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Dirigible Balloons
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        :PG.Title: Dirigible Balloons
        :PG.Id: 63234
        :PG.Rights: Public Domain
        :PG.Producer: James Simmons
        :PG.Credits: This file was produced from page images at the Internet Archive.
        :DC.Creator: Charles B. Hayward
        :DC.Title: Dirigible Balloons
        :DC.Language: en
        :DC.Created: 1918
        :PG.Released: 2020-09-18
        :coverpage: images/CoverImage.jpg

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.. topic:: Transcriber's Note

    This book was transcribed from scans of the original found at the Internet Archive. 
    I have rotated some images. The caption for Figure 20 was illegible in the scanned
    pages so I used a description from a paragraph that referred to it.

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       DIRIGIBLE BALLOONS 
       
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       INSTRUCTION PAPER 
       
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       PREPARED BY 
 
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       CHARLES B. HAYWARD 

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       MEMBER, SOCIETY OF AUTOMOBILE ENGINEERS; MEMBER, THE AERONAUTICAL SOCIETY; 
       
       FORMERLY SECRETARY, SOCIETY OF AUTOMOBILE ENGINEERS; FORMERLY 

       ENGINEERING EDITOR, "THE AUTOMOBILE" 


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       AMERICAN SCHOOL OF CORRESPONDENCE 
       
       CHICAGO ILLINOIS 
       
       \U.S.A. 


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    COPYRIGHT, 1912, 1918, BY 

    AMERICAN SCHOOL OF CORRESPONDENCE 

    COPYRIGHTED IN GREAT BRITAIN 
    
    ALL RIGHTS RESERVED 

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DIRIGIBLE BALLOONS
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INTRODUCTION
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Of the first attempts of men to emulate the flight of birds, we 
have no knowledge, but one of the earliest, perhaps, is embodied 
in the myth of Icarus and Daedalus. Xerxes, it is said, possessed 
a throne which was drawn through the air by eagles. The Chinese 
have sometimes been given credit for the invention of the balloon, 
as they have for many other scientific discoveries. It is related that 
a balloon was sent up at Pekin in 
celebration of the ascension of the 
throne by an emperor in the 
beginning of the fourteenth century. 

.. figure:: images/Image1.jpg
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   :alt: Fig. 1. De Lana Airboat.
   
   Fig. 1. De Lana Airboat.

**Early Attempts.** Leonardo da 
Vinci devoted some time to the 
problem of artificial flight. His 
sketches show the details of 
batlike wings which were to spread 
out on the downward stroke and 
fold up with the upward stroke. 

Francisco de Lana planned to make 
a flying ship the appearance of which 
was somewhat like that shown in 
Fig. 1, by exhausting the air from 
metal spheres fastened to a boat. The boat was to be equipped  
with oars and sails for propulsion and guiding. The method in which 
he purposed to create the vacuum in the spheres consisted of filling 
them with water, thus driving out the air, then letting the water run 
out. He thought that if he closed the tap at the proper time, there 
would be neither air nor water in the spheres. His flying ship was 
never constructed, for he piously decided that God would never 
permit such a change in the affairs of men. 

**The First Flying Machine.** In 1781, Meerwein of Baden, 
Germany, constructed a flying machine, and was the first, perhaps, 
to intelligently take into account the resistance of the air. He took 
the wild duck as a basis of calculation, and found that a man and 
machine weighing together 200 pounds would require a wing surface 
of from 125 to 130 square feet. It is of interest to note that Lilienthal, 
who met his death in trying to apply these principles, over one 
hundred years later found these figures to be correct. Two views of 
Meerwein’s apparatus are shown in Fig. 2. The construction involved 
two wood frames covered with cloth. The machine weighed 56 
pounds and had a surface area of 111 square feet. The operator 
was fastened in the middle of the under side of the wings, and over 
a rod by which he worked the wings. His attempts at flight were 
not successful, as his ideas of the power of a man were in error. 

.. figure:: images/Image2.jpg
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   :alt: Fig. 2. Meerwein Flying Machine 
   
   Fig. 2. Meerwein Flying Machine 

**Classification.** All attempts at human flight have gone to 
show that there are four possible ways in which man may hope to 
navigate the air. He may imitate the flight of birds with a machine 
with moving or flapping wings; he may use vertical screws or helices 
to pull himself up; he may use an aeroplane and sail the air like an 
eagle; or, lastly, he may raise himself by means of a gas bag and 
either drift with the wind or move forward by means of propellers. 

In these attempts, apparatus of several different types has been 
developed. The types are classed in two general divisions based 
on their weight relative to that of the atmosphere, viz, the 
*lighter-than-air machines* and the *heavier-than-air machines*. 
Lighter-than-air machines are those which employ a bag filled with a gas whose 
specific gravity is sufficiently less than that of the air to lift the bag 
and the necessary attachments from the earth, and include simple 
balloons and dirigibles. Heavier-than-air machines, which will 
neither rise nor remain in the air without motive power, include all 
forms of aeroplanes. 

