expect. They got quick response to the slightest movement of the front
elevator, which promised to be satisfactory in maintaining fore and
aft balance. At first, they fastened the warping mechanism, to make it
inoperable, and had only the elevator to manipulate, for they feared
that, inexperienced as they were, if they tried to use both, then
they might be unsuccessful with either. But even without the use of
the warping mechanism it was possible to make glides of from five to
ten seconds before the sidewise tilt of the machine forced a landing.
Before making the last three or four flights the Wrights loosened the
warping wires to permit the sidewise control to be used.
When these experiments of 1900 ended, instead of the hours of practice
in the air the Wrights had hoped to have, they had flown the machine
as a kite with a man aboard barely ten minutes, and had had only two
minutes of actual gliding.
Now that the experiments for that year were ended and they had no
further use for the glider, the brothers weighted the machine with sand
and left it on the hill. When “Bill” Tate saw that they were through
with the glider he asked if he might have it, and they gladly gave
it to him. Mrs. Tate used the sateen that covered the wings to make
dresses for her two small daughters. She noted that it appeared to
be unusually good fabric, more closely woven and better than she had
seen in the stores. Some of her neighbors, when they saw the dresses
she made of it, remarked that it seemed too bad to use such excellent
material on a kite.
Though the amount of practice was less than they had expected, all
the Wrights had learned in that season of 1900 seemed to confirm the
correctness of certain opinions held at the beginning. Their method of
warping or twisting the wings to maintain lateral balance was better
than dependence on either the dihedral angle or shifting the weight
of the operator; better than any method yet tried. And their front
elevator had been highly satisfactory as a means for directing the
machine up and down. Before leaving Kitty Hawk they decided that their
next experiments would be with a glider large enough to be flown as a
kite, with an operator aboard, in winds ordinarily to be counted on.
When the brothers set to work on their glider for the experiments of
1901, they decided to make it of the same general design as the first
one, and with the same system of control. But they carried out their
plan to give it considerably more area, to provide greater lifting
power. Another change they made was to increase the curvature of the
wings to conform to the shape on which Lilienthal had based his tables
of air pressures. It had wings of about seven-foot chord (the straight
line distance between the front and rear edges) with a total span of
twenty-two feet, and weighed ninety-eight pounds. After a section
twenty inches wide had been removed from the middle of the lower wing,
and the rear corners of the wings rounded off, the total lifting area
was 290 square feet, as compared with 165 in the previous glider. The
front elevator, with its rear edge about two and one half feet away
from the front edge of the wings, had a four-and-one-half foot chord
and an area of eighteen square feet.
This was a much larger machine than anyone had ever tried to fly. The
Wrights knew it could not be controlled simply by shifting the pilot’s
weight, as others had done, but they had faith in their own operable
front elevator and believed they could manage it. If their calculations
were correct, it would be supported in a wind of seventeen miles an
hour, with the wing surfaces at an “angle of incidence” of only three
degrees. (“Angle of incidence,” now more often called “angle of
attack,” has been defined as the angle at which the plane presents
itself to the air in advancing against it.)
As it would be impractical to keep so large a machine with them in the
tent, as they had done with the smaller glider, the brothers built near
Kill Devil Hill a rough frame shed, twenty-five feet long, sixteen
feet wide, and seven feet high at the eaves. Both ends of the building
except the gable parts were made into doors, hinged above. When open,
the doors provided an awning at each end of the building. For living
quarters they still used a tent. By driving a pipe ten or twelve feet
into the sand they got a water supply.
Though the great stretch of sandy waste seemed too desolate for
anyone to bother about owning, yet it was all under the ownership of
one person or another and the Wrights took the precaution to obtain
permission to erect their buildings.
This year they were to have company in camp. Octave Chanute, with whom
they had been in correspondence for about a year, stopped in Dayton
in June, 1901, at their invitation, to get better acquainted. When
he learned that the Wrights had carried on their experiments in 1900
without the presence of a doctor in camp, and were intending to do so
again, he told them he thought that was too risky, considering the kind
of work and the isolation of the experiment ground. He said he knew a
young man in Coatesville, Pennsylvania, George A. Spratt, “an amateur”
in aeronautics, who had had some medical training. Spratt had never
seen any gliding experiments, and Chanute thought he would be eager
for the opportunity. If the Wrights would board him at camp, Chanute
said, he would be glad to pay Spratt’s traveling expenses to Kitty Hawk
and would consider himself “compensated by the pleasure given to him.”
Chanute also proposed that they have in camp with them E. C. Huffaker,
of Chuckey City, Tennessee, who was building a glider that Chanute was
financing, and the Wrights consented. Thus there were four regularly
in camp that season, and for a time Chanute himself was with them as a
guest.
