SEA-PLANES AND AIRSHIPS
Biplanes and monoplanes with floats--A flying
boat--The airship--Its growth from the balloon and
development into types--Large craft with rigid
hulls.
As military flying produces special forms of aircraft, so the needs of
the Navy make themselves felt; and the first task set the designers of
aeroplanes was to provide a machine which should alight upon water. They
did so by fitting floats, or pontoons, below an ordinary land aeroplane,
these taking the place of the wheeled chassis; and then by degrees a
special type of air and water craft was developed, and came to be known
as the flying boat.
In Fig. 39, it may be remembered, was illustrated a biplane which would
rest on wooden pontoons, and so ride upon the water; and this method of
a hollow float was adopted and improved by the modern builders. In Fig.
68 will be seen a typical hydro-biplane, water-plane, or sea-plane--the
name last mentioned being that adopted by our Admiralty when referring
to such craft. The machine is an Avro, and its appearance is that of a
land aeroplane, save that it has a set of three pontoons to support it
on the water--two main floats beneath the sustaining planes, and a third
to bear the weight of the tail. Several needs have to be considered when
such floats are built. One is that they should be buoyant enough to bear
upon the water the weight of the machine, and its pilot, passenger, and
fuel. In the case of the craft shown, this represents a total of 2200
lbs. Another point is that the float should detach itself readily from
the surface of the water.
[Illustration: FIG. 68.--An Avro Sea-Plane.
A. Propeller; B. 100-h.p. Gnome motor, hidden by shield; C.C.
Main-planes; D. Observer’s seat; E. Pilot’s seat; F. Rudder; G.
Elevating-plane; H. Float to support tail; I. Main floats to bear the
weight of the machine.]
The sea-plane, when a flight is made, is launched upon the water down a
slipway; then the pilot and his passenger embark, the motor is started,
and the propeller draws the machine across the water at a rapidly
increasing pace. The floats raise themselves higher and higher upon the
water, as the air-planes exercise a growing lift, until they only just
skim the surface. And now comes the moment when the airman, drawing back
his elevating lever, seeks to raise his craft from the water into the
air. At first only the front of the floats rise, the rear sections
clinging to the surface; then, in another instant, the whole float frees
itself from the water in a scatter of spray, and the craft glides at a
gently-sloping angle into the air. It is the aim of builders, by the
curve they impart, to make the floats leave the water with as little
resistance as possible. In the floats of the Avro (Fig. 68) will be
noticed a notch, or cut-away section, which occurs at about the centre
of the float upon its lower side. This is called a “step,” and is to
help the float to lift from the water. When the main-planes draw upward,
as the craft moves prior to its flight, the floats tend, as has been
said, to raise themselves in the water; and as they do so, lifting first
towards the bow, there comes a space between the upward-cut “step” and
the surface of the water. Into this space air finds its way and, by
helping still further to free the float from the surface, aids greatly
at the moment when the pilot--operating his hand-lever--seeks the final
lift which will carry him aloft.
When in flight, as when skimming upon the surface of the water, a
sea-plane must carry its floats with it; and this introduces a
complication, inasmuch as the floats offer a resistance to the air and
tend to reduce speed. Another need is thus shown; the builder of a float
must so shape it that it will move through the air with the least
possible friction. This is accomplished by making it long and tapering
in form and by curving and polishing its surface.
England, in the building and handling of sea-planes has come well to the
fore, and our machines are more advanced than those of other countries.
The Admiralty has recognised that, acting as a coastal scout in time of
war, such craft would be of the utmost value; thus we find air-stations
dotted round our seaboard, from which machines may fly in a regular
patrol. By the employment of hundreds of craft, operating upon a
well-ordered plan, it will be possible in the future to girdle our
shores completely; and such machines would not only spy out the approach
of an enemy’s fleet, but give battle to hostile aeroplanes or airships
which might seek to pass inland. The type of machine we have just
described was a biplane, but there are monoplane sea-craft, and a
Bleriot fitted for alighting upon the water is shown in Fig. 69.
[Illustration: FIG. 69.--A Bleriot Sea-plane.]
Another form of craft is being developed successfully--the flying boat.
This is not merely a land aeroplane with floats instead of wheels; it is
a boat with a sea-going hull, which has lifting planes upon it; and it
assumes the distinctive form seen in Fig. 70. When on the surface of the
water the machine floats like a ship; then, when driven rapidly across
the surface, its planes raise it into the air and it flies. A closer
view of the hull of such a craft is given in Fig. 71.
