hundreds of pounds to the square inch strikes the first set of vanes
on the drum, passes them and meets the first set of chest-vanes, is
turned from its course on to the second set of drum-vanes, and so on
to the other end of the chest. Its power arises entirely from its
expansive velocity, which, rather than turn a number of sharp corners,
will, if possible, compel the obstruction to move out of its way. If
that obstruction be from any cause difficult to stir, the steam must
pass round it until its pressure overcomes the inertia. Consequently
the turbine differs from the cylinder engine in this respect, that
steam _can_ pass through and be wasted without doing any work at all,
whereas, unless the gear of a cylinder moves, and power is exerted,
all steam ways are closed, and there is no waste. In practice,
therefore, it is found that a turbine is most effective when running
at high speed.
The first steam-turbines were used to drive dynamos. In 1884 Mr.
Parsons made a turbine in which fifteen wheels of increasing size
moved at the astonishing rate of 300 revolutions per second, and
developed 10 horse-power. In 1888 followed a 120 horse-power turbine,
and in 1892 one of 2000 horse-power, provided with a condenser to
produce suction. So successful were these steam fans for electrical
work, pumping water and ventilating mines, that Mr. Parsons determined
to test them as a means of propelling ships. A small vessel 100 feet
long and 9 feet in beam was fitted with three turbines--high, medium,
and low pressure, of a total 2000 horse-power--a proportion of motive
force to tonnage hitherto not approached. Yet when tried over the test
course the _Turbinia_, as the boat was fitly named, ran in a most
disappointing fashion. The screws revolved _too fast_, producing what
is known as _cavitation_, or the scooping out of the water by the
screws, so that they moved in a partial vacuum and utilised only a
fraction of their force, from lack of anything to “bite” on. This
defect was remedied by employing screws of coarser pitch and larger
blade area, three of which were attached to each of the three
propeller shafts. On a second trial the _Turbinia_ attained 32-3/4
knots over the “measured mile,” and later the astonishing speed of
forty miles an hour, or double that of the fast Channel packets. At
the Spithead Review in 1897 one of the most interesting sights was the
little nimble _Turbinia_ rushing up and down the rows of majestic
warships at the rate of an express train.
[Illustration: _H.M.S. Torpedo Destroyer “Viper.” This vessel was the
fastest afloat, attaining the enormous speed of 41 miles an hour. The
screws were worked by turbines, giving 11,000 horse-power. She was
wrecked on Alderney during the Naval Manoeuvres of 1901._]
After this success Mr. Parsons erected works at Wallsend-on-Tyne for
the special manufacture of turbines. The Admiralty soon placed with
him an order for a torpedo-destroyer--the _Viper_--of 350 tons; which
on its trial trip exceeded forty-one miles an hour at an estimated
horse-power (11,000) equalling that of our largest battleships. A
sister vessel, the _Cobra_, of like size, proved as speedy.
Misfortune, however, overtook both destroyers. The _Viper_ was wrecked
August 3, 1901, on the coast of Alderney during the autumn naval
manoeuvres, and the _Cobra_ foundered in a severe storm on September
12 of the same year in the North Sea. This double disaster casts no
reflections on the turbine engines; being attributed to fog in the one
case and to structural weakness in the other. The Admiralty has since
ordered another turbine destroyer, and before many years are past we
shall probably see all the great naval powers providing themselves
with like craft to act as the “eyes of the fleet,” and travel at even
higher speeds than those of the _Viper_ and _Cobra_.
The turbine has been applied to mercantile as well as warlike
purposes. There is at the present time a turbine-propelled steamer,
the _King Edward_, running in the Clyde on the Fairlie-Campbelltown
route. This vessel, 250 feet long, 30 broad, 18 deep, contains three
turbines. In each the steam is expanded fivefold, so that by the time
it passes into the condensers it occupies 125 times its boiler volume.