SIMPLE BALLOONS
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**Theory.** The balloon-like airship has been more highly developed 
than any other type of aerial craft, probably because it offers the 
most obvious means of overcoming the force of gravitation. It 
depends on the law of Archimedes: 

*"Every body which is immersed in a fluid is acted upon by an 
upward force, exactly equal to the weight of the fluid displaced by the 
immersed body."*

That is, a body will be at rest if immersed in a fluid of equal 
specific gravity or equal weight, volume for volume; if the body has 
less specific gravity than the fluid in which it is immersed it will 
rise; if it has a greater specific gravity it will sink. Therefore, if 
the total weight of a balloon is less than the weight of all the air it 
displaces it will rise in the air. It is, then, necessary to fill the balloon 
with some gas whose specific gravity is enough less than, that of the 
air to make the weight of the gas itself, the bags, and the 
attachments, less than the weight of the air displaced by the whole 
apparatus. The gases usually employed are *hydrogen*, *coal gas*, and *hot 
air*. 

At atmospheric pressure and freezing temperature, the weight 
of a cubic foot of air is about .08 pound; the weight of a cubic foot 
of hydrogen is about .005 pound, under the same conditions. 
According to the law of Archimedes, a cubic foot of hydrogen would be 
acted upon by a force equal to the difference, or approximately .075 
pound, tending to move it upwards. In the same way, a cubic foot 
of coal gas, which weighs .04 pound, would be acted upon by an 
upward force of .04 pound. 

It is evident, then, that a considerable volume of gas is required 
to lift a balloon with its envelope, net, car, and other attachments. 

Further, it requires almost twice as much coal gas as hydrogen, 
under the same conditions, for we have seen that the upward force 
on it is only half as great. The lifting power of hot air is less than 
one-eighth as great as that of hydrogen at the highest temperature 
that can possibly be used in a 
balloon. 

.. figure:: images/Image3.jpg
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   :alt: Fig. 3. Montgolfier Balloon 
   
   Fig. 3. Montgolfier Balloon 

The general type of lighter-than-air machines may be divided 
into *aerostats* (ordinary balloons, 
which are entirely dependent on 
wind currents for lateral 
movement, and which are often the 
chief features at country fairs) 
and dirigible balloons or *aeronats* 
(air swimmers). Dirigible 
balloons employ the gas bag for 
maintaining buoyancy, and have 
rudders to guide them and 
propellers to drive them forward 
through the air in much the 
same way that ships are driven 
through the water. 

**The First Balloon.** For several 
years, Joseph and Steven 
Montgolfier had been experimenting 
with a view to constructing a 
balloon: in the first place by filling 
bags with *steam*; then by filling 
bags with *smoke*, and finally by 
filling bags with *hydrogen*. These attempts were all failures, for the 
steam rapidly condensed and the smoke and hydrogen leaked through 
the pores in the bags. They finally hit upon the idea of filling the 
bag with *hot air*, by means of a fire under its open mouth. Several 
balloons were burned up, but the next was always made larger, until, 
at their first public exhibition on June 5, 1783, the bag had become 
over 35 feet in diameter. On this occasion, it rose to a height of 
between 900 and 1,000 feet, but the hot air was gradually escaping, 
and at the end of ten minutes the balloon fell to the ground. 

The Montgolfiers then went to Paris, where, after suffering 
the loss of a paper balloon by rain, they sent up a waterproofed linen 
one carrying a sheep, a duck, and a rooster in a basket. A rupture in 
the linen caused the three unwilling aeronauts to make a landing 
at the end of about ten minutes. The Montgolfiers received great 
honor, and small balloons of this type became a popular fad. One 
of these balloons is shown in Fig. 3, making an ascension. 

**Rozier.** The first man to go up in a balloon was Rozier, who 
ascended in a captive balloon to a height of about 80 feet, in the 
latter part of the year 1783. Later, in 
company with a companion, he made a 
voyage in a free balloon, remaining in the 
air about half an hour. In these balloons, 
the air within was kept hot by means of 
a fire carried in a pan immediately below 
the mouth of the bag, as shown in Fig. 4. 
Accidents were numerous on account of 
the fabric becoming ignited from the fire 
in the pan. 

.. figure:: images/Image4.jpg
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   :alt: Fig. 4. Rozier Hot-Air Balloon 
   
   Fig. 4. Rozier Hot-Air Balloon 

**Improvements by Charles.** The 
physicist, Charles, was working along these lines 
at the same time. He coated his balloon 
with a rubber solution to close up the 
pores, and was thereby enabled to 
substitute hydrogen for the hot air. Shortly 
after the Montgolfiers’ first public 
exhibition, Charles sent up his balloon for the benefit of the *Academie des 
Sciences* in Paris. The balloon, which weighed about 19 pounds, 
ascended rapidly in the air and disappeared in the clouds, where it 
burst and fell in a suburb of the city. The impression produced upon 
the peasants at seeing it fall from the heavens was hardly different 
from what could be expected. They believed it to be of devilish 
origin, and immediately tore it into shreds. Charles subsequently built a 
large balloon quite similar to those in use today. A net was used to 
support the basket, and a valve, operated by means of ropes from the 
basket, was arranged at the top to permit the gas to escape as desired. 

**The Balloon Successful.** The English Channel was first crossed 
in 1785. Blanchard, an Englishman, and Jeffries, an American, 
started from Dover on January 7 in a balloon equipped with wings 
and oars. After a very hazardous voyage, during which they had 
to cast overboard everything movable to keep from drowning, they 
landed in triumph on the French coast. 

