flights in September and October, 1902. Several glides were of
more than six hundred feet, and a number of them were against a
thirty-six-mile-an-hour wind. No previous experimenter had ever dared
to try gliding in so stiff a wind. That the Wrights were successful
at such feats gave proof of the effectiveness of their devices for
control. Some of their flights lasted more than a minute and at times
it was possible to soar in one spot without any descent. So impressive
were such exhibitions that Bill Tate’s brother Dan solemnly offered the
opinion: “All she needs is a coat of feathers to make her light and she
will stay in the air indefinitely.”
About one time in fifty, however, the machine behaved in a manner quite
mysterious. It would turn up sidewise and come sliding to the ground in
spite of all the warp the operator could give to the wing tips. At one
trial the lateral control would work perfectly and then the next time,
under conditions that seemed to be about the same, it was impossible
to prevent one wing end from striking the sand with a kind of spinning
movement that the brothers called “well-digging.”
This new problem, that had not occurred in their previous gliders,
came from the fact that the machine had a tail. Those “well-digging”
accidents were tail-spins--though that term did not come into use
until several years afterward. But even after it was evident that
the tail had something to do with the machine’s peculiar behavior,
neither brother was prepared to explain _why_. Then one night Orville
drank more than his customary amount of coffee. Instead of going to
sleep as usual the moment he got into bed, he lay awake for several
hours. Those extra cups of coffee may have been important for the
future of practical flight for, as he tossed about, he figured out the
explanation of the phenomenon caused by the tail. Here it is, as he
eagerly gave it to Wilbur, and to their brother Lorin, who was visiting
them, at breakfast the next morning:
When the machine became tilted laterally it began to slide sidewise
while advancing, just as a sled slides downhill or a ball rolls down
an inclined plane, the speed increasing in an accelerated ratio. If
the tilt happened to be a little worse than usual, or if the operator
were a little slow in getting the balance corrected, the machine slid
sidewise so fast that this movement caused the vertical vanes to strike
the wind on the side toward the low wing instead of on the side toward
the high wing, as it was expected to do. In this state of affairs the
vertical vanes did not counteract the turning of the machine about a
vertical axis, caused by the difference of resistance of the warped
wings on the right and left sides; on the contrary, the vanes assisted
in the turning movement, and the result was worse than if there were no
fixed vertical tail.
If his explanation was sound, as Orville felt sure it was, then, he
said, it would be necessary to make the vertical tail movable, to
permit the operator to bring pressure to bear on the side toward
the higher wing. (This is the form of the Wright system of control
generally used today--the independent control of aileron and rudder.)
Wilbur promptly saw that the explanation was probably correct and
nodded approvingly. And he immediately made a suggestion. A particular
relation existed, he said, in the desired pressures on the tail, no
matter whether the trouble was due to difference of resistance of
the wing tips or on account of sliding. Whatever the reason, it was
desirable to get rid of the pressure on the side toward the low wing,
to which a greater angle of incidence must be imparted in restoring
lateral balance, and bring pressure on the side of the tail toward the
high wing where there must be a reduced angle. So why not have the
mechanism that controlled the wing warping and that which moved the
tail operated in conjunction? Then the pilot, instead of having to
control three things at once, would need to attend only to the front
elevator and the wing-warping device. The brothers at once attached
the wires controlling the tail to those that warped the wings--and
they also changed the tail from two vertical fins to a single vertical
rudder.
After the changes in the 1902 glider, the Wrights had their machine
in about the form pictured and described in the drawings and
specifications of their patent, applied for on the 23rd of the next
March.
With their accurate data for making calculations, and a system of
balance effective in winds as well as in calms, the brothers believed
that they now could build a successful power-flyer.
VI
FIRST POWER FLIGHT
Immediately on their return to Dayton after the 1902 glider flights,
the Wrights set to work to carry out plans, already begun at Kitty
Hawk, for a power machine. The satisfactory performance of the glider
had demonstrated the accuracy of the laboratory work on which its
design was based, and they now felt sure they could calculate in
advance the performance of any machine they built with a degree of
accuracy not possible with the data available to their predecessors.
Early in their preparations, they took steps to obtain a suitable
engine. They knew that a steam engine might do well enough for their
purpose, but a gasoline engine would be simpler and better. Some time
previously they had built an air-cooled, one-cylinder gas engine for
operating the machinery of their small workshop; but they did not feel
experienced enough to build the kind they now needed and preferred to
buy one.
[Illustration: INSIDE THE 1902 CAMP. The kitchen corner of the 1902
camp at Kitty Hawk.]
They wanted a motor to produce at least eight horsepower and to weigh,
without accessories, not more than twenty pounds per horsepower.