Flying boats are at present small and lightly built, and they have
difficulty in weathering rough waves when floating upon the water; but
already the tendency is to make them larger, and to give them more
powerful motors, and such machines for naval work, as developed in the
future, may be as large as a torpedo-boat-destroyer and capable of high
speeds both on water and in the air.
[Illustration: THE MACHINE SEEN FROM ABOVE,
showing the shape of wings and tail, and the positions of the pilot and
passenger within the hull.
A. Hull; B. seats for crew; C.C. Planes; D. Motor; E. Propeller; F.
Rudder; G. Elevators.
MACHINE SEEN FROM IN FRONT,
showing the span of the main-planes, and the curve of the boat-shaped
hull.
FIG. 70.--A Flying Boat.]
[Illustration: FIG. 71.--The hull of a Flying-Boat.
A. Pilot’s seat and controlling wheel; B. Passenger’s seat; C. Movable
flap to facilitate entering the hull; D. Handle, like that of a car, for
starting the engine; E. The engine; F.F. Fuel tanks; G. The propeller.]
There is another type of craft that is being adapted and improved for
naval use, and this is the airship. Although it is costly to build,
requires a huge shed in which to house it, and needs also the service
of trained crews to handle it when ascending or alighting, the airship
is a vastly important machine for the purposes of war. Its ability to
make flights lasting several days, and the power of its pilot to
manœuvre it at night, render it particularly suitable for naval use. Our
Admiralty is buying large machines, aiming at a preliminary fleet of
fifteen, and the German Navy is organising a squadron of Zeppelins.
The airship, although in use before the aeroplane, has developed more
slowly, and is even to-day in a crude form. This has been due to the
cost of experiments. Whereas a new aeroplane may be built and tested for
£1000 or so, the construction of an airship and the provision of its
shed spells an expenditure of many thousands. This money may, as in the
case of the aeroplane, be lost as a result of one mishap. In Germany
Count Zeppelin spent a fortune upon airships, before the Government and
the nation helped him with funds. With very few exceptions, none but
Governments--which have long purses to draw upon--can afford to build
large airships.
[Illustration: FIG. 72.--A modern Balloon.]
The airship is a development of the balloon; and the balloon we owe to
Stephen and Joseph Montgolfier--two French brothers who, after watching
clouds floating in the sky, had the notion that if they could fill a
light envelope with “some substance of a cloud-like nature” it would
raise itself into the air. Their father was a paper manufacturer, and so
they had facilities for making a number of very large paper bags. Under
these they lit fires of chopped straw, allowing the hot air and smoke to
rush up into the bags, and, when they were released the bags ascended,
carried up by the lifting influence of the heated air within them. Thus
was invented the hot-air balloon; and we buy paper replicas of it
to-day.
Delighted with their first success, the Montgolfiers built a paper
balloon 30 ft. in diameter, and this was sent up at Annonay, in France,
on 5th June 1783. It flew for ten minutes before the heated air inside
it became cold, and reached a height estimated at more than a mile.
After this came the ascent of a spherical balloon--one, that is to say,
the shape of a modern-type balloon. It was made of linen, covered with
paper, and had a small car attached. At Versailles, in France, on 19th
September 1783, this balloon was sent up with passengers in the car;
not human beings, though, for no man cared to ascend, fearing that the
upper atmosphere might have some strange effect upon him. The actual
occupants were a sheep, a cock, and a duck; and these three unwilling
voyagers made a flight which lasted eight minutes. When they descended
the sheep and the duck were found to be unharmed, although greatly
perturbed; but the cock showed symptoms of not being well! At first,
when learned men examined him, it was thought the rarefied atmosphere
had in some way affected him, and this view was held until practical
folk were able to show that the bird had been trampled upon by the
sheep.
From this, of course, the next step was the ascent of a man, and on 15th
October 1783 an adventurous youth named Pilatre de Rozier went up in a
balloon built by the Montgolfiers. The balloon was attached to a rope
and not allowed to ascend more than 100 feet; and at this altitude the
aeronaut remained for about four minutes. A month later de Rozier and a
passenger--the Marquis d’Arlandes--were bold enough to risk a flight in
a Montgolfier balloon. This time the ascent was made from Paris, and the
balloonists flew for five minutes before descending, reaching a height
of 500 feet.
[Illustration: FIG. 72A.--The car of a modern Balloon.
A.A. Ballast bags filled with sand; B. Instruments (such as a
statoscope, which shows at any moment whether the balloon is rising or
falling; and an altitude meter); C. Ring by which car is attached to
balloon.]