The new machine was completed and ready for trial on the afternoon
of July 27. Since it was designed to be flown in a wind of seventeen
miles, and there was but thirteen miles of wind on that day, the
brothers took the machine to the big Kill Devil Hill for its first
trial. After five or six short tuning-up flights they made a glide of
315 feet in nineteen seconds. Although several flights on this first
day of experiments in 1901 exceeded the best made the year before,
yet it was soon evident that in several respects the machine was not
as good as the first one. It was found that the wings, with a camber
of one to twelve--the camber recommended by Lilienthal, and used by
Chanute and others--was not so good as the camber of one to twenty-two,
used by the Wrights in 1900. (Camber of one to twenty-two means that
the length of the chord, the straight-line distance between the front
and rear edges of the wings, is twenty-two times the distance _from_
the chord to the deepest part of the wing curve.) This was demonstrated
by the fact that the 1901 machine could not glide on a slope as nearly
level as had the earlier machine. The Wrights found, too, that a
machine with wings of one to twelve camber was not so easily controlled
fore and aft as when the wings were of one to twenty-two camber. They
decided therefore to reduce the camber of the wings to make them more
like those of the earlier machine. When they resumed their gliding,
after the camber had been reduced (one to eighteen), the control of
the machine appeared to be as good as it was the year before, and they
then made flights in winds of twenty-two to twenty-seven miles an hour,
without accident. Though in most of these flights the lateral control
was highly effective, in a few others--under conditions seemingly the
same--the wing warping appeared to have no effect at all.
The Wrights now made the discovery that in free flight, when the wing
on one side of the machine was presented to the wind at a greater
angle than that on the other side, the wing with the greater angle,
instead of rising as it was expected to do, sometimes descended. The
explanation was that the greater angle of the wing at one side gave
more resistance to forward motion and thus reduced the speed on that
side. This decrease in speed more than counter-balanced the effect of
the larger angle of the wing in producing lift. (The Wrights had not
discovered this when flying the glider as a kite, because, when held by
ropes, the wings always maintained equal air speeds, even when their
resistances were unbalanced.)
It was evident to the brothers that their present method of controlling
equilibrium was not yet complete. Something was needed to maintain
equal speeds at the two wing tips. The idea occurred to them that the
addition of a vertical fin attached to the machine at some distance in
the rear of the wings might be the solution of the problem. But the
test of such a fin had to be left until another season.
The behavior of the glider in these various flights forced the Wrights
to give thought to another scientific problem, that regarding the
center of air pressure on curved surfaces. Contrary to the teachings of
scientific books on the subject, it was becoming more and more evident
that the travel of the center of pressure on a cambered surface is not
always in the same direction as the travel on a plane surface. When
the angle of attack on a plane surface is decreased, the center of
pressure moves toward the front edge; but on a cambered surface this
is true only when larger angles are being decreased. When the angle of
attack on a cambered surface is decreased from, say, thirty degrees
to twenty-five degrees, the center of pressure moves forward, as it
does on a plane surface; but when a certain angle (between twelve
and fifteen degrees) is reached, then the movement of the center of
pressure is reversed. From there on, the center of pressure moves
toward the rear so long as any further decrease is made in the angle
of attack. The Wrights proved this by a series of experiments with a
single surface from their plane. Knowledge of the phenomenon of this
reversal of center of pressure was of great importance to them in their
later work of designing aeroplanes.
Scientific problems were not the only ones to perplex the Wrights. A
sore trial were the mosquitoes and sandfleas, particularly numerous
and aggressive in that summer of 1901. As Orville Wright recalled
in later years, there were times when he thought, while fighting
mosquitoes through the night, that if he could just survive until
morning he would pack up and return home. Those mosquitoes might have
caused a long postponement of the conquest of the air.
By the time they left Kitty Hawk on August 20, the brothers had
satisfied themselves that a glider of large surfaces could be
controlled almost as easily as a smaller one, provided the control is
by manipulation of the surfaces themselves instead of by movements
of the operator’s body. So far as they knew, judging from figures
previously published, they had broken all records for distance in
gliding. Chanute, who had witnessed part of the 1901 experiments,
insisted that the results were better than had ever been attained
before. All that was encouraging. But, on the other hand, if most of
the supposedly scientific information available was worthless, then
their task was even more formidable than they had expected. With no
dependable previous knowledge to guide them, who were they to determine
how man should fly? Wilbur seemed much discouraged. Possibly he had
entertained hopes of actually flying, though he had always disclaimed
having such an idea. He was ready to drop the experiments altogether.
On the way home, Wilbur declared his belief: Not within a thousand
years would man ever fly!
Chanute urged the brothers not to drop their experiments, arguing that
if they did it would be a long time before anyone else would come as
near to understanding the problem or how to work toward its solution.
