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Aviation History
1928
1928 - 0132.PDF
16 SUTPLBMBBT TO FLIGHT Top Longerons. Bottom Longerons. Vertical Struts. Diagonals. 1 Member. fBLJ BK IBJ [BH fAC1 AD *> AE1 AF [AG fCLJDK IE J[FH fBC LD 1 KE JF THE AIRCRAFT ENGINEER TABLE II.—FOR SOLID-DRAWN TUBULAR 2 3 ! Length. ! Area. L. 26 33 31 29 14-2 26-3 33-4 31-3 29-3 20-6 250 30-8 360 23 0 33-5 42-0 440 47 5 A. 0-057 0-057 0-057 0-057 0-057 0 057 0-057 0-057 0-057 0-029 0 035 0 035 0 035 — 4 Radius of Gyration. K. — 0-425 0-425 0-425 0-425 0-425 0-21 0-260 0-260 0-260 — 5 L/K. — 33-3 62-0 78-5 73-5 69-0 98-0 96-5 118-6 138-5 — 6 — 78,000 50,200 36,000 40,400 44,000 25,000 26,800 18,600 14,100 — 7 P. 7,000 7,000 7,000 7,000 4,450 2,860 2,050 2,300 2,500 725 940 650 495 1,050 1,050 1,050 1,050 1,050 FRAME 8 Actual Load in Member. 5501 1,280 1 1,875 f 2,260j 5551 1,294 1,900 • 2,285 2,560j 700 565"] 455 > 385J 900] 930 760 y 530 435J FEBRUARY ?3, 1928 9 Description of Member. ljin. o/dia. x 28 S.W.G. (T.5). li in. o/dia. X 28 S.W.G. (T.5). f in. o/dia, X 28 S.W.G. (T.5). | in. o/dia. X 28 S.W.G. (T.5). 4 B.A. tie rods. stresses ; apart from military aircraft, where members are liable to damage in action, there is no need for bulkhead bracing at all, since it is found experimentally, and by calcula- tion, that such bracing does not affect the strength or rigidity of the structure. A panel point having no bulkhead bracing is shown in Fig. 4. A simple comparative weight and strength estimate will be made of a structure as described, and a similar frame built from T.5 tube and wires. The dimensions of the uni-planar structure are given in Fig. 1. It is assumed that a load of 800 lbs. is suspended from 0 and the flat frame is held at XX. Figs. 8, 9 and 10 are sections of longerons, ties and struts made from steel strip to Specification S. 40. These have been designed to support the loads given in column 8. The sizes of the struts have been derived from the appro- priate curve, as shown in Fig. 11. In Tables I and II, the full particulars of the " strip " and " tubular " fuselages are given. For the section of Table I marked " Diagonals," the load has been reversed ; these members have to act both as ties and compression members, and obviously the case to consider is when these diagonal bracings act as struts. A moment's thought will show that this procedure does not alter the numerical value of the load in the members, but merely the signs. In Table II it is assumed that these struts are replaced by two swaged wires, complete with fork ends and pins. In each case, column 1 denotes the member; column 2 its length, L ; column 3 its area, A ; column 4 the radius of gyration, K ; column 5 the ratio, L/K ; column 6 the corresponding value of stress, P/A, obtained from the graph ; column 7 the loads from columns 6 and 3 ; in column 8 the forces induced by the applied load ; and in column 9 a description of the member is given. A comparison of the figures in column 7 in the tables gives the relative strengths of the two frames, which, in the worst cases, are approximately equal. A simple computation of the relative rigidities of these frames is not possible, but tests which have been made show this to be decidedly in favour of the strip construction. From the lengths and areas of members given, the weight of each is quickly derived ; Figs. 8, 9 and 10. U6d
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