THE TESLA TURBINE
DR. NIKOLA TESLA TELLS OF HIS NEW STEAM TURBINE ENGINE A MODEL
OF WHICH, THE SIZE OF A DERBY HAT, DEVELOPS MORE THAN 110
HORSEPOWER
"How would you like to have an engine for your motor boat that you
could almost cover with a man's derby hat and yet which would give
110 horsepower?" asked the scientist of his young friend one day when
they had been talking about boats and engines.
"I never heard of any real engine as small as that," said the boy. "I
used to play with toy engines, but they wouldn't give anywhere near
one horsepower, much less 110."
"Well, I think I can show you a little engine that, for mechanical
simplicity and power is about the most wonderful thing you ever have
seen, if you would like to make another visit to Dr. Nikola Tesla,
who told us all about his invention for the wireless transmission of
power the other day. Doctor Tesla invented this little engine and he
is going to do great things with it."
Of course the boy jumped at the opportunity, for what real boy would
miss a chance to find out all about a new and powerful engine?
"Is it a gasoline engine?" he asked.
"No, it is a steam turbine, but if you know anything at all about
turbines you will see that it is entirely different from any you ever
have seen, for Doctor Tesla has used a principle as old as the hills
and one which has been known to men for centuries, but which never
before has been applied in mechanics."
After a little more talk the scientist promised to arrange with Tesla
to take the young man over to the great Waterside power-house, New
York, where the inventor is testing out his latest invention. We will
follow them there and see what this wonderful little turbine looks
like.
Picking his way amid the powerful machinery and the maze of
switchboards, the scientist finally stopped in front of a little
device that seemed like a toy amid the gigantic machines of the
power-house.
"This is the small turbine," says Tesla. "It will do pretty well for
its size."
The little engine looked like a small steel drum about ten inches in
diameter and a couple of inches wide, with a shaft running through
the centre. Various kinds of gauges were attached at different
points. Outside of the gauges and the base upon which it was mounted,
the engine almost could have been covered by a derby hat. The whole
thing, gauges and all, practically could have been covered by an
ordinary hat box.
Yet when Tesla gave the word, and his assistant turned on the steam,
the small dynamo to which the turbine shaft was geared, instantly
began to run at terrific speed. Apparently the machine began to run
at full speed instantly instead of gradually working up to it. There
was no sound except the whir of well-fitted machinery. "Under tests,"
said Tesla, "this little turbine has developed 110 horsepower."
Just think of it, a little engine that you could lift with one hand,
giving 110 horsepower!
"But we can do better than that," added the inventor, "for with a
steam pressure of 125 pounds at the inlet, running 9,000 revolutions
per minute, the engine will develop 200 brake-horsepower."
Nearby was another machine a little larger than the first, which
seemed to be two identical Tesla turbines with the central shafts
connected by a strong spring. Gauges of different kinds, to show
how the engine stood the tests, were attached at various places.
When Tesla gave the word to open the throttle on the twin machines
the spring connecting the shafts, without a second's pause, began
to revolve, so that it looked like a solid bar of polished steel.
Outside of a low, steady hum and a slight vibration in the floor,
that steadied down after the engine had been running a little while,
there was no indication that enough horsepower to run machinery a
hundred times the weight and size of the turbine was being generated.
"You see, for testing purposes," said Doctor Tesla, "I have these
two turbines connected by this torsion spring. The steam is acting
in opposite directions in the two machines. In one, the heat energy
is converted into mechanical power. In the other, mechanical power
is turned back into heat. One is working against the other, and by
means of this gauge we can tell how much the spring is twisted and
consequently how much power we are developing. Every degree marked
off on this scale indicates twenty-two horsepower." The beam of light
on the gauge stood at the division marked "10."
