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Aviation History
1942
1942 - 1697.PDF
AUGUST 13TH, 1942 FLIGHT 175 AVRO LANCASTER The Lancaster is characterised by underslung engines, a fairly thin wing, and twin rudders. Length - Span - - the British aircraft indus try, has graduated to his present position through the hard school of works managership, and has re tained his insistence upon the manufacturing aspect being kept prominently in mind during the design stage. It would be fair to say that the Lancaster was vir tually designed around a chassis'' formed hy the bomb bay roof, the wing centre section, and the un dercarriages. The floor is of great length to aecorr.mo- date the bomb load, which may include the largest bomb visual ised at present, and is slung from the spars of the wing centre section, so that these two frames form the fore- and-aft and transverse limbs of the cross-shaped chassis which is the backbone of the whole aircraft. * In its turn, the main structure of ^-the roof of the bomb bay are two extruded double-channel or "pi" sections. If one adopts the latter name, the arrangement can be visual ised as the Greek letter pi lying on its side (see sketches). This extrusion is a very fine piece of work, and prac tically no machining is necessary, even the shallow- recesses for the skin plating of the fuselage being formed during the extrusion process, and not by subsequent machining. The Centre Section The centre section of the wing is of equally simple construction. The spars are, somehow, reminiscent of the old days of wooden aircraft, when it was common practice to gouge out the spar flanges on spindle machines. In the Lancaster these flanges are light alloy channels of impressive dimensions, and the manner of using them is interesting. Instead of placing the channel sections with their 69ft. 6in. - 102ft. Height - - 20ft. 6in Weight - - 60,000 lb Fuselage construction and the " pi- section " longeron of the bomb bay. backs towards the wing covering, they lie on their sides, and the solid sheet spar web plating is riveted to the closed sides of the channels. It will be seen that this arrangement greatly facilitates the attachment (by bolting) of other structure members, equipment, etc. The similarity to wood construction goes farther. The spar flange channels ate routed out in much the same way, and the taper ia the spar flanges from centre section to wing tips is obtained by milling away portions of the channel walls. Centre- section ribs are in the form of N- girders, the limbs ol the N being simple channels, with the free edges turned inwards so that there is only a fairly narrow gap left between them. Such sections can be very simply joined together by plain gusset plates and rivets. Use of Castings When it came to attaching the un dercarriages to the ends of the centre- section front spars the metal founders came to the aid of the Avro designers. The Northern Aluminium Company produced some rather remarkable castings in a new light alloy, and these, with a minimum of machining •of faces for the pick-up points, sup port the undercarriage units and the inner engines. To have built up these large brackets would have entailed a very complicated and heavy structure. The castings are light and the job greatly simplified. Reference has been made to the girder ribs ef the wing centre section. In the outer wing portions the ribs have L-section flanges and sheet webs, with spanwise stringers bracing them laterally and stiffening the skin covering. The leading edge is a
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