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In
Their Own Words
 he
article which follows is the first popular account of their experiments
prepared by the inventors. Their accounts heretofore have been brief
statements of bare accomplishments, without explanation of the manner in
which results were attained. The article will be found of special
interest, in view of the fact that they have contracted to deliver to
the United States Government a complete machine, the trials of which are
expected to take place about the time of the appearance of this number
of THE CENTURY. –THE EDITOR of The Century Magazine.
The Wright Brothers Aeroplane
by Orville and Wilbur Wright
Century Magazine, September 1908
THOUGH THE SUBJECT of aerial navigation is generally considered new,
it has occupied the minds of men more or less from the earliest ages.
Our personal interest in it dates from our childhood days. Late in the
autumn of 1878, our father came into the house one evening with some
object partly concealed in his hands, and before we could see what it
was, he tossed it into the air. Instead of falling to the floor, as we
expected, it flew across the room till it struck the ceiling, where it
fluttered awhile, and finally sank to the floor. It was a little toy,
known to scientists as a "hélicoptère," but which we, with sublime
disregard for science, at once dubbed a "bat." It was a light frame of
cork and bamboo, covered with paper, which formed two screws, driven in
opposite directions by rubber bands under torsion. A toy so delicate
lasted only a short time in the hands of small boys, but its memory was
abiding.
Several years later we began building these hélicoptères for
ourselves, making each one larger than that preceding. But, to our
astonishment, we found that the larger the "bat," the less it flew. We
did not know that a machine having only twice the linear dimensions of
another would require eight times the power. We finally became
discouraged, and returned to kite-flying, a sport to which we had
devoted so much attention that we were regarded as experts. But as we
became older, we had to give up this fascinating sport as unbecoming to
boys of our ages.
It was not till the news of the sad death of Lilienthal reached
America in the summer of 1896 that we again gave more than passing
attention to the subject of flying. We then studied with great interest
Chanute's "Progress in Flying Machines," Langley's "Experiments in
Aerodynamics," the "Aeronautical Annuals" of 1895, 1896, and 1897, and
several pamphlets published by the Smithsonian Institution, especially
articles by Lilienthal and extracts from Mouillard's "Empire of the
Air." The larger works gave us a good understanding of the nature of the
flying problem, and the difficulties in past attempts to solve it, while
Mouillard and Lilienthal, the great missionaries of the flying cause,
infected us with their own unquenchable enthusiasm, and transformed idle
curiosity into the active zeal of workers.
In the field of aviation there were two schools. The first,
represented by such men as Professor Langley and Sir Hiram Maxim, gave
chief attention to power flight; the second, represented by Lilienthal,
Mouillard, and Chanute, to soaring flight. Our sympathies were with the
latter school, partly from impatience at the wasteful extravagance of
mounting delicate and costly machinery on wings which no one knew how to
manage, and partly, no doubt, from the extraordinary charm and
enthusiasm with which the apostles of soaring flight set forth the
beauties of sailing through the air on fixed wings, deriving the motive
power from the wind itself.
The balancing of a flyer may seem, at first thought, to be a very
simple matter, yet almost every experimenter had found in this the one
point which he could not satisfactorily master. Many different methods
were tried. Some experimenters placed the center of gravity far below
the wings, in the belief that the weight would naturally seek to remain
at the lowest point. It was true, that, like the pendulum, it tended to
seek the lowest point; but also, like the pendulum, it tended to
oscillate in a manner destructive of all stability. A more satisfactory
system, especially for lateral balance, was that of arranging the wings
in the shape of a broad V, to form a dihedral angle, with the center low
and the wingtips elevated. In theory this was an automatic system, but
in practice it had two serious defects: first, it tended to keep the
machine oscillating; and, second, its usefulness was restricted to calm
air.
In a slightly modified form the same system was applied to the
fore-and-aft balance. The main aeroplane was set at a positive angle,
and a horizontal tail at a negative angle, while the center of gravity
was placed far forward. As in the case of lateral control, there was a
tendency to constant undulation, and the very forces which caused a
restoration of balance in calms, caused a disturbance of the balance in
winds. Notwithstanding the known limitations of this principle, it had
been embodied in almost every prominent flying-machine which had been
built.
After considering the practical effect of the dihedral principle, we
reached the conclusion that a flyer founded upon it might be of interest
from a scientific point of view, but could be of no value in a practical
way. We therefore resolved to try a fundamentally different principle.
We would arrange the machine so that it would not tend to right itself.
