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Aviation History
1934
1934 - 0289.PDF
fL,iyjni, iVIAKCH ii, Fig. 2 : Appearance of surface when stringers buckle. the question of the use of multi- spar wings, considering in parti- cular the economic distribution of the material and the cost, Bur- gess's method (Ref. 14) of esti- mating the forces in the separate- members of a multi-spar wing due to torsion, being used. Concerning the question of manufacture, the lecturer said that panel beating on a ia>ge scale could be avoided by the use of developable surfaces and by care- ful selection of the shape of sheet- ing. The stringers and hoops should be continuous, the hoops being deeper than the stringers and a hole cut in the former to allow the uninterrupted passage of the latter, no connection other than through the medium of the skin being necessary between the hoops and stringers. Rivetting was stated to be a most expensive item, and every effort should be made to reduce it. A search for means to do this had brought to the fore the question of electric re- sistance, spot or roller welding. Two causes had delayed their general adoption by aircraft manufacturers, the first being the scarcity of suitable materials which after weld- ing, and without subsequent heat treatment, have mechani- cal properties requisite for aircraft structures, and the second the absence of fool-proof welding machines. Several of these latter were, however, now said to be available. Owing to the increase in drag on the skin due to the use of snap heated rivets (Ref. 15), flush rivetting was very desirable, and electric resistance welding made an obvious appeal for this reason as well. Much experimen- tation had been done at Bristol in connection with steel spars, and reference was made to the effective after-weld- ing heat treatment of Ni-Cr steel spars by A. V. Roe, Ltd., at Newton Heath, Manchester, where the spars were assembled by roller welding and the complete member heat treated by the electric resistance method (see FLIGHT for April 27, 1933). Interest was also shown in the recently discovered atomic hydrogen method of welding developed by Metropolitan- Vickers, Ltd., which appeared to have definite advantages over oxy-acetylene in as much as carburisation or oxidisa- tion of the weld could not take place. As there can be no question of heat treatment of light alloy, stressed skin structures, subsequent to welding, the production of re- liable welds in these materials seemed improbable, until the aluminium-rich Mg-Mn alloy known as 4S. was tried. Thisalloy was made to Air Ministry specification D.T.D.209, and fatigue tests have shown it to be most eonsistent sofar as welding was concerned. This material has been developed by the Northern Aluminium Company, and thefollowing table gives its physical properties. PHYSICAL TESTS ON 4S SHEET MATERIAL 4SO. . 4SJH 4S1H 4SJH 4SH •- I Gauge 0-040 (1-022 0-036 (1-064 0-018 0-018 0-048 0016 0-064 0 048 Yield Stress tons/sq. in. 4-87 11! 12-95 11-9 13-3 15-6 13-7 16-9 E =- 4 0-1 per cent. Proof Stress tnns/sq. in. 8-1 12-75 12-45 13-3 13-3 14-70 16 • 25 15-8 17-55 19-0 15-7 l«-9 ,400 tuns per sq. in. 0 • 5 per cent. Proof Stress tons/sc]. in. 8-75 13-4 13-5 13-4 14-7 15-5 17 2 17-3 Max. Klonga- Stress ti»n per tons/sq. cent, on in. 2 in. 12 5 13-95 14-15 14-05 15-5 lfi-3 17 • 65 17-S 19 1 17-9 lfi-O 4-0 60 60 40 3-5 4-0 3-0 3 0 5-5 Coming to the subject of corrosion, Mr. Pollard dealt briefly with both stove enamelling in the case of steel, and anodic treatment for aluminium alloys, referring also to special corrosion resistant materials such as Alclad and steels of the " two-score " type. References 2 The strength of thin plates in compression. PasadenaPublication No. 13. A. & M. 54-5. Theodor vonKarman, E. E. Sechler, and L. H. Donnell. 3.—Survey of problems of thinwalled structures. Theodor von Karman, E. E. Sechler,and L. H. Donnell. 4.—N.A.C.A. Technical Note455. Comparison of three methods for calculating thecompressive strength of flat and slightly curved sheetand stifiener combinations. Eugene E. Lundquist. 7.—N.A.C.A. Technical Memo-randum 490. Structures of thin metal, their designand construction. H. Wagner. 8.—N.A.C.A. Technical Memo- Fig. 6 : Sheet-web spar. Stiffeners widely spaced. Booms deformed.
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