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Aviation History
1956
1956 - 0901.PDF
FLIGHT, 6 July 1956 45 which the skin is flush-riveted in large panels. The frames immediatelyadjacent to door cut-outs are attached directly to the skin to provide duplicate load paths; the areas between the windows are protected bytear-stopping, closely-pitched vertical stiffeners attached directly to the skin. Aerodynamic calculation and tests show that a tail skid or bumperwill not be required but at least for preliminary flight testing a steel rubbing plate will be fitted at the area of contact in the event of anabnormal tail-down or flapless landing. The upper floor is composed of removable light-alloy panels stiffenedby longitudinal channel sections and designed as a passenger floor only. Rail fixings are employed for seats, bulkheads and other items of furnish-ing, such as buffets and wardrobes. The level freight floor is stressed to a local intensity of 200 lb/sq in and a general loading of 150 lb/sq ft. Basically the windows are identical with those of the Viscount, inthat they are ellipses 26inxl9in; 25 are standard windows in the parallel fuselage section, eight are arranged as emergency exits and fiveare handed left and right owing to the contour of the rear fuselage. There are in addition seven portholes for toilet and pantry regions. Inthe flight deck a forged frame carries eleven large windscreen panels. The main entrance door, forward to port, measures 73in x 39in andincorporates hydraulically operated folding steps; the latter are separate from the door which is at present arranged to hinge outwards on parallellinks to lie 6in from the fuselage skin when open. Opposite is an emergency exit and service door 66in x 26in. At the rear of the cabinis a second passenger entrance door and steps identical with the first with a similar 66in x 26in door opposite. A third emergency exit,50in x 24in, is provided further aft on the port side. Each freight hold is served by doors 66in wide x 51in on the starboard side, each splitlongitudinally into halves hinged upwards and downwards. All doors open outwards and are sealed pneumatically, a valve preventing open-ing with a dP greater than 0.4 lb/sq in. Wing. After extensive investigation, the optimum section was foundto be that of the Viscount, slightly thinned down to 15 per cent at the root and 13 per cent at the tip. The chief evidence of fail-safe designis the employment of three shear webs, any pair of which can maintain an adequate torsion box. This structure marks no lack of belief in thesingle-spar principle of the Viscount, but is merely better suited to the Vanguard. One reason is that integral tankage is essential for the bestrange and such construction is impracticable with a single spar. There are five main sections: the centre section projecting just beyondthe fuselage skin, two inner planes extending immediately beyond the outboard engines and two outer wings. The outers are not normallyremoved for overhaul but could be replaced for repair. The basis of the wing is a torsion box formed by the three shear webs and top andbottom machined integrally stiffened panels, together with closely- pitched pressed ribs. In general the panels are 20 to 23.26in wide andhave six or seven flanges. They are untapered and fade out at the sides as they meet the leading and trailing spar webs. The two upper centrepanels of each wing are bolted to the shear webs, the remainder being riveted. Except for the centre section, the complete torsion box with its endribs is sealed to form integral tankage. Access to the interior is gained through four bolted hatches on the upper surface of the inner planesand in the outer wings via access panels in the forward or rear webs after removing the detachable leading edge or aileron. The tips aredetachable metal pressings. Anchoring points for the powerplants and undercarriage are all external to the torsion box, on massive machinedribs. The machined panels in the torsion box are painted to prevent corrosion. Tail. Here the structure is conventional. The fin is divided into alower portion attached to the same frames as is the tailplane, and an upper section joined to the lower by removable pins. The leading edge,incorporating de-icing elements, is detachable. The rudder is made as a single surface with horn balance and spring and balance tabs alongalmost the entire trailing edge. Each half of the fixed-incidence tail- plane has 15 deg dihedral and is anchored to a centre section integralwith the rear fuselage. Three shear webs carry multiple ribs and the leading edge, with electro-thermal de-icing elements, can be unboltedfrom its location on the front shear web. The elevators have horn balance, set-back hinges and