We would make it as inert as possible to the effects of change of
direction or speed, and thus reduce the effects of wind-gusts to a
minimum. We would do this in the fore-and-aft stability by giving the
aeroplanes a peculiar shape; and in the lateral balance, by arching the
surfaces from tip to tip, just the reverse of what our predecessors had
done. Then by some suitable contrivance, actuated by the operator,
forces should be brought into play to regulate the balance.
Lilienthal and Chanute had guided and balanced their machines by
shifting the weight of the operator's body. But this method seemed to us
incapable of expansion to meet large conditions, because the weight to
be moved and the distance of possible motion were limited, while the
disturbing forces steadily increased, both with wing area and with wind
velocity. In order to meet the needs of large machines, we wished to
employ some system whereby the operator could vary at will the
inclination of different parts of the wings, and thus obtain from the
wind forces to restore the balance which the wind itself had disturbed.
This could easily be done by using wings capable of being warped, and by
supplementary adjustable surfaces in the shape of rudders. As the forces
obtainable for control would necessarily increase in the same ratio as
the disturbing forces, the method seemed capable of expansion to an
almost unlimited extent. A happy device was discovered whereby the
apparently rigid system of superposed surfaces, invented by Wenham, and
improved by Stringfellow and Chanute, could be warped in a most
unexpected way, so that the aeroplanes could be presented on the right
and left sides at different angles to the wind. This, with an
adjustable, horizontal front rudder, formed the main feature of our
first glider.
The period from 1885 to 1900 was one of unexampled activity in
aeronautics, and for a time there was high hope that the age of flying
was at hand. But Maxim, after spending $100,000, abandoned the work; the
Ader machine, built at the expense of the French Government, was a
failure; Lilienthal and Pilcher were killed in experiments; and Chanute
and many others, from one cause or another, had relaxed their efforts,
though it subsequently became known that Professor Langley was still
secretly at work on a machine for the United States Government. The
public, discouraged by the failures and tragedies just witnessed,
considered flight beyond the reach of man, and classed its adherents
with the inventors of perpetual motion.
We began our active experiments at the close of this period, in
October, 1900, at Kitty Hawk, North Carolina. Our machine was designed
to be flown as a kite, with a man on board, in winds of from fifteen to
twenty miles an hour. But, upon trial, it was found that much stronger
winds were required to lift it. Suitable winds not being plentiful, we
found it necessary, in order to test the new balancing system, to fly
the machine as a kite without a man on board, operating the levers
through cords from the ground. This did not give the practice
anticipated, but it inspired confidence in the new system of balance.
In the summer of 1901 we became personally acquainted with Mr.
Chanute. When he learned that we were interested in flying as a sport,
and not with any expectation of recovering the money we were expending
on it, he gave us much encouragement. At our invitation, he spent
several weeks with us at our camp at Kill Devil Hill, four miles south
of Kitty Hawk, during our experiments of that and the two succeeding
years. He also witnessed one flight of the power machine near Dayton,
Ohio, in October, 1904.
The machine of 1901 was built with the shape of surface used by
Lilienthal, curved from front to rear like the segment of a parabola,
with a curvature 1/12 the depth of its cord; but to make doubly sure
that it would have sufficient lifting capacity when flown as a kite in
fifteen- or twenty-mile winds, we increased the area from 165 square
feet, used in 1900, to 308 square feet -- a size much larger than
Lilienthal, Pilcher, or Chanute had deemed safe. Upon trial, however,
the lifting capacity again fell very far short of calculation, so that
the idea of securing practice while flying as a kite, had to be
abandoned. Mr. Chanute, who witnessed the experiments, told us that the
trouble was not due to poor construction of the machine. We saw only one
other explanation -- that the tables of air-pressures in general use
were incorrect.
We then turned to gliding -- coasting down hill on the air -- as the
only method of getting the desired practice in balancing a machine.
After a few minutes' practice we were able to make glides of over 300
feet, and in a few days were safely operating in twenty-seven-mile
winds. In these experiments we met with several unexpected phenomena. We
found that, contrary to the teachings of the books, the center of
pressure on a curved surface traveled backward when the surface was
inclined, at small angles, more and more edgewise to the wind. We also
discovered that in free flight, when the wing on one side of the machine
was presented to the wind at a greater angle than the one on the other
side, the wing with the greater angle descended, and the machine turned
in a direction just the reverse of what we were led to expect when
flying the machine as a kite. The larger angle gave more resistance to
forward motion, and reduced the speed of the wing on that side. The
decrease in speed more than counterbalanced the effect of the larger
angle. The addition of a fixed vertical vane in the rear increased the
trouble, and made the machine absolutely dangerous. It was some time
before a remedy was discovered. This consisted of movable rudders
working in conjunction with the twisting of the wings. The details of
this arrangement are given in our patent specifications, published
several years ago.