Without knowing it, Chanute made a great contribution to aviation
history, for the Wrights heeded his repeated admonitions against
ceasing their efforts. Without the proddings of Chanute they might not
have gone on.
Chanute performed another great service for aeronautics when he, as
president of the Western Society of Engineers, invited Wilbur Wright to
address that body at a meeting in Chicago, September 18, 1901, on the
subject: Some Aeronautical Experiments.
Wilbur shrank from the idea of making such a talk and would hardly have
done so except to oblige his friend. He cautioned Chanute, though,
not to make the speech a prominent feature of the program, because,
he said, he made no pretense of being a public speaker. Chanute did
nevertheless plan to use the announcement of the talk as a means to
help make the meeting a big success. He wanted to know if it would be
all right to make the occasion “Ladies’ Night.” Wilbur decided that he
would already be as badly scared as a man could be and the presence of
women would not make the situation much worse. But he insisted on one
thing, that he must not be expected to appear in formal evening dress.
In this speech Wilbur boldly declared that the best sets of figures
obtainable regarding air pressure against airplane surfaces appeared
to contain many serious errors. Orville, at the shop in Dayton, was a
little alarmed about that part of the speech. What if something about
their own work had been wrong and the figures compiled by various
scientists should finally be proved correct? Certainly it was no small
responsibility for anyone so little known as Wilbur or he to denounce
publicly the work of eminent scientists, dignified by preservation in
books long regarded as authoritative. It would be both presumptuous and
risky to brand supposedly established facts as untrue unless the person
doing so could be unassailably sure of his ground.
In this cautious state of mind Orville rigged up a little wind-tunnel
for the purpose of making a series of tests. This tunnel consisted
simply of what appeared to be an old starch box, not more than eighteen
inches long, that was lying in the shop. In it he placed a hastily
constructed apparatus, a main part of which was simply a metal rod
pivoted in the manner of a weather vane. Without attempting to give
technical details of the method used, it may be said that a curved
surface was balanced against a plane surface in an air current passing
through the box. As Orville had provided the box with a glass top he
could measure the angles to the wind at which the curved surface and
the plane surface of equal area produced equal pressures.
The experiments with this crude apparatus lasted only one day. They
were conclusive enough so far as they went, indicating errors in
published figures relating to air pressure on curved surfaces. But
as Orville was later to learn, the published errors were greatest in
regard to wing surfaces set at small angles, such as would be used in
flying, and he had tested thus far only larger angles. With the tests
thus incomplete, Orville and Wilbur decided, on the latter’s return
from Chicago, that it might be prudent to stay on the safe side and
omit from the published record of Wilbur’s speech the more severe
part of his criticism of available figures. They would wait until
further wind-tunnel experiments could give more detailed knowledge.
Consequently, when Wilbur’s speech appeared in the December, 1901,
issue of the _Journal of the Western Society of Engineers_, it was a
bit less startling than the one he had actually delivered--though, even
after the deletions, there still remained strong hints that accepted
tables of figures might be wrong. And the record of the speech was
treated as of great importance. It has probably been reprinted and
quoted as often as any other article ever written on the subject of
flying.
The Wrights were not sure they would ever build another glider. But
their curiosity, their passion for getting at truth, had now been too
much aroused for them to quit studying the problem of air pressures.
They decided to build another wind-tunnel, less crude than the one
Orville had hastily used, and continue their experiments. The new
tunnel consisted of an open-ended wooden box about sixteen inches
square on the inside by six feet long. Into one end would come a
current of air and the draft thus created would be “straightened,”
as well as made uniform, by having to pass through a set of small
pigeon-holes. It would have been a great convenience to use an electric
fan for sending the air into the tunnel. But the Wrights had no
electric current in their shop--still lighted by gas--and the fan was
driven by a one-cylinder gas engine they had previously made. They
attached the fan to a spindle that had held an emery wheel. A new
measuring device, or balance, was built of wire intended for bicycle
spokes, and pieces of hacksaw blades. These experiments were now done
with much more refinement than at first, and the measurements were
for both “lift” and “drift.” But as each curved surface measured was
balanced against the pressure on a square plane, exposed at ninety
degrees to the same air current, it was not necessary to know the
precise speed of the air current.
During that autumn and early winter of 1901, the brothers tested in
the wind-tunnel more than two hundred types of wing surfaces. They
set these at different angles, starting with the angle at which the
surface begins to lift, and then at 2½ degree intervals, up to twenty;
and at five degree intervals up to forty-five degrees. They measured
monoplane, biplane, and triplane models; also models in which one
wing followed the other, as used by Langley in his experiments. They
measured the lift produced by different “aspect ratios”--that is, the
ratio of the span of the wing to its chord. They found that the greater
the span in proportion to the chord the more easily the wing may be
supported. They measured thick and thin surfaces. One surface had a
thickness of nearly one-sixth of its chord.