An attempt to duplicate this feat was made shortly afterward by 
Rozier. He constructed a balloon filled with hydrogen, below which 
hung a receiver in which air could be heated. He hoped to replace 
by the hot air the losses due to leakage of hydrogen. Soon after the 
start the balloon exploded, due to the escaping gas reaching the fire, 
and Rozier and his companion were dashed on the cliffs and killed. 

EARLY DIRIGIBLES
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**Meusnier the Pioneer.** The fact that the invention of the 
dirigible balloon and means of navigating it were almost 
simultaneous is very little known today and much less appreciated. Like 
the aeroplane, its development was very much retarded by the lack 
of suitable means of propulsion, and the actual history of what has 
been accomplished in this field dates back only to the initial circular 
flight of La France in 1885. Still the principles upon which success 
has been achieved were laid down within a year of the appearance 
of Montgolfier’s first gas bag. Lieutenant Meusnier, who 
subsequently became a general in the French army, must really be credited 
with being the true inventor of aerial navigation. At a time when 
nothing whatever was known of the science, Meusnier had the 
distinction of elaborating at one stroke all the laws governing the 
stability of an airship, and calculating correctly the conditions of 
equilibrium for an elongated balloon, after having strikingly 
demonstrated the necessity for this elongation. This was in 1781 and 
Meusnier’s designs and calculations are still preserved in the engineering 
section of the French War Office in the form of drawings and tables. 

But as often proved to be the case in other fields of research, 
his efforts went unheeded. How marvelous the establishment of 
these numerous principles by one man in a short time really is, can 
be appreciated only by noting the painfully slow process that has 
been necessary to again determine them, one by one, at considerable 
intervals and after numerous failures. Through not following the 
lines which he laid down, aerial navigation lost a century in futile 
groping about; in experiments absolutely without method or sequence. 

.. figure:: images/Image5.jpg
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   :alt: Fig. 5. Meusnier Dirigible Balloon 
   
   Fig. 5. Meusnier Dirigible Balloon 

Meusnier’s designs covered two dirigible balloons and that he 
fully appreciated the necessity for size is shown by the dimensions 
of the larger, which unfortunately was never built. This was to be 
260 feet long by 130 feet in diameter, in the form of an ellipse, the 
elongation being exactly twice the diameter. In other words, a perfect 
ellipsoid, which was a logical and, in fact, the most perfect 
development of the spherical form. Although increased knowledge of wind 
resistance and the importance of the part it plays has proved his 
relative dimensions to be faulty, a study of the principal features 
of his machine shows that he anticipated the present-day dirigible 
of the most successful type at practically every point, barring, of 
course, the motive power, as there was absolutely nothing available 
in that day except human effort. As the latter weighs more than 
one-half ton per horse-power, it goes without saying that Meusnier’s 
balloon would have been dirigible only in a dead calm. 

He adopted the elongated form, conceived the girth fastening, 
the triangular or indeformable suspension, the air balloonet and its 
pumps, and the screw propeller, all of which are to be found in the 
dirigibles of present-day French construction, Fig. 5. It need scarcely 
be added that the French have not only devoted a greater amount 
of time and effort to the development of the dirigible than any other 
nation, but have also met with the greatest success in its use. It 
was not until 1886, or more than a century after Meusnier had first 
elaborated those principles, that their value became known. They 
were set forth by Lieutenant Letourne, of the French engineers, in 
a paper presented to the *Academie des Sciences* by General Perrier. 

In one form or another, the salient features of Meusnier’s 
dirigible will be found embodied in the majority of attempts of later 
days. His large airship was designed to consist of double envelope, 
the outer container of which was to provide the strength necessary, 
and it was accordingly reinforced by bands. The inner envelope was 
to provide the container for the gas and was not called upon to 
support any weight. This inner bag or balloon proper was designed 
to be only partially inflated and the space between, the two was to be 
occupied by air which could be forced into it at two points at either 
end, by pumps, so as to maintain the pressure on the gas bag uniform 
regardless of the expansion or contraction of its contents. Here in 
principle was the air balloonet of today. Instead of employing a net 
to hang the car from the outer envelope, the former was attached 
by means of a triangular suspension system fastened to a heavy rope 
band, or girth, encircling the outer envelope. At the three points 
where the lifting rope members met, a shaft running the length of 
the car and carrying what Meusnier described as "revolving oars" 
was installed. These constituted the prototype of the screw 
propeller, invented for aerial navigation at a time long antedating the 
use of steam for marine use. Thus he devised: (1) The air balloonet 
to husband the gas supply and thus prevent the deformation of the 
outer container or support, as well as to provide stability; (2) the 
triangular suspension to attain longitudinal stability; and (3) the 
screw propeller for propulsion, beside selecting the proper location 
for the latter. 

PROBLEMS OF THE DIRIGIBLE
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**Ability to Float.** If ability to rise in the air depended merely 
upon a knowledge of the principle that made it possible, it 
undoubtedly would have been accomplished many centuries ago. As already 
mentioned, Archimedes established the fact that a body upon 
floating in a fluid displaces an amount of the latter equal in weight to 
the body itself, and upon this theory was formulated the now 
well-known law, that every body plunged into a fluid is subjected by this 
fluid to a pressure from below, equivalent to the weight of the fluid 
displaced by the body. Consequently, if the weight of the latter 
be less than that of the fluid it displaces, the body will float. It is 
by reason of this that the iron ship floats and the fish swims in water. 
If the weight of the body and the displaced water be the same, the 
body will remain in equilibrium in the water at a certain level, and 
if that of the body be greater, it will sink. All three of these factors 
are found in the fish, which, with the aid of its natatory gland, can 
rise to the surface, sink to the bottom, or remain suspended at 
different levels. To accomplish these changes of specific gravity, the fish 
fills this gland with air, dilating it until full, or compressing and 
emptying it. In this we find a perfect analogy to the air balloonet 
of the dirigible, which serves the same purposes. The method by 
which lifting power is obtained in the dirigible is exactly the same 
as in the case of the balloon. 

