the U.S.A.F.decides to buy, and they have announced that they will not ask for funds for B-58 production until the fiscal year 1958. .- .,-»> •
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