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Aviation History
1912
1912 - 1239.PDF
DECEMBER 28, 1912. An aeroplane lifts by accelerating downwards a certain mass of air, and it is the function of an aerocurve to do this in the simplest possible manner, i.e., with the least disturbance and with the minimum propulsive power. According to this view if we take the aerocurve illustrated in Fig. 1 A, B, C, and instead of using a single surface employ a double one, forming these surfaces with due regard to the pressure curves there shown, we should expect that such a surface would show an increased lift. Because now our air stream follows far more closely (it can never do so exactly) the two surfaces, and we have a final combined downward acceleration, the resultant of the two, and therefore of increased magnitude. The double correctly-shaped thick plane will lift more than the single plane alone, but is it more efficient ? Considered in terms of propeller thrust, certainly not; but in practice, our aerocurves' surfaces must have rigidity and strength; in other words, they must be thick. By experi- mentthen, or by mathematical analysis (which in itself must be founded on data culled from experiment), we must find exactly where and in what manner our aerocurves can be thickened (i.e., strengthened) without reducing their efficiency. The foregoing experiments, although conducted only on a small scale, when pushed to a logical conclusion, do give us a form of aerocurve in approximate agreement with those in actual practice ; and the experiments have at least this merit—that they are perfectly genuine ones—and were not made with the idea of being fitted into any particular niche either of theory or practice—but solely for the purpose of gaining information. They were essentially experiments made on a model scale—their actual cost some fifteen shillings, and I publish the same with a view to encourage others to undertake similar kinds of experiments. The actual time taken in making them was about a fortnight. The motive power used to provide the necessary air draught was an ordinary foot lathe fitted with a very heavy fly-wheel. Discing. By G. V. UPWARD. I HAVE during the last three years been making some experiments with discs, the result of which may be of some interest to your readers. The discs cost practically nothing and afford endless scope for experiment and amusement. First get a piece of tin and cut it in circular form. I find the most useful size to have a circumference of about 21 ins., diameter On a ozs. calm 1* day a light disc is desirable, not more than from s. in weight. For moderate winds 2 ozs. weight should be used, and in strong winds 2j ozs. should be the weight ot the disc. , . c , On a calm day take a light disc, camber it slightly, being carem to keep the hollow surface skywards. Then with the right.nana well back on the left side of the body launch the disc with con siderable force. For 50 yards it should mount gradually, then when the force of the throw is spent it will turn over and glide beautiiully for a distance of from 100 to 150 yards further. If the camber is too great the disc will come to the ground with two somersaults at a distance of about 80 yards. If the camber insufficient the disc will turn over at about 70 yards distant and tall edgeways, burying itself in the ground. . In a strong wind, a heavier disc is necessary Against the wind there should be very little, if any, camber, and as a rule> tt.is ad visable to throw low. I have thrown 100 yards with the disc at.no time more than a foot above the ground. In moderate wrods, stability will often be obtained by cutting holes of various desgns in the centre of the disc. I have got good results from the designs illustrated. With these, and other types, I have had^flights oi: ^yards the throws are made on a gentle down-slope, flights a favourable If great wind to distance will be secured, and the discs, with aid them, will rise to extraordinary^eights The beauty of witnessing a disc sailing like a mru 1 flight high in the buoyant air is a joy to behold, and.thegnc^witt which it sweeps earthwards with long vol plant is a s>ght as exniiar ating as the descent of the most skilful aviator. As a game, discing is worthy of attention Wl* a^£^££ of various weights anddesigns in one's pocket, on *> -^ with fellow discers over any arranged course j^mrowth is not over hedges, ditches, roads, anywhere where the undergrowtn too thick to hide the disc when it falls. h ,A course, say of five miles across foutttryjsofiXUp°n'- winner covering the distance in the least number of fl 1/liGHfl As a sport this is surely equal to the best; great skill being required not only in selecting the right disc for the right occasion but also in negotiating corners, and soaring above hedges, trees and other obstacles that happen to be in the course. I can commend discing with confidence to your readers as a fascinating sport and one from which the aeromodellist may quite possibly cull new ideas. A Practical Determination of the Coefficient of Friction between Rubber Surfaces with Various Lubricants. Mr. N. F. H. Clarke sends us the following interesting com munication re the above. The value of soft soap as a lubricant is very clearly shown. BC is a base board graduated in centimetres. AB is a block fixed at right angles to BC and Q'8 centimetres high. EC is a smooth rubber surfaced !>oard resting on A and C, also graduated in centimetres. D is a weight also rubber surfaced. To use the apparatus D is placed on EC, and then EC is moved up or down as at E'C1 as required until D just begins to slide. Now the coefficient of friction is given by the tangent of the angle of inclination of the surfaces to the horizontal. Therefore A? gives the required coefficient for • the tangent rC * t* of the angle FCB. This experiment is repeated several times with the rubber coated with various lubricants. Below is a table giving some results :— Lubricants. 1 None 2 Water 3 5 per cent, soda water ... 4 10 per cent, soda water... 5 20 per cent, soda water. . 6 Saturated soda water ... 7 5 per cent, soap solution 8 10 per cent, soap solution 9 20 per cent, soap solution Saturated soap solution... Soft soap Soft soap and black lead •7- 72 1 '7a = •69 •68 = •66 j = '3» ^ 10 11 12 >.i 14 '5 Black lead French chalk 80 per cent, solution soft soap Coefficient 9-8 I3S 9J^ I3'5 98 135 9-8 I4'3 9-8 i4-4 9-8 142 9-8 30 9 3° 9 4' 9 47 9'8=: 51-7 9"8 = 18-5 24-S 9-« = 26 • 4 3'4 = Remarks. In all these cases there appeared to be a sucker-like action between the surfaces. = •25 *3 e -20 •19 'S3 •28 '37 All these solutions gave better results when hot. A rather sticky mix- ture. 06 I 5i'S The pressure between the two surfaces was constant throughout, and was 13'I grammes per square centimetre. Replies in Brief. T C. BEI.LAIRS.—Dunne, Tunc: 18th and 25th, 1910; Deper- dussin, February 17th, 1912, September 7th, 1912, August 19th, 1911. The model hydro-aeroplane you refer to is no longer in existence, and neither photograph nor drawings of it were ever taken. If yoa try this type use one long chief central float and two small balancers. The other is extremely difficult to deal with in model form. E. STIER.—YOU must fit a rudder. 1231
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