But once in the air, a balloon is, to all intents and purposes, 
a part of the atmosphere. There is absolutely no sensation of 
movement, either vertically or horizontally. The earth appears to drop 
away from beneath and to sweep by horizontally, and regardless of 
how violently the wind may be blowing, the balloon is always in a 
dead calm because it is really part of the wind itself and is traveling 
with it at exactly the same speed. If it were not for the loss of 
lifting power through the expansion and contraction of the gas, making 
it necessary to permit its escape in order to avoid rising to 
inconvenient heights on a very warm day, and the sacrifice of ballast to 
prevent coming to earth at night, the ability of a balloon to stay up 
would be limited only by the endurance of its crew and the quantity 
of provisions it was able to transport. As the use of air balloonets 
in the dirigible takes care of this, the question of lifting power presents 
no particular difficulty. It is only a matter of providing sufficient 
gas to support the increased weight of the car, motor and its 
accessories, and the crew of the larger vessel, with a factor of safety to 
allow for emergencies, in order to permit of staying in the air long 
enough to make a protracted voyage. 

**Air Resistance vs. Speed.** Unless a voyage is to be governed 
in its direction entirely by the wind, the dirigible must possess a 
means of moving contrary to the latter. The moment this is 
attempted, resistance is encountered, and it is this resistance of the 
air that is responsible for the chief difficulties in the design of the 
dirigible. To drive it against the wind, it must have power; to 
support the weight of the motor necessary, the size of the gas bag must 
be increased. But with the increase in size, the amount of resistance 
is greatly multiplied and the power to force it through the air must 
be increased correspondingly. The law is approximately as follows: 

*Where the surface moves in a line perpendicular to its plane, the 
resistance is proportional to the extent of the surface, to the square of 
the speed with which the surface is moved through the air, and to a 
coefficient, the mean value of which is 0.125.* 

This coefficient is a doubtful factor, the figure given having been 
worked out years ago in connection with the propulsion of sailing 
vessels. Its value varies according to later experimenters between 
.08 and .16, the mean of the more recent investigations of Renard, 
Eiffel, and others who have devoted considerable study to the matter, 
being .08. This is dwelt upon more in detail under "Aerodynamics" 
and it will be noted that the values of the coefficient *K*, given here, 
do not agree with those stated in that article. They serve, 
however, to illustrate the principles in question. 

In accordance with this law, doubling the speed means 
quadrupling the resistance of the air. For instance, a surface of 16 square 
feet moving directly against the air at a speed of 10 feet per second 
will encounter a resistance of 16 X 100 (square of the speed) X 0.125 
= 200 pounds pressure. Doubling the speed, thus bringing it up 
to 20 feet per second, would give the equation 16 X 400 X 0.125 = 800 
pounds pressure, or with the more recent value of the coefficient 
of .08, 512 pounds pressure. The first consideration is 
accordingly to reduce the amount of surface moving at right angles. The 
resistance of a surface having tapering sides which cut through or 
divide the molecules of air instead of allowing them to impinge 
directly upon it, is greatly diminished; hence, Meusnier’s principle 
of elongation. If we take the same panel presenting 16 square feet 
of surface and build out on it a hemisphere, its resistance at a speed 
of 10 feet per second will be exactly half, or a pressure of 100 pounds. 

By further modifying this so as to represent a sharp point, or 
acute-angled cone, it will be 38 pounds. There could accordingly be no 
question of attempting 
to propel a spherical 
balloon. 

.. figure:: images/Image6.jpg
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   :alt: Fig. 6. Giffard Dirigible 
   
   Fig. 6. Giffard Dirigible 

It is necessary to 
select a form that 
presents as small a surface 
as possible to the air as 
the balloon advances, 
while preserving the 
maximum lifting power. But 
experience has strikingly 
demonstrated the analogy between marine and aerial practice—not 
only is the shape of the bow of the vessel of great importance but, 
likewise, the stern. The profile of the latter may permit of an easy 
reunion of the molecules of air separated by the former, or it may 
allow them to come together again suddenly, clashing with one 
another and producing disturbing eddies just behind the moving body. 
To carry the comparison with a marine vessel a bit further, the form 
must be such as to give an easy "shear," or sweep from stem to 
stern. 