It seemed doubtful if such a motor as they required was then being
manufactured; but perhaps one of the automobile companies could build
one light enough by reducing the weight of the flywheel and using more
aluminum than in the regular output. On December 3, 1902, they sent
letters to a number of automobile companies, and to gasoline motor
manufacturers, altogether to nearly a dozen, asking if they could
furnish a motor that would develop eight brake horsepower and weigh
not more than 200 pounds. Orville Wright was not sure in after years
whether he and Wilbur revealed in their letters the use they planned
for the motor they were seeking; but most of the companies replied
that they were too busy with their regular business to undertake such
a special order. There is reason to suspect the companies may have got
wind of the purpose to which the motor would be put and were afraid to
become implicated in the project. If a company provided a motor for a
so-called flying-machine, and this fact should leak out, it could hurt
their business prestige, because it might look as if they considered
human flight a possibility.
[Illustration: FROM ORVILLE WRIGHT’S DIARY. Part of the entry for
December 17, 1903--the day of the first power flight.
Thursday, Dec. 17th
When we got up a wind of between 20 and 25 miles was blowing
from the north. We got the machine out early and put out the
signal for the men at the station. Before we were quite ready,
John T. Daniels, W. S. Dough, A. D. Etheridge, W. C. Brinkley
of Manteo, and Johnny Moore of Nags Head arrived. After running
the engine and propellers a few minutes to get them in working
order, I got on the machine at 10:35 for the first trial. The
wind, according to our anemometers at this time, was blowing
a little over 20 miles (corrected) 27 miles according to the
Government anemometer at Kitty Hawk. On slipping the rope
the machine started off increasing in speed to probably 7 or
8 miles. The machine lifted from the truck just as it was
entering on the fourth rail. Mr. Daniels took a picture just
as it left the tracks. I found the control of the front rudder
quite difficult on account of its being balanced too near the
center and thus had a tendency to turn itself when started so
that the rudder was turned too far on one side and then too
]
One company replied, however, that they had motors, rated at eight
horsepower, according to the French system of ratings, which weighed
only 135 pounds, and if the Wrights thought this would develop enough
power for their purpose, they could buy one. After an examination of
the particulars of this motor, from which they learned that it had but
a single cylinder, of four-inch bore and five-inch stroke, the Wrights
decided that its power was probably much overrated.
Finally the brothers decided that they would have to build their
motor themselves. They estimated that they could make one of four
cylinders, of four-inch bore and four-inch stroke, weighing not more
than two hundred pounds, with accessories included. Their mechanic,
Charlie Taylor, gave them enthusiastic help. In its final form, the
bare engine, without magneto, weighed 152 pounds; with accessories,
170 pounds. At 1,200 revolutions per minute, it developed sixteen
horsepower--but only for the first fifteen seconds after starting;
after a minute or two it did not give more than about twelve
horsepower. Since, however, they had not counted on more than eight
horsepower, for a machine of a total weight of 600 pounds, now they
could add 150 pounds for strengthening wings and other parts. Not yet
knowing how much power an engine of that size ought to have developed,
the Wrights were much pleased with its performance. Long afterward they
found out that the engine should have provided about twice as much
power as it did. The trouble, as they later said, was their “lack of
experience in building gasoline motors.”
The wings of this new power machine had a total span of a few inches
more than forty feet, and the upper and lower wing surfaces were six
feet apart. To reduce the danger of the engine ever falling on the
pilot, it was placed on the lower wing a little to right of center.
The pilot would ride lying flat, as on the glider, but to the left of
center, to balance the weight. To guard against the machine rolling
over in landing, the sled-like runners were extended farther out in
front of the main surfaces than on the glider. These two runners were
four feet, eight inches apart. The tail of the machine had twin movable
vanes instead of a single vane as in the 1902 glider.
The Wrights left the designing of the propellers until the last,
because they felt sure that part of the job would be easy enough.
Their tables of air pressures, derived from wind-tunnel experiments,
would enable them, they thought, to calculate exactly the thrust
necessary to sustain the machine in flight. But to design a propeller
that would give the needed amount of thrust, with the power at their
command, was a problem they had not yet considered. No data on air
propellers were available, but the Wrights had always understood that
it was not difficult to obtain an efficiency of fifty per cent with
marine propellers. All that should be necessary would be to learn the
theory of the operation of propellers from books on marine engineering
and then substitute air pressures for water pressures. What could be
simpler or easier? Accordingly, the brothers got several such books
from the Dayton Public Library. But when they began to read those
books, they discovered to their surprise that much less was known about
propellers than they had supposed.
All the formulae on propellers in the books were found to be based on
experiment and observation rather than on theory. The marine engineers,
when they saw that a propeller would not move a boat fast enough, had
then tried one larger, or of a different pitch, until they got one
that would serve their purpose. But they could not design a propeller
on paper and foresee exactly what its performance on a certain type
of motor-boat would be. Exact knowledge of the action of the screw
propeller, though it had been in use for a century, was still lacking.
