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Aviation History
1913
1913 - 0767.PDF
JULY 19, 1913. TESTS ON WING SPARS. i/usis By ALEC OGILVIE. [IN consequence of the uncertainty that exists respecting the nature and magnitude of the stresses in the wing spars of aeroplanes, which has been the subject of very much discussion of late, Mr. Alec Ogilvie has carried out at his shed at Eastchurch a series of practical tests, the result of which he has communicated to us without delay, so that they may be immediately published for the benefit of all concerned.—ED.] The object of these tests was to determine the relative strengths By the theorem of three moments, the thrust, /„ in the strut, B E, of variously sectioned wing spars under a loading similar to that is found to be 36 lbs. under normal conditions of flight at 42 experienced in flight. m.p.h. As the stresses are more severe in the case of the upper rear spar Similarly the thrust, /2, in the strut, F C, is 305 lbs. than in any other spar of a biplane, this particular member was The upper rear spar, D E F, is a uniformly-loaded continuous " Flight " Copyright. Photograph illustrating the spar testing apparatus employed by Mr. Alec Ogilvie at his shed at Eastchurch. The spar is rigged up to represent the upper rear spar of a biplane. Load is applied by bricks carried in boxes, which are hung on to the spar by steel straps, spaced apart at distances corresponding to the wing ribs. The load due to the lower plane, which is transmitted through the struts, is applied locally by the transverse beams that carry the extra boxes. " Flight " Copyright. Sketch illustrating the at' tachment of the shoulder of the spar to the upright in the wall of the shed; also the hook attachment of the wire support to the spar. Both attachments are standard fittings as used on the Wright biplane. used for the tests. The wing structure in question is that employed on the Wright biplane. The loads imposed by the lower wing are calculated as follows:— Total weight of machine fully loaded, with pilot, passenger, and five hours' fuel ... 1,550 lbs. Weight of wings 250 ,, Difference producing stress i>3°° ,, Wing span 40 ft. Normal flight speed ... ... ... ... 42 m.p.h. Speed range ... .., ... ... ... 40-50 ,, Under the normal conditions of flight at 42 m.p.h., the distribution of wing pressure is such that the centre of pressure is situated 0*36 of the chord from the leading edge. The rear spar thus carries 58 per cent, of the load on the wing. In a biplane, the upper plane carries more than half the load. It is here assumed that it carries 55 per cent, ol the load. Thus, for the purposes of calculation the upper plane carries 715 lbs. of the 1,300 lbs. in flight. Of this 715 lbs., the rear spar carries 58 per cent, in normal flight at 42 m.p.h., which on a span of 40 ft. represents a distributed load of io-3 lbs. per foot run. At 60 m.p.h., which might conceivably be attained during an excessive dive, the distribution of pressure over the wing section is such that the c.p. lies 0*505 of the chord from the front edge, so that the rear spar carries 83-5 per cent, of the load on the wing. Calculated for the upper wing on the previous assumption, this corresponds to a distributed load of 14-8 lbs. per foot run. A diagram of the bracing of the warping portions of the upper and lower rear spars of the Wright biplane is shown in Fig. I. The lower spar, A, B, C, is a uniformly-loaded continuous girder, supported at the three points, A, B, C, by the wing hinge at A, and by the strut thrusts at B and C. girder, supported at the three points, D, E, and F, by the wires, A E and A F, with additional loads due to the forces, /, and /2, applied at E and F. Owing to the compression set up in the spars by the oblique pull of the bracing wires, Ti and T2, very considerable difficulty is found " Flight" Copyright. Diagram illustrating the application of the load in the testing apparatus. 793
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