.. figure:: images/Image7.jpg
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   :alt: Fig. 7. De Lome Dirigible 
   
   Fig. 7. De Lome Dirigible 

That early investigators appreciated this is 
shown by the fact that 
Giffard in 1852, Fig. 6, 
De Lome in 1872, Fig. 7, 
Tissandier in 1884, and 
Santos-Dumont in his 
numerous attempts, 
adopted a spindle-shaped 
or "fusiform" balloon. In 
other words, their shape, 
equally pointed at either 
end, was symmetrical in 
relation to their central plan. However, that the shape best 
adapted to the requirements of the bow did not serve equally well 
for the stern, was demonstrated for the first time by Renard, to 
whom credit must be given for a very large part of the scientific 
development of the dirigible. Almost a century earlier, 
Marey-Monge had laid down the principle that to be successfully 
propelled through the air, the balloon must have "the head of a cod 
and the tail of a mackerel." Nature exemplifies the truth of this 
in all swiftly moving fishes and birds. Renard accordingly adopted 
what may best be termed the "pisciform" type, viz, that of a 
dis-symmetrical fish with the larger end serving as the bow; and the 
performances of the Renard, Lebaudy, and Clement-Bayard airships 
have shown that this is the most advantageous form. 

The pointed stern prevents the formation of eddies and the 
creation of a partial vacuum in the wake which would impose 
additional thrust on the bow. Zeppelin has disregarded this factor by 
adhering to the purely cylindrical form with short hemispherical 
bow and stern, but it is to be noted that while other German 
investigators originally followed this precedent, they have gradually 
abandoned it, owing to the noticeable retarding effect. 

**Critical Size of Bag.** Next in importance to the best form to 
be given the vessel, is the most effective size—something which has 
a direct bearing upon its lifting power. This depends upon the 
volume, while the resistance is proportional to the amount of 
surface presented. Greater lifting power can accordingly be obtained 
by keeping the diameter down and increasing the length. But the 
resistance is also proportionate to the square of the speed, while 
the volume, or lifting power, varies as the cube of the dimensions 
of the container, so that in doubling the latter, the resistance of the 
vessel at a certain speed is increased only four times while its lifting 
capacity is increased eight times. Consequently the larger dirigible 
is very much more efficient than the smaller one since it can carry 
so much more weight in the form of a motor and fuel in proportion 
to its resistance to the air. As an illustration of this, assume a 
rectangular container with square ends 1 foot each way and 5 feet long. 
Its volume will be 5 cubic feet and if the lifting power of the gas be 
assumed as 2 pounds per cubic foot, its total lifting power will be 5 
pounds. If a motor weighing exactly 5 pounds per horse-power 
be assumed, it will be evident that the motor which such a balloon 
could carry would be limited to 1 horse-power, neglecting the weight 
of the container. 

Double these dimensions and the container will then measure 
2 X 2 X 10 feet, giving a volume of 40 cubic feet, and a lifting power, on 
the basis already assumed, of a motor capable of producing 8 
horsepower, and this without taking into consideration that as the size 
of the motor increases, its weight per horse-power decreases. The 
balloon of twice the size will thus have a motor of 8 horse-power to 
overcome the resistance of the head-on surface of 4 square feet, or 
2 horse-power per square foot of transverse section, whereas the 
balloon of half the size will have only 1 horse-power per square foot 
of transverse section. It is, accordingly, not practicable to construct 
small dirigibles such as the various airships built by Santos-Dumont 
for his experiments, while, on the other hand, there are numerous 
limitations that will be obvious, restricting an increase in size beyond 
a certain point, as has been shown by the experience of the various 
Zeppelin airships. 

To make it serviceable, what Berget terms the "independent 
speed" of a dirigible, i.e., its power to move itself against the wind, 
must be sufficient to enable it to travel under normally prevailing 
atmospheric conditions. These naturally differ greatly in different 
countries and in different parts of the same country. Where 
meteorological tables showed the prevailing winds in a certain district 
to exceed 15 miles an hour throughout a large part of the year, it 
would be useless to construct an airship with a speed of 15 miles 
an hour or less for use in that particular district, as the number 
of days in the year in which one could travel to and from a certain 
starting point would be limited. This introduces another factor 
which has a vital bearing upon the size of the vessel. Refer to the 
figures just cited and assume further that by doubling the dimensions 
and making the airship capable of transporting a motor of 8 
horse-power, it has a speed of 10 miles an hour. It is desired to double this. 
But the resistance of the surface presented increases as the square of 
the speed. Hence, it will not avail merely to double the power of 
the motor. Experience has demonstrated that the power necessary 
to increase the speed of the same body, increases in proportion to 
the cube of the speed, so that instead of a 16-horse-power motor in the 
case mentioned, one of 64 horse-power would be needed. There are, 
accordingly, a number of elements that must be taken into 
consideration when determining the size as well as the shape of the balloon. 

**Static Equilibrium.** Having settled upon the size and shape, 
there must be an appropriate means of attaching the car to carry 
the power plant, its accessories and control, and the crew. While 
apparently a simple matter, this involves one of the most important 
elements of the design—that of stability. A long envelope of 
comparatively small diameter being necessary for the reasons given, 
it is essential that this be maintained with its axis horizontal. In 
calm air, the balloon, or container, is subjected to the action of 
two forces: One is its weight, applied to the center of gravity of 
the system formed by the balloon, its car, and all the supports; 
the other is the thrust of the air, applied at a point known as the 
center of thrust and which will differ with different designs, 
according as the car is suspended nearer or farther away from the balloon. 
If the latter contained only the gas used to inflate it, with no car 
or other weight to carry, the center of gravity and the center of 
thrust would coincide, granting that the weight of the envelope were 
negligible. As this naturally can not be the case, these forces are 
not a continuation of each other. But as they must necessarily be 
equal if the balloon is neither ascending nor descending, it follows 
that they will cause the balloon to turn until they are a 
continuation of each other, and in the case of a pisciform balloon, this will 
cause it to tilt downward. Like a ship with too much cargo 
forward, it would be what sailors term "down at the head." 

