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Aviation History
1959
1959 - 0161.PDF
FLIGHT, 9 January 1959 65 Fuselage. Flying in the same well-explored altitude band asth" Viscount, and hence working to the same pressure differential, the changes from the latest Viscount standards are few. Structureis conventional, and consists in the main of channel-section frames at about 20in pitch supporting Z-section stringers to which theskin panels are flush-riveted. Both stringers and frames are con- tinuous; and the latter, whilst basically floating, are cleated to theskin throughout. Nowhere is there more than about 100 sq in (20inX5in) of unsupported skin. All material is Alclad, single-heat-trea,ted, the skin being L.72 and the stringers L.73. Sheeting is Alocromed and the entire structure is painted. Basic structural philosophy has been to obtain long life freefrom fatigue and, at the same time, to provide alternative load- paths wherever appropriate, together with provision for arrestingcracks or ruptures which might otherwise grow too rapidly between inspection cycles. The lower left illustration on p. 74should suggest the efforts which have been made in the field of crack-stopping and structural integrity. The thickness of thepressurized skins and their lower working stress-levels are aimed at long life, and allow the rivets to be cut countersunk (the rivetsare of a 70-deg pattern, originally developed for the Valiant). It is worth noting three basic structural changes from the Vis-count. First, the complete fuselage splices are in single circum- ferential planes, instead of with staggered skin plating and alter-nately staggered stringers on either side of a frame; this eliminates the slightly obscure stress-raising potential of the staggered prin-ciple which results from the distribution of local structural stiff- ness. Second, the cockpit floor is not pressure-bearing and thenose undercarriage is retracted into a pressure-box let into an otherwise continuous pressure-shell (as on the V.1000). Third,the cockpit structure is an integral part of the basic fuselage; the structural surrounds for the cockpit glazing are machined fromquite large forgings and it is worth noting that only five main forgings are used for the complete set of 13 windows (or 11 on theT.C.A. type, which has a redesigned direct-vision window arrangement). In the first stage of fuselage construction the stringers, windowsurrounds and similar pieces are assembled to the individual panels. Most of the fuselage is constant-section, so the majorityof these panels have single-degree curvature and complex stretch- ing is avoided. These panel assemblies are then attached to theframes and door surrounds to form half-bodies of fuselage split on the centre-line (sketch, top of p. 76). The subsequent stage bringsthese sections together, with closing panels at the top and bottom, on to the basic floor structure which has been previously loadedinto the final sub-assembly jig. Individual floor panels and beams are readily replaceable, and glass-fibre beams are used above thewing so that this portion of floor can "breathe" with wing bending. Pre-assembled nose and tail-cone structures are joined at this stageand, together with an integrally assembled centre-fuselage and wing, are mated in the final brief structural-assembly stage. Infact, only one final fuselage-assembly jig is required for each two sets of major sub-assembly jigs. Door openings are rectangular, and the doors operate on aparallel linkage developed on the 800-series Viscount. All doors embody forged and machined surround frames, with extensiveReduxed and riveted doubling plates for a second load path. Each door has multiple claws, with over-centre locking. As shown onpage 75 a new type of seal, inflated by cabin pressure, has super- seded the pneumatically inflated type of the V.800/810 series. Thepopular elliptical window of the Viscount has been retained. The emergency-exit windows are of a revised type, held by four sprungplungers. The double-bubble fuselage cross-section originated in a B.E.A.expressed passenger-preference for a high-wing layout, such as on the Elizabethan (Ambassador). After considerable theoreticalinvestigation into structure-weights, aerodynamic cleanliness, undercarriage design, propeller ground-clearance, etc., Vickersmade a detailed survey of the opinions of the world's major opera- tors. Whilst most airlines tended to support the passenger-appealfeature of the high wing, there were very strong objections on other grounds. These were forcibly expressed by a sufficientnumber of operators to increase the reluctance to a high-wing design to the point where reluctance became refusal. Theseobjections were associated with: ditching characteristics, and pas- senger evacuation in