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Aviation History
1910
1910 - 0228.PDF
yFlgwT MARCH 26, 1910. THE GOVERNMENT FLIGHT OFFICE. REPORT OF THE NATIONAL PHYSICAL LABORATORY FOR 1909. As our readers are aware, from particulars that have appeared in FLIGHT, notably Vol. I, pages 289, 489, the National Physical Laboratory at Teddington is actively engaged in experimental research in aeronautics and aviation on behalf of the Government. It was only last May that the Prime Minister made his announcement in the House of Commons of the part that the Government intended to take by way of recognising this very important subject; while everyone remembers Mr. Haldane's very satisfactory recent speech concerning official doings and official intentions that we reported and commented upon in our issue of two weeks ago. Research work is necessarily very slow at Bushey House but it comes as welcome news that the authorities have already made a good beginning; and we are pleased to be able to publish herewith the following abstracts from the first official report that has emanated from there and that— needless to state—is as self-explanatory as it is in teresting :— An Aeronautical Division has been organised in the Engineering Department of the Laboratory. Mr. Bairstow, who for some time past had assisted in the wind pressure work, was put in general charge under Dr. Stanton, and a staff of assistants and skilled mechanics appointed. An account of the researches proposed is given in Dr. Stanton's report. A building 80 ft. square has been erected to hold a whirling table, an air channel for resistance experiments has been built, and two steel towers for experiments in the open have been put up, by the permission of His Majesty the King, in the Park, just outside the Laboratory grounds. Apparatus which will be used for testing motors to 50-h.p. submitted in competition for a prize of ,£1,000 offered by Mr. Patrick Alexander, is being installed. Meanwhile experience has shown that the space available in the Engineering Laboratory is insufficient for the work, and the Lords Commissioners of H.M. Treasury have intimated their readiness to place a sum of ^3,ODO in the estimates for 1910-11 to provide an extension. Department o' Eng Bering Research Work. A. General Iavestigations. The Effect of Wind Pressure on Structures (Dr. Stanton).— In accordance with the scheme of work stated in the Report for 1908, records have been taken during the past year of the maximum wind pressures indicated by two instruments, one connected to a single Dines tube 50 ft. from the ground, and the other to two similar tubes, at the same height, but distant about 40 ft. apart horizontally and connected together in parallel. On windy days the instruments were read two or three times a day. The mean of the results obtained show quite clearly that the maximum intensity of the wind in any gale very rarely reaches the same intensity at two points 40 ft. apart at the same instant. The mean of fifty obser vations gave a value of the pressure in the single tube approximately 11 per cent, greater than that registered by the tubes in parallel, so that the pressure in one of the tubes in parallel was, on the average, 22 per cent, below the pressure in the other, corresponding to a difference in the velocities of 11 per cent. This set of experiments came to a conclusion in June, as the site of the experimental wind tower was required for the experimental tank. A similar arrange ment has been erected on the two 60 ft. towers recently constructed for the aeronautical experiments, and will be ready for use early in the coming year. In this case the tubes in parallel are 350 ft. apart. On the Resistance of Plates and Models in a Uniform Current of Water (Dr. Stanton.)—The experimental channel for this work described in the Report for 1908 was completed in January, 1909, and the resulis of a series of experiments on the resistance of submerged plates and models were communicated to the Institution of Naval Architects in a paper read at the Spring Meeting in April. The chief advantages of the method are the rapidity with which the experiments can be made compared with that obtainable in a tank with a moving carriage, and the simplicity of the arrangement for measuring the resultant pressure on the plate or model in any required direction. For this purpose the spindle to which the plate or model is attached passes through, and is per pendicular to, the knife edge of the weighing beam, so that by arranging the whole weighing mechanism to rotate about the centre of the spindle as an axis, the resultant pressure on the model in any direction is at once obtained by setting the knife edge of the weighing beam perpendicular to this direction. The method of estimating the velocity of the current is by a measurement of the excess of pressure in a Pitot tube facing the current over that in a small orifice drilled in the side of the channel at the same height as the Pitot tube. The disturbances of the water entering the channel are corrected by layers of wire gauze, and the surface waves are damped by horizontal plates, which are adjusted to the correct height by screws in the supporting plate. The results of the experiments on normal pressures on inclined plates were found to exhibit precisely the same characteristics as those which are obtained in air currents with the same form of plate, and were in substantial agreement with the results of previous ex perimenters using plates of considerably greater dimensions in water. By placing fixed models in front of the plates, to represent the action of the stern of a ship, very considerable reductions in the normal pressure were observed. Experiments were also made on parallel plates at small inclina tions to the current in order to investigate the interference of propeller blades with each other. An interesting fact brought out in these observations was the marked effect of one plate on another directly behind it. Thus, in the case of two plates inclined at 6° to the current in which the aft plate was completely screened, the reduction in the normal pressure on the latter was still considerable, even when the forward plate was nine lengths in front of it. Observations on submerged solids of revolution showed clearly the marked effect of the fineness of the stern on the resistance. As an example of this, in the case of three models of precisely the same form of bow and middle, but with sterns in the form of cones of angles 6°, io° and 20°, the resistances were as I: 1*15: I '95, or per unit of volume as I : i-9 : 4*8. B. Aeronautics. (Dr. Stanton, Mr. Bairstow, Mr. Booth, Mr. Rowell and Mr. Hyde.) In accordance with the scheme of research work to be undertaken in the Engineering Department, which has been approved by the Advisory Committee for Aeronautics, the following researches have been commenced :— 1. The determination of the resistance of plates and models in an experimental wind channel. 2. The resistance of large sized plates and models mounted on steel towers in the open and exposed to the action of the wind. 3. Experiments on the efficiency of air propellers on a whirling table. 4. Tests on the efficiency and endurance of petrol motors for aeronautical work. 5. Tests on the strength and elasticity of fabrics for balloons and airships. The progress of these researches up to the end of 1909 was as follows:— 1. Experimental Wind Channel.—For the experiments on models in a uniform current of air, a horizontal channel 4 ft. by 4 ft. in section and 20 ft. long has been constructed. The channel is supported in the centre ot a similar channel 8 ft. by 8 ft. in section, so that the air drawn through the 4 ft. channel can be returned through the space between the channels and used again. The method of producing the flow is by using a 6 ft. Sirocco fan, belt driven from a 15-h.p. dynamo, and making about 150 revolutions per minute. The fan is so arranged that the inner channel in which the experiments are made is the suction pipe of the fan, as experience shows that this is the most favouiable position for steady air flow. In the experiments the model is attached to one end of a lever which projects into the channel, and which is supported by a cross- head attached to a bracket outside the channel. The suspension of the lever and cross-head is such that the motion of the lever may take place about either a horizontal or vertical axis. The other side of the lever is utilised as a weigh-beam for vertical forces on the model, and there is an auxiliary weigh-beam at the exterior end to measure horizontal forces. In this way the horizontal and vertical forces on the model, e.g., the drift and lift of an inclined plane, can be measured at one setting. Provision is also made for rotating the model about a horizontal axis without stopping the current, which will save time in observations on inclined planes. The lever is provided with an oil dash-pot to damp out oscillations either horizontally or vertically. 226
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