PART I: THE EVOLUTION OF THE AEROPLANE

II. EARLY EXPERIMENTS ( Page 6 )  <<Previous   Next >>

Continued from page 5......
Hence the whole mass of the bird rebounds, making a fresh leap through the air; whence it follows that flight is simply a motion composed of successive leaps accomplished through the air. And I remark that a wing can easily beat the air in a direction almost perpendicular to its plane surface, although only a single one of the corners of the humerus bone is attached to the scapula, the whole extent of its base remaining free and loose, while the greater transverse feathers are joined to the lateral skin of the thorax. Nevertheless the wing can easily revolve about its base like unto a fan. Nor are there lacking tendon ligaments which restrain the feathers and prevent them from opening farther, in the same fashion that sheets hold in the sails of ships.

No less admirable is nature's cunning in unfolding and folding the wings upwards, for she folds them not laterally, but by moving upwards edgewise the osseous parts wherein the roots of the feathers are inserted; for thus, without encountering the air's resistance the upward motion of the wing surface is made as with a sword, hence they can be uplifted with but small force. But thereafter when the wings are twisted by being drawn transversely and by the resistance of the air, they are flattened as has been declared and will be made manifest hereafter.'

Then with reference to the resistance to the air of the wings he explains: 'The air when struck offers resistance by its elastic virtue through which the particles of the air compressed by the wing-beat strive to expand again. Through these two causes of resistance the downward beat of the wing is not only opposed, but even caused to recoil with a reflex movement; and these two causes of resistance ever increase the more the down stroke of the wing is maintained and accelerated. On the other hand, the impulse of the wing is continuously diminished and weakened by the growing resistance. Hereby the force of the wing and the resistance become balanced; so that, manifestly, the air is beaten by the wing with the same force as the resistance to the stroke.'

He concerns himself also with the most difficult problem that confronts the flying man of to-day, namely, landing effectively, and his remarks on this subject would be instructive even to an air pilot of these days: 'Now the ways and means by which the speed is slackened at the end of a flight are these. The bird spreads its wings and tail so that their concave surfaces are perpendicular to the direction of motion; in this way, the spreading feathers, like a ship's sail, strike against the still air, check the speed, and so that most of the impetus may be stopped, the wings are flapped quickly and strongly forward, inducing a contrary motion, so that the bird absolutely or very nearly stops.'

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