A History of Aeronautics | Page 9

flight, he observed that so long as a bird keeps its wings outspread it cannot fall directly to earth, but must glide down at an angle to alight--a small thing, now that the principle of the plane in opposition to the air is generally grasped, but da Vinci had to find it out. From observation he gathered how a bird checks its own speed by opposing tail and wing surface to the direction of flight, and thus alights at the proper 'landing speed.' He proved the existence of upward air currents by noting how a bird takes off from level earth with wings outstretched and motionless, and, in order to get an efficient substitute for the natural wing, he recommended that there be used something similar to the membrane of the wing of a bat--from this to the doped fabric of an aeroplane wing is but a small step, for both are equally impervious to air. Again, da Vinci recommended that experiments in flight be conducted at a good height from the ground, since, if equilibrium be lost through any cause, the height gives time to regain it. This recommendation, by the way, received ample support in the training areas of war pilots.
Man's muscles, said da Vinci, are fully sufficient to enable him to fly, for the larger birds, he noted, employ but a small part of their strength in keeping themselves afloat in the air--by this theory he attempted to encourage experiment, just as, when his time came, Borelli reached the opposite conclusion and discouraged it. That Borelli was right--so far--and da Vinci wrong, detracts not at all from the repute of the earlier investigator, who had but the resources of his age to support investigations conducted in the spirit of ages after.
His chief practical contributions to the science of flight--apart from numerous drawings which have still a value--are the helicopter or lifting screw, and the parachute. The former, as already noted, he made and proved effective in model form, and the principle which he demonstrated is that of the helicopter of to-day, on which sundry experimenters work spasmodically, in spite of the success of the plane with its driving propeller. As to the parachute, the idea was doubtless inspired by observation of the effect a bird produced by pressure of its wings against the direction of flight.
Da Vinci's conclusions, and his experiments, were forgotten easily by most of his contemporaries; his Treatise lay forgotten for nearly four centuries, overshadowed, mayhap, by his other work. There was, however, a certain Paolo Guidotti of Lucca, who lived in the latter half of the sixteenth century, and who attempted to carry da Vinci's theories--one of them, at least, into practice. For this Guidotti, who was by profession an artist and by inclination an investigator, made for himself wings, of which the framework was of whalebone; these he covered with feathers, and with them made a number of gliding flights, attaining considerable proficiency. He is said in the end to have made a flight of about four hundred yards, but this attempt at solving the problem ended on a house roof, where Guidotti broke his thigh bone. After that, apparently, he gave up the idea of flight, and went back to painting.
One other a Venetian architect named Veranzio. studied da Vinci's theory of the parachute, and found it correct, if contemporary records and even pictorial presentment are correct. Da Vinci showed his conception of a parachute as a sort of inverted square bag; Veranzio modified this to a 'sort of square sail extended by four rods of equal size and having four cords attached at the corners,' by means of which 'a man could without danger throw himself from the top of a tower or any high place. For though at the moment there may be no wind, yet the effort of his falling will carry up the wind, which the sail will hold, by which means he does not fall suddenly but descends little by little. The size of the sail should be measured to the man.' By this last, evidently, Veranzio intended to convey that the sheet must be of such content as would enclose sufficient air to support the weight of the parachutist.
Veranzio made his experiments about 1617-1618, but, naturally, they carried him no farther than the mere descent to earth, and since a descent is merely a descent, it is to be conjectured that he soon got tired of dropping from high roofs, and took to designing architecture instead of putting it to such a use. With the end of his experiments the work of da Vinci in relation to flying became neglected for nearly four centuries.
Apart from these two experimenters, there is little to record in the matter either of experiment or study until the seventeenth century.