"Two hundred and twenty horsepower," said Doctor Tesla. "We can do
better than that." He opened the steam valves a trifle more, giving
more power to the motive end of the combination and more resistance
to the "brake" end. The scale indicated 330 horsepower. "These
casings are not constructed for much higher steam pressure, or I
could show you something more wonderful than that. These engines
could readily develop 1,000 horsepower.
"These little turbines represent what mechanical engineers have
been dreaming of since steam power was invented--the perfect rotary
engine," continued Doctor Tesla, as he led the way back to his
office. "My turbine will give at least twenty-five times as much
power to the pound of weight as the lightest weight engines made to
date. You know that the lightest and most powerful gasoline engines
used on aeroplanes nowadays generally develop only one horsepower to
two and one half pounds of weight. With that much weight my turbine
will develop twenty-five horsepower.
"That is not all, for the turbine is probably the cheapest engine
to build ever invented. Its mechanical simplicity is such that any
good mechanic could build it, and any good mechanic could repair
such parts as get out of order. When I can show you the inside of
one of the turbines, in a few moments, however, you will see that
there is nothing to get out of order such as most turbines have, and
that it is not subjected to the heavy strains and jerks that all
reciprocating engines and other turbines must stand. Also you will
see that my turbine will run forward or backward, just as we desire,
will run with steam, water, gas, or air, and can be used as a pump or
an air compressor, just as well as an engine."
"But most of your research has been in electricity," Tesla was
reminded, for no one can forget that Tesla's inventions largely
have made possible most of the world's greatest electrical power
developments.
"Yes," he answered, "but I was a mechanical engineer before I was
an electrical engineer, and besides, this principle was worked out
in the course of my search for the ideal motor for airships, to be
used in conjunction with my invention for the wireless transmission
of electrical power. For twenty years I worked on the problem, but
I have not given up. When my plan is perfected the present-day
aeroplanes and dirigible balloons will disappear, and the dangerous
sport of aviation, as we know it now with its hundreds of accidents,
and its picturesque birdmen, will give way to safe, seaworthy
airships, without wings or gas bags, but supported and driven by
mechanical means.
"As I told you before when we were talking of the wireless
transmission of power, the mechanism will be a development of
the principle on which my turbine is constructed. It will be so
tremendously powerful that it will make a veritable rope of air above
the great machine to hold it at any altitude the navigators may
choose, and also a rope of air in front or in the rear to send it
forward or backward at almost any speed desired. When that day comes,
airship travel will be as safe and prosaic as travel by railroad
train to-day, and not very much different, except that there will
be no dirt, and it will be much faster. One will be able to dine in
New York, retire in an aero Pullman berth in a closed and perfectly
furnished car, and arise to breakfast in London."
Tesla's plans for the airship are far in the future, but his turbine
is a thing of the present, and it has been declared by some of the
most eminent authorities in the world in mechanical engineering
to be the greatest invention of a century. The reason for this is
not altogether on account of the wonderful feats of Tesla's model
turbines, but because in them he has shown the world an entirely
unused mechanical principle which can be applied in a thousand useful
ways.
James Watt discovered and put to work the expansive power of steam,
by which the piston of an engine is pushed back and forth in the
cylinder of an engine, but it has remained for Nikola Tesla to prove
that it is not necessary for the steam to have something to push
upon--that the most powerful engine yet shown to the world works
through a far simpler mechanism than any yet used for turning a gas
or a fluid into the driving force of machinery.
"How did you come to invent your turbine while you were busy with
your wonderful electrical inventions?" Tesla was asked.
"You see," he answered, "while I was trying to solve the problem
of aerial navigation by electrical means, the gasoline motor was
perfected; and aviation as we know it to-day became a fact. I
consider the aeroplane as it has been developed little more than a
passing phase of air navigation. Aeroplaning makes delightful sport,
no doubt, but as it is now it can never be practical in commerce.
Consequently I abandoned for the time being my attempts to find the
ideal airship motor in electricity, and for several years studied
hard on the problem as one of mechanics. Finally I hit upon the
central idea of the new turbine I have just been showing you."
