minute as compared with the great surface of material, but
on the other hand, a shrapnel bursting just in front of may
cause a rapid fall. It is therefore considered prudent to
keep the balloon well away from an enemy, and two miles are
laid down as the nearest approach it should make habitually.
Besides being of use on land for war purposes, balloons have
been tried in connexion with the naval service. In France
especially regular trials have been made of inflating balloons
on board ships, and sending them aloft as a look-out; but it
is now generally contended that the difficulties of storing
the gas and of manoeuvring the balloon are so great on
board ship as to be hardly worth the results to be gained.
A very important development of military ballooning is the navigable
balloon. If only a balloon could be sent up and driven in any
required direction, and brought back to its starting-point, it
is obvious that it would be of the very greatest use in war.
Dirigible balloons.
From the very first invention of balloons the problem has
been how to navigate them by propulsion. General J. B. M.
C. Meusnier (1754-1793) proposed an elongated balloon in
1784. It was experimented on by the brothers Robert, who
made two ascensions and claimed to have obtained a deviation
of 22 deg. from the direction of a light wind by means of aerial
oars worked by hand. The relative speed was probably about
3 m. an hour, and it was so evident that a very much more
energetic light motor than any then known was required to
stem ordinary winds that nothing more was attempted till
1832, when Henri Giffard (1825-1882) as ascended with a
steam-engine of then unprecedented lightness. The subjoined
table exhibits some of the results subsequently obtained :---
Year. Inventor. Length. Dia- Con- Lifting Weight Weight H.P. Speed
meter. tents. Capa- of of per
city. Ballon. Motor. hour.
Ft. Ft. Cub.ft. lb. lb. lb. Miles
1852 Giffard 144 39 88,300 3,978 2,794 462 3.0 6.71
1872 Dupuy de
Lome 118 49 120,088 8,358 4,728 2000 0.8 6.26
1884 Tissandier 92 30 37,439 2,728 933 616 1.5 7.82
1885 Renard and
Krebs 165 27 65,836 4,402 2,449 1174 9.0 14.00
1897 Schwarz 157 {46 39} 130.500 8,133 6,800 800? 16.0 17.00
1900 Zeppelin I 420 39 400,000 25,000 19,000 1500 32.0 18.00
1901 Santos
Dumont VI. 108 20 22,200 .. .. .. 16.20 19.00
1908 ``Repub-
lique'' 195 35 130,000 3,100 .. .. 80 30
1908 Zeppelin IV 446 42 1/2 450,000 .. .. .. 220 ..
Giffard, the future inventor of the injector, devised a
steam-engine weighing, with fuel and water for one hour,
154 lb. per horse-power, and was bold enough to employ it in
proximity to a balloon inflated with coal gas. He was not
able to stem a medium wind, but attained some deviation.
He repeated the experiment in 1855 with a more elongated
spindle, which proved unstable and dangerous. During the
siege of Paris the French Government decided to build a
navigable balloon, and entrusted the work to the chief naval
constructor, Dupuy de Lome. He went into the subject very
carefully, made estimates of all the strains, resistances and
speeds, and tested the balloon in 1872. Deviations of 12 deg.
were obtained from the course of a wind blowing 27 to 37 m. per
hour. The screw propeller was driven by eight labourers, a
steam-engine being deemed too dangerous; but it was estimated
that had one been used, weighing as much as the men, the
speed would have been doubled. Tissandier and his brother
applied an electric motor, lighter than any previously built,
to a spindle-shaped balloon, and went up twice in 1883 and
1884. On the latter occasion he stemmed a wind of 7 m. per
hour. The brothers abandoned these experiments, which
had been carried on at their own expense, when the French
War Department took up the problem. Renard and Krebs, the
Officers in charge of the War Aeronautical Department at
Heudon, built and experimented with in 1884 and 1885 the
fusiform balloon `` La France,'' in which the `` master''
or maximum section was about one-quarter of the distance
from the stem. The propelling screw was at the front of
the car and driven by an electric motor of unprecedented
lightness. Seven ascents were made on very calm days, a
maximum speed of 14 m. an hour was obtained, and the balloon
returned to its starting-point on five of the seven occasions.
Subsequently another balloon was constructed, said to be
capable of a speed of 22 to 28 m. per hour, with a different
motor. After many years of experi- ment Dr Wolfert built and
experimented with in Berlin, in 1897, a cigar-shaped balloon
driven by a gasoline motor. An explosion took place in the
air, the balloon fell and Dr Wolfert and his assistant were
killed. It was also in 1897 that an aluminium balloon was
built from the designs of D. Schwarz and tested in Bedin.
It was driven by a Daimler benzine motor, and attained a
greater speed than ``La France''; but a driving belt slipped,
and in coming down the balloon was injured beyond repair.