(On the _Viper_ the steam entered the turbine through an inlet eight
inches in diameter, and left them by an outlet four feet square.) In
cylinder engines thirty-fold expansion is considered a high ratio;
hence the turbine extracts a great deal more power in proportion from
its steam. As a turbine cannot be reversed, special turbines are
attached to the two outside of the three propeller shafts to drive the
vessel astern. The steamer attained 20-1/2 knots over the “Skelmorlie
mile” in fair and calm weather, with 3500 horse-power produced at the
turbines. The _King Edward_ is thus the fastest by two or three knots
of all the Clyde steamers, as she is the most comfortable. We are
assured that as far as the turbines are concerned it is impossible by
placing the hand upon the steam-chest to tell whether the drum inside
is revolving or not!
Every marine engine is judged by its economy in the consumption of
coal. Except in times of national peril extra speed produced by an
extravagant use of fuel would be severely avoided by all owners and
captains of ships. At low speeds the turbine develops less power than
cylinders from the same amount of steam, but when working at high
velocity it gives at least equal results. A careful record kept by the
managers of the Caledonian Steamship Company compares the _King
Edward_ with the _Duchess of Hamilton_, a paddle steamer of equal
tonnage used on the same route and built by the same firm. The record
shows that though the paddle-boat ran a fraction of a mile further
for every ton of coal burnt in the furnaces, the _King Edward_
averaged two knots an hour faster, a superiority of speed quite out of
proportion to the slight excess of fuel. Were the _Duchess_ driven at
18-1/2 knots instead of 16-1/2 her coal bill would far exceed that of
the turbine.
As an outcome of these first trials the Caledonian Company are
launching a second turbine vessel. Three high-speed turbine yachts are
also on the stocks; one of 700 tons, another of 1500 tons, and a third
of 170 tons. The last, the property of Colonel M’Calmont, is designed
for a speed of twenty-four knots.
Mr. Parsons claims for his system the following advantages: Greatly
increased speed; increased carrying power of coal; economy in coal
consumption; increased facilities for navigating shallow waters;
greater stability of vessels; reduced weight of machinery (the
turbines of the _King Edward_ weigh but one-half of cylinders required
to give the same power); cheapness of attending the machinery; absence
of vibration, lessening wear and tear of the ship’s hull and assisting
the accurate training of guns; lowered centre of gravity in the
vessel, and consequent greater safety during times of war.
The inventor has suggested a cruiser of 2800 tons, engined up to
80,000 horse-power, to yield a speed of forty-four knots (about fifty
miles) an hour. Figures such as these suggest that we may be on the
eve of a revolution of ocean travel comparable to that made by the
substitution of steam for wind power. Whether the steam-turbine will
make for increased speed all round, or for greater economy, remains to
be seen; but we may be assured of a higher degree of comfort. We can
easily believe that improvements will follow in this as in other
mechanical contrivances, and that the turbine’s efficiency has not yet
reached a maximum; and even if our ocean expresses, naval and
mercantile, do not attain the one-mile-a-minute standard, which is
still regarded as creditable to the fastest methods of land
locomotion, we look forward to a time in the near future when much
higher speeds will prevail, and the tedium of long voyages be greatly
shortened. Already there is talk of a service which shall reduce the
trans-Atlantic journey to three-and-a-half days. The means are at hand
to make it a fact.
_Note._--In the recently-launched turbine destroyer _Velox_ a
novel feature is the introduction of ordinary reciprocating
engines fitted in conjunction with the steam turbines. These
engines are of triple-compound type, and are coupled direct to
the main turbines. They take steam from the boilers direct and
exhaust into the high-pressure turbine. These reciprocating
engines are for use at cruising speeds. When higher power is
needed the steam will be admitted to the turbines direct from
the boilers, and the cylinders be thrown out of gear.
MECHANICAL FLIGHT.
Few, if any, problems have so strongly influenced the imagination and
exercised the ingenuity of mankind as that of aërial navigation. There
is something in our nature that rebels against being condemned to the
condition of “featherless bipeds” when birds, bats, and even minute
insects have the whole realm of air and the wide heavens open to them.