trim, balance and spring tabs along almostthe whole trailing edge. Thickness/chord ratio of the horizontal tail is 14 per cent at the root and 12 at the tip, and the junction with therear fuselage has been carefully developed to prevent break-away at high Mach numbers. Undercarriage. This is of Vickers design and manufacture. Thenose undercarriage has twin wheels steered by twin hydraulic cylinders through ± 70 deg, sufficient to pivot the aircraft about either main leg(with 360 deg movement when disconnected); the unit retracts forwards hydraulically into an unpressurized bay with twin doors. Each main leg—identical port and starboard—is hinged to forg-ings carried beneath the main wing box. Each unit has twin wheels with large 53in tyres inflated to the low pressure (by modern standards)of 98 lb/sq in, and retracts hydraulically forwards into the inner nacelles which are closed by double doors. Wheel and brake equipment is speci-fied by Dunlop or Goodyear, the brakes being of the multi-piston disc type with anti-skid control. All undercarriage units can be mech-anically unlocked to free-fall (assisted by a sprung toggle strut) in emergency; wheels-down limit is 200 kt e.a.s., since use as an airbrake appears unnecessary. Flying Controls. All flying controls are manually operated by push-pull rods and spring tabs. Relatively speaking the tabs do more than on the Viscount and they occupy virtually the whole trailing edge of eachsurface. Elevator balance is 25 per cent set-back hinges and horns (as on the Viscount 810). The rudder also has horn balance and a roundednose with a small gap. Apart from the use of spring tabs the ailerons resemble those of the Viscount, with a leading-edge beak and fabricseal. The dual cockpit control columns are pivoted at floor level. Mech- anical locks are designed to meet tail gusts of 80 kt and are tied to theengine throttles by the conventional nuisance-bar technique. Fowler-type flaps are employed, with a maximum angle of 40 deg. Double-slotted flaps would, for the same lift, have needed to run outto a greater angle and the increased drag would have adversely affected approach and baulked-landing climb performance. There are four sec-tions on each wing, the chord being constant throughout. All the flap portions are actuated by a hydraulic jack, in the inner wing, through acontinuous torque tube and a conventional cable system. Emergency operation is effected by an electrically driven pump feeding the samejack through a separate pipe system. Each flap section runs out along internal steel tracks (at one stage in the design these tracks projectedexternally), adjacent sections being linked by bogies running in the tracks on rollers. POWERPLANT. The engine is the Rolls-Royce Tyne 500-seriesturboprop. Each engine drives a 14ft 6in four-blade airscrew (de Havilland or Rotol are specified), fitted for auto-feathering (or pitch-coarsening), feathering and reversing, with electric de-icing and ad- vanced safety features.The Tyne has two axial compressor spools, the design pressure ratio being 13:1. The high-pressure assembly is self-contained but the three-stage low-pressure turbine drives both the front compressor spool and the double-reduction, quiet-running gearbox (0.064:1) to the air-screw. The first Vanguards will have the "stage I" Tyne rated at 4,020 s.h.p. (4,470 e.h.p.) dry. Stage II engines will be available in1961, with improved turbine-disc cooling and blade materials to permit the top temperature to be raised to a value giving 4,600 s.h.p. (5,075e.h.p.) wet; it will be possible to convert engines to this standard retro- actively. By early 1963 the stage III Tyne should be in service, ratedat 5,500 e.h.p. by improving the cooling of the h-p. turbine blades. All engines are interchangeable, complete with airscrews. Each unitis mounted on a triangulated structure off the firewall and can be changed (leaving the cowling and accessory gearbox undisturbed) inapproximately 30 min. If required, water/methanol injection is avail- able. The exhaust gas leaves through a tailpipe—partly single andpart-bifurcated—which passes across the wing to a propelling nozzle above the trailing edge. The cross-section of the nacelle and pipefairing is reduced above the wing to minimize local airflow acceleration at high Mach numbers. A Rotol accessory gearbox is mounted in the lower part of eachnacelle with a mechanical drive from the 1-p. spool. Each box drives an airscrew parking brake and a 50 kVA de-icing alternator; the innerboxes also drive cabin blowers and hydraulic pumps. Engine starting is electric by a D.C. starter/generator which also serves as the mainsource of electric power. The starter drives the h-p. spool only, the
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