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Aviation History
1910
1910 - 0229.PDF
MARCH 26, 1910. For the estimation of the velocity of the current the combination of Pitot tube and static pressure tube used in the previous experi ments on air resistance has been adopted, the pressure being measured on a sensitive gauge containing castor oil and water. In the preliminary trials of the apparatus considerable difficulties were encountered owing to the fluctuations of pressure which took place in the channel. These fluctuations had a period of about 10 seconds, and on investigation appeared to be due to the constric tion and sudden enlargement of the return channel at the outlet of the fan chamber. On fitting a large number of guide blades and making the sectional area of the outlet gradually diverging, the fluctuations of the static pressure in the inner channel were practically destroyed, but there was still a good deal ot variation in the velocity of the current ; steps are being taken to remedy this. 2. The Experimental Wind Towers.—For the purpose of the experiments on the action of the wind on large scale models, the use of a strip of ground about 150 yards long and 12 yards broad on the west side of the Laboratory grounds has been granted by the Office of Works. This site is practically the only one in the vicinity which is suitable for the purpose ; from this point, in the direction from which the most prevalent winds blow, there is open ground, free from trees and other obstructions, for about 600 yards. On this strip two steel towers, each 60 ft. high, have been erected. On the top of each tower there is a rotating platform 20 ft. long by 3 ft. wide, so that it will be possible to gain access to plates and models of fairly large areas when exposed to the wind. The upper 40 ft. of the towers is parallel, 8 ft. by 8 ft. in section, and this expands to 12 ft. by 12 ft. at the foundations. There is a platform every 10 ft., which is reached by a ladder inside the main framework from the platform below, so that access to all parts of the towers is easy. The two towers are 110 yards apart, and an observation hut has been erected half-way between them. For observations on intensity of pressure a number of lead pipes have been carried up to the top of the towers, and are brought along the ground in an earthenware channel to the hut in which the pressure recorders are to be placed. 3. The Whirling Table.—For the whirling table of 60 ft. diameter, which has been designed chiefly for making tests on model propellers, a special corrugated iron building has been erected on the east side of the main block of the Engineering Department. It was considered that a clearance of 10 ft. between the walls and the end of the long arm of the table would be sufficient to prevent any dis turbance from the walls, so that the floor of the building was made 80 ft. by 80 ft. The clear space in which the table will revolve is 80 ft. by 80 ft. by 12 ft., with the exception of a small observation desk in one corner. The table is attached to a vertical shaft mounted in ball-bearings in the centre of the room, and driven through a worm gear by a variable speed electrical motor of 14 b.h.p. By this means the velocity of the models can be varied from 25 to 100 ft. per second. The arms of the table are made of double lengths of thin steel tubing, tapering in steps from IJ ins. at the axis to I in. at the ends, with horizontal struts at intervals of 6 ft., and supported by steel wire ties to the centre post. For driving the propellers a light high-speed motor will be mounted on the rotating arm, and provided with a speed regulator worked from the observation table. _ The arm opposite to that carrying the models is only 10 ft. long, and carries a weight to balance the whole a»rangement. 4. MotOf'Testing Plant.—For the tests on the efficiency and endurance of petrol motors, machined cast-iron rails have been let into the floor of the experimental bay. These are provided with adjustable cross rails so as to accommodate any size of motor. For the absorption and measurement of the power a 10-h.p. dynamo has been fitted into a cradle which is suspended on knife edges, with a lever and balance-weights for measuring the torque. The balance-weights rest on a vertical spindle, which works in an oil dash-pot at its lower end to damp out any oscillations that may lie set up. The energy from the dynamo is dissipated on special resistance mats, which are so arranged that by means of switches any required power can be absorbed. 