"What is this principle?"
"The idea of my turbine is based simply on two properties known to
science for hundreds of years, but never in all the world's history
used in this way before. These properties are adhesion and viscosity.
Any boy can test them. For instance, put a little water on a sheet of
metal. Most of it will roll off, but a few drops will remain until
they evaporate. The metal does not absorb the water so the only thing
that makes the water remain on the metal is adhesion--in other words,
it adheres, or sticks to the metal.
"Then, too, you will notice that the drop of water will assume a
certain shape and that it will remain in that form until you make it
change by some outside force--by disturbing it by touch or holding it
so that the attraction of gravitation will make it change.
"The simple little experiment reveals the viscosity of water, or, in
other words, reveals the property of the molecules which go to make
up the water, of sticking to each other. It is these properties of
adhesion and viscosity that cause the 'skin friction' that impedes
a ship in its progress through the water, or an aeroplane in going
through the air. All fluids have these qualities--and you must keep
in mind that air is a fluid, all gases are fluid, steam is fluid.
Every known means of transmitting or developing mechanical power is
through a fluid medium.
"It is a surprising fact that gases and vapours are possessed of this
property of viscosity to a greater degree than are liquids such as
water. Owing to these properties, if a solid body is moved through a
fluid, more or less of the fluid is dragged along, or if a solid is
put in a fluid that is moving it is carried along with the current.
Also you are familiar with the great rush of air that follows a
swiftly moving train. That simply means that the train tends to carry
the air along with it, as the air tries to adhere to the surface of
the cars, and the particles of air try to stick together. You would
be surprised if you could have a picture of the great train of moving
air that follows you about merely as you walk through this room.
"Now, in all the history of mechanical engineering, these properties
have not been turned to the full use of man, although, as I said
before, they have been known to exist for centuries. When I hit upon
the idea that a rotary engine would run through their application, I
began a series of very successful experiments."
Tesla went on to explain that all turbines, and in fact all engines,
are based on the idea that the steam must have something to
push against. We shall see a little later how these engines were
developed, but it will suffice for the moment to listen to Doctor
Tesla's explanation.
"All of the successful turbines up to the time of my invention," he
says, "give the steam something to push upon. For instance"--taking a
pencil and a piece of paper--"we will consider this circle, the disk,
or rotor of an ordinary turbine. You understand it is the wheel to
which the shaft is attached, and which turns the shaft, transmitting
power to the machinery. Now it is a large wheel and along the outer
edge is a row of little blades, or vanes, or buckets. The steam is
turned against these blades, or buckets, in jets from pipes set
around the wheel at close intervals, and the force of the steam
on the blades turns the wheel at very high speed and gives us the
power of what we call a 'prime mover'--that is, power which we can
convert into electricity, or which we can use to drive all kinds of
machinery. Now see what a big wheel it is and what a very small part
of the wheel is used in giving us power--only the outer edge where
the steam can push against the blades.
"In my new turbine the steam pushes against the whole wheel all at
once, utilizing all the space wasted in other turbines. There are no
blades or vanes or sockets or anything for the steam to push against,
for I have proved that they hinder the efficiency of the turbine
rather than increase it."
Comparing his turbine to other engines Tesla says, "In reciprocating
engines of the older type the power-giving portion--the cylinder,
piston, etc.--is no more than a fraction of 1 per cent. of the total
weight of material used in construction. The present form of turbine,
with an efficiency of about 62 per cent., was a great advance, but
even in this form of machine scarcely more than 1 per cent. or 2 per
cent. is used in actually generating power at a given moment. The
only part of the great wheel that is used in actually making power is
the outside edge where the steam pushes on the buckets.
"The new turbine offers a striking contrast using as it does
practically the entire material of the power-giving portion of the
engine. The result is an economy that gives an efficiency of 80 per
cent. to 90 per cent. With sufficient boiler capacity on a vessel
such as the _Mauretania_, it would be perfectly easy to develop,
instead of some 70,000 horsepower, 4,000,000 horsepower in the same
space--and this is a conservative estimate.
