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Aviation History
1919
1919 - 0710.PDF
MAY 29, 1919^ METAL CONSTRUCTION OF AIRCRAFT BY A. P. THURSTON, B-.Sc,, F.R.AE.S., F.R.MET.S., M.I.A.E. Continued from page 684) FIGS. 12 to 14 show photographs of the modified fittings of the Rudge spars. In this case the lift and anti-lift wires are pivoted to the central tube. The photographs are self-explanatory. Fig. 12. The flange is provided with two corrugations having flat horizontal edges. The centre portions of the webs are stamped with flanged holes as in the early Rudge spars, and are pro vided with longitudinal corrugations above and below these holes. The edges of the web are doubled over to embrace the flat edges of the flanges, and the spar is completed by suitably placed rivets. This spar is extremely efficient under test. A spar made from material whose ultimate tensile strength was given by the manufacturers as 40 tons, developed a stress of 43.5 tons per square inch in the flanges before failure. It is claimed that this spar is 12 per cent, lighter than a spruce spar and will sustain 70 per cent, in creased bending moment. The first specimens were rolled from 40-ton steel .018-in. thick. Flanges of steel with higher tensile strength are now used, and the ultimate strength of the flanges is developed simultaneously with the ultimate shear stress of the webs. Fig. 16 shows an early specimen in shackles, taken after testing to destruction. The flange of this specimen is pro vided with a single shallow corrugation, and failed before the full strength of the specimen had been developed. The dent in the flange shows where the spar failed.. Fig. 17 shows a photograph of a complete pair of wings provided with Boulton and Paul spars. Humber Spars The spars previously described have been made from rolled strip. A second alternative is to construct spars from Fig. 13. Fig. 14. Boulton and Paul Spars Very interesting experiments have been carried out by Boulton and Paul with a modified type of Rudge spar shown in Fig. IS- metal sheet which can be obtained in lengths up to 10 ft. from firms such as Sankey's and Firth's. Valuable and useful work has been carried out in developing this form of construction by Col. J. A. Cole and Mr. Nibblet, Fig. 15. Fig. 16. 710
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