The experiments of 1901 were far from encouraging. Although Mr.
Chanute assured us that, both in control and in weight carried per
horse-power, the results obtained were better than those of any of our
predecessors, yet we saw that the calculations upon which all
flying-machines had been based were unreliable, and that all were simply
groping in the dark. Having set out with absolute faith in the existing
scientific data, we were driven to doubt one thing after another, till
finally, after two years of experiment, we cast it all aside, and
decided to rely entirely upon our own investigations. Truth and error
were everywhere so intimately mixed as to be undistinguishable.
Nevertheless, the time expended in preliminary study of books was not
misspent, for they gave us a good general understanding of the subject,
and enabled us at the outset to avoid effort in many directions in which
results would have been hopeless.
The standard for measurements of wind-pressures is the force produced
by a current of air of one mile per hour velocity striking square
against a plane of one square-foot area. The practical difficulties of
obtaining an exact measurement of this force have been great. The
measurements by different recognized authorities vary fifty per cent.
When this simplest of measurements presents so great difficulties, what
shall be said of the troubles encountered by those who attempt to find
the pressure at each angle as the plane is inclined more and more
edgewise to the wind? In the eighteenth century the French Academy
prepared tables giving such information, and at a later date the
Aeronautical Society of Great Britain made similar experiments. Many
persons likewise published measurements and formulas; but the results
were so discordant that Professor Langley undertook a new series of
measurements, the results of which form the basis of his celebrated
work, "Experiments in Aerodynamics." Yet a critical examination of the
data upon which he based his conclusions as to the pressures at small
angles shows results so various as to make many of his conclusions
little better than guess-work.
To work intelligently, one needs to know the effects of a multitude
of variations that could be incorporated in the surfaces of
flying-machines. The pressures on squares are different from those on
rectangles, circles, triangles, or ellipses; arched surfaces differ from
planes, and vary among themselves according to the depth of curvature;
true arcs differ from parabolas, and the latter differ among themselves;
thick surfaces differ from thin, and surfaces thicker in one place than
another vary in pressure when the positions of maximum thickness are
different; some surfaces are most efficient at one angle, others at
other angles. The shape of the edge also makes a difference, so that
thousands of combinations are possible in so simple a thing as a wing.
We had taken up aeronautics merely as a sport. We reluctantly entered
upon the scientific side of it. But we soon found the work so
fascinating that we were drawn into it deeper and deeper. Two
testing-machines were built, which we believed would avoid the errors to
which the measurements of others had been subject. After making
preliminary measurements on a great number of different-shaped surfaces,
to secure a general understanding of the subject, we began systematic
measurements of standard surfaces, so varied in design as to bring out
the underlying causes of differences noted in their pressures.
Measurements were tabulated on nearly fifty of these at all angles from
zero to 45 degrees, at intervals of 2 1/2 degrees. Measurements were
also secured showing the effects on each other when surfaces are
superposed, or when they follow one another.
Some strange results were obtained. One surface, with a heavy roll at
the front edge, showed the same lift for all angles from 71/2 to 45
degrees. A square plane, contrary to the measurements of all our
predecessors, gave a greater pressure at 30 degrees than at 45 degrees.
This seemed so anomalous that we were almost ready to doubt our own
measurements, when a simple test was suggested. A weather-vane, with two
planes attached to the pointer at an angle of 80 degrees with each
other, was made. According to our tables, such a vane would be in
unstable equilibrium when pointing directly into the wind; for if by
chance the wind should happen to strike one plane at 39 degrees and the
other at 41 degrees, the plane with the smaller angle would have the
greater pressure, and the pointer would be turned still farther out of
the course of the wind until the two vanes again secured equal
pressures, which would be at approximately 30 and 50 degrees. But the
vane performed in this very manner. Further corroboration of the tables
was obtained in experiments with a new glider at Kill Devil Hill the
next season. In September and October, 1902, nearly one thousand gliding
flights were made, several of which covered distances of over 600 feet.
Some, made against a wind of thirty-six miles an hour, gave proof of the
effectiveness of the devices for control. With this machine, in the
autumn of 1903, we made a number of flights in which we remained in the
air for over a minute, often soaring for a considerable time in one
spot, without any descent at all. Little wonder that our unscientific
assistant should think the only thing needed to keep it indefinitely in
the air would be a coat of feathers to make it light!
