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Aviation History
1912
1912 - 0882.PDF
IftlGHT SEPTEMBER 28, 1912. AN ATTEMPT TO INVESTIGATE THE PHYSIC£** .*« PROPERTIES OF A TWISTED SKEIN OF RUBBER. By W. W. HASTINGS RIDER and ALLAN P. HITCHENS, B.Eng. (Liverpool). As the twisted skein of rubber is the recognised power unit ol model aeroplanes, five series of experiments were conducted to ascertain the following joints :— 1. The total energy that can be stored in one pound of rubber under given conditions. 2. The maximum number of revolutions that can be given to a certain skein of rubber. 3. The maximum and mean torque thereof. 4. The effect of various lubricants. 5. The effect of an initial stretch in the skein. 6. The drop in torque and energy due to continued use. The apparatus used was entirely of our own design and manufacture. ;an values of both torque and end-pull over any given range of revolutions from zero to fracture can be determined. See 1 able £. The following is a brief description of the principal parts of the apparatus, the letters having reference to the accompanying lettered sketches:— . • • , . . A, bed of apparatus, composed of a piece of pine 29 ms. by 6 ins. by I in. B, geared winder (5 to l). C, strip of wood, which, by engaging with the pin, D, prevents the rubber unwinding while a reading is being taken. E, skein of rubber, generally 10 ins. long, stretched to 10& ins. (5 per cent, stretch). Its governing principle is, that the torque of the rubber, transmitted through a hook and shaft, is counteracted by that of a known sliding weight placed at a certain distance along the arm of a balanced lever, the end pull of the rubber being neutralised by that of a spring balance placed on the side of the lever opposite to the rubber. The chief advantages of our apparatus are :— 1. No loss of energy in friction, <•.,?., where the rubber is made to lift a weight by means of gearing and pulleys. 2. The actual energy Stored right up to the point of fracture can be measured. 3. Such measurement accurate to within 2 per cent. 4. Large range of action possible. 5. By one experiment on one skein of rubber the maximum and F, shield of three-ply fretwood, to prevent the lever and bearings being damaged when a specimen of rubber fractures. g, collar and ball-bearing enclosing the shaft through which the torque of the rubber is transmitted to the lever. H, balanced and graduated lever 24 ins. long and ^ in. thick, carrying on one arm an aluminium carrier, R, and scale-pan, S, which together weigh -15 oz. K, L-shaped arm carrying the Stops which limit the rotation of the lever. L, double loop of linen thread acting as a link between the lever and the spring balance to obviate the damping effect which the latter might have on the rotation of the lever. M, spring-balance reading in ounces up to 5 lbs. TABLE b.—Analysis of Experiment B7. Range. Single Double ... ( Treble - Fracture ... 6-2 «*3 50*0 \ 6o-o 700 800 1 900 105 "o Area i'| Max. T each y/fi Torque. Ratios. : separate r, Tin.-ors. Percent. Strip. •565 I ' &!• ins 8 II 16 '9 0 5 | 5 8 247 3' 40 61 2 6 •0 Total Area. A sq. ins. «3 19 25 32 40 51 67 100 '22 '23 '55 62 01 '44 34 79 '22 i-45 5'oo 6-62 8-63 11-07 I4'4i 21-20 Mean Torque = 20OA « = /in.- ! T 4-0 7-6 112 12-4 13-8 15-6 180 22'7 TF Energy each separate Strip. Ft.-lbs. •5 •66 •68 •627 •56 •50* •44 37 1 -066 •125 •184 •203 •226 -256* "295 | •37 Ratios. Total Percent. Energy. Ft.-lbs. t> .- j Total Ratios, T? Per ! Energy cent- j &*. i 1-42 8-oi 23-131 i io-6o I i i3'3o( ; 16-90 f 22-co I 44'ooJ I 1*1 6-2 100 In columns 6 and II, Strip refers to the portion of the torque-revs, graph included between twoordinates at 882 1-42 9'47 32-60 43-20 56-50 72-40 9400 138-00 1 7 23 31 41 52 68 100 38 253 870 1,150 1,500 *>93° 2,500- 3,680 successive values of R'.
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