these circumstances; relative passenger vul-nerability in the serious belly-landing type of accident; and the difficulty of visual confirmation by the crew of satisfactory snowclearance from the top surface of the wing while a take-off was in progress. For the ditching argument, a survey was made of the numberof important airports throughout the world in which the take-off was made over water—even though the flight might be a domesticover-land service. Not only was the total number of such flights of considerable surprise to the investigators, but the incidence ofditchings which had occurred in relatively shallow water, near to land soon after take-off, was too significant to be ignored. On the subject of serious belly-landing accidents, Viscountexperience alone had indicated the vital part which is played by the under-floor belly holds and surrounding structure in protect-ing the passengers from injury. Accordingly, a high-wing layout was not adopted. Neverthe-less, a number of the secondary advantages of a high wing were still demanded—such as a freight flc_ at truck-bed height, withadequate interior working depth, whilst retaining adequate pro- peller ground-clearance. These logical requirements effectivelyfixed the low-mid wing arrangement; and once the passenger- cabin floor area, and the freight-hold depth and position, had beenfixed, the resulting aerodynamic and structural envelope auto- matically determined the freight-hold volume. Choice of adouble-bubble cross-section was also effectively automatic. Once the passenger cabin width at elbow level (128in) had been fixed,together with the under-floor freight-hold depth (51in), the logical structural envelope is a double-bubble and not a circle. Empennage and Flying Controls. Fin and tailplane structuraldesign follows directly from that of the wing. Each of these sur- faces incorporates a twin-torsion-box structure, but the skins areof conventional skin/stringer construction. The tailplane is con- tinuous through the fuselage, and both the fin and tailplane shearwebs are attached to the same three fuselage frames in an unpres- surized tail-cone. Construction of the elevators and rudder isunusual, and exceedingly neat. Spanwise members are used at the leading and trailing edges, and ribs are placed flanking thehinges and at the ends of each surface. The structure is completed by pre-formed skins of sandwich construction, each panel beinga Redux-bonded honeycomb some 0.5in thick. Honeycomb con- struction is not employed in the ailerons, which are each splitinto three portions to take up wing deflections. Flying controls follow directly from the Viscount, with entirelymanual operation. The short-cut method of power controls, or the compromise of power boost, were discarded after fair evalua-tion and having regard to operators' opinions. All flying-control surfaces are manually operated through large servo or spring tabs.Tab profile is critical, and each tab is honeycomb-stiffened. Aero- dynamic balance is provided by set-back hinges on the elevatorsand rudder, and by Irving-type shrouded balances on the ailerons. Trimming is manual and conventional, and the tailplane is fixed.The operation of the controls through spring-tabs means that neither the ailerons nor the elevators are directly connected acrossthe aircraft. Flight development of the Vanguard controls has been carried out on a specially modified Viscount 810. Flaps. The Fowler-type flaps are divided into four sections oneach wing, and are operated from a large hydraulic screw-jack in the starboard inner plane just behind the main torsion box. Thisdrives all eight flap sections via a span-wise torsion shaft and cables attached to the guide-rail trolleys of the flap sections. Take-off and landing settings are respectively 20 and 40 deg.As is usual with the Fowler pattern, nearly all the angular deflection occurs after the major part of the rearward travel has taken place.Flap angle is controlled by trolleys which run in double-tracked guide rails inside the rear nacelle-fairings; unlike the Viscount,telescopic tie-rods are not employed. Appropriate precautions have been taken to arrest the flaps, and avoid asymmetric blow-back, in the event of shaft or cable failure. An important feature of these flaps is their parallel motion, which results from the useof constant chord, rather than constant percentage-chord as on the Viscount. The geometry of a constant-percentage-chord flapresults in a complex motion, which contributed to some of the earlv problems with the Viscount system. Undercarriage. Of Vickers design and manufacture, the under- The first hull, before furnishing. Inferior volume above the floor is 5,690 cu ft, maximum height is 86.5in and the maximum width 128in
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