THE WRIGHT MOTOR-DRIVEN PLANE
Final gliding tests--Building of the motor--How
a petrol engine works--Driving, control, and
launching of the Wright machine.
Although everything induced them to hasten--for they feared another
inventor might forestall them with a power-driven craft--the Wrights
still went methodically to work, refusing to use a motor until they had
gained a fuller knowledge of the air. So they built more gliders, and
with one of them--that used in 1902--they were able to make over a
thousand flights. Only once, in all their practice, did they come near
disaster; and this was one day when Orville was testing a machine. The
accident was described by Wilbur Wright:
“My brother Orville started on a flight with one wing slightly
higher than the other. This caused the machine to veer to the
left. He waited a moment to see whether it would right itself,
but finding that it did not, then decided to apply the control.
At the very instant he did this, however, the right wing most
unexpectedly rose much higher than before, and led him to think
that possibly he had made a mistake. A moment of thought was
required to assure himself that he had made the right motion, and
another to increase the movement. Meanwhile he had neglected the
front rudder, by which the fore-and-aft balance was maintained.
The machine turned up in front more and more till it assumed a
most dangerous attitude. We who were on the ground noticed this in
advance of the aviator, who was thoroughly absorbed in the attempt
to restore the lateral balance, but our shouts of alarm were
drowned by the howling of the wind. It was only when the machine
came to a stop and started backward that he at length realised
the true situation. From the height of nearly 30 feet the machine
sailed diagonally backward till it struck the ground. The unlucky
aeronaut had time for one hasty glance behind him, and the next
instant found himself the centre of a mass of fluttering wreckage.
How he escaped injury I do not know, but afterwards he was unable
to show a scratch or bruise anywhere, though his clothes were torn
in one place.”
The amount of practice the brothers obtained began to tell its tale, and
they became sufficiently experienced to glide in winds of 37 miles an
hour. It was Wilbur who, emphasising this need for constant flying,
declared: “By long practice, the management of a machine should become
as instinctive as the balancing movements a man unconsciously employs
with every step in walking.”
After the experience with the 1902 machine, and not before, did the
brothers feel encouraged to build a craft with a motor. They decided to
construct the engine themselves, so that they might have it ready for
use in 1903. They were capable engineers, they had their own workshops,
and above all they knew just what they wanted. So they made a petrol
engine with four cylinders, developing about 25 horse-power. It was
water-cooled, and followed upon the lines of a motor-car engine--save
that it was lightened where they considered weight could be spared. As a
matter of fact, when compared with the light and ingenious motors
afterwards made in France, this engine was a heavy and clumsy piece of
work, weighing as it did about 200 lbs. But they had calculated what
load their machine would bear; and they wanted to ensure that the motor
should run reliably. They attempted, therefore, no drastic cutting down
of weight.
[Illustration: FIG. 31.--Man lifting a 100 horse-power aeroplane motor.]
An explanation may well be interposed as to the working of the petrol
motor, seeing that it plays so large a part in aviation. First should be
remembered the steam engine and its disadvantages--its boiler, weight of
water, and need for a heating agent to make this water boil. In the
petrol-motor none of these are required--none, at least, save a tank
with liquid fuel and another, a smaller tank, containing lubricating
oil. Beyond these tanks and their contents, the weight of the engine is
no more than the weight of metal which composes it; and so it is
possible, with a specially-lightened motor, to deliver one horse-power
of energy for a weight of less than 3 lbs. How lightly a petrol engine
can be made was demonstrated by the firm constructing the Antoinette
motor, with which many of the pioneers fitted their craft. A 16-cylinder
engine was made so that a man could raise it upon his shoulders--as
shown in Fig. 31--and carry it without much difficulty; and yet this
same motor, which one man could lift from the ground, developed 100
horse-power.
The principle of the petrol engine is simple. From the tank containing
petrol runs a pipe, and the liquid passes through this into the
carburettor,--a small chamber in which the petrol is vapourised and made
to mix with air and so become explosive. Petrol is a liquid which, when
in contact with air, evaporates in the form of vapour, and this forms a
powerful explosive, only needing a spark to ignite it. In the
carburettor, therefore, the petrol and air are mingled until they form
an explosive mixture, then they pass through another pipe to the engine
itself.
[Illustration: FIG. 32.--The working of a petrol motor.]
The petrol engine resembles a steam engine in these respects: it has a
cylinder in which the driving force is compressed, a piston-rod this
driving power pushes down, and a fly-wheel the piston actuates, and
which carries round the piston-rod by its momentum, pushing it towards
the top of the cylinder again after one down stroke, so that it may
obtain another thrust. What the fly-wheel does, in a word, is to store
up energy between each thrust upon the piston, and thus keep the motor
in regular motion.
