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Aviation History
1914
1914 - 1097.PDF
NOVEMBER 6, 1914. [fij^l INSTRUMENTS USED IN EXPERIMENTS ON AEROPLANES. AERONAUTICAL research is very frequently regarded as limited to the work carried on either in or in connection with a laboratory, probably because the investigations made are of more or less general application, and the results obtained are freely published. There is, however, another branch of experimental work which under normal conditions goes on practically continually, but of which comparatively little is heard, because it is conducted on actual aeroplanes, and, as such, is of more particular interest to the constructor who carries out the test. For MKMw Fig. I.—A diagrammatic sketch showing: the internal arrangement and details of the Ripograph. the carrying out of these tests it is necessary to have certain instruments, and three of them are dealt with in the following notes. Descriptions of the earlier forms of the trajectograph and the tautness-meter, which, as well as the ripograph, are manufactured by the Cambridge Scientific Instrument Co., have already appeared in FLIGHT, but various im provements have since been incorporated in their design, and the present construction is shown in the accompanying illustrations. The ripograph (see Figs. 1 and 2) has been most extensively employed by the staff of the R.A.F. in their full-scale experimental work, and enables records to be taken of many of the more important data required to determine the performance of an aeroplane in flight. The nine different quantities—the altitude, the speed relative to the air, the longitudinal inclination of the aero plane, the time, the engine speed, the positions (3) of the control levers and the rolling movement—are automati cally recorded upon a band of photographic paper which is drawn by the drum, K (Fig! 1), at a speed of 100 mm. per minute around the outside of the box containing the lamps L, L1, Lu. The drum is rotated by clockwork, and the records are made by three shadow photographs on the inside of the paper and six pencils on the outside surface. The altitude is measured by means of an altimeter, A, which consists of a double U tube partly filled with liquid and connected to a Dewar flask, M. The cock, N, is first opened so that the pressure in the Dewar fiask and the outer limbs of the altimeter is that of the air at the surface of the earth, but previous to commenc ing a flight this cock is closed. The pressure of the air in the inner tube of the altimeter is then constant, namely, that of the air originally introduced; but since the pressure on the outer limbs is that at the elevation at which the aeroplane fitted with the instrument may be flying, the height of the liquid in the tube may be made to indicate the altitude of the aeroplane. The object in view in arranging the two limbs of the double U tube symmetrically about the tube communicating with the Dewar flask, is to compensate for errors due to the possible tilting of the instrument. The air speed is ascertained by means of an instrunnni that resembles the Velometer air-speed indicator in principle, as well as in general construction—the static and dynamic sides of the pressure head, B, which is mounted in a suitable position, as usual, at some distance from the body of the aeroplane, being connected by tubing to the cocks, O and P. The fore and aft clinometer, C, is formed by a triangular tube, which is partly filled with a special liquid, and is arranged in a vertical plane contain ing the normal direction of motion, so that it shows by the movement of the liquid in its vertical limb, the longitudinal motion of the aeroplane. The object of fitting the large bulb at the apex of the triangle is to increase the movement of the liquid in the vertical limb for a given angular displacement of the aeroplane, and thus permit of greater accuracy in the records. The readings on these instruments are registered by shadow photographs of their respective liquid columns, A, B and C, projected by the lamps, L, L', L", on the sensitised side of the photographic paper (see Fig. 1). The lime is registered on the paper by dashes marked by the pencil, D, which is depressed by the electro magnet, D1; and this is operated from an accumulator every quarter of a minute by a four-spoked fitting which is rotated once per minute by the clock drum, J. The engine speed is recorded in a series of dashes which are Fig. 2.—An outside view of the Ripograph. made every 100 revolutions by the pencil, E, the latter being actuated by an electromagnet, E1, the circuit through which is controlled by a cam placed on a spindle driven by a worm reduction gear (giving a speed reduction of 1 : 100) off the crank-shaft of the engine by flexible shafting. The pencils, D and E, are placed in the same vertical plane in order to facilitate the reading off of the speed of revolution of the engine. For recording the movement of the controls, a Bowden wire from the elevator lever operates the T-shaped lever, L, and the movement is transmitted to the pencil, F, 1097
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