The Wrights knew that rough estimates, which might be near enough for
a motor-boat, would not do for an airplane. On a boat a propeller
having only a fraction of one per cent of the desired efficiency could
move the boat a little; but on an airplane, unless the propeller
had the full amount of thrust needed, it would be worthless, for it
couldn’t lift the plane into the air at all! In short, the Wrights had
to have a propeller that would do exactly what was expected of it.
And they had neither the time nor money to carry on a long series of
experiments with different kinds of propellers until they could hit on
one suitable. They couldn’t afford to make mistakes except on paper.
They must somehow learn enough about how propellers acted, and why, to
enable them to make accurate calculations.
It was apparent to the Wrights that a propeller was simply an airfoil
traveling in a spiral course. As they could calculate the effect of an
airfoil traveling in a straight course, why should they not be able to
calculate the effect in a spiral course? At first thought that did not
seem too difficult, but they soon found that they had let themselves
into a tough job. Since nothing about a propeller, or the medium in
which it acts, would be standing still, it was not easy to find even a
point from which to make a start. The more they studied it, the more
complex the problem became. “The thrust depends upon the speed and
the angle at which the blade strikes the air; the angle at which the
blade strikes the air depends upon the speed at which the propeller
is turning, the speed the machine is traveling forward, and the speed
at which the air is slipping backward; the slip of the air backward
depends upon the thrust exerted by the propeller, and the amount of
air acted upon.” It was not exactly as simple as some of the problems
in the school arithmetic--to determine how many sheep a man had or how
many leaps a hound must make to overtake a hare.
In trying to work out a theory about the action of screw propellers,
Wilbur and Orville got into many arguments. Right here it may be noted
that this habit the brothers had of arguing technical points was one of
the reasons why they were able to accomplish all they finally did in
a relatively short time. Neither was a “yes” man to the other. But in
their arguments about propellers a peculiar thing happened. “Often,”
Orville later reported, “after an hour or so of heated argument, we
would discover that we were as far from agreement as when we started,
but that _each had changed to the other’s original position_.”
Many months passed before the intricacies of the problem began to
untangle themselves. The Wrights finally got a better understanding of
the action of screw propellers than anyone had ever had before. The
time came when they felt sure of their ability to design propellers of
exactly the right diameter, pitch, and area for their needs.
A calculation indicated that 305 revolutions of the propeller would be
required to produce 100 pounds thrust. Later, actual measurement showed
that only 302 instead of 305 propeller turns were required, or just
under one per cent of the calculated amount. The propellers delivered
in useful work 66 per cent of the power expended. That was about
one-third more than either Hiram Maxim or Professor Langley in their
attempts at flying had ever been able to attain.
For two reasons the Wrights decided to use two propellers. First,
they could in that way obtain a reaction against a greater quantity
of air, and at the same time use a larger pitch angle; and, by having
the propellers run in opposite directions, the gyroscopic action of
one would neutralize that of the other. The propellers were on tubular
shafts about ten feet apart, both driven by chains running over
sprockets, somewhat as on a bicycle.
L. M. Wainwright, president of the Diamond Chain Company, of
Indianapolis, became interested in the Wrights’ transmission problem,
and gave them valuable advice.
The Wrights found that the chains would have to be run through guides
to prevent slapping and to overcome undue stresses on the machine.
They adopted tubular guides and found that they could cross one of
the chains in a figure eight and thus have the propellers running in
opposite directions.
Not until September 23 was all in readiness for the Wrights to set out
for Kitty Hawk. They were able to make good connections with a boat
and arrived at camp two days later, on a Friday. Discussing en route
what they hoped to accomplish, neither had the slightest doubt about
the fulfillment of their dreams. Besides being full of confidence they
also felt the exuberance of excellent physical condition. Orville was
now thirty-two years old and Wilbur thirty-six. Five foot ten and a
quarter inches in height, Wilbur was the taller of the two by a little
more than an inch and a half. Orville weighed 145 pounds, about five
more than Wilbur. Each of them had grayish-blue eyes and they might
have been recognized as brothers, though in their own family Wilbur at
that time was considered “more of a Wright” in his facial conformation.
Orville looked a little more like his mother. Both were suitably built
for bird men.
Plenty of annoyances, difficulties, and delays were still to be faced.
When they reached their camp near Kill Devil Hill, the Wrights found
that a storm had blown it from its foundation posts. They repaired the
shed and also built a new one. With two sheds they had enough space
for housing both the 1902 glider and the power machine, and also for a
better workshop.
Just as the new building was nearing completion, the Kitty Hawk region
had one of the worst storms in years. It came without warning, soon
blowing forty miles an hour, and increased during the night until the
next day the wind was more than seventy-five miles an hour. Orville
risked climbing to the roof to nail down some of the more exposed
parts. But by the time he got to the roof edge, the wind had blown his
coat about him in a manner to pinion his arms and leave him helpless.
