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Aviation History
1957
1957 - 1565.PDF
PLIGHT, 25 October 1957 653 ARROW ... At the extreme rear of the body is the short rear-fuselageassembly which fairs-in the propelling nozzles. In the centre is a fairing which forms the tail of the fuselage proper, and housesthe braking parachute. Readily detachable to the rear as a single unit, the rear fuselage incorporates a considerable amount oftitanium alloy and stainless steel, and stainless-steel blanket- shrouds are also provided around both engines. Like the wing, the fin is of exceedingly strong multi-sparconstruction, and it is designed to bear immense air-loads. Each of the swept fin spars terminates at its lower end in a fork-fittingin high-strength steel, the geometry of the joint being shown by the large drawing. The joint is finally covered by a small fairingwhich forms a continuation of the dorsal spine. The rudder is attached at several points along a hinged axis swept at 46 deg. As already noted, the main wing structure is separated fromthe control surfaces by what are described either as the control boxes or the trailing-edge members. These are immensely strongassemblies, which, by an incredible display of ingenuity, have been persuaded to accommodate all the operating jacks and controlcircuits for the elevators and ailerons. Avro were responsible for the design of the powered controls, and they have employed asingle large jack, made by Jarry Hydraulics, for each surface. The control surfaces themselves are attached by piano hingesextending across the entire span of each portion (a fact which emphasizes the immense strength of the wing since any appreci-able bending would render such hinges inoperable). Each control surface is gapless and unbalanced, and no tabs are to be seen.Moreover, the trailing edges are slightly blunted, particularly on the ailerons, to reduce drag and flow-breakaway. It will be appreciated that a fighter of this type, weighing morethan 30 long tons and—like all deltas—with its nose high, requires an undercarriage of no mean proportions. The design of the gearwas, however, complicated by the presence of the armament pack in the fuselage, which made it imperative that the entire mainunits should be capable of stowage inside the exceedingly thin wing. The firm which finally obtained the contract for the maingear was Dowry Equipment of Canada, and a recent paper by G. F. W. McCaffrey, their chief engineer, has highlighted someof the immense problems which his firm met and overcame. One of the greatest of these problems was the development of manu-facturing processes in steel with an ultimate tensile strength of 260,000 to 280,000 lb/sq in. Each main leg measures some 104in from the upper hinge-axisto the bogie pivot. In order to permit the entire unit to lie within the wing the leg is hung from a skewed axis and the complete gearis shortened, twisted and trimmed during the retraction cycle. Twin wheels are used on each leg and, unlike the CF-100, theseare arranged in tandem in order to restrict the complete unit to the very limited depth available inside the wing. The centre ofthe bogie beam is pivoted to a tubular member which is restrained against vertical movement by a Dowty Liquid Spring shock-strut. Upon landing, the rear wheel makes initial contact with theground and rotation of the bogie beam is then resisted by tension in the collapsible tie member. Accordingly, the Liquid Springcloses, and the vertical velocity of the front wheel is held to the rate of descent of the aircraft, rather than twice this value. Duringretraction, the torque-carrying members of the gear are dis- engaged, thus allowing .the whole bottom part of the under-carriage to rotate through some 40 deg under the action of a cam while linkage from the pivot cross-shaft pulls up the lower partof the leg through a distance of some 8iin. Horizontal loads are resisted by a telescopic side-stay which also contains an internallock to hold the unit in the down position. The back-stay is not telescopic, and it is worth noting that it was the forward (anti-drag) loading on the leg which designed the structure in bending. Wheels and brakes on the Arrow Mk 1 are by Goodyear. Rigidpipe, employing swivel joints and trombone slides, is used for all braking piping, and twin brake-links prevent pitching. One could write a book on the work which Dowty had to do toturn this undercarriage into a production job. The basic material for the main outer leg, the sliding member, the bogie beam andthe back-stay are all forged in the company's Dowcan 110 ultra- high-strength steel (which approximates to S.A.E. 4340). Thelargest forging, the main outer leg, initially weighs about 1,000 lb; machining reduces this value to 167 lb in the finished state.The bogie beam, although smaller, is particularly tricky in view of the fact that it has a complex shape with material in threemutually perpendicular directions. U.H.T. steel bar is also used for the operating sleeve, the cross-shaft, die side-stay and severalsmaller details. Carbide tools are widely used for machining in the heat-treated state, and both cadmium and chromium platingis employed (both processes requiring tremendous research pro- grammes). It is worth noting, incidentally, that the U.S.A.F.Wright Air Development Center prohibit cadmium plating on parts heat-treated above 200,000 lb/sq in. Yet anodier relevantfactor is the incidence of static fatigue in U.H.T. steel parts, although Dowty believe that by the time the aircraft has beenbuilt and prepared for its first flight static fatigue would either have already occurred or no longer be a problem. During die design of the Arrow gear an absolutely rationalstress analysis on derived loads had to be investigated, owing to the dynamic interaction of the flexible undercarriage and flexiblewing. It involved seven or eight times as many calculations as were necessary when the company designed the undercarriage ofthe CF-100. Extensive drop-testing was necessary to prove both the behaviour of the main gear and the performance of the LiquidSpring shock absorbers for both the main and nose units. Principal contractor for die nose gear is Jarry Hydraulics.Like Dowty's main legs, the nose gear is manufactured in U.H.T. steel, the members being machined from heavy forgings. At theupper end of the leg a Y-junction and diagonal arms lead to the widely spread hinge axes, die assembly being joined by foursubmerged-arc welds. Levered suspension is used to compress the Dowty Liquid Spring, and wheels and tyres are by Dunlop. Particularly worthy of note is Jarry's patent steering geometry,which employs a vertical jack and bell-crank to which is hinged die upper half of the main scissors-linkage, which in turn movesthe lower half of the scissors via a ball joint. Except for the piston, die steering system is of light alloy and it operates at thefull pressure of the hydraulic system. The complete assembly retracts forwards. The nose unit has undergone cyclic retractiontests, using electric heaters and dry-ice packs to simulate speci- fied extremes of temperature. Very successful drop testing—widia complete absence of shimmy—has been carried out against Jarry's 12ft-diameter drum, which can be spun up to a simulatedspeed of 200 m.pJi., well above the Arrow touch-down speed. Jarry have also conducted extensive research into high-temperature hydraulic systems. In special applications they are producing units in which the ends of actuator rods remain at880 deg F, ambient temperature being 550 deg F and fluid tem- perature being 450 deg F. Sealing materials and shapes havebeen developed largely at dieir own expense, and diey are well advanced in systems capable of operation from — 65 deg F up tothe temperature limits of die Arrow. All indications seem to suggest that die Arrow Mk 1 should be capable of reaching itsperformance boundaries while still using MIL-5606 fluid. Virtually all the systems of the Arrow are subject to securityrestrictions, and no quantitative data may be given. It is, how- ever, possible to comment on the air-conditioning system, forwhich die contractor is AiResearch. Included in this circuit is the largest stainless-steel heat exchanger yet developed for air-borne use (the choice of material being dictated by the arduous bleed-air conditions). Development of this heat exchanger hasspurred a complete family of related units, all of which utilize plate and fin construction assembled by a new vacuum-brazingtechnique to give homogeneous bonds devoid of impurities. Downstream of die heat exchanger is an AiResearch coolingturbine which feeds the cockpit; odier items developed by AiResearch include five oil coolers, two actuators and an elec-tronic temperature control. Avro, however, make all the air- A recent view of Bay I at Mai ton, showing (front to rear): the final "marry-up" jig; a row of Mk 1 centre fuselages; a complete Mk 1; and the metal mock-up, by the exit door.
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