As this would be neither convenient nor compatible with rapid 
propulsion, it must be avoided by distributing the weight along the 
car in such a manner that when the balloon is horizontal, the forces 
represented by the pressure above and the weight below, must be in 
the same perpendicular. This is necessary to insure static equilibrium, 
or a horizontal position while in a state of rest. To bring this about, 
the connections between the car and the balloon must always 
maintain the same relative position, which is further complicated by the 
fact that they must be flexible at the same time. 

**Longitudinal Stability.** But the *longitudinal stability* of the 
airship as a whole must be preserved, and this also involves its 
*stability of direction*. Its axis must be a tangent to the course it 
describes, if the latter be curvilinear, Or parallel with the direction 
of this course where the course itself is straight. This is apparently 
something which should be taken care of by the rudder, any 
tendency on the part of the airship to diverge from its course being 
corrected by the pilot. But a boat that needed constant attention to 
the helm to keep it on its course would be put down as a 
"cranky"—in other words, of faulty design in the hull. A dirigible having 
the same defect would be difficult to navigate, as the rudder alone 
would not suffice to correct this tendency in emergencies. Stability 
of direction is, accordingly, provided for in the design of the balloon 
itself, and this is the chief reason for adopting the form of a 
large-headed and slender-bodied fish, as already outlined. This brings 
the center of gravity forward and makes of the long tail an effective 
lever which overcomes any tendency of the ship to diverge from the 
course it should follow, by causing the resistance of the air itself to 
bring it back into line. However, the envelope of the balloon itself 
would not suffice for this, so just astern of the latter, "stabilizing 
surfaces" are placed, consisting of vertical planes fixed to the envelope. 
These form the keel of the dirigible and are analogous to the keel of 
the ship. Stability of direction is thus obtained naturally without 
having constant recourse to the rudder, which is employed only 
to alter the direction of travel. 

The comparison between marine and aerial navigation must be 
carried even further. These vertical planes, or "keel," prevent 
rolling; it is equally necessary to avoid pitching—far more so than 
in the case of a vessel in water. So that while the question of 
stability of direction is intimately connected with longitudinal stability, 
other means are required to insure the latter. The airship must 
travel on an "even keel," except when ascending or descending, 
and the latter must be closely under the control of the pilot, as 
otherwise the balloon may incline at a dangerous angle. This shows 
the importance of an unvarying connection between the car and the 
envelope to avoid defective longitudinal stability. Assume, for 
instance, that the car is merely attached at each end of a single 
line. The car, the horizontal axis of the balloon, and the two 
supports would then form a rectangle. When in a state of equilibrium 
the weight and the thrust are acting in the same line. Now suppose 
that the pilot desires to descend and inclines the ship downward. 
The center of gravity is then shifted farther forward and the two 
forces are no longer in line. 

But as the connections permit the car to swing in a vertical 
plane, they permit the latter to move forward and parallel with the 
balloon, thus forming a parallelogram instead of a rectangle. This 
causes the center of gravity to shift even farther, and as one of the 
most serious causes of longitudinal stability is the movement of the 
gas itself, it would also rush to the back end and cause the balloon 
to "stand on its head." As the tendency of the gas is thus to 
augment any inclination accidentally produced, the vital necessity of 
providing a suspension that is incapable of displacement with 
relation to the balloon is evident. Here is where the importance of 
Meusnier’s conception of the principle of triangular suspension comes in. 
Instead of being merely supported by direct vertical connections 
with the balloon, the ends of the car are also attached to the 
opposite ends of the envelope, forming opposite triangles. This gives 
an unvarying attachment, so that when the balloon inclines, the car 
maintains its relative position, and the weight and thrust tend to pull 
each other back in the same line, or, in other words, to "trim ship."
 
**Dynamic Equilibrium.** In addition to being able to preserve 
its static equilibrium and to possess proper longitudinal stability, 
the successful airship must also maintain its dynamic 
equilibrium—the equilibrium of the airship in motion. This may be made clear 
by referring to the well-known expedients adopted to navigate 
the ordinary spherical balloon. To rise, its weight is diminished by 
gradually pouring sand from the bags which are always carried as 
ballast. To descend, it is necessary to increase the total weight of 
the balloon and its car, and the only method of accomplishing this 
is to permit the escape of some of the gas, the specific lightness 
of which constitutes the lifting power of the balloon. As the gas 
escapes, the thrust of the air on the balloon is decreased and it 
sinks—the ascensional effort diminishing in proportion to the 
amount of gas that is lost. The balloon, or the container itself, 
being merely a spherical bag, on the upper hemispherical half of 
which the net supporting the car presses at all points, the question 
of deformation is not a serious one. Before it assumed 
proportions where the bag might be in danger of collapsing, the balloon 
would have had to come to earth through lack of lifting power 
to longer sustain it. Owing to its far greater size, as well as to the 
form of the surface which it presents to the air pressure, such a crude 
method is naturally not applicable to the dirigible. 