Wilbur rushed to his assistance and held down his coat, but the
wind was so strong that it was almost impossible to swing a hammer
accurately enough to hit a nail.
Three weeks were needed for assembling the new machine. From time
to time, also, they took out the 1902 glider, still in fairly good
condition in the shed where they had left it, and got practice. After
the first few trials each brother was able to make a new world’s record
by gliding for more than a minute.
It was hoped to have the power machine ready for its first trial
early in November. But at the first run of the motor on the completed
machine, an unexpected strain from back-firing twisted one of the
propeller shafts and tore loose the cross-arm to which the propeller
was fastened. Both shafts were then sent back to the bicycle shop at
Dayton to be made stronger. Dr. Spratt had arrived on October 23 to
witness tests of the new machine, but the weather had become so wintry
that he started home on November 5, taking with him as far as Norfolk
the shafts for shipment to Dayton.
Octave Chanute came, on invitation, the next day, but he too found
it difficult to be comfortable with the weather increasingly wintry
and he stayed less than a week. Before leaving camp, Chanute had
unintentionally given them something else to worry about. He had
remarked that at least twenty per cent usually must be allowed in chain
transmission for loss in power. As the Wrights had allowed only five
per cent, they felt considerable alarm.
Since Chanute was a capable and famous engineer, it seemed prudent to
find out whose estimates were more nearly correct. After Chanute had
gone, the brothers suspended one of the drive chains over a sprocket
and hung a bag of sand at each end of the chain. By measuring the
amount of weight on one side needed to lift that on the other, they
calculated the loss in transmission. As nearly as they could tell,
this loss was even less than the five per cent they had estimated.
The shafts, made of larger and heavier tubing, arrived from Dayton on
November 20. When they were tested again, a new difficulty appeared.
The sprockets, which were screwed to the shafts and locked with nuts
of opposite thread, kept coming loose. This was a small problem, and
yet the brothers did not at once see any way to solve it. They went to
bed discouraged. The next day, however, they tried, as they often did,
something they had learned in the bicycle business. They had found a
great variety of uses for the kind of cement intended for fastening
tires to rims. Once they had used it successfully in fastening the
hands of a stop-watch that several watchsmiths had said was beyond
repair. Why not try tire cement on those sprockets? They heated the
propeller shafts and sprockets, poured melted cement into the threads
and screwed them together. There were no more loose sprockets.
Just as the machine was ready for test, bad weather set in. There was
rain or snow for several days and a wind of twenty-five to thirty miles
an hour from the north. But while being delayed by the weather the
Wrights were not idle. They busied themselves contriving a mechanism
to measure automatically the duration of a flight from the time the
machine started to move forward to the time it stopped, the distance
traveled through the air in that time, and the number of revolutions
made by the motor and propeller. A stop-watch took the time; an
anemometer measured the air traveled through; and a counter took the
number of revolutions made by the motor. The watch, anemometer,
and revolution counter were all automatically started and stopped
simultaneously.
During this time, the Wrights occupied themselves also in making tests
of the strength of the wings, as well as many satisfactory tests of the
engine. During a test of the engine, on November 28, they discovered
that one of the recently strengthened tubular shafts had developed a
flaw and cracked!
With winter almost upon them, there was no time to trust to express
service in getting the shafts to Dayton. Orville decided he would go
there at once. Instead of tubular shafts, they would use solid tool
steel, necessary, it seemed, to take up the shock of premature or
missed explosions of the engine.
Not until Friday, December 11, did Orville get back to camp. (En route,
he had read in a newspaper of the last unsuccessful attempt to fly the
Langley machine over the Potomac at Washington.)
It didn’t take long to install the new propeller shafts and the next
afternoon, Saturday, the machine was again ready for trial. But the
wind was so light that a start could not have been made from the level
ground with a run of only sixty feet permitted by the monorail track
to be used. Nor was there enough time before dark to take the machine
to one of the near-by hills, where, by placing the track on the steep
incline, enough speed could be promptly attained for starting in calm
air.
All day Sunday the Wrights just sat at the camp and read, hoping
for suitable weather the next day. They were now particularly eager
to avoid delay because of their boyish craving to be at home by
Christmas. If there should be a spell of bad wintry weather they might
have to stay at Kitty Hawk for another two or three weeks.
Monday, December 14, dawned beautifully clear, but cold, and there was
not enough wind to permit a start from level ground near the camp. The
Wrights therefore decided to attempt a flight from the side of Kill
Devil Hill. With a relatively light wind it should be all the easier
to handle the machine. The pilot, whichever one of them it should be,
ought to be able not only to fly successfully but to go on down far
beyond the Kitty Hawk life-saving station, nearly five miles away,
before landing.