With accurate data for making calculations, and a system of balance
effective in winds as well as in calms, we were now in a position, we
thought, to build a successful power-flyer. The first designs provided
for a total weight of 600 pounds, including the operator and an eight
horsepower motor. But, upon completion, the motor gave more power than
had been estimated, and this allowed 150 pounds to be added for
strengthening the wings and other parts.
Our tables made the designing of the wings an easy matter; and as
screw propellers are simply wings traveling in a spiral course, we
anticipated no trouble from this source. We had thought of getting the
theory of the screw-propeller from the marine engineers, and then, by
applying our tables of air-pressures to their formulas of designing air-
propellers suitable for our purpose. But so far as we could learn, the
marine engineers possessed only empirical formulas, and the exact action
of the screw-propeller, after a century of use, was still very obscure.
As we were not in a position to undertake a long series of practical
experiments to discover a propeller suitable for our machine, it seemed
necessary to obtain such a thorough understanding of the theory of its
reactions as would enable us to design them from calculation alone. What
at first seemed a simple problem became more complex the longer we
studied it. With the machine moving forward, the air flying backward,
the propellers turning sidewise, and nothing standing still, it seemed
impossible to find a starting-point from which to trace the various
simultaneous reactions. Contemplation of it was confusing. After long
arguments, we often found ourselves in the ludicrous position of each
having been converted to the other's side, with no more agreement than
when the discussion began.
It was not till several months had passed, and every phase of the
problem had been thrashed over and over, that the various reactions
began to untangle themselves. When once a clear understanding had been
obtained, there was no difficulty in designing suitable propellers, with
proper diameter, pitch, and area of blade, to meet the requirements of
the flyer. High efficiency in a screw-propeller is not dependent upon
any particular or peculiar shape, and there is no such thing as a "best"
screw. A propeller giving a high dynamic efficiency when used upon one
machine, may be almost worthless when used upon another. The propeller
should in every case be designed to meet the particular conditions of
the machine to which it is to be applied. Our first propellers, built
entirely from calculation, gave in useful work 66 per cent. of the power
expended. This was about one third more than had been secured by Maxim
or Langley.
The first flights with the power-machine were made on the 17th of
December, 1903. Only five persons besides ourselves were present. These
were Messrs. John T. Daniels, W. S. Dough, and A. D. Etheridge of the
Kill Devil Life Saving Station; Mr. W. C. Brinkley of Manteo, and Mr.
John Ward of Nagshead. Although a general invitation had been extended
to the people living within five or six miles, not many were willing to
face the rigors of a cold December wind in order to see, as they no
doubt thought, another flying-machine not fly. The first flight
lasted only twelve seconds, a flight very modest compared with that of
birds, but it was, nevertheless, the first in the history of the world
in which a machine carrying a man had raised itself by its own power
into the air in free flight, had sailed forward on a level course
without reduction of speed, and had finally landed without being
wrecked. The second and third flights were a little longer, and the
fourth lasted fifty-nine seconds, covering a distance of 852 feet over
the ground against a twenty-mile wind.
After the last flight, the machine was carried back to camp and set
down in what was thought to be a safe place. But a few minutes later,
while we were engaged in conversation about the flights, a sudden gust
of wind struck the machine, and started to turn it over. All made a rush
to stop it, but we were too late. Mr. Daniels, a giant in stature and
strength, was lifted off his feet, and falling inside, between the
surfaces, was shaken about like a rattle in a box as the machine rolled
over and over. He finally fell out upon the sand with nothing worse than
painful bruises, but the damage to the machine caused a discontinuance
of experiments.
In the spring of 1904, through the kindness of Mr. Torrence Huffman
of Dayton, Ohio, we were permitted to erect a shed, and to continue
experiments, on what is known as the Huffman Prairie, at Simms Station,
eight miles east of Dayton. The new machine was heavier and stronger,
but similar to the one flown at Kill Devil Hill. When it was ready for
its first trial, every newspaper in Dayton was notified, and about a
dozen representatives of the press were present. Our only request was
that no pictures be taken, and that the reports be unsensational, so as
not to attract crowds to our experiment grounds. There were probably
fifty persons altogether on the ground. When preparations had been
completed, a wind of only three or four miles was blowing, --
insufficient for starting on so short a track, -- but since many had
come a long way to see the machine in action, an attempt was made. To
add to the other difficulty, the engine refused to work properly. The
machine, after running the length of the track, slid off the end without
rising into the air at all. Several of the newspaper men returned the
next day, but were again disappointed. The engine performed badly, and
after a glide of only sixty feet, the machine came to the ground.
