THE DEVELOPMENT OF THE AIRSHIP
Before free balloons were successfully motor driven and steered, stern
necessity had pressed them into the service of war. During the siege
of Paris, in 1870, when the Parisians were cut off from all means of
escape, there were only a few balloons in Paris; but the successful
escape of some aëronauts in them was considered encouraging enough to
establish an aërial highway involving a more wholesale manufacture
of balloons than had been accomplished before. The disused railway
stations were converted into balloon factories and training schools for
aëronauts. In four months sixty-six balloons left Paris, fifty-four
being adapted to the administration of post and telegraph; 160
persons were carried over the Prussian lines; three million letters
reached their destination; 360 pigeons were taken up, of which only
fifty-seven came back, but these brought 100,000 messages, by means of
microphotographical despatches. In these a film 38 by 50 mm. contained
2,500 messages. The pigeons usually carried eighteen films, with 40,000
messages.
At this time the French Government attempted to produce a navigable
balloon, and employed Dupuy de Lôme on the task of designing and
building it. This was to be driven by hand power, the screw being
driven by eight labourers. The balloon was actually made and tested.
Considering the h.p. was 0.8, it is needless to say it was not
successful.
It was during the siege of Paris that Krupp constructed the first
special gun for attacking balloons, a relict which has been preserved
at Berlin.
If such was the utility of balloons that merely drifted at the mercy
of the aërial currents they encountered, it was not to be wondered
at that, soon after the Franco-Prussian War, new attempts were made
to make them navigable. Though the term airship might reasonably be
applied to all the forms of navigable aircraft still in this country,
it has been applied in a less wide sense to those machines that
are lighter than air. In these pages the term will be used in this
connection.
The effort to navigate balloons almost dates back to the invention of
the balloon itself. It was, indeed, early realised that the spherical
shape of the ordinary balloons that drift with the winds would be
unsuitable for a craft that would have to travel against the wind. In
1784 Meusnier designed an elongated airship, in which the brothers
Robert actually ascended. It is noticeable that in this early design of
Meusnier was the now well-known ballonet, or inner balloon, which forms
an essential feature of modern non-rigid and semi-rigid airships for
preserving the rigidity of the outer envelope and facilitating ascent
or descent.
If we except the effort of Dupuy de Lôme, the next remarkable attempt
at airship construction was in 1852, when the Parisian Giffard made his
steam-driven elongated balloon, with which he made two experiments.
These merely proved that successful navigation against a wind would
require much larger motive power than his Lilliputian steam-engine of 3
h.p. Giffard, however, was the pioneer of the airship driven by other
than hand power. The following are the dimensions, etc., of what will
ever be an historic balloon:--
Length 44 metres
Diameter 12.00 metres
Cubic capacity 2,500 cubic metres
Horse power 3.0
Estimated speed per hour 6.71 miles
The experiments of Krebs and Renard in 1885 were noteworthy. They were
the first in which direct return journeys were made to the place whence
the balloon started.
These experiments showed the importance of the military factor in the
development of aërial navigation. Krebs and Renard were the officers
in charge of the French Military Aëronautical Department at Meudon,
and they applied national funds to the construction of an airship. It
was the development of the electrical industry and the production
of electric motors at that time which stimulated the experiments.
The brothers Tissandier had, in 1883, propelled an elongated balloon
against a wind of some three metres a second by means of an electric
bichromate battery which supplied the power to an electric motor. It
was thought that those experiments had been sufficiently successful for
further trial of the powers of electricity.
Renard made profound and exhaustive researches into the science of the
navigable balloon. To him we are, indeed, indebted for the elucidation
of the underlying principles that have made military airships possible.
The navigable balloon “La France” was dissymmetrical, being made very
much in the shape of a fish or bird. Its master diameter was near the
front, and the diameters diminished gradually to a point at the back.
The following were the dimensions of the envelope:--
Length 50.40 metres
Diameter 8.40 metres
Length in diameters 6.00 metres
The airship was remarkably steady on account of the minute precautions
taken to counteract the instability produced by a somewhat excessive
length. Any device which modifies pitching at the same time lessens
the loss of speed resulting from the resistance of the air when the
ship is moving at an angle. A direct means of reducing pitching is
the dissymmetrical form given to the envelope by placing the master
diameter near the front. The resistance of the air falls on the front
surface, which in this dissymmetric form of envelope is much shortened,
while the compensating surface at the back is augmented. Many experts
are of opinion that in this form of envelope Krebs and Renard came
nearer perfection than any other navigable balloon constructor.
Like the brothers Tissandier, they used an electric battery and motor
to drive their screw, their motive power being 9 h.p.
It was claimed that out of seven journeys, the airship returned five
times to the place whence it started. As an example of these journeys,
on September 22nd, 1885, a journey was made from Meudon to Paris and
back again. On this day the wind was blowing at a velocity of about
3.50 metres a second--what we should call a calm. Few, perhaps, who saw
the small naval airship, the “Beta,” manœuvring over London this autumn
realised that a navigable balloon, not so very much unlike it in form,
was speeding its way over Paris as long ago as 1885. The advent of
the first at all practical military airship was forgotten because the
experiments, comparatively successful as they were, suddenly ceased.
They came to an end because it was found that though electricity as a
motive power could afford an airship demonstration, it was unfitted for
serious and prolonged use.
One industry has often to wait for another--the world had to wait for
the missing link in aërial navigation. That was the light petroleum
motor. With its coming came the era of airships and aëroplanes.