Who has not, like Solomon, pondered upon “the way of a bird in the
air” with feelings of envy and regret that he is chained to earth by
his gross body; contrasting our laboured movements from point to point
of the earth’s surface with the easy gliding of the feathered
traveller? The unrealised wish has found expression in legends of
Dædalus, Pegasus, in the “flying carpet” of the fairy tale, and in the
pages of Jules Verne, in which last the adventurous Robur on his
“Clipper of the Clouds” anticipates the future in a most startling
fashion.
Aeromobilism--to use its most modern title--is regarded by the crowd
as the mechanical counterpart of the Philosopher’s Stone or the Elixir
of Life; a highly desirable but unattainable thing. At times this
incredulity is transformed by highly-coloured press reports into an
equally unreasonable readiness to believe that the conquest of the air
is completed, followed by a feeling of irritation that facts are not
as they were represented in print.
The proper attitude is of course half-way between these extremes.
Reflection will show us that money, time, and life itself would not
have been freely and ungrudgingly given or risked by many
men--hard-headed, practical men among them--in pursuit of a
Will-o’-the-Wisp, especially in a century when scientific calculation
tends always to calm down any too imaginative scheme. The existing
state of the aërial problem may be compared to that of a railway truck
which an insufficient number of men are trying to move. Ten men may
make no impression on it, though they are putting out all their
strength. Yet the arrival of an eleventh may enable them to overcome
the truck’s inertia and move it at an increasing pace.
Every new discovery of the scientific application of power brings us
nearer to the day when the truck will move. We have metals of
wonderful strength in proportion to their weight; pigmy motors
containing the force of giants; a huge fund of mechanical experience
to draw upon; in fact, to paraphrase the Jingo song, “We’ve got the
things, we’ve got the men, we’ve got the money too”--but we haven’t
as yet got the machine that can mock the bird like the flying express
mocks the strength and speed of horses.
The reason of this is not far to seek. The difficulties attending the
creation of a successful flying-machine are immense, some unique, not
being found in aquatic and terrestrial locomotion.
In the first place, the airship, flying-machine, aerostat, or whatever
we please to call it, must not merely move, but also lift itself.
Neither a ship nor a locomotive is called upon to do this. Its ability
to lift itself must depend upon either the employment of large
balloons or upon sheer power. In the first case the balloon will, by
reason of its size, be unmanageable in a high wind; in the second
case, a breakdown in the machinery would probably prove fatal.
Even supposing that our aerostat can lift itself successfully, we
encounter the difficulties connected with steering in a medium
traversed by ever-shifting currents of air, which demands of the
helmsman a caution and capacity seldom required on land or water. Add
to these the difficulties of leaving the ground and alighting safely
upon it; and, what is more serious than all, the fact that though
success can be attained only by experiment, experiment is in this case
extremely expensive and risky, any failure often resulting in total
ruin of the machine, and sometimes in loss of life. The list of those
who have perished in the search for the power of flight is a very long
one.
Yet in spite of these obstacles determined attempts have been and are
being made to conquer the air. Men in a position to judge are
confident that the day of conquest is not very far distant, and that
the next generation may be as familiar with aerostats as we with
motor-cars. Speculation as to the future is, however, here less
profitable than a consideration of what has been already done in the
direction of collecting forces for the final victory.
To begin at the beginning, we see that experimenters must be divided
into two great classes: those who pin their faith to airships lighter
than air, _e.g._ Santos Dumont, Zeppelin, Roze; and those who have
small respect for balloons, and see the ideal air-craft in a _machine_
lifted entirely by means of power and surfaces pressing the air after
the manner of a kite. Sir Hiram Maxim and Professor S. P. Langley, Mr.
Lawrence Hargrave, and Mr. Sydney Hollands are eminent members of the
latter cult.
As soon as we get on the topic of steerable balloons the name of Mr.
Santos Dumont looms large. But before dealing with his exploits we may
notice the airship of Count Zeppelin, an ingenious and costly
structure that was tested over Lake Constance in 1900.
The balloon was built in a large wooden shed, 450 by 78 by 66 feet,
that floated on the lake on ninety pontoons. The shed alone cost over
£10,000.