Further trial was postponed till the motor could be put in better
running condition. The reporters had now, no doubt, lost confidence in
the machine, though their reports, in kindness, concealed it. Later,
when they heard that we were making flights of several minutes'
duration, knowing that longer flights had been made with air-ships, and
not knowing any essential difference between airships and flying
machines, they were but little interested.
We had not been flying long in 1904 before we found that the problem
of equilibrium had not as yet been entirely solved. Sometimes, in making
a circle, the machine would turn over sidewise despite anything the
operator could do, although, under the same conditions in ordinary
straight flight, it could have been righted in an instant. In one
flight, in 1905, while circling around a honey locust-tree at a height
of about fifty feet, the machine suddenly began to turn up on one wing,
and took a course toward the tree. The operator, not relishing the idea
of landing in a thorn- tree, attempted to reach the ground. The left
wing, however, struck the tree at a height of ten or twelve feet from
the ground, and carried away several branches; but the flight, which had
already covered a distance of six miles, was continued to the
starting-point.
The causes of these troubles -- too technical for explanation here --
were not entirely overcome till the end of September, 1905. The flights
then rapidly increased in length, till experiments were discontinued
after the 5th of October, on account of the number of people attracted
to the field. Although made on a ground open on every side, and bordered
on two sides by much traveled thoroughfares, with electric cars passing
every hour, and seen by all the people living in the neighborhood for
miles around, and by several hundred others, yet these flights have been
made by some newspapers the subject of a great "mystery."
A practical flyer having been finally realized, we spent the years
1906 and 1907 in constructing new machines and in business negotiations.
It was not till May of this year that experiments (discontinued in
October, 1905) were resumed at Kill Devil Hill, North Carolina. The
recent flights were made to test the ability of our machine to meet the
requirements of a contract with the United States Government to furnish
a flyer capable of carrying two men and sufficient fuel supplies for a
flight of 125 miles, with a speed of forty miles an hour. The machine
used in these tests was the same one with which the flights were made at
Simms Station in 1905, though several changes had been made to meet
present requirements. The operator assumed a sitting position, instead
of lying prone, as in 1905, and a seat was added for a passenger. A
larger motor was installed, and radiators and gasoline reservoirs of
larger capacity replaced those previously used. No attempt was made to
make high or long flights.
In order to show the general reader the way in which the machine
operates, let us fancy ourselves ready for the start. The machine is
placed upon a single rail track facing the wind, and is securely
fastened with a cable. The engine is put in motion, and the propellers
in the rear whir.
You take your seat at the center of the machine beside the operator.
He slips the cable, and you shoot forward. An assistant who has been
holding the machine in balance on the rail, starts forward with you, but
before you have gone fifty feet the speed is too great for him, and he
lets go. Before reaching the end of the track the operator moves the
front rudder, and the machine lifts from the rail like a kite supported
by the pressure of the air underneath it. The ground under you is at
first a perfect blur, but as you rise the objects become clearer. At a
height of one hundred feet you feel hardly any motion at all, except for
the wind which strikes your face. If you did not take the precaution to
fasten your hat before starting, you have probably lost it by this time.
The operator moves a lever: the right wing rises, and the machine swings
about to the left. You make a very short turn, yet you do not feel the
sensation of being thrown from your seat, so often experienced in
automobile and railway travel. You find yourself facing toward the point
from which you started. The objects on the ground now seem to be moving
at much higher speed, though you perceive no change in the pressure of
the wind on your face. You know then that you are traveling with the
wind. When you near the starting point, the operator stops the motor
while still high in the air. The machine coasts down at an oblique angle
to the ground, and after sliding fifty or a hundred feet comes to rest.
Although the machine often lands when traveling at a speed of a mile a
minute, you feel no shock whatever, and cannot, in fact, tell the exact
moment at which it first touched the ground. The motor close beside you
kept up an almost deafening roar during the whole flight, yet in your
excitement, you did not notice it till it stopped.
Our experiments have been conducted entirely at our own expense. In
the beginning we had no thought of recovering what we were expending,
which was not great, and was limited to what we could afford for
recreation. Later, when a successful flight had been made with a motor,
we gave up the business in which we were engaged, to devote our entire
time and capital to the development of a machine for practical uses. As
soon as our condition is such that constant attention to business is not
required, we expect to prepare for publication the results of our
laboratory experiments, which alone made an early solution of the flying
problem possible.
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