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Aviation History
1911
1911 - 0883.PDF
OCTOBER 14, 1911. June 25th, 1910 At 12.35.—^ vulture turning in thin cloud near seen to slacken secondaries of outside wing. June 26th, 1910. At 11.36.—Two vultures ease-gliding, and then commencing to descend. I formed the impression that the tightening of the inside wing secondaries occurred while turning. fu GHT and it appears more probable that the chief function of this muscle is of a less important nature, such as arranging the feathers on furling the wing. Secondly, I investigated the relation between change of camber and change 01 flexing. On holding the wing loose in the hand and Fig. 28.—Dissection of wing of an adjutant showing "camber muscle." H humerus, R radius, U ulna, CI carpal joint, Al alula, Mc J metacarpal joint, P basis of primary quills (eleven in number in this specimen instead ol the more usual number, ten), S bases of secondary quills, C M camber muscle, T insertion of tendon of camber muscle into lower end of ulna. Tendonous extensions (E) of this tendon are inserted into the outer eight or nine secondary quills. After the turn (which was a turn in the horizontal plane), the secondaries of both wings were tightened. (That is to say, the wings were adjusted for descent by increase of camber to maximum.) Two vultures descending showed a double dip, accompanied by increased flexing of wings. In each case, at the time of increased flexing, a relaxation of secondaries was seen. What I have described in the above diary extracts as "relaxation of secondaries " was a moving upwards of the posterior margin of the inner or cambered part of the wing. The movement cannot in any case have been as much as an inch in birds of 7 or 8 ft. span. These observations, therefore, were difficult to make, and at the time entirely unexpected. It will be seen that they refer to two kinds of relaxation ; one, quite momentary, coincident with a momentary but visible increase of flexing, the other lasting perhaps for several seconds, in which no increase of flexing was observed. That in this latter case a slight increase of flexing must have occurred, will be shown in the sequel. It will also be shown that, in each case, the relaxation of the secondaries was equivalent in a decrease of camber, and was a disposition for increase of speed. We have now to consider more closely the nature of the wing- flexing shown by the descending vulture. When taking their time of descent with a stop-watch, I soon learnt to distinguish at a glance between a descending and a flex-gliding bird. There was some difference in the appearance of the flexed wing in the two cases, but not a difference that I could grasp sufficiently to express in words. It will facilitate description if I mention two theories that I formed to account for the appearance of the descending bird. Firstly, it occurred to me that possibly in fast flex-gliding the flexure is more at the elbow joint, while in descending possibly the flexure was more at the carpal joint. It was conceivable that the ligaments of the wing should be so arranged that one kind of flexing would affect camber and the other have no effect on camber. Secondly, the idea occurred to me that the maintenance of camber in the descending vulture might be due to direct muscular action. I had some recollection of a muscle that I had found in the wing of a vulture that appeared to be capable of producing this adjustment. After my return to Agra I put these theories to the test by dissection of an adjutant bird of nine feet span, and later on of a vulture of seven feet span. Firstly, with regard to the idea that change of camber may be due to muscular action, as I expected I found a muscle that originates on the lower end of the humerus. Its tendon does not run straight, but follows a somewhat curved course with its convexity backwards. This tendon is inserted into the lower end of the ulna. As shown in Fig. 28, extensions from this tendon go to the membrane that binds together the bases of the outer secondary quills. The result of this arrangement is that, on pulling the muscle, its main tendon becomes straightened. There is, therefore, a pull on the extensions. The outer secondaries are thereby drawn downwards and also inwards towards the body of the bird. This displacement of the secondaries is in effect an increase of camber, but the action is slight. It cannot therefore be denied that the action of this muscle may have to do with the maintenance of camber. But its possible action does not seem proportionate to the effect actually observed, extending and flexing the different joints, no certain effect on camber can be observed. But a different result accrues when the wing is held firmly by clamps attached to the radius and ulna. It is advisable to clamp the wing horizontally and upside down so that the weight of the quill feathers to some extent imitates the effect on them of the pressure of the air when in use. On fully extending a wing so clamped, the camber is seen to be at its maximum. Flexing at the elbow joint is found to have only a slight effect in describing the camber. On flexing at the carpal ioint the camber decreases B B Fig. 29.—Sections of wing of an adjutant at elbow-joint, at A with wing ext"nded, at B with wing flexed. For taking these sections the wing was held upside down. The quill feathers assumed the position given to them by their own weight only. Fig. 30.—Sections of wing of an adjutant taken at junction of middle and inner thirds of the wing. For taking the sections the wing was held upside down. A weight of 10 grammes was attached to each quill feather to imitate the effect of air pressure, at A with wing extended, at B with -wing flexed. Fig. 31.—Sections of wing of adjutant taken at junction of middle and inner thirds of the wing, at A with wing extended and a weight of 10 grammes attached to each quill feather, at B with wing flexed and a 30 gramme weight attached. 885
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