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Aviation History
1913
1913 - 0806.PDF
JULY 26, 1913. Edited by V. E, The Wind Tunnel as an Aid to Model Research. IN a paper read some little time ago to the Aeronautical Society by Mr. A. P. Thurston, on "Aeronautical Research in the Home," there was described a small wind tunnel some I ft. square, made of three-ply wood, and through which air could 1* drawn at any speed up to 20 m.p.h. by a 4-bladed fan mounted on a f h.p. electric motor costing about £2. In conjunction with such must be used tome form of anemometer which shall measure the velocity of the air in the tunnel. In order to read lift and drift ratios of aerofoil and other surfaces, head resistances, &c, some form of balance or parallel link motion is generally made use of. Some form of lattice work or grids are also usually employed to prevent rotation of the air current drawn through the tunnel. It is obvious the tunnel may be either horizontal or vertical, or a combination of both. It is also evident that it is a great advantage for the balance or recording instruments to be mounted on a section or case which is easily and quickly detachable ; and which can be fixed to the tunnel in various positions. So far as model research work is concerned, a wind tunnel velocity of 15 to 25 m.p.h. would be the most suitable ; with regard to the dimension of the tunnel, most models have a considerably greater span than 12 ins. Thus, making due allowance for the relation which should hold between the height and breadth of the tunnel, and the specimen experimented on, a tunnel having a section 4 ft. square would be necessary to experiment with the general run ot existing models. But if we increase our linear dimensions 4 fold, the area is increased 16 fold, or the amount of air to be drawn through to produce the same velocity in the larger as in the smaller tunnel is 16 times as great. As we increase the size of our tunnels, the necessary power required increases in such a manner as to render such experiments prohibitive where the ordinary aeromodellist is concerned, unless the wind tunnel be quite small. It is quite possible to drive an air blast of 25 m.p.h. through a wind tunnel 1 ft. sq. section by means of a fan driven by foot power, making use of a heavy well-balanced and easily-running flywheel; and to do this fsr a time quite sufficient for a single test. Instead of using an electric motor, a water motor might be used, provided a 60 lb. pressure was available and the motor run direct off the tap. This would work out considerably cheaper than if an electric motor were employed. As Mr. Thurston says, "a vast number of useful experiments may be made in such a tunnel." The particular experiments described in the paper referred to were: " The dis tribution of pressure on rods and struts," " An apparatus for deter mining the travel of centre of pressure, the control torque, and the longitudinal stability coefficient of various plan forms of aeroplanes," and also some experiments on " Air Friction," with a view to determine the value of skin friction. On the assumption that the matter was carried out by those who Were prepared to give their time and lend all the mechanical assist ance in their power, as well as anything they might have in the nature of scrap material, a series of very interesting and possibly valuable experiments could undoubtedly be carried out for a sum of not more than £s% and very possibly even much less than this. If there is anywhere where FLIGHT penetrates, any individual or body of indi viduals, who are keen on carrying out such a series of experiments, we shall be pleased to hear from them, and to put them in touch with those from whom they can obtain further assistance and guid ance. Should such, unfortunately, not exist, then it is scarcely worth while going further into the matter. Apart altogether from wind tunnels, there exists other and totally different types of apparata, such as whirling tables, &c, in which the body to be tested is carried through the air instead of the air past the body. A whirling table was constructed by the writer more than twenty years ago, by means of which he was able to rotate bodies of fair Im, through the air, up to a speed of 4=; m.p.h., bv hud-power alone. The consideration of such must, however be left over until our next issue. Some Interesting Experiments with Hydro-Aeroplanes. The following has been sent us by Messrs. H. C. H Bracev H. B Brown and T. P. Lealand, of Birmingham :-«it wTll be seen from the accompanying illustrations that the model has floats of high aspect ratio. The photographs were taken before any trials **?,—*: 1>»l»,%* ha. «nce been moved forward to a e JOHNSON, M.A. the tips of the trailing edge rounded off. Propellers, 8 ins. diameter, 24 ins. pitch. The rear float, 1 19 ins. by 275 ins., is placed with its leading edge 075 in.| behind the e.g.—the e.g. being 2 ins. forward of the leading edge of the main plane. This float is curved upwards to the tips, and is set at a small angle of incidence, the bottom of the float being at about an angle of I in 16. " With regard to the section, it will be seen that the upper surface is given a camber which is approximately Eiffel's No. XIII bis. " The front float has a span of 10 ins., and is set at a large angle of incidence. The mcdel complete weighs 7J ozs. " After flotational and hydroplaning tests, actual free flight was attempted ; the water was choppy. The results were as follows :— 1st flight, very quick rise, alighted, after a short flight, on rear float and slowed up. 2nd flight, another quick rise, machine very unstable in the air, after a short flight the model side-slipped, the tip of one of the floats touched the water, with the result that it capsized and submarined, leaving only the bottom of the floats above the water. 3rd flight, a wave caught the propellers on starting, but in spite of the resultant splash, the model hydroplaned, finally leaving the surface quite easily. The machine was, however, over-elevated, and after a steep rise, the model dived ; it did not, however, either capsize or dive [i.e., in the water], but the front float skimming over the surface of the water, the machine, after a short run, was in the air again. This performance was repeated. After this followed a side-slip, and finally a submarine. 4th flight, alighted on both floats simultaneously, bumped and skimmed. 5th flight, steady in the air, struck the skull [hull ?] of another boat on alighting, but did not upset. The model never fails to rise ; it leaves the water in the following manner : The front float skims almost immediately the machine is released; the rear one is more heavily loaded, and takes longer. The front then leaves the surface, the rear one following it out, the model rising in less than 12 ft. The machine is very unstable in the air. We intend trying the effect of a non-lifting tail and vertical fin. Another trouble we have experienced is float leakage. The floats are constructed of birch spars and satin walnut section plates, with silk covering. At first we varnished with Canada balsam. This leaked, and we added a coat of shellac varnish. This kept the water out until the battering position under the main plane. The central rod is 30 ins. lone Th main plane of bamboo 24 ins. by 4 ins., with slightly upturned tips. The elevator, 9 ins. by 2-25 ins., with a dihedral angl™ 832 Messrs. Bracey, Brown and Lealand and their model hydro aeroplane.
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