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Aviation History
1911
1911 - 0909.PDF
OCTOBER 21, 1911. circling is still a matter of inference rather than of observation. There is still more doubt as to the significance of the movement. If I am right in supposing that the wing tip retirement is due to carpal and not to metacarpal flexing, then perhaps the movement is some kind of adjustment for steering in a direction opposite to that which would be produced by a full dip movement of the same wing. For instance:— September 4th, 1910.—At Jharna Nullah, 11.3.—A vulture seen to change from slow flex-gliding to circling by retiring of outside wing tip. No dip of inside wing took place. The facts hitherto brought forward make it probable that birds possess two distinct methods of steering in the horizontal plane. Facts to be described in Chapter XXXIII will be found to prove definitely that this is the case, and to suggest a simple explanation as to why two methods of steering are required. f/licHT raised (rotated up) this wing tip for making a turn, that is to say, for steering in the horizontal plane, preparatory to ease- gliding up the valley. It must be obvious that the facts described in this and the preceding chapter give ample room for discussion as to the functions of the wing tips. It is to be hoped that the matter may be further elucidated by later observations. CHAPTER XXVI.—Flapping Flight. The Poising of the Pied Kingfisher. IT will be found that the study of flapping flight throws an unexpected light on several problems connected wi:h gliding flight. A difficulty in understanding flapping flight lies in the fact that the bird may, at one and the same time, be making movements CHAPTER XXV.—Observations on a Deformed Vulture. ANY theory that the use of Wright's method is indispensable for soaring flight must be regarded as disproved by the following observations on a deformed vulture. The view that lateral stability in birds is produced by a twisting upwards of one wing tip, as the other is twisted downwards, involves a corollary, namely, that in the absence of a balancing movement the wing tip is not so twisted. The deformed vulture, whose movements I am about to describe, has the phalangeal quills of one wing permanently rotated upwards, and apparently immovably fixed. On the 18th June, 1910, at Naini Tal, I saw a large, brown vulture circling near the top of Sher-ka Danda Mountain. Just before it glided over the crest of this mountain out of sight, it made a circle, which I observed carefully. In so doing it made a dip movement of the right wing. During the time of this dip I noticed that the tip of the left wing was directed upwards to an unusual degree. I thought at the time that I had at last seen Wright's method in use. But on the following day I got a better view of this vulture, and soon saw that the turning up of the left wing tip was due to a deformity. I saw this vulture on several occasions. A few of my observations are comprised in the follow- ng extracts :— June 19th, 1910.—Ballia Ravine, 11.54-—The deformed vulture again started. When turning to the left, half-dip move ments of the right wing were observed four times, each half dip being followed by a change of course. After I had made these observations, the bird glided into a cloud and remained out of sight. June 22nd, 1910.—At Ballia Ravine, 4.55.—The deformed vulture watched through the binocular for about five minutes. It was circling over a hill at about a mile's distance, being only just visible to the naked eye. It always circled with the efficient wing on the inside. Sometimes it turned in the other direction, so that the efficient wing was outside, but this was always only for a short time, and without completing a circle. After circling for several minutes, it ease-glided for about a mile, and went out of sight behind a hill. While ease-gliding, the efficient wing tip was never seen turned up. It seemed to be permanently directed slightly downwards. Dip movements of the efficient wing tip were seen, but at the distance at which it was flying half dips could not be distinguished. June 29th, 1910.—At Ballia Ravine, 2.55.—The deformed vulture seen circling below my level in the valley below the Brewery (distance of Brewery from me 5,300 feet). While circling, the efficient wing was on the inside, and showed frequent dips of more or less amplitude. The efficient wing tip was always either depressed, or perhaps sometimes horizontal. (Note.—If horizontal, there must have been air pressure on the under side of the phalangeal quills). After a few circles had been observed, the bird reversed, so that the bad J wing was on the inside. It only made'one circle in this direction, during which circle the efficient wing tip remained turned upwards except during two small dips (Figs. 35 and 36). The vulture then reversed to its original direction of circling, later it again made a circle in reverse direction showing the same disposition and movements of the efficient wing tip. Shortly afterwards, during a circle with the efficient wing, as usual, inside, the efficient wing tip was seen to make two dips, one large and one small (the latter presumably a half-dip). The bird then glided out of sight. 3.5.—The deformed vulture again seen. It was observed to turn the efficient wing tip upwards for making a turn. July 1st, 19IO.—Ballia Ravine. At 10.25.—The deformed vulture seen circling with the good wing tip as usual, inside. It Fig. 35,—Deformed vulture circling with efficient wing tip inside. Fig. 36.—Deformed vulture circling with efficient wing tip outside. having different objects; for instance, movements of propulsion, movements in opposition to gravity, movements for balance, and movements for directing its cours;. In addition, there may be movements or adjustments for checking speed independently of those used before perching. It is necessary to find a simple form of flight in which the pro pulsive movement may be studied alone. This desideratum is supplied in a very satisfactory way by the poising of the pied king fisher in calm air. The pied kingfisher (Ceryle Rudis) differs from other species of kingfisher in having a habit of poising in the air and then suddenly diving down head foremost on to its prey. While poising, the bird appears as if fixed in one position, with its wings in rapid motion. It may remain thus poised for several seconds at a time. The following measurements were obtained from a specimen of this bird :— Weight 90 grammes, say 3 ozs. ' Area of wings ... '352 sq.ft. Span 18 ins. Loading 76 lbs. Length n£ „ In the case of the pied kingfisher poising in still air, since the wings are propelling it vertically upwards, the propelling move ment has no admixture with any other movement or disposition for counteracting gravity. Also there are no directive movements, as the bird is not travelling from place to place. If a pied kingfisher is watched under these conditions, it will be seen that the movement of the wings is not up and down, but to and fro in a perfectly horizontal direction. It will be convenient, Fig. 37.—Pied kingfisher poising at commencement of down stroke A'minute Fig. 38.—Pied kingfisher poising at end of down stroke. and " down stroke/'l in however, to use the terms " up stroke " describing the movement of its wings. Fig. 37 shows the position of the wing at the commencement of the down stroke. Fig. 38 shows the position at the end of the down stroke. During the down stroke, as shown in Fig. 39, the wing is moving horizontally forwards. The quill feathers, by the pressure of the air, are bent backwards. The area of the wing, therefore, forms a slanting surface. The pressure of the air on this slanting surface results in a component tending to lift the bird. The position of the wing during the up stroke is shown in Fig. 140. Oil
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