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Aviation History
1914
1914 - 1098.PDF
(/ysig NOVEMBER 6, 1914. through a safety spring device, which takes up the excess motion of the lever should it be accidentally moved too far. The mechanisms for registering the position of the rudder and the amount of warp are similar in construc tion to that used for recording the motion of the elevator; while the rolling motion of the aeroplane is recorded by a large weighted pendulum, Q, which is carried in ball bearings at the back of the instrument. This pendulum has a long period, and is suitably connected to a pencil, which makes a record of the motion on the paper passing over the drum, K. The weight of this apparatus, com plete, is 84 lbs. The trajectograph is essentially a simpler form of the ripograph, since it contains the devices used in the latter for determining the altitude and the velocity. This instrument was designed by the staff of the R.A.F., and was used in the Military Aeroplane Trials of 1912 for measuring the gliding angles and velocities and the gradients in ascents of the competing machines. The instrument consists of a double box, one part of which is light tight, while the other part contains the illuminating apparatus. In the former are—(1) an alti meter; (2) a-specially designed pressure gauge, which is connected to a pressure head and is used for determining the air speed of the aeroplane; (3) the necessary clock work mechanism for driving a band of sensitised paper past the two gauges; and (4) a time marker, which gives a shadow record on the moving paper at intervals of 30 sees. But as the method of operation and the con struction of these devices are similar to those of corre sponding parts in the ripograpb, it is unnecessary to describe them further here. It may, however, be mentior.ed that the trajectograph can be loaded in day light with new spools of paper 5 ins. wide and 10 ft. long. The tantness-meter, which in its original form was designed by Mr. Mervyn O'Gorman, is shown in Fig. 3, and has been extensively employed at the R.A.F. for the purpose of ascertaining the stresses in cables, wires, &c., in the assembling and trueing up of aeroplanes, as well as during flight. The instrument is applied to the cable, so that the latter rests in the grooves in the pulleys, C C1. The pulley, C, is carried on a bell-crank lever, P, pivoted at N on a rigid framework, on which the other pulley, C, is directly mounted at the opposite end. The support P1 is rigidly connected to the cross-bar, and between the extremities of P and P1 is a strong spiral spring, S S, which is enclosed within two metal tubes— one of which telescopes into the other. A screwed Fig. 3.—The Tautness-meter. piece, B, mounted upon the framework, presses on the cable at a point midway between the two pulleys, so that when the screw, F, is screwed down sufficiently, it bends the cable slightly, thus putting a light load on the spring, S S, which is recorded on the graduated scale cut along the outer of the two tubes enclosing the spring. In practice, as the extension on the cable increases, or de creases, either when adjusting the turnbuckles, or due to the loading produced under varying flight conditions, the cable becomes straighter, or more bent, and hence further increases, or decreases, the load upon the spring, which may then be read off directly from the scale in lbs., kilos., or tons. This iustrument is supplied by the Cambridge Scientific Instrument Co. at a price of £7. ® ® ® & HOW BAROGRAPHS USED DURING ATTEMPTS ON HEIGHT RECORDS ARE TESTED. AN account of the procedure adopted in examining baro graphs taken from aeroplanes upon which attempts have been made to establish height records is given in the report of the Director of the National Physical Laboratory for 1913-14, and should prove of considerable interest to readers of FLIGHT. The instrument is received at the Laboratory in exactly the same state as it was found on the aeroplane after the completion of the flight, except that the pointer has been lifted from the paper. The testing apparatus contains two receivers, one in which the test on the baro graph is carried out, and the other an auxiliary receiver which is used to control the pressure inside the first receiver. The pressures are determined by means of a standard gauge barometer of the U type and can be estimated to o-ooi of an inch. The clockwork is set going and the instrument placed in the receiver of the testing apparatus, in which the pressure is adjusted so that the pointer falls on the beginning of the trace. As the drum revolves the pointer is made, by suitable varia tion of the pressure, to follow closely over the trace made during the flight. At intervals along the trace, the corres ponding true pressures are read on the standard gauge barometer. In this way a very accurate estimate of the true pressure corresponding to the maximum point on the trace can be made. To arrive at the actual height reached above ground level, it is necessary to know the following data:—(1) The place of ascent and its height above mean sea level; (2) the date and hour of ascent; (3) the difference between the pressure at ground level and that at the maximum height. The particulars given under (1) and (2) are referred to the Meteorological Office, to ascertain as closely as possible from their records the atmospheric conditions at the time and place of flight. Item (3) is got direct from the calibration of the barograph at the Laboratory. The information necessary for calculating the maximum height attained is then complete. The degree of accuracy to which the height can be certified depends partly upon the closeness of the baro graph scale and the thickness of the trace, and partly on the amount of information available as to the atmo spheric conditions at the time of the flight. For the two instruments tested during the past year, the results were given to within ± 200 feet. 1098
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