In starting an engine, the petrol tap is turned on, and some of the
spirit allowed to run into the carburettor. Then, usually with a handle,
the engine is made to revolve so that the piston-rod moves down inside
the cylinder and sucks in the explosive mixture. As the piston sinks in
the cylinder, it draws in a charge of the gas; then rising again, it
compresses this charge between the head of the piston and the top of the
cylinder. Now comes the moment when, if the most forcible thrust is to
obtained from the air and gas, it should be ignited, and this is done by
causing an electric spark to jump between two metal points on what is
called the sparking-plug. This plug is screwed into the head of the
cylinder; the sparking end is inside the cylinder where the gas charge
is compressed, and to the outside are fixed wires which run to the
magneto--a small electrical machine which, driven by the motor, makes
sparks in the plug each time the gas is to be fired. Just at the right
instant, therefore, the spark flashes in the cylinder, and the gas is
exploded. Being compressed within the walls and top of the cylinder, the
explosion can only exert its force in one way--upon the head of the
piston, to which it gives a sudden downward thrust. The power is
transmitted to the fly-wheel, which is set in motion, and thus the
engine runs, driven by the series of explosions which takes place in the
cylinder.
The majority of petrol engines operate upon what is known as the
four-stroke principle. This action is as follows: First the pistons are
driven down by a charge of gas, then they ascend in the cylinders so
that the spent and useless gas fumes may be forced out through valve
ports; then the pistons descend again so that a fresh charge may be
drawn into the cylinders, and then, for a fourth time, the pistons move
so that the gas may be compressed and fired. During the period the
engine is not driven by the explosions, the fly-wheel has to do its
work, carrying the piston up and down while it expels waste gas and
obtains a new supply. In Fig. 32 is a diagram to illustrate the
principle of the petrol engine and it amplifies this explanation.
An additional point is needed to explain how motors were lightened for
aviation work. The fly-wheel has been described as vital to the engine,
and so it is, unless a number of cylinders are used. But if a maker
builds a motor with, say, eight cylinders, the driving impulses are so
frequent that there is no danger of the engine ceasing to revolve
between explosions, even if no fly-wheel is fitted. It can be so
arranged, indeed, by the timing of the explosions, that there is a
smooth, even thrust upon the crank-shaft, and by omitting the fly-wheel
there is a perceptible lessening in the weight of the motor.
When the Wrights had built an engine, there was still the question how
they should make it drive their aeroplane. They inclined naturally to
the idea of an aerial propeller such as that illustrated in Fig. 7. Two
courses lay open to them; they could fit one propeller running at high
speed and coupled directly to the motor, or they could use two
propellers, revolving at slower speed and geared in some way to the
engine. They decided upon the latter course, placing two propellers
behind the main planes of their machine and driving them from the engine
by means of light chains, these running in guiding tubes. This system
of propulsion is shown in Fig. 33.
[Illustration: FIG. 33.--Wright Motor and Propellers.
A. Motor; B. Gear-wheels upon motor crank-shaft; C.C. Tubes carrying
driving chains; D.D. Sprocket-wheels over which chains pass; E.E.
Propellers.]
The propellers revolved in opposite directions, and in order to gain
this effect one chain, as will be seen from the sketch, had to be
crossed in its tube. The Wrights preferred the use of two propellers,
even though this necessitated gearing such as might have been avoided
had a single propeller been coupled directly to the motor. They
considered the thrust upon the aeroplane would be smoother with two
screws. By using a couple of large propellers also, and running them
rather slowly, they reckoned to obtain more efficiency than with a
single high-speed screw. In illustration of this it may be mentioned
that, whereas the single propellers upon some of the French machines
made 1000 or 1500 revolutions a minute, the Wrights’ two screws made
only 450 a minute. That their system was extremely efficient they were
able to prove beyond question. Many critics condemned as clumsy the use
of gearing chains, and pointed out the danger that existed should a
chain break--causing one propeller to stop, while the other, by
continuing its thrust, tended to throw the machine out of equilibrium.
Such a system, indeed, never came into general use, but in fairness to
the Wrights it should be said that very few accidents were ever
attributed to the breaking of a chain.
[Illustration: FIG. 34.--The Wright Biplane.
A.A.--Main-planes; B. Double front elevator; C. Rudder (two narrow
vertical planes); D. Motor; E. Propellers; F. Pilot’s lever; G. Skids
upon which machine landed.]
It is now possible to describe, as a completed craft, the Wright
power-driven plane; Fig. 34 shows its appearance; and in looking at it
one is struck by the fact that, save for one or two modifications, and
the fitting of motor and propellers, the machine is practically a
glider, such as the Wrights used for soaring tests. Of the changes to be
observed, the most interesting concern the elevator and rear-rudder.