The balloon itself was nearly 400 feet long, with a cylindrical
diameter of 39 feet, except at its ends, which were conical, to offer
as little resistance as possible to the air. Externally it afforded
the appearance of a single-compartment bag, but in reality it was
divided into seventeen parts, each gas-tight, so that an accident to
one part of the fabric should not imperil the whole.
A framework of aluminium rods and rings gave the bag a partial
rigidity.
Its capacity was 12,000 cubic yards of hydrogen gas, which, as our
readers doubtless know, is much lighter though more expensive than
ordinary coal-gas; each inflation costing several hundreds of pounds.
Under the balloon hung two cars of aluminium, the motors and the
screws; and also a great sliding weight of 600 lbs. for altering the
“tip” of the airship; and rudders to steer its course.
On June 30 a great number of scientific men and experts assembled to
witness the behaviour of a balloon which had cost £20,000. For two
days wind prevented a start, but on July 2, at 7.30 P.M., the balloon
emerged from its shed, and at eight o’clock commenced its first
journey, with and against a light easterly wind for a distance of
three and a half miles. A mishap to the steering-gear occurred early
in the trip, and prevented the airship appearing to advantage, but a
landing was effected easily and safely. In the following October the
Count made a second attempt, returning against a wind blowing at three
yards a second, or rather more than six miles an hour.
[Illustration: _The air-ship of M. Santos-Dumont rounding the Eiffel
Tower during its successful run for the Henri Deutsch Prize._]
Owing to lack of funds the fate of the “Great Eastern” has overtaken
the Zeppelin airship--to be broken up, and the parts sold.
The aged Count had demonstrated that a petroleum motor could be used
in the neighbourhood of gas without danger. It was, however, reserved
for a younger man to give a more decided proof of the steerableness of
a balloon.
In 1900 M. Henri Deutsch, a member of the French Aero Club, founded a
prize of £4000, to win which a competitor must start from the Aero
Club Park, near the Seine in Paris, sail to and round the Eiffel
Tower, and be back at the starting-point within a time-limit of
half-an-hour.
M. Santos Dumont, a wealthy and plucky young Brazilian, had,
previously to this offer, made several successful journeys in motor
balloons in the neighbourhood of the Eiffel Tower. He therefore
determined to make a bid for the prize with a specially constructed
balloon “Santos Dumont V.” The third unsuccessful attempt ended in
disaster to the airship, which fell on to the houses, but fortunately
without injuring its occupant.
Another balloon--“Santos Dumont VI.”--was then built. On Saturday,
October 19th, M. Dumont reached the Tower in nine minutes and
recrossed the starting line in 20-1/2 more minutes, thus complying
with the conditions of the prize with half-a-minute to spare. A
dispute, however, arose as to whether the prize had been actually won,
some of the committee contending that the balloon should have come to
earth within the half-hour, instead of merely passing overhead; but
finally the well-merited prize was awarded to the determined young
aeronaut.
The successful airship was of moderate proportions as compared with
that of Count Zeppelin. The cigar-shaped bag was 112 feet long and 20
feet in diameter, holding 715 cubic yards of gas. M. Dumont showed
originality in furnishing it with a smaller balloon inside, which
could be pumped full of air so as to counteract any leakage in the
external bag and keep it taut. The motor, on which everything
depended, was a four-cylinder petrol-driven engine, furnished with
“water-jackets” to prevent over-heating. The motor turned a large
screw--made of silk and stretched over light frames--200 times a
minute, giving a driving force of 175 lbs. Behind, a rudder directed
the airship, and in front hung down a long rope suspended by one end
that could be drawn towards the centre of the frame to alter the trim
of the ship. The aeronaut stood in a large wicker basket flanked on
either side by bags of sand ballast. The fact that the motor, once
stopped, could only be restarted by coming to earth again added an
element of great uncertainty to all his trips; and on one occasion the
mis-firing of one of the cylinders almost brought about a collision
with the Eiffel Tower.