From 1897 onwards Count Ferdinand von Zeppelin, of the German
army, was engaged in constructing an immense balloon, truly an
airship, of most careful and most intelligent design, to carry
five men. It consisted of an aluminium framework containing
sixteen gas bags with a total capacity of nearly 400,000
cub. ft., and it had two cars, each containing a 16 h.p.
motor. It was first tested in June 1900, when it attained
a speed of 18 m. an hour and travelled a distance of 3 1/2
m. before an accident to the steering gear necessitated the
discontinuance of the experiment. In 1905 Zeppelin built
a second airship which had a slightly smaller capacity
but much greater power, its two motors each developing 85
h.p. This, after making some successful trips, was wrecked
in a violent gale, and was succeeded by a third airship,
which, at its trial in October 1906, travelled round Lake
Constance and showed itself able to execute numerous curves and
traverses. At a second series of trials in September 1907,
after some alterations had been effected, it attained a
speed of 36 m. an hour, remaining in the air for many hours
and carrying nine or eleven passengers. A fourth vessel of
similar design, but with more powerful motors, was tried in
1908, and succeeded in travelling 250 m. in 11 hours, but
owing to a storm it was wrecked when on land and burnt at
Echterdingen on the 5th of August. Subscriptions, headed by
the emperor, were at once raised to enable Zeppelin to build
another. Meanwhile in 1901 Alberto Santos Dumont had begun
experiments with dirigible balloons in Paris, and on the 19th
of October won the Deutsch prize by steering a balloon from
St Cloud round the Eiffel tower and back in half an hour,
encountering on his return journey a wind of nearly 5 metres a
second. An airship constructed by Pierre and Paul Lebaudy in
1904 also made a number of successful trials in the vicinity
of Paris; with a motor of 40 h.p., its speed was about 25 m. an
hour, and it regularly carried three passengers. In October
1907 the ``Nulli Secundus,'' an airship constructed for the
British War Office, sailed from Farnborough round St Paul's
Cathedral, London, to the Crystal Palace, Sydenham, a distance
of about 50 m., in 3 hours 35 minutes. The weight carried,
including two occupants, was 3400 lb., and the maximum speed
was 24 m. an hour, with a following wind of 8 m. an hour.
Thus the principles which govern the design of the dirigible
balloon may be said to have been evolved. As the lifting
power crows as the cube of the dimensions, and the resistance
approximately as the square, the advantage lies with the
larger sizes of balloons, as of ocean steamers, up to the
limits within which they may be found practicable. Count
Zeppelin gained an advantage by attaching his propellers
to the balloon, instead of to the car as heretofore; but
this requires a rigid framework and a great increase of
weight. Le Compagnon endeavoured, in 1892, to substitute
flapping wings for rotary propellers, as the former can
be suspended near the centre of resistance. C. Danilewsky
followed him in 1898 and 1899, but without remarkable
results. Dupuy de Lome was the first to estimate in detail
the resistances to balloon propulsion, but experiment showed
that in the aggregate they were greater than he calculated.
Renard and Krebs also found that their computed resistances
were largely exceeded, and after revising the results they
gave the formula R=0.01685 D2V2, R being the resistance in
kilograms, D the diameter in metres and V the velocity in
metres per second. Reduced to British measures, in pounds,
feet and miles per hour, R=0.0006876 D2V2, which is somewhat
in excess of the formula computed by Dr William Pole from
Dupuy de Lome's experiments. The above coefficient applies
only to the shape and rigging of the balloon ``La France,''
and combines all resistances into one equivalent, which is
equal to that of a flat plane 18% of the ``master section.''
This coefficient may perhaps hereafter be reduced by one-half
through a better form of hull and car, more like a fish than a
spindle, by diminished sections of suspension lines and net,
and by placing the propeller at the centre of resistance.
To compute the results to be expected from new projects, it
will be preferable to estimate the resistances in detail. The
following table shows how this was done by Dupuy de Lome, and
the probable corrections which should have been made by him:--
RESISTANCES--DUPUY DE LOME'S BALLOON
Computed by Dupuy de Lome. More Probable Values.
V = 2.22 m. per sec. V = 2.82 m. per sec.
Area Coeffici- Air Resist- Coeffici- Air Resist-
Part. Sq. ent. Pres- ance, ent. Pres- ance,
Metres sure. Kg. sure Kg.
Hull,
without net 172.96 1/30 0.665 3.830 1/15 0.875 10.091
Car 3.25 1/5 ,, 0.432 1/5 ,, 0.569
Men's bodies 3.00 1/5 ,, 0.400 1/5 ,, 1.312
Gas tubes 6.40 1/5 ,, 0.850 1/2 ,, 2.750
Small cords 10.00 1/2 ,, 3.325 1/2 ,, 4.375
Large cords 9.90 1/3 ,, 2.194 1/3 ,, 2.887
11.031 21.984
When the resistances have been reduced to the lowest minimum
by careful design, the attainable speed must depend upon the
efficiency of the propeller and the relative lightness of the
motor. The commercial uses of dirigible balloons, however,
will be small, as they must remain housed when the wind aloft is
brisk. The sizes will be great and costly, the loads small,
and the craft frail and short-lived, yet dirigible balloons
constitute the obvious type for governments to evolve,
until they are superseded by efficient flying machines. (See
further, as to the latter, the article FLIGHT AND FLYING.)
Practice of aerostation.
The chief danger attending ballooning lles in the descent; for
if a strong wind be blowing, the grapnel will sometimes trail
