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Aviation History
1911
1911 - 0487.PDF
JUNK 3, 1911. (/ycHf] THE VORTEX PRINCIPLE OF FLIGHT. By T. A. BRIEFLY stated, the problem of flight is the problem of propelling n heavy body in the atmosphere in both horizontal and vertical planes, whilst preserving its longitudinal and lateral stability. The factors to be considered are four, viz. :— A. Constant force. Gravity. B. Variable force. Application of laws of motion. C. Solid body. Bird, rased, or flying machine. D. Gaseous body. The air. Gravity admits of no control, nor does it admit of any neglect. At every step its presence must be recognised, and the fact that its power varies only with the " mass'' of the object to be sustained, regardless of its size and shape. Fig. I Fig. 2. Figs. 1 and 2.—Gadfly at rest, wings extended and wings closed. Figs. The laws of motion can be applied in two ways : — £. Motion of translation, or motion in a straight line, and F. Motion of rotation, or motion round a central point. Both these forms of motion can be applied to the two bodies, •C and D. All existing flying-machines of the heavier-than-air type depend, like their prototype the bird, upon motion of translation ; translation •of the machine itself by progression through the atmosphere, and translation of masses of air through the operation of wings or pro pellers. Motion of r station is used in only one of its two possible applications, namely in rotating a solid body (the propeller), for the purpose of procuring motion of translation of masses of air. No attempt has yet been made, so far as the writer is aware, to employ motion of rotation of masses of air, and yet it is by this application of the laws of motion that Nature produces her greatest demonstra tions of force, the whirlwind, the waterspout, and the cyclone. Just as motion of translation applied to masses of air produces a •reaction in the contrary direction, so must motion of rotation, and if use can be made of the first-named reaction for purposes of mechanical flight there would seem to b 2 no reason why the second should not •also be used. How Nature employs it in the flight of certain insects will be shown. DRING. B. Flapping-wing flight.—The commonest form. The flight of butterflies and of most of the British moths. C. Rotary-wing flight.—-Nature's complete solution of the problem of flight. The principle employed by hawk-moths, bees, flies, and beetles. If "A," which is the rudimentary stage for both birds and insects, be eliminated, all insects, for purposes of flight, fall into two groups, which represent respectively the two forms of motion, viz., motion of translation and motion of rotation. Flapping-wing flight. — Insects using the reciprocating or flapping wing possess four wings, of very large area compared with the body. The fore-wing on each side of the body has a considerable lateral motion, as well as a very ex tended radius of action in the vertical plane. On the down stroke the fore and under wings are fully extended, and the thrust against the air is back wards as well as downwards, giving a propulsive and a lifting reaction. On the up stroke the fore wing slides back above the under wing, thus reducing the total area ol the wings, and, consequently, the force of the upward thrust and its reaction. The up-strokc, however, assists in the forward propulsion. The path described by the front edge of the fore wing is thus an ellipse, the long diamoter varying in length with the sweep of the wing in the vertical plane, whilst the short diameter represents the lateral motion. Kach surface of the wing, alternately, is followed by a stream of expanded air, due to a partial vacuum, and preceded by a cushion of compressed air, the filaments of the latter which lie next the wing expanding and flowing round the edges to join the current of expanded air at the back. There is thus a constant flow of compressed air from the front to the back of the wing, and k is the creation and carrying forward of this cushion of air which produces the reactions upon which the flight of the insect depend*. Increase of speed in the flapping of the wings tends to reduce the radius of action in the vertical plane until, with certain insects, a point is reached when the ellipse becomes a circle. The substitution of a circular for a reciprocating motion renders the sliding of the fore wing over the under wing no longer necessary for purposes of flight, and Nature, following her invariable rule, proceeds to suppress the useless member. In the humming-bird hawk-moth, one of the four-winged insects employing rotary wings, 3 and 4.—Plan and front view of gadfly suspended in air, wings in motion. Fig. 5.—Vortex. Inflowing currents of expanded air. Fig. 6. Vortex. Outflowing currents of compressed air. Fig. 7.—Insect suspended in air. Front elevation, showing course of air currents. Fig. 8.—Reactions to air current* shown in Fig. 7. The flight of all British birds depends upon motion of translation, and miy be classified under three heads : — A. Gliding flight.—Motion of translation of the body of the bird only. B. Flapping-wing flight.—" A," combined with motion of transla tion of masses of air due to the action of the wings. C. Soaring flight.—Natural motion of masses of air (e.g., wind), the bird sustaining itself by balancing the force of gravity against the kinetic force of the wind. A close sLudy of flying insects reveals the fact that Nature in their <:ase employs not only motion of translation, but also motion of rotation of masses of air, which she never does in the case of birds, -save perhaps the humming-bird. The flight of insects may be classified as follows :— A. Gliding-flight.—Confined to the grasshopper, so far as the -writer is aware. This is but little seen in this country, but it is •extremely common in the Swiss and Austrian Alps. the size of the under wing is considerably less than that of the fore wing. In bees and wasps it is but half the size, and it has lost its power of independent motion and acts as if it were part of the fore wing. In the humble-bee the under wing is so small that it easily escapes observation. In flies the under wing has disappeared alto gether, nothing but stumps remaining to indicate its former existence. Rotary-wing flight.—The gadfly (Figs. 1 and 2), an insect resembling a small wasp in appearance, is familiar to everyone. Poised in the perfectly still air of a hot summer's day (Figs. 3 and 4), its motionless body suspended, as it were, by an invisible thread, the wings a mere blurr from their rapid motion, it is obviously employing some different principle of flight to that of the butterfly, or the little fluttering four-winged moths of its own size, whose bodies are in a state of constant vibration, and which are never seen to take up a position of poise. The feeble, jerky movements of the latter are a contrast in every way to the beautifully smooth and powerful movements of the fly. 489
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