5. The Testing of the Strength and Elasticity of Fabrics for Balloons and Airships-—Several sets of tensile tests on ® ® Territorial Balloonists. IN reply to a question in the House of Commons last week. Mr. Haldane, the Secretary for War, said that the Territorial Balloon Company is not yet equipped for mobilisation. The future organisation of the Regular Balloon Companies is at present under consideration, and the organisation of this company will depend on the decision arrived at. The Balloon Company forms part of Army troops, and is not allotted to any division on mobilisation. |/yGHT) abrics have been carried out during the year. The method of test has been to suspend the upper grips from a crane hook, and load the lower grips by dead weights added in equal increments until fracture occurs. To enable these tests to be carried out more rapidly a special testing machine has been ordered from Messrs. Avery, in which the load will be added by the well known shot method. An investigation is proceeding for the purpose of deter mining the best form of test specimen for these fabrics. Apparatus for making bursting tests has also been put in hand. Department of Metallurgical Chemistry. Aeronautics Division (Dr. Rosenhain, Mr. Barr).—This division has been established to carry out the chemical and allied work required in connection with the work of the Laboratory for the Advisory Committee for Aeronautics. The work principally con templated at present is concerned with the testing of balloon and aeroplane fabrics, as well as such matters as the detection of hydrogen leakage from balloons, and similar problems. Work in connection with light alloys and other metals employed for aeronautical purposes will be undertaken by the Metallurgy Division. In regard to the testing of balloon and aeroplane fabrics, a comprehensive scheme of tests has been drawn up and submitted to the Advisory Committee; the tests proposed include testing for leakage of hydrogen, with the influence of crumpling and folding on this property, uniformity of weight and thickness and occurrence of " pin holes," hygroscopicity and moisture-absorption, both from a damp atmosphere and an immersion in water, durability and weathering properties, including resistance to exposure to ultra violet light, heat-transmission and inflammability, behaviour under extreme cold and allied properties. An apparatus for testing the leakage of hydrogen through such fabrics has been designed and constructed (with the aid of the Engineering Department), and has been in actual use for several weeks. The apparatus works on the principle of sending slow currents of pure dry air and pure dry hydrogen through two chambers separated by a diaphragm con sisting of the fabric to be tested ; after passing through this chamber the air is led through a heated combustion - tube packed with platinised silica, and the water formed is weighed after absorption in a calcium-chloride tube. Although the actual rates of leakage are very low (as little as 2*5 litres per square metre of fabric per 24 hours) they can be readily detected and measured by this apparatus, and perfectly steady results are obtained so long as the temperature remains constant; the rate of diffusion, however, increases rapidly with rising temperature, and the temperature-coefficient will be determined early in the year. This type of apparatus, it may be mentioned, possesses the very considerable advantage that the hydrogen to be determined is weighed in the form of water, which weighs nine times as much as the hydrogen it contains, and the results given by the apparatus are practically independent of the gas-tightness of the instrument itself, so* long as there is no large leakage at any point. The entire apparatus is arranged to regulate itself in an automatic manner—the hydrogen, for instance, being produced by an electrolytic generator which cuts off the curreut if the pressure of hydrogen rises beyond the desired amount—so that very little actual attention is required except in inserting the fabric, and at intervals of several hours, taking the weight of the absorption bulb. For the purpose of testing the behaviour of fabrics under ultra violet light, a special chamber has been designed and is now under construction, while arrangements for carrying out the other tests mentioned above are in active preparation. Library (Mr. Selby). In connection with the work carried out at the Laboratory for the Advisory Committee for Aeronautics, a collection of works and publications relating to aeronautics is being formed. It would be of interest that this should be made as complete as possible, and gifts of old periodicals and books dealing with the subject would be welcomed. ® ® Entries for Nice Meeting. PRACTICALLY the opening aviation meeting of the year in France will be that at Nice, from April 12th to 24th, and this has attracted 14 entries, which are almost identical with those who were at Heliopolis. They include Rougier, Latham, Grade, Reimsdyck, Sands, Mortimer Singer, Van den Born, Metrot, Le Blon, Duray, Effimof, Chavez, Olieslagers, Swenson. The meeting will be held on the Napoule Racecourse, where Count Lambert taught several of the Wright pupils. 227
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