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Aviation History
1955
1955 - 0765.PDF
3 June 1955 763 FRIENDSHIP Basic Simplicity Plus some New Techniques bulkhead, is of the two-radius section already mentioned. Theupper part (that above the cabin floor level) is constructed of main frames, form frames, Z-section stringers and 24-S.T. sheetskinning. In the cylindrical section the stringers are Redux- bonded to the skin, and the main frames are riveted through angle-pieces to the skin, and the form frames are riveted to the stringers to prevent buckling under compression. In the double-curva-ture section near the door the stringers and form frames are riveted to the skin. There is a degree of flexibility in theconstruction of the main fuselage in that it can be made up by joining five sub-assembled sections, i.e., the stringers do not runcontinuously along the whole length. At the end frames of each subsection, the riveted joints are reinforced by Reduxed andriveted gussets. The design of the window cut-outs aims at maintaining a lowgeneral stress-level in the vicinity, and this has been achieved by again employing Redux-bonded reinforcing plates, both overa wide surrounding area and in the immediate vicinity of the riveted window-frames.The bottom section of the main fuselage was so designed as to provide extra strength against the possibility of an emergencywheels-up landing. It comprises two stiffened longitudinal beams, cross-formers, and longitudinal side-members, all rivetedto 24-S.T. light-alloy sheeting. The formers are of a greater radius than the upper-section fuselage frames, and there is aresulting compressive stress on the floor itself. Transverse panels of one-inch-thick metal honeycomb, glued by means of Reduxfilm (together with a 1-in wide wooden framework) between two 24-S.T. sheets were adopted for this main-cabin floor. The eight-point wing attachment is based on the four forgedfuselage-brackets of 75-S.T. zinc-bearing aluminium alloy. The four-point internal connection is formed by the ends of thebrackets being attached to lugs on the appropriate spar; externally, a lug on each bracket projects through the pressure-cabin skin andis connected via a double link to the spar attachment fittings. The lower surface of the centre-section, passing across the fuselage,forms the top of the pressure cabin in that area; and shaped top- fuselage skin sections, accommodating the contour-changeimmediately ahead of the wing front spar and aft of the rear spar, are joined to the centre-section by means of Z-section attach-ment pieces. At all internal joints in the pressure cabin, E.C. sealing compound is applied. Fillets between the "step-down" in fuselage section and thewing leading-edge ensure a smooth change in cross-section and accommodate control-cable runs along the top of the fuselage.The dorsal fairing (running above the elevator and rudder-cable tunnel) aft of the wing is constructed of light ribs and longitudinalstringers. The main passenger entrance on the port side measures5ft 5in X 2ft 5in, the sliding door moving inwards and rearwards. The standard 28-seat interior layout is as shown in the diagram,the lightweight double-seat units being of Fokker/Rumbold design. The seats are directly attached, through the floor, to thelongitudinal crash-members beneath, and are capable of with- standing a deceleration of 9g, facing fore or aft. Emergency exits are combined with two of the cabin windows,and a floor-level emergency exit, 3ft 8inX2ft 5in, is provided on the starboard side of the cabin, opposite the main entrancedoor. In the pilots' cockpit, the aft-sliding starboard side- window, 19in X 22in, is available as an escape route. Behind the rear pressure-bulkhead—which is stiffenedvertically and horizontally—the air-conditioning equipment is to be located. The tail-cone itself, of conventional construction,incorporates riveted stringer/skin techniques on the prototype aircraft, but Redux will be used for production machines.Wings. The Friendship wing, of stressed-skin construction, comprises the centre-section, which carries the engine nacelles,and two detachable outer-wing sections. Both centre-section and outer wings possess three main component parts; a rigid torsioncell, leading-edge section and trailing-edge section. The use of 75-S.T. light-alloy in the torsion cell has resulted in a rela-tively low weight, combined with good fatigue properties. The torsion cell is formed by front and rear main spars, topand bottom 75-S.T. skin panels, main and form ribs, and closely spaced top-hat-section stringers. The spars are of particularinterest, the booms being made up of glued laminations formed into angle-sections and T-sections, as shown in the diagram onpage 767. The change in section is effected by progressively reducing the number of laminations along the spar, thus com- bining optimum strength properties with lightness and simplicityof construction. Another important use of glued laminations is seen on parts ofboth upper and lower skins near the six wing-junctions (two centre-section/outer-wing junctions, plus joints between the threeskin-and-stringer panels of each outer wing). At these positions, progressively laminated reinforcing panels are glued to the skin.The centre-section has 2 mm (bottom) and 2\ mm (top) inter- spar skins of 75-S.T. alloy, riveted to the bottom stringers andglued to those supporting the top surface. The outer wing incor- porates a machine-tapered (from 2 mm to 1.3 mm) skin over thetwo inboard sections; over the whole length, the stringer/skin attachment is by glueing, with riveted end-sections, boltedattachment rods and glued reinforcing panels at the inter-section junctions. The main attachment of the outer wing to the centre-section, just outboard of the heavy forged centre-section rib, is by means of connecting bars, screwed interleaving doubler plates (topand bottom) and, along the top of the attachment only, riveted fork fittings held by shear bolts. Along the wing, a small numberof ribs are riveted to the skin, but the majority are riveted to the parallel stringers, thus assisting (together with the glued stringers)in providing an extremely smooth skin surface. For the leading edge, which has to accommodate the sameelongation as the inter-spar section, Fokker's requirement was for a material with a relatively low modulus of elasticity. Thecompany's work on laminated glasscloth impregnated with polyester resin led to the selection of Fibreglass for the centre-section leading edge and, indeed, for many other similar parts in the aircraft. The centre-section leading-edge assembly includesribs and U-stiffeners also made of Fibreglass. The same type of material is employed for the outer-wing leading edge on theprototype: in subsequent machines, however, the requirements of the de-icing system will involve a metal leading-edge structurein place of Fibreglass. The trailing-edge ribs are of mixed plastics and metal con-struction, riveted to the rear spar, and they support a Fibreglass skin (with metal area aft of the jet-pipe outlet). The rear mainspar extends at 60 per cent chord as far as the second joint in the outer wing, where, at the flap/aileron junction, its positionchanges to 51.25 per cent, remaining thus for the length of the outboard wing section. This will be replaced on series machinesby one continuous rear spar. The integral fuel-tanks are located in the outer wing betweenthe front and rear spar, and between two closed tank ribs, with intermediate tank baffles. The inboard tank rib is adjacent to thewing attachment to the centre section. All joints, as in the pressure cabin, are coated with E.C. sealing compound, and eachtank compartment is provided with an inspection panel. Total capacity is 818 gallons. To ensure a continuous fuel flow to dieengines and to reduce the residual fuel, a small collector tank with Standard 28-seat version provides 282 cu ft cargo space; the 36-seater, 177 cu ft. Each layout features 100 cu ft rear baggage space. Con- version to 24-seat and 32-seat versions is practicable.
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