"You see this is obtained by the new application of this principle in
physics which never has been used before, by which we can economize
on space and weight so that the most of the engine is given over to
power producing parts in which there is little waste material."
Tesla then went on to explain the details of his new turbine. Leading
the way to a small model in his office he unscrewed a few bolts and
lifted off the top half of the round steel drum or casing. Inside
were a number of perfectly smooth, circular disks mounted upon one
central shaft--the shaft that extends through the machine, and
corresponds to the crankshaft of an ordinary engine. The disks all
were securely fastened to the rod so that they could not revolve
without making it also turn in its carefully adjusted bearings. The
disks, which were only about one sixteenth of an inch in thickness,
and which he said were constructed of the finest quality of steel,
were placed close together at regular intervals, so that a space of
only about an eighth of an inch intervened between them. They were
solid with the exception of a hole close to the centre. The set of
disks is called the rotor or runner.
When the casing is clamped down tight, the steam is sent through
an inlet or nozzle at the side, so that it enters at the periphery
or outside edge of the set of disks, at a tangent to the circle
of the rotor. Of course the steam is shot into the turbine under
high pressure so that all its force is turned into speed, or what
the scientists call velocity-energy. The steel casing of the rotor
naturally gives the steam the circular course of the disks, and as
it travels around the disks the vapour adheres to them, and the
particles of steam adhere to each other. By the law that Tesla has
invoked, the steam drags the disks around with it. As the speed of
the disks increases the path of the steam lengthens, and at an
average speed the steam actually travels a distance of twelve to
fifteen feet. Starting at the outside edge of the disks it travels
around and around in constantly narrowing circles as the steam
pressure decreases until it finally reaches the holes in the disks
at their centre, and there passes out. These holes, then, we see act
as the exhaust for the used-up steam, for by the time the steam,
which was shot into the turbine by the nozzle under high pressure,
reaches the exhaust, it registers no more than about two pounds gauge
pressure.
[Illustration: DIAGRAM OF THE TESLA TURBINE
A--Steam Inlet. B--Disks. C--Path of the Steam. D,D´D´´--Exhaust.
E--Reverse Inlet. F--Shaft.]
For reasons which will be explained later, ordinary turbines cannot
be reversed, but Tesla's invention can run backward just as easily
as forward. The reverse action is accomplished simply by placing
another nozzle inlet on the other side of the rotor so that the
steam can be turned off from the right side of the engine, for
instance, and turned into the left side, immediately reversing its
direction, with the change in the direction of the steam. The action
is instantaneous, too, for as we saw in the experiments Tesla showed
us, the turbine began to run at practically top speed as soon as the
steam was turned on.
The disks in the little 110-horsepower engine which we saw, were only
a little larger than a derby hat were only nine and three quarter
inches in diameter, while in his larger turbines he simply increases
the diameter of the disks.
Tesla further explained that the 110-horsepower turbine represented
a single stage engine, or one composed simply of one rotor. Where
greater power is required he explained that it would be easy to
compound a number of rotors to a double, or triple or even what he
calls a multi, or many stage, turbine. In engineering the single
stage is called one complete power unit, and a large engine could be
made up of as many units as needed, or practicable.
"Then do you mean to say," Tesla was asked, "that the only thing that
makes the engine revolve at this tremendous speed is the passage of
steam through the spaces between those smooth disks?"
"Yes, that is all," he answered, "but as I explained before, the
steam travels all the way from the outer edge to the centre of
the disks, working on them all the time; whereas in the ordinary
turbines the steam only works on the outside edge, and all the rest
of the wheel is useless. By the time it leaves the exhaust of my
engine practically all the energy of the steam has been put into the
machine."
