CHAPTER IITHE DEVELOPMENT OF THE AIRSHIP
Beforefree 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; threemillion 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. Thoughthe 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, withwhich 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 historicballoon:—
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 industryand 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 theenvelope:—
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 madefrom 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.