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Aviation History
1919
1919 - 0711.PDF
MAY 29, 1919 1/j^sJ Fig. 17. of Humber's, Ltd. An original design from which this firm's design was developed was very courteously placed at their disposal by Capt. Green, of Siddeley Deasy. A drawback to all the designs heretofore described is the difficulty in applying them t© existing machines without re-designing the fittings. Messrs. Humber have produced a design which solves this difficulty, and they constructed a metal machine in record time. Fig. 18. The first section (Fig. 18) was made of 25 gauge 31 ton steel sheet for both flange and web. The width of the flange was 2 ins. and a stiffening bead or longitudinal corrugation was rolled in the centre of the flange throughout its length. The web was lightened by circular holes punched on either side of a longitudinal bead or corrugation in the centre of the web and slightly smaller than the flange. This section is the same in all over-all dimensions as the standard Avro spar. The spar was made up of four lengths joined together by staggered lap joints, three of these lengths being identical, the fourth being tapered to suit the outer extremity of the wing. The webs and flanges were pressed to shape in a stamping machine. The ultimate section decided on was similar to the above but of 35 ton steel with the flange and web of 26 gauge. Fig. 19 shows a photo of the first plane built up on metal spars and tested at Farnborough, where it successfully with stood the required load. Fig. 20 shows in detail the method of attach ing the internal bracing and strut sockets and wiring plates to this wing. Standard Avro fittings are used throughout. The interplane strut fittings are raised from the spar by means of a very light steel box. The spar is stiffened to take internal bracing by means of a pressed steel cross transmitting the strain radially from the transverse bolt to the flanges and webs of the spar. The spar itself is stiffened to take torsional strain by means of aluminium distance pieces, the webs being connected by means of aluminium rivets passing through the distance pieces. The thrust of the interplane struts is taken on an aluminium pillar passing radially through the spar directly under the strut, the pillar being pierced by the trans verse bolt which passes through pressed steel crosses. These crosses distribute the load over a large area of the spar. Figs. 21 and 22 show another method of attaching the fittings which is self-explana tory. The specimen has been tested to destruction and shows the failure of the flange in the centre. Struts The solution of the strut problem is much simpler than that of the metal spar. There are several principles which must be kept in mind in tackling the problem. Since the external shape must be such as to offer the minimum head resistance, we are limited — -T Fig. 19. iWm -• " •PHl*w*i**w f -1 ij. • 711
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