This is only one of the many advantages that Tesla points out in his
invention, for the turbine is the exemplification of a principle, and
hence more than a mechanical achievement. "With a 1,000-horsepower
engine weighing only 100 pounds, imagine the possibility in
automobiles, locomotives, and steamships," he says.
Explaining the large engines that he is testing, one against the
other, at the power plant, the inventor said:
"Inside of the casings of the two larger turbines the disks are
eighteen inches in diameter and one thirty-second of an inch thick.
There are twenty-three of them, spaced a little distance apart, the
whole making up a total thickness of three and one half inches. The
steam, entering at the periphery, follows a spiral path toward the
centre, where openings are provided through which it exhausts. As the
disks rotate and the speed increases the path of the steam lengthens
until it completes a number of turns before reaching the outlet--and
it is working all the time.
"Moreover, every engineer knows that, when a fluid is used as a
vehicle of energy, the highest possible economy can be obtained only
when the changes in the direction and velocity of movement of the
fluid are made as gradual and easy as possible. In previous forms
of turbines more or less sudden changes of speed and direction are
involved.
"By that I mean to say," explained Doctor Tesla, "that in
reciprocating engines with pistons, the power comes from the backward
and forward jerks of the piston rod, and in other turbines the steam
must travel a zigzag path from one vane or blade to another all the
whole length of the turbine. This causes both changes in velocity and
direction and impairs the efficiency of the machine. In my turbine,
as you saw, the steam enters at the nozzle and travels a natural
spiral path without any abrupt changes in direction, or anything to
hinder its velocity."
But the Tesla turbine engine, claims the inventor, will work just
as well by gas as by steam, for as he points out gases have the
properties of adhesion and viscosity just as much as water or steam.
Further, he says that if the gas were introduced intermittently in
explosions like those of the gasoline engine, the machine would
work as efficiently as it does with a steady pressure of steam.
Consequently Tesla declares that his turbine can be developed for
general use as a gasoline engine.
The engine is only one application of the principle of Tesla's
turbine, because he has used the same idea on a pump and an air
compressor as successfully as on his experimental engines. In his
office in the Metropolitan Tower he has a number of models. Pointing
to a little machine on a table, which consisted of half a dozen small
disks three inches in diameter, he said: "This is only a toy, but
it shows the principle of the invention just as well as the larger
models at the power plant." Tesla turned on a small electric motor
which was connected with a shaft on which the disks were mounted, and
it began to hum at a high number of revolutions per second.
"This is the principle of the pump," said Tesla. "Here the electric
motor furnishes the power and we have these disks revolving in the
air. You need no proof to tell you that the air is being agitated and
propelled violently. If you will hold your hand down near the centre
of these disks--you see the centres have been cut away--you will feel
the suction as air is drawn in to be expelled from the outer edges.
"Now, suppose these revolving disks were enclosed in an air-tight
case, so constructed that the air could enter only at one point and
be expelled only at another--what would we have?"
"You'd have an air pump," was suggested.
"Exactly--an air pump or a blower," said Doctor Tesla. "There is one
now in operation delivering ten thousand cubic feet of air a minute."
But this was not all, for Tesla showed his visitors a wonderful
exhibition of the little device at work. "To make a pump out of this
turbine," he explained; "we simply turn the disks by artificial means
and introduce the fluid, air or water at the centre of the disks,
and their rotation, with the properties of adhesion and viscosity
immediately suck up the fluid and throw it off at the edges of the
disks."
The inventor led the way to another room, where he showed his
visitors two small tanks, one above the other. The lower one was full
of water but the upper one was empty. They were connected by a pipe
which terminated over the empty tank. At the side of the lower tank
was a very small aluminum drum in which, Tesla told his visitors,
were disks of the kind that are used in his turbine. The shaft of a
little one twelfth horsepower motor adjoining was connected with the
rotor through the centre of the casing. "Inside of this aluminum case
are several disks mounted on a shaft and immersed in water," said
Doctor Tesla. "From this lower tank the water has free access to the
case enclosing the disks. This pipe leads from the periphery of the
case. I turn the current on, the motor turns the disks, and as I open
this valve in the pipe the water flows."
