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Aviation History
1911
1911 - 0488.PDF
[/JJGHI] The gad-fly weighs from five to six hundred times the weight of the air displaced by its body. It can turn sharply, as on a pivot passing through its thorax, it can dart backwards, and it can shoot forwards at a speed that the eye cannot follow. It can rise and fall in a directly vertical line, and, at any point in its career, it can in stantly stop its forward motion and resume ils position of poise. Its relative, the house-fly, saunters to and fro in the air without any JUNE 3, 1911. the bird and from insects employing the flapping wing, the speed of whose flight is directly related to the rapidity of movement of the wings. Mechanical application.—The wing employed by the fly to produce vortex and whirlwind currents is a lever of the third order, and wonderful as are the results obtained, the device is not one that can compare with the wheel and axle. Its efficiency is reduced by the fig.ll. 03) Fig. 9.—Plan of insect suspended in air, showing direction of air currents. Fig. 10.—Reactions to air current in Fig. 9, showing balance of forces. Fig. 11.—Side view, showing the resultant of reactions in forward flight. Fig. 12.—Plan of reactions in forward flight. apparent effort, suddenly darts forward to meet another fly, waltzes round at a high speed for a moment, and again resumes its leisurely motion. The wasp, whose flight depends upon the same principle, has a lifting power equal to twice its own displacement in water. These insects have complete command of the air, in every possible sense of the word, by a principle which needs none of the delicate adjustments involved in flight by motion of translation, and which lends itself to application by modern machinery even more readily than it lends itself to the mechanism of the insect—the muscles and wings. The wings of flies, bees, and wasps do not flap or vibrate, but rotate. The front and back edges of each wing describe intersecting necessity of leathering the blade at two points in each rotation, and a high velocity is required. The reproduction by mechanical means of the wing movement having proved conclusively the soundness of the theory just described, experiments were made with revolving shafts to which vanes of various descriptions were attached, with the object of producing similar currents that might be used for purposes of flight. The shape of the earlier vanes was a rough copy of the insect's wing, but quite recently a series of experiments has been carried out to determine the best shape and angle of inclination of the vanes, and for this purpose a start was made with simple geometrical forms, such as the parallelogram, the right-angled triangle, and the obtuse-angled triangle. It was found that the Fig 1 + Fig. 1? Fig. 13.—Plan of insect, showing formation of couple by tilt of wings in opposite directions. Fig. 14.—Plane showing the result of turning moment produced by couple. Figs. 15 and 16.—Vortex propeller in elevation and plan. cones of about 450, the apices of which are co-incident with the root of the wing at its junction with the body. The effect of this motion upon the air is the creation of a vortex, the air stream which formerly followed the reciprocating wing in a more or less straight line, being now drawn in at and above the tip in the form of a funnel or hollow cone with a spiral motion. The air cushions, which formed in front of the reciprocating wing, and flowed to the back, now form an air stream driven outwards by centrifugal force, and fed by the inflowing stream passing through the vortex. These outflowing currents are driven off at a tangent to the circle of rotation, and at an obtuse angle to the axis of rotation, forming a truncated cone or ellipse. The reactions to the discharge give a resultant force in the line of the axis of rotation. In flight this axis is inclined upwards at an acute angle, and the resultant forces, acting in an outward direction along the axes of the two rotating wings, become the components of a second resultant giving a vertical lift. In the horizontal plane the insect retains its position by the perfect balance of the currents discharged in a forward and backward direction respectively (Figs. 9 and 10). But the insect can readily vary the angle which the axes of the rotating wings make with the body, either vertically or horizontally. By a slight tilt of the wings in the horizontal plane it can obtain a third resultant force giving a backward or forward motion combined with the vertical lift (Figs. 11 and 12). By inclining the axes in opposite directions a couple is produced giving a turning moment about a point in the centre of the thorax, enabling the insect to steer to the right or left (Figs. 13 and 14). The movement of the insect in the horizontal plane depends entirely upon the angles made with the body by the two axes and the resultants obtained therefrom, and does not necessarily vary with the speed of rotation of the wings. It differs in this respect from latter was incomparably the best form, and from this has been evolved the shape of vane now adopted. Figs. 15 and 16 show in elevation and plan a Vortex propeller, of which several types are covered by the original patents and the patents of addition. The essential features of this propeller are the outline and angle of inclination of the vanes, and the fact that the vanes are perfectly flat. The propeller illustrated is composed of a. Fig. 17. Fig. 17.—Application of two vortex propellers to a flying machine—section amidships. system of three vanes set radially upon a conical hub attached to the end of a revolving shaft. The model has been thoroughly tested with perfectly satisfactory results. Compared with a single vane rotating in the manner of a fly's wing at 1,000 rotations per minute, the propeller with three vanes of similar size revolving at the same speed gave results estimated as being from ten to twelve times as efficient. 49O
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