From Paris M. Dumont went to Monaco at the invitation of the prince of
that principality, and cruised about over the bay in his balloon. His
fresh scheme was to cross to Corsica, but it was brought to an abrupt
conclusion by a leakage of gas, which precipitated balloon and
balloonist into the sea. Dumont was rescued, and at once set about new
projects, including a visit to the Crystal Palace, where he would have
made a series of ascents this summer (1902) but for damage done to the
silk of the gas-bag by its immersion in salt water and the other
vicissitudes it had passed through. Dumont’s most important
achievement has been, like that of Count Zeppelin, the application of
the gasolene motor to aeromobilism. In proportion to its size this
form of motor develops a large amount of energy, and its mechanism is
comparatively simple--a matter of great moment to the aeronaut. He has
also shown that under favourable conditions a balloon may be steered
against a head-wind, though not with the certainty that is desirable
before air travel can be pronounced an even moderately simple
undertaking. The fact that many inventors, such as Dr. Barton, M.
Roze, Henri Deutsch, are fitting motors to balloons in the hopes of
solving the aërial problem shows that the airship has still a strong
hold on the minds of men. But on reviewing the successes of such
combinations of lifting and driving power it must be confessed, with
all due respect to M. Dumont, that they are somewhat meagre, and do
not show any great advance.
The question is whether these men are not working on wrong lines, and
whether their utmost endeavours and those of their successors will
ever produce anything more than a very semi-successful craft. Their
efforts appear foredoomed to failure. As Sir Hiram Maxim has observed,
a balloon by its very nature is light and fragile, it is a mere
bubble. If it were possible to construct a motor to develop 100
horse-power for every pound of its weight, it would still be
impossible to navigate a balloon against a wind of more than a certain
strength. The mere energy of the motor would crush the gas-bag against
the pressure of the wind, deform it, and render it unmanageable.
Balloons therefore must be at the mercy of the wind, and obliged to
submit to it under conditions not always in accordance with the wish
of the aeronaut.
Sir Hiram in condemning the airship was ready with a substitute. On
looking round on the patterns of Nature, he concluded that, inasmuch
as all things that fly are heavier than air, the problem of aërial
navigation must be solved by a machine whose natural tendency is to
fall to the ground, and which can be sustained only by the exertion of
great force. Its very weight would enable it to withstand, at least to
a far greater extent than the airship, the varying currents of the
air.
The lifting principle must be analogous to that by which a kite is
suspended. A kite is prevented from rising beyond a certain height by
a string, and the pressure of the wind working against it at an angle
tends to lift it, like a soft wedge continuously driven under it. In
practice it makes no difference whether the kite be stationary in a
wind or towed rapidly through a dead calm; the wedge-like action of
the air remains the same.
Maxim decided upon constructing what was practically a huge compound
kite driven by very powerful motors.
But before setting to work on the machine itself he made some useful
experiments to determine the necessary size of his kites or
aeroplanes, and the force requisite to move them.
He accordingly built a “whirling-table,” consisting of a long arm
mounted on a strong pivot at one end, and driven by a 10 horse-power
engine. To the free end, which described a circle of 200 feet in
circumference, he attached small aeroplanes, and by means of delicate
balances discovered that at 40 miles an hour the aeroplane would lift
133 lbs. per horse-power, and at 60 miles per hour every square foot
of surface sustained 8 lbs. weight. He, in common with other
experimenters on the same lines, became aware of the fact that if it
took a certain strain to suspend a stationary weight in the air, _to
advance it rapidly as well as to suspend it took a smaller strain_.
Now, as on sea and land, increased speed means a very rapid increase
in the force required, this is a point in favour of the
flying-machine. Professor Langley found that a brass plate weighing a
pound, when whirled at great speed, was supported in the air by a
pulling pressure of less than one ounce. And, of course, as the speed
increased the plate became more nearly horizontal, offering less
resistance to the air.
It is on this behaviour of the aeroplane that the hopes of Maxim and
others have been based. The swiftly moving aeroplane, coming
constantly on to fresh air, the inertia of which had not been
disturbed, would resemble the skater who can at high speed traverse
ice that would not bear him at rest.