Coal-gas superseded hot air in the filling of balloons, the latter being
unsatisfactory, seeing that it cooled rapidly and allowed the balloon to
descend; the only alternative being to do what some of the first
aeronauts did, and burn a fire below the neck of their balloon even when
in the air. But the dangers of this were great, seeing that the whole
envelope might easily become ignited. With balloons filled with
coal-gas--modern examples of which are seen in Figs. 72 and 72A--long
flights were possible, but they had always this disadvantage--the
voyagers were at the mercy of the wind, and could not fly in any
direction they might choose. If the wind blew from the north then they
were driven south, the balloon being a bubble in the air, wafted by
every gust. Aeronauts became disgusted with this inability to guide the
flight of a balloon, and many quaint controls were tested; such, for
example, as the use of a large pair of oars with which the balloonist,
sitting in the car of his craft, rowed vigorously in the air. But this
method found little favour; and it was followed in due course by the use
of small steam engines and electric motors, which were made to turn
propellers such as are used in aeroplanes. For such experimental craft,
the rounded form of gas-container was abandoned and a cigar-shaped
envelope adopted, pointed at both ends, which could be more easily
driven through the air. An airship of a crude and early type is seen in
Fig. 73. It was built by an experimenter named Gifford, and in 1852 it
flew at the rate of seven miles an hour.
[Illustration: FIG. 73.--An Experimental Airship.
A. Gas-containing envelope; B. Car suspended below envelope, which
carried the aeronaut and a 3-horse-power steam engine; C. Two-bladed
propeller driven by the engine; D. Rudder (in the form of a sail) by
which the machine could be steered from side to side.]
When petrol engines became available, they gave an impetus to the
building of airships; for, like the aeroplane, the airship needed a
motive agent which gives a high power for a low weight. One of the first
to use a petrol motor in an airship with success was M. Santos-Dumont,
whose name has been mentioned in connection with aeroplanes. He tested
small, light airships, driven by petrol engines and two-bladed
propellers--as illustrated in Fig. 74; and with one of these, on a calm,
still day, he flew over Paris and round the Eiffel Tower.
[Illustration: FIG. 74.--Santos-Dumont’s Airship.
A. Gas envelope; B. Wheeled framework which carried motor, propeller,
and pilot’s seat; C. Elevating-plane; D. Horizontal rear-plane; E.
Rudder.]
Then by degrees came larger craft, more powerfully engined, and built to
attain greater speed. Hydrogen, far more buoyant than coal-gas, was used
to inflate their envelopes, and so they obtained a greater “lift.” Speed
with the airship was recognised as vital. If it could not fly fast it
was at the mercy of the wind, gusts striking powerfully against its
envelope, and driving it off its course.
[Illustration: FIG. 75.--Early-type Airship.
A. Gas envelope; B. Car suspended below envelope; C. Motor, which drives
propeller (D) through a shaft; E. Small horizontal plane for rising or
descending; F. Fixed fin, or keel plane, to give stability; G. Rudder.]
[Illustration: FIG. 76.--Airship “ballonette.”
A. Gas envelope; B. The interior ballonette, or collapsible chamber,
which is filled with air through the pipe C.]
A typical craft, representing the first of those navigated with any
certainty, is shown in Fig. 75. A gas-containing envelope, made of a
light, strong, varnished fabric, is kept taut by the pressure of the gas
within; the car, constructed of wood or metal tubing, is suspended by
ropes from the envelope, and contains engine and crew, with a two-bladed
propeller revolving astern. Such a machine, in its control, had an
elevating-plane and rudder, upon the same principle as those of the
aeroplane. One of the difficulties to be overcome was the expansion and
contraction of gas in the envelope owing to differences in altitude and
temperature. When the craft ascended, its envelope completely inflated,
the gas began to dilate owing to the outer air becoming less dense; and
some had to be allowed to escape through automatic valves. Then, should
the machine descend to a lower level, there was not sufficient gas in
the envelope to keep it tightly stretched, and it tended to sag at the
bow as it was driven through the air. To prevent this kinking, which
would have reduced the speed of the airship, and made it difficult to
control, an interior chamber, called the “ballonette,” was fitted to the
envelope, as shown in Fig. 76. When the gas-container was tightly
filled, this ballonette lay empty upon its lower surface; but, should
the envelope tend to become flaccid, through a loss of gas, a fan pumped
air into the ballonette; and, swelling out within the balloon, it
compensated for the gas which had escaped, and prevented the envelope
from losing its shape.