[Illustration: THE MARVELLOUS TESLA TURBINE
The 200-horsepower engine, which a man could lift with one hand.
How the Tesla Turbine compares in size with a man.]
[Illustration: THOMAS A. EDISON AND HIS CONCRETE FURNITURE
The white cabinet is a piece of Edison's poured concrete
furniture, while the other one is the ordinary wooden phonograph
cabinet.]
[Illustration: MODEL OF EDISON POURED CONCRETE HOUSE
This little house, which stands on a table in Edison's
laboratory, shows what he expects to do with the poured concrete
house.]
He turned the valve and the water certainly did flow. Instantly a
stream that would have filled a barrel in a very few minutes began to
run out of the pipe into the upper part of the tank and thence into
the lower tank.
"This is only a toy," smiled the inventor. "There are only half a
dozen disks--'runners,' I call them--each less than three inches in
diameter, inside of that case. They are just like the disks you saw
on the first motor--no vanes, blades or attachments of any kind.
Just perfectly smooth, flat disks revolving in their own planes and
pumping water because of the viscosity and adhesion of the fluid.
One such pump now in operation, with eight disks, eighteen inches in
diameter, pumps 4,000 gallons a minute to a height of 360 feet.
"From all these things, you can see the possibilities of the new
turbine," he continued. "It will give ten horsepower to one pound of
weight, which is twenty-five times as powerful as many light weight
aeroplane engines, which give one horsepower of energy for every two
and one half pounds of weight.
"Moreover, the machine is one of the cheapest and simplest to build
ever invented and it has the distinct advantage of having practically
nothing about it to get out of order. There are no fine adjustments,
as the disks do not have to be placed with more than ordinary
accuracy, and there are no fine clearances, because the casing does
not have to fit more than conveniently close. As you see, there are
no blades or buckets to get broken or to get out of order. These
things, combined with the easy reversibility, simplicity of the
machine when used either as an engine, a pump or an air compressor,
and the possibility of using it either with steam, gas, air, or water
as motive power, all combine to afford limitless possibilities for
its development."
Doctor Tesla calls the invention the most revolutionary of his
career, and it certainly will be if it fulfils the predictions that
so many eminent experts are making for it.
It is interesting to think that although this latest and most modern
of all steam engines is a turbine, the first steam engine ever
invented, also was a turbine.
Though most of us usually think of James Watt as the inventor of
the steam engine, he was not the first by any means, for the very
first of which history gives us any record was a turbine, which was
described by Hero of Alexandria, an ancient Egyptian scientist, who
wrote about 100 B.C.
Hero's engine was a hollow sphere which was made to turn by the
reaction of steam as it escaped from the ends of pipes, so placed
that they would blow directly upon the ball.
Centuries later--in 1629, about the time the New England States
were being colonized--a scientist named Branca made use of the
oldest mechanical principle in the world--the paddle-wheel--which,
turned by the never-ceasing river, goes on forever in the service
of mankind. Branca's invention was simply a paddle-wheel turned by
a jet of steam instead of by a water current. The engine was really
a turbine, for that type is simply a very high development of this
idea--the pushing power of a fluid on a paddle-wheel.
The picture of Branca's crude machine shows the head and shoulders
of a great bronze man suspended over a blazing wood fire. Evidently
it is intended to convey the idea that the figure's lungs are filled
with boiling water, for he is pictured breathing a jet of steam on to
the blades of a paddle-wheel, the revolving of which sets some crude
machinery in motion.
After Branca, however, the turbine dropped from view and what
few inventors did experiment with steam worked on the idea of a
reciprocating engine.
