A History of Aeronautics | Page 9

'A man, when flying, shall be free from the waist up, that he
may be able to keep himself in equilibrium as he does in a boat, so that
the centre of his gravity and of the instrument may set itself in
equilibrium and change when necessity requires it to the changing of
the centre of its resistance.'
Here, in this last quotation, are the first beginnings of the inherent
stability which proved so great an advance in design, in this twentieth
century. But the extracts given do not begin to exhaust the range of da
Vinci's observations and deductions. With regard to bird 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