The craft shown in Fig. 75 is of the non-rigid type; its car, that is
to say, is hung by ropes from the envelope; and when the envelope is
deflated it can be detached from the car and the machine packed away in
a relatively small space. But as airships were built larger, and greater
speeds were obtained, it became necessary to strengthen the envelopes
with some form of keel; and this led to a type which is known as the
semi-rigid, and is developed successfully in France. Fig. 77 illustrates
an airship of this build. Along the lower side of its envelope is placed
a light, rigid framework or keel, and from this is suspended the car
which contains engines and crew.
[Illustration: FIG. 77.--Semi-rigid Airship.
A. Gas-containing envelope; B. Strengthening keel; C.C.
Stabilising-planes; D. Rudder; E. Car carrying engines, propeller, and
crew.]
The car of an airship, showing its construction and the disposition of
motors and propellers, is sketched in Fig. 78; while in Fig. 79 may be
seen the pilot’s driving platform with wheels, dials, and speaking-tube
to the engineers.
[Illustration: FIG. 78.--The Car of an Airship.
A.A. Propellers; B. Motors; C. Engineer’s platform; D. Pilot’s
controlling platform; E. Elevating-planes; F. Fuel tanks; G. Passenger’s
platform.]
[Illustration: FIG. 79.--Control platform of an Airship.
A.A. Wheels operating elevating-planes and rudder; B. Height recorder;
C. Speaking-tube to communicate with engineers.]
[Illustration: FIG. 80.--Hull of a Zeppelin during construction.]
Craft of the semi-rigid type provide a link between small, non-rigid
ships and the very large machine which is built with an entirely rigid
framework, and has its example in the Zeppelin. The maker forms a
skeleton hull of aluminium or some light metal alloy, a method that is
shown in Fig. 80. The hull of a Zeppelin, slightly more than 500 feet in
length, is sheathed with tightly stretched fabric; and within it are the
gas-containers--a row of seventeen separate balloons, each in a
compartment by itself, and containing a total of nearly 1,000,000 cubic
feet of gas--which give these airships a lifting power of close upon 30
tons. The arrangement of the gas-holders, and the general outline of the
machine, may be observed from Fig. 81. The vessel offers comparatively
little resistance to the air, despite its size, and this is due to the
finely tapering shape of the hull; while its rigidity allows it to be
driven at speeds of more than 50 miles an hour. The lifting capacity,
also, enables long flights to be made. Taking up crew and petrol, such a
craft can remain aloft for several days, and travel distances of more
than 1000 miles.
[Illustration: FIG. 81.--A Zeppelin Airship.
A.A. Rigid hull covered by fabric; B. Section showing the skeleton
framework of hull; C. Arrangement of the interior gas chambers; D.
Elevating-planes; E.E. Rudders; F.F. The two cars containing engines and
crew; G. Passage-way between the cars; H. One of the propellers, of
which the craft has four--two at the front of the hull, upon either
side, and two at the rear.]
At first, flying slowly and with unreliable motors, these very large
airships were at the mercy of the wind, particularly when manœuvring
near the ground. Trained crews were necessary to handle them, and they
had to be housed in huge and expensive sheds, as will be realised from a
glance at Fig. 82. But for the one ardent pioneer, Count Zeppelin, it is
doubtful whether large, rigid craft would have been built at all. After
costing many thousands, they ran the risk of being dashed to earth in a
squall and hopelessly wrecked. Such a fate, indeed, befell one ship
after another that Count Zeppelin launched. But he refused to be
discouraged, and went on doggedly until his private fortune was gone.
Then, magnificent flights having been made, the Government came to his
aid; while the German people, immensely proud of his achievements,
subscribed more than £300,000 for the furtherance of his tests. And so
now the Zeppelin--powerfully engined, better built, and handled by
expert crews--is the Dreadnought of the German air-fleet, flying
hundreds of miles over the North Sea, co-operating with warships as a
scout, and flashing messages by wireless for distances of 300 miles.
[Illustration: FIG. 82.--An Airship leaving its shed.
A. The machine emerging stern first; B. A sister craft in dock; C.C. The
launching crews; D.D. Rails upon which the cars of the airship move, so
as to prevent its swinging sideways in a gust; E. Outlook station upon
the roof of the shed; F. Workshops; living quarters for the crews; plant
for making hydrogen gas.]
The airship, for long-distance reconnoitring, stands at present
unrivalled. It can remain in the air for days, sweeping over sea or
land, and reporting constantly to its headquarters. For night flying,
also, it is at present the superior of the aeroplane, being navigable in
darkness, and having an ability to hover above a given spot, its engines
silent, and its presence undetected by those below.