The principle of the reciprocating engine, as most boys know from
their own experiments with toy steam engines, and as was discovered
by Watt, is simply the utilization of the power of steam for
expanding with great force when let into first one side, and then the
other side of the cylinder. Thus, as the steam expands, it pushes the
piston back and forth at a high rate of speed, transmitting motion to
shafts and flywheels.
In 1888 the world was ready for a bigger and more powerful type of
steam engine; and C. A. Parsons, an Englishman, and Dr. G. de Laval
of Stockholm, brought forth successful turbines at about the same
time.
The machines were developed to a high state of efficiency, and are
still in general use, although most turbines for driving heavy
electrical machinery in the United States are the great Curtiss
engines, which are a combination of the principles of both the De
Laval and Parsons machines. All of them are run by the old principle
of the water-wheel. Instead of the steam being turned into a cylinder
to push the piston, it is turned into a steel drum or casing in which
wheels or disks are mounted on the central shaft. All along the edge
of these wheels are hundreds of little vanes or blades or buckets
against which the steam flows from many nozzles placed all around the
inside of the casing. The steam flows with great force, and naturally
pushing against the blades, starts the wheels and the engine shaft
to revolving. After expending its force on the blades that turn the
steam passes on to a set of stationary blades which then shoot it out
against the next set of moving blades.
In the Curtiss turbine the wheels at one end of the shaft are smaller
than those at the other, and the steam enters at the small end,
where it is under heavy pressure. After having expended its force
on the blades of the first wheel, the steam passes through holes in
a partition at the side and zigzags back so that it strikes the
vanes or blades on the next larger disk. It then repeats the process,
expands a little, and goes to a larger disk. Finally, by the time
the steam has expanded to its full capacity, the greater part of its
force has been expended against the disks of the turbine.
[Illustration: THE CURTISS TURBINE
Diagram of Steam Diaphragm Showing Nozzles and Fixed and Moving
Blades
A--Single stage turbine wheel. B--Steam nozzles.
B´--Steam exhausts. C--Moving blades. D--Stationary blades.]
From this we see the main points of difference between reciprocating
engines and turbines, and between most turbines and Tesla's invention.
While most turbines take advantage of the expansive power of steam,
the main idea is to make use of the velocity of the vapour as it is
driven from a set of nozzles around the turbine wheel, under high
pressure.
Also it will be seen that Tesla's invention is a turbine in form, but
that it is entirely different from either of the two earlier types,
because instead of giving the steam something to push against, it is
allowed to follow its own natural course around between the smooth
disks, and drag them after it.
Some kind of a crank motion is necessary in all reciprocating
engines, to convert the backward and forward movement of the piston
to the rotary motion of the shaft, but this is done away with
entirely in the turbine. What engineers call a "direct drive" is
substituted in its place. In other words, the turbine wheels or
disks, fastened to the shaft, turn it, and drive the machinery
directly from the source of power. The speed of the machine is
regulated by gears.
The great advantage of the "direct drive," particularly for big
steamships and for turning big electric dynamos, will be plain to
every boy when he thinks of the long narrow body of a ship in which
can lie the turbine engines working directly on the propeller shafts
(with the exception of certain gears, of course, for regulating the
speed) instead of the big flywheels, and flying cranks of marine
reciprocating engines. Also with dynamos it is just as important
to have the power applied directly to save space and increase the
general efficiency of the machine.
The greatest disadvantage of the usual kinds of turbines for most
machinery, including steamships, is the fact that they cannot be
reversed. To solve this difficulty, all the great ocean and coast
liners, battleships, cruisers, and torpedo boats that are equipped
with turbines have two sets of engines, one for straight ahead and
one for backward.
With the Tesla turbine this disadvantage, as we have seen, is
entirely done away with, and the one turbine can be reversed as
easily and simply as it can be started.
And so, while we are waiting for the world-moving wireless
transmission of power and for the completion of Tesla's invention for
safe and stable airships, we can look for the speedy development of
his turbine in practically all departments of mechanical engineering.