Among other things, these experiments proved the fallacy of the sharp
edge at the front of an airplane wing and the inefficiency of deeply
cambered wings as then generally advocated by others. Sometimes they
got a result so unexpected that they could hardly believe their own
measurements--as, for example, when they discovered that, contrary to
all previously published figures by students of the subject, a square
plane gave a greater pressure when set at thirty degrees than at
forty-five degrees.
These wind-tunnel experiments in the bicycle shop were carried on for
only a little more than two months, and were ended before Christmas,
1901. The Wrights discontinued them with great reluctance; but, after
all, they were still in the bicycle business, still obliged to give
thought to their means for earning a living, and with no idea that
this scientific research could ever be financially profitable. In
those few weeks, however, they had accomplished something of almost
incalculable importance. They had not only made the first wind-tunnel
in which miniature wings were accurately tested, but were the first
men in all the world to compile tables of figures from which one might
design an airplane that could fly. Even today, in wind-tunnels used in
various aeronautical laboratories, equipped with the most elaborate
and delicate instruments modern science can provide, the refinements
obtained over the Wrights’ figures for the same shapes of surfaces
are surprisingly small. But it is doubtful if the difficulties and
full value of the Wrights’ scientific researches within their bicycle
shop are yet appreciated. The world knows they were the first to
build a machine capable of sustained flight and the first actually
to fly; but it is not fully aware of all the tedious, grueling
scientific laboratory work they had to do before flight was possible.
Important as was the system of control with which the Wrights’ name
has been connected, it would not have given them success without their
wind-tunnel work which enabled them to design a machine that would lift
itself.
The Wrights had a double reason for making sure of their figures.
With little money to spend on a hobby, it was much cheaper to rectify
mistakes on paper than after the idea was put into material form. They
knew that if they should decide to go on to further gliding attempts,
they could not afford to spend much more money on apparatus built
according to unreliable data.
After compiling their own tables of figures, the Wrights gave copies
of them to their friend Chanute and others interested in the problem
of aerodynamics. Chanute well knew that the Wrights now had knowledge
of aeronautics far beyond that of anyone else in the world, and he
felt that for them to go on with their experiments was almost a duty.
He much regretted, in the interest of science, he said, that they had
reached a stopping-place, for he was sure further experiments on their
part promised “important results.”
Chanute might well have felt pride in the effectiveness of his
insistence that the Wrights should go on experimenting, as well as in
the results of his invitation to Wilbur to make that Chicago speech.
Except for that speech and its daring statements that Orville thought
needed more confirmation, there probably would have been no wind-tunnel
tests; and without the kind of knowledge then obtained, neither the
Wrights nor anyone else could have built a practical flying-machine.
Those wind-tunnel experiments marked one of the great turning points in
the long history of attempts at human flight.
It still remained for the Wrights to put their new knowledge to actual
test in gliding, and they set out on August 25, 1902, for their third
stay at Kitty Hawk. But not until September 8 were they able to begin
the work of assembling their new glider, for the camp, battered by
winter gales, needed much repairing; and they decided to build an
addition to it for living quarters. They did not have their machine
ready for its first trial until September 19.
This new glider was of not much greater lifting area than that of
the previous year, though the wing span had been increased from
twenty-two to thirty-two feet. But since the wind-tunnel experiments
had demonstrated the importance of the “aspect ratio,” the total span
was now about six times the chord instead of three. One minor change
also may be noted. In the earlier gliders, the wing-warping mechanism
had been worked by movement of the operator’s feet; but now in this
1902 glider it was done by sidewise movement of one’s hips resting on
a “cradle.” The most noticeable change was the addition of a tail,
consisting of fixed twin vertical vanes, with a total area of a trifle
less than twelve square feet. Its purpose was to correct certain
difficulties encountered in some of the flights with the 1901 machine.
When the wing surfaces at the right and left sides were warped to
present different angles toward the wind, the wing that had the greater
angle, and therefore the more resistance, tended to lag behind, and
then the slower speed offset what otherwise would have been the greater
lifting power of that wing. The tail was expected to counter-balance
that difference in resistance of the wing tips. If the wing on one
side tended to swerve forward, on a vertical axis, then the tail, more
exposed to the wind on that same side, should, it was thought, stop
the machine from further turning.
Entirely apart from any advantages to be gained from the use of the
tail, the first trials of the new machine were highly encouraging for
another reason. It was soon evident that by disregarding all tables
of air pressures used by their predecessors and building according to
the figures obtained from their wind-tunnel experiments, the Wrights
had made a big advance toward flight. Because of the knowledge they
now had, not possessed by any previous experimenter, of how the wings
should be shaped, this 1902 machine was of just about twice the
“dynamic efficiency” of any other glider ever built; it could have been
flown with probably less than half the power required for any other
glider.