Dynamic equilibrium must take into account not only its weight 
and the sustaining pressure of the air, but also the resistance of the 
air exerted upon its envelope. This resistance depends upon the 
dimensions and the shape of that envelope, and in calculations the 
latter is always assumed to be invariable. Assume, for instance, 
that to descend the pilot of a dirigible allowed some of the hydrogen 
gas to escape. As the airship came down, it would have to pass 
through strata of air of constantly increasing pressure as the earth 
is approached. The reason for this will be apparent as the lower 
strata bear the weight of the entire atmosphere above them. The 
confined gas will no longer be sufficient to distend the envelope, 
the latter losing its shape and becoming flabby. As the original 
form is no longer retained, the center of resistance of the air will 
likewise have changed together with the center of thrust, and the 
initial conditions will no longer obtain. But as the equilibrium of 
the airship depends upon the maintenance of these conditions, it 
will be lost if they vary. 

**Function of Balloonets.** In the function of balloonets is realized 
the importance of the principle established by Meusnier. It was 
almost a century later before it was rediscovered by Dupuy de Lome 
in connection with his attempts to make balloons dirigible. That 
the balloon must always be maintained in a state of perfect 
inflation has been pointed out. But gas is lost in descents and to a 
certain extent, through the permeability of the envelope. Unless 
it is replaced, the balloon will be only partially inflated. In view 
of the great volume necessary, it requires no explanation to show 
that it would be impossible to replace the gas itself by fresh hydrogen 
carried on the car. It would have to be under high pressure and 
the weight of the steel cylinders as well as the number necessary to 
transport a sufficient supply would be prohibitive. Hence, 
Meusnier conceived the idea of employing air. But this could not be 
pumped directly into the balloon to mix with the hydrogen gas, 
as the resulting mixture would not only still be as inflammable as 
the former alone, but it would also contain sufficient oxygen to 
create a very powerful and infinitely more dangerous explosive. 
This led to the adoption of the *air balloonet*. 

In principle the balloonet consists of dividing the interior of the 
envelope into two cells, the larger of which receives the light gas 
while the smaller is intended to hold air and terminates in a tube 
extending down to a pump in the car. In other words, a fabric 
partition adjacent to the lower part of the envelope inside and 
subject to deformation at will. In actual practice it consists of a 
number of independent cells of this kind, longitudinally disposed along 
the lower half of the interior of the envelope. 

When the balloon is completely inflated with hydrogen, as at 
the beginning of an ascent, these balloonets lie flat against the lower 
part of the envelope, exactly like a lining. As the airship rises, the 
gas expands owing to the reduction in atmospheric pressure at a 
higher altitude, as well as to the influence of heat. With the increase 
in pressure, uniform inflation is maintained by the escape of a 
certain amount of gas through the automatic valves provided for the 
purpose. Unless this took place, the internal pressure might assume 
proportions placing the balloon in danger of blowing up. To avoid 
this, a pressure gauge communicating with the gas compartment 
is one of the most important instruments on the control board of 
the car, and should its reading indicate a failure of the automatic 
valves, the pilot must reduce the pressure by operating a hand 
valve. But as the car descends, the increased external pressure 
causes a recontraction of the gas until it no longer suffices to fill the 
envelope. To replace the loss the air pumps are utilized to force 
air into the air balloonets until the sum of the volumes of gas and 
air in the different compartments equals the original volume. In 
this manner, the initial conditions, upon which the equilibrium of 
the airship is based, are always maintained. 

This is not the only method of correcting for change in volume, 
nor of maintaining the longitudinal stability of the whole fabric, 
the importance of which has already been detailed, but experience 
has shown that it is the most practical. It is possible to give the 
balloon a rigid frame over which the envelope is stretched and to 
attach the car by means of a rigid metal suspension, as in the various 
Zeppelin airships, or to take it semi-rigid, as in the Gross, another 
German type in which Zeppelin’s precedent was followed only in 
the case of the suspension. To prevent deformation by this means, 
the balloon is provided with an absolutely rigid skeleton of aluminum 
tubes. This framing is in the shape of a number of uniform 
cylindrical sections, or gas compartments, each one of which 
accommodates an independent balloon, while over the entire frame a very 
strong but light fabric constituting the outer or protecting envelope 
is stretched taut. The idea of the numerous independent balloons 
is to insure a high factor of safety as the loss of the entire contents 
of two or three of them through accident would not dangerously 
affect the lifting power of the whole. The numerous wrecks which 
attended the landings of these huge non-flexible masses during 
the early stages of their development led to the provision of some 
form of shelter wherever they were expected to land. Even now, 
they are practically unmanageable in the air during a fierce wind 
and must be allowed to sail under control until the wind has 
spent itself. 

The system of air balloonets has accordingly been adopted by 
every other designer, in variously modified forms, as illustrated by 
the German dirigible Parseval, in which but two air bags were 
employed, one at either end. They were interconnected by an external 
tube to which the air-pump discharge was attached, and were also 
operated by a counterbalancing system inside the gas bag, by means 
of which the inflation of one balloonet, as the after one, for example, 
caused the collapse of the other. 

