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Aviation History
1910
1910 - 0118.PDF
[pjGHT] give the information—what is the number of revolutions at which the 85 by 92 engine gives off the 9-h.p., and also what is the total weight of the engine. If it is merely an ordinary standard pattern engine, then the machine is severely handicapped by carrying a lot of unnecessary weight, and if it were equipped with a specially designed light engine, like the Continental machines, he would obtain far superior results. An engine with such a short stroke as he mentions should be quite capable of running satisfactorily at 2,50) revs, per minute, and at that speed it should give off more than 9-b.h.p., that is assuming that the ports and passages, &c., are properly designed for that speed. And if 9-h.p. is all the power that is actually required, then a still smaller engine, with consequent reduction in weight, should do the work. Barnes. CYLINDER. FIRST MOTOR-DRIVEN MODEL. [349] Enclosed you will find two photographs of a working model monoplane, which is, I believe, the first of its kind fitted with a petrol engine. The machine is more or less a scale copy of the Bleriot, has an 8 ft. spread, and an overall length of 6 ft. It is fitted with one of the Automobile Supply Co.'s J-h.p. air-cooled petrol engines, weight ready for flight is under 15 lbs. The FEBRUARY 12, 1910. PROPELLERS. [350] Replying to F. C. Harrop's letter (268), in your issue of the 1st inst., I enclose herewith diagrammatic sketch showing an apparatus suitable for ascertaining the thrust of small screws. The arrangement consists of an electric motor, R, mounted on a frame work consisting of four straight pieces of metal on each side of the motor. The metal pieces are pivoted at A, B, C and D, the bottom, piece being fixed to the wooden support, E, secured to the base, F, in such a manner that the motor can swing from right to left, and via versd, but the frame is normally kept in position by one of the side pieces, G, being extended downwards, and provided with a counterweight which can be slid up or down. When at rest the centre mark, H, at the bottom extremity of G, coincides with the pointer, J. Different propellers which it is desired to test can be mounted on the motor shaft, K. When the propeller is fixed in position and the motor started, the thrust will cause G to swing into a position out of the vertical, as indicated by the dotted line, L, when the motor has reached the correct speed, the weight, M, is slipped down until H again coincides with the pointer, J. The part of G, below the pivot, C, is marked with divisions so that the exact Mr. J. Urlwia's working model monoplane, side view. f 1^- H M - y i 0 0 \ ! ~—i. F \ The framework has been constructed of close-grain deal through out, and particular attention was given to the manufacture of the ribs for the main-planes. Two hundred and fifty of these were cut from the solid, and the best specimens selected. The planes are single surfaced on the upper side. Rubber-proofed fabric has been used, the fabric being fastened in the first place by drawing-pins, and gradually stretched. • • There are several original features in the construction of the machine, one of which is the shock-absorber, and another the method of tilting the main-planes to vary the angle of incidence. The object of the model is to experiment on the subject ot inherent stability in machines of this type. Bletchingley. J. URLWIN. position of the weight, M, necessary to bring G back to the vertical under the influence of the thrust can be noted. If an ammeter is fixed in the motor-circuit, it will indicate the proportionate power required by different propellers to produce the thrust indicated by the position of the weight, M, at any given speed. An electric motor takes current exactly in proportion to the power absorbed (the current required to run the motor light should be deducted from each reading). The divisions on G can be arranged to indicate the thrust in lbs. or other suitable unit. By noting the speed, current, and position of M, and tabulating these results, a good deal of information as to the merits of different propellers could be obtained. Holland Park. JAMES F, CLUNAS. Front view of Mr. J. Urlwin's model monoplane. 114
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