The former, it will be seen, has a double plane; it is, in fact, a
smaller biplane on the principle of the main-planes. Needing to increase
the surface of the elevator, the brothers fixed one plane above another
so as to make the construction stronger and occupy less space. The
rear-rudder, acting like that of a ship, worked upon the system
described in Fig. 14. With this, as with the elevator, in order to
economise space and obtain rigidity, two narrow planes were fitted side
by side.
So now the practical aircraft stood complete--each part adapted and
perfected; and, having traced its development step by step, we see how
the pioneers had helped the Wrights to their conquest. Sustaining
planes, propellers, controlling surfaces--all had been foreshadowed, all
hinted at and sketched crudely; but what had been lacking was the skill
which should put these theories into shape; and this skill, and also
this patience, Wilbur and Orville Wright provided to the full.
Having discussed the construction of the machine, the method by which it
was controlled when in the air may be described. In Fig. 35 the operator
is seen in the driving seat; and near him will be observed the motor
which drives the craft. In his left hand--that is to say in the one
nearest us--he grasps the lever which operates the elevating planes. The
rod from lever to plane can be seen, and the motions the pilot makes are
these: should he wish to rise, he draws the lever towards him and tilts
up the elevating planes in the manner already described, increasing the
lifting power of the main-planes and so causing the machine to ascend;
by a reverse movement of the lever--by pushing it away from him, that
is to say--he makes the craft glide downward.
[Illustration: FIG. 35.--Driving seat of Wright Biplane.
A. Motor; B. Lever operating elevating planes; C. Lever working rudder
and wing-warp.]
In the pilot’s right hand is another lever; this combines two actions in
an ingenious way. It actuates not only the rear-rudder of the machine,
but also the wing-warping for the control of sideway balance. How the
one rod combines these operations is shown by Fig. 36. Here, looking
from behind, one sees the lever which the aviator holds. Towards the
lower end is a rod projecting rearwards, and this is coupled to the
extremity of another rod set at right angles to it, and pivoted in its
centre; while from this pivoted rod run the wires which operate the
rudder-planes. If the pilot swings his hand-lever either forward or
backward, it moves to and fro the rod which is connected with it, and
this imparts a forward or backward movement to the pivoted rod, with the
result that one or other of the rudder wires is drawn forward--thus
turning the rudder-planes from side to side.
The hand-lever is free also to move from side to side; and if it is so
moved it will draw with it the swinging rod which projects from the end
of it--below that operating the rudders--and to the upright section of
which the wing-warping wires are fixed. A movement either side upon the
hand-level will pull over the wing-warping wires, therefore, and bring
the flexible plane-ends into operation. Thus the dual movement of the
lever is obtained--forward and backward for the rudder, from side to
side for the warp.
[Illustration: FIG. 36.--Rudder and wing-warp control (Wright Biplane).
A. Controlling handle; B. Pivoted rod carrying wires to rudder; C.C.
Rudder wires; D. Sideway swinging rod carrying wing-warp wires; E.E.
Wing-warp wires.]
The Wrights did not use their feet in any controlling movement, although
in practically all modern aeroplanes, as will be explained later, the
airman’s feet are utilized for pushing upon a bar and operating the
rudder of the machine; but the Wrights preferred to make all actions
with their hands.
[Illustration: FIG. 37.--Wright Launching Rail.
A. Biplane; B. Rail; C. Rope passing from the aeroplane round the
pulley-wheel (D.) and thence to the derrick (E.); (F.) Falling weight.]
Details of propulsion and control being arranged, there remained the
question of how the machine should be launched into the air. In their
gliding tests, it will be remembered, the Wrights employed assistants,
who held the machine by the wing-tips and ran forward with it. But the
weight of the power-driven machine, and its greater size, prevented such
a plan as this. They decided, therefore, to launch it from a rail, and
to aid its forward speed, at the moment of taking the air, by a derrick
and a falling weight. This method is illustrated in Fig. 37. The biplane
is seen mounted upon a truck, or under-carriage, which runs upon wheels
along a rail. To the front of the aeroplane is fixed a rope, which
passes round a pulley some distance ahead of it, and is then carried
back to the derrick, from which can be seen hanging a heavy weight.
Before making a flight the engine was set in motion, whirling the two
propellers; then, at a given signal, the weight upon the derrick was
released. Drawn forward by the pull of this weight, and aided by the
thrust of its propellers, the biplane moved rapidly along the rail, and
soon attained a speed of more than thirty miles an hour. Then, just
before the end of the rail was reached, the pilot released a catch which
freed the aeroplane from its trolley, tilted up his elevating plane and
the machine, now moving fast enough for its planes to sustain it in
flight, glided from earth to air, flying low at first but gradually
increasing his altitude.