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Aviation History
1955
1955 - 1147.PDF
19 August 1955 foresee that avoidance of highly stressed booms, susceptible to fatigue, will greatly increase the life of the wing. Shear loads are taken by three lightly loaded web members. The outer wings are attached to the centre-section by numerous bolts which carry the load from the outer wings into the sandwich skin-panels. The centre-section comprises a centre box, leading edge and trailing edge. The centre box has a corrugated metal sandwich- skin and three vertical webs, the centre web being a corrugated metal sandwich and the other webs built up of stiffened light- alloy plate. This form of construction effectively reduces the number of ribs required; in fact, the only ribs are those at the load- carrying attachment points, namely the centre-section-to-fuselage attachment, nacelle and undercarriage pick-up points, and wing joints. The centre-section is attached to the fuselage by rigid fittings and hinge-links on the front and rear webs, ensuring that wing deflections are not transmitted to the fuselage. Normal stressed-skin construction is used for the outer wings, each of which has two webs and pressed diaphragm ribs. The skin over the leading edge is spot-welded to shallow members having chordwise corrugations, and a gap of approximately O.lin between the corrugations and the skin is used for the distribution of hot air when a leading edge anti-icing system is installed. The trailing edge has a false spar to accommodate the flap shroud and closely pitched riblets covered by a single skin. The centre box in the centre-section, outboard of the inner engine nacelle, houses the fuel tanks, and space is available for additional tanks at the root of the outer wing. Housed in the leading edge, forward of the centre box, are the engine and aileron controls, electrical wiring, and cabin heating and pressurization ducts. The flap controls, hydraulic pipelines, fuel lines and pressure-head piping run behind the centre box. Hinged doors in the undcr-surface of the wing give access to the controls and service-piping runs. The ailerons extend from the outboard ends of the metal- covered Fowler flaps to a point 15in inboard of each wing tip. Each is mass-balanced by a weight carried on an arm operating within the tip itself, and aerodynamic balance is achieved by geared tabs and an internal forward balance. Each aileron has a spring tab and in the port one is a trim tab. The fuselage is of stressed-skin construction and of constant section over the greater portion of the cabin. The cross-section is formed by two circles intersecting on two chine beams running longitudinally at floor level. Below these beams construction utilizes top-hat section stringers and pressed frames, the frames supporting the floor; above, top-hat stringers and Z-section frames are employed. The skin panels are spot-welded to stringers which are in turn pop-riveted to the frames. Supporting the wing are two box-section main frames of sufficient strength to withstand belly-landing loads. There are three main bulkheads. One, at the aft end of the cabin, and another, at the forward end of the cockoit, are pressure bulkheads; the third forms the rear of the cockpit. Extending the whole length of the cabin are two top-hat- section floor beams, carried on top of the lower-frame pressings, and carrying the inboard anchorages for the seats. Outboard anchorages are carried on members between the frames at the cabin wall above floor level. In the port side of the fuselage are doors for crew, passengers and freight. The crew door is just behind the cockpit, which is entered through the radio and freight compartment. A large double doorway at the rear of the fuselage is for the handling of freight; only the forward half is used for passenger entry. Between the frames and on both sides of the cabin are circular windows, having dry-air insulation to prevent misting. Each pane can withstand the full pressurization load. There are two escape hatches on the starboard side, the forward one measuring 2ft 9in high by lft lOin wide, and the rear one (which extends to the cabin floor) 4ft 2in high by 2ft wide. The cockpit canopy com- prises five flat window panels, the side windows being arranged to slide for direct vision. The fuel cross-feed pipe runs over the fuselage, inside the wmg. Electrical and hydraulic services are kept apart; electric cable- runs are in the roof; and hydraulic pipelines under the floor, as are the elevator and rudder control runs. Aileron and engine con- trols and hot-air and pressurization ducts are in the fuselage roof. Removable panels in the ceiling and floor give ready access to the services. The use of fluted skin renders construction of the tail extremely simple, for internal structure is reduced to a minimum. The effect on drag is negligible. Each tailplane sub-assembly is built round three spars with fluted light-alloy skins and pressed light-alloy sheet ribs; each elevator has two spars, main and nose nb, a tab- attachment member, and a tip fairing. Here again, covering is fluted light-alloy. The fin is built up from spars and pressed 261 The Herald's main undercarriage legs retract forward, as shown, into the inboard engine nacelles. light-alloy sheet ribs, and it too has a fluted skin. The spars are bolted to the attachment bulkhead at the rear of the fuselage. Similar in construction is the rudder. The leading edges of die fin and tailplane have shallow chordwise corrugations beneath the outer skin to act as distribution ducts for hot air when the anti-icing system is installed. The elevators have sloping horn balances and are joined by a torque tube. Aerodynamic balance is by geared tabs and an internal forward balance. The port geared tab can be mechanically operated for trim by the pilot. The rudder also has a sloping horn balance to contain the mass-balance weights, and this, too, is aero- dynamically balanced by means of geared tabs and internal forward balance. There are two tabs, one above the other; both are geared balance tabs, but the upper one can be mechanically operated for trim. All three units of the Electro-Hydraulics undercarriage have single oleo pneumatic struts, with twin wheels mounted on stub axles and all are locked in their extreme positions by hydraulic jacks. The main units are hinged from forgings attached to the mainplane rear web and ribs, and each is stayed by a drag strut secured to the mainplane front web and ribs. The units retract forward into die inboard nacelles. The nosewheel unit is of simple cantilever type and retracts forwards into an unpressurized bay in the nose; it can be steered hydraulically by a wheel on the control column through an angle of plus or minus 55 deg, and has an hydraulic self-centring mechanism and can be released, by a spring-loaded catch, to castor through 360 deg. The wheels have hydraulic disc brakes and the tyres are of low-pressure (50 lb/sq in) type, to permit operation from grass runways. Wheels, tyres and brakes are of Goodyear manufacture. The undercarriage is lowered and retracted by a gated lever operating a solenoid selector. Inadvertent retraction when the air- craft is on the ground is prevented by an electrical switch on the undercarriage leg. Three flap positions—up, take-off and landing— are possible. The four Alvis Leonides Major engines are attached by dynafocal mountings to a frame which, in turn, is attached to the nacelle at four points on the fireproof bulkhead. Each cowling has four petals—two large ones at the side and smaller ones at the top and bottom. The bottom petal is hinged across die fire- proof bulkhead, but die odier diree are hinged behind the bulk- head. Fastening is by quick-release toggle fasteners, and opening of die side petals gives access for normal servicing. Just behind the engine induction casing is a fireproof shoulder cowl, in order to protect die accessory bay and piping from fire hazards. A fireproof flexible seal makes contact with this cowl and the petal (Continued on p. 264, after double-page cut-away drawing of the Herald) Flap in take-off and fully down positions. Also in- dicated here is the hot airflow of the (optional) leading-edge de-icing system.
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