*Influence of Fish Form of Bag.* But a condition of dynamic 
equilibrium can not be obtained with the combined aid of the 
precautions already noted to secure longitudinal stability and that of 
the air balloonet in maintaining uniform inflation. Why this is so 
will be clear from a simple example. If a simple fusiform or 
spindle-shaped balloon be suspended in the air in a horizontal plane, the 
axis of which passes through its center of gravity, it would be 
practically pivoted on the latter and would be extremely sensitive to 
influences tending to tilt it up or down. It would be in a state of 
"indifferent" longitudinal equilibrium. As long as the axis of the 
balloon remains horizontal and the air pressure is coincident with that 
axis, it will be in equilibrium, but an equilibrium essentially unstable. 
Experiment proves that the moment the balloon inclines from 
the horizontal in the slightest degree, there is a strong tendency 
for it to revolve about its center of gravity until it stands vertical 
to the air current, or is standing straight up and down. This, of 
course, refers to the balloon alone without any attachments. Such 
a tendency would be fatal, amounting as it does to absolute instability. 

If instead of symmetrical form, tapering toward both ends, a 
pisciform balloon be tried, it will still evidence the same tendency, 
but in greatly diminished degree. This is not merely the theory 
affecting its stability but represents the findings of Col. Charles 
Renard, who undoubtedly did more to formulate the exact laws 
governing the stability of a dirigible than any other investigator in 
this field. His data is the result of a long and methodically carried 
out series of experiments. In the case of the pisciform balloon, the 
disturbing effect is due in unequal degree, to the diameter of the 
balloon and its inclination and speed, whereas the steadying effect 
depends upon the inclination and diameter, but not on the Speed. 
The disturbing effect, therefore, depends solely on the speed and 
augments very rapidly as the speed increases. It will, accordingly, 
be apparent that there is a certain speed for which the two effects 
are equal, and beyond which the disturbing influence, depending on 
speed, will overcome the steadying effect. 

To this rate of travel, Renard applied the term "critical speed," 
and when this is exceeded the equilibrium of the balloon becomes 
unstable. To obtain this data, keels of varying shapes and 
dimensions were submitted to the action of a current of air, the force of 
which could be varied at will. In the case of the La France, the first 
fish-shaped dirigible, the critical speed was found to be 10 meters, 
or approximately 39 feet per second, a speed of 21.6 miles per hour, 
and a 24-horse-power motor suffices to drive the airship at this rate 
of travel. But the internal combustion motor is now so light that 
a dirigible of this type could easily lift a motor capable of generating 
80 to 100 horse-power. With this amount of power, its theoretic 
speed would be 50 per cent greater, or 33 miles an hour. But this 
could not be accomplished in practice as long before it was reached 
the stability would become precarious. As Colonel Renard observed 
in the instance just cited, "If the balloon were provided with a 
100-horse-power motor, the first 24 horse-power would make it go and 
the other 76 horse-power would break our necks."

*Steadying Planes.* It is accordingly necessary to adopt a further 
expedient to insure stability. This takes the form of a system of 
rigid planes, both vertical and horizontal, located in the axis of the 
balloon and placed a considerable distance to the rear of the center 
of gravity. With this addition, the resemblance of the after end of 
the balloon to the feathering of an arrow is apparent, while its 
purpose is similar to that of the latter. For this reason, these steadying 
planes have been termed the *empennage*, which is the French 
equivalent of "arrow feathering," while its derivative *empennation* is 
employed to describe the counteraction of this disturbing effect. 
In the La France, which measured about 230 feet in length by 40 
feet in diameter, the area of the planes required to accomplish this 
was 160 square feet, and the planes themselves were placed almost 100 
feet to the rear of the center of gravity. By referring to the 
illustrations of the various French airships, the various developments 
in the methods of accomplishing this will be apparent. 

.. figure:: images/Image8.jpg
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   :alt: Fig. 8. La Ville de Paris Showing Balloonets 
   
   Fig. 8. La Ville de Paris Showing Balloonets 

In the Lebaudy balloon, it took the form of planes attached to 
the framework between the car and the balloon. In La Patrie 
and La Republique, the resemblance to the feathered arrow was 
completed by attaching four planes in the form of a cross directly 
to the stern of the balloon itself. But as weight, no matter how slight, 
is a disturbing factor at the end of a long lever, such as is represented 
by the balloon, Renard devised an improvement over these 
methods by conceiving the use of hydrogen balloonets as steadying 
planes. The idea was first embodied in La Ville de Paris, Fig. 8, 
in the form of cylindrical balloonets, and as conical balloonets on 
the Clement-Bayard. These balloonets communicate with the gas 
chamber proper of the balloon and consequently exert a lifting 
pressure which compensates for their weight, so that they no longer 
have the drawback of constituting an unsymmetrical supplementary 
load. 

**Location of Propeller.** The final factor of importance in the 
design of the successful dirigible is the proper location of the 
propulsive effort with relation to the balloon. Theoretically, this 
should be applied to the axis of the balloon itself, as the latter 
represents the greater part of the resistance offered to the air. At 
least one attempt to carry this out in practice resulted disastrously, 
that of the Brazilian airship Pax, while the form adopted by Rose, 
in which the propeller was placed between the twin balloons in 
a plane parallel with their horizontal axes, was not a success. 
In theory, the balloon offers such a substantial percentage of the 
total resistance to the air that the area of the car and the rigging 
were originally considered practically negligible by comparison. 
Actually, however, this is not the case. Calculation shows that in 
the case of any of the typical French airships mentioned, the sum 
of the surface of the suspending rigging alone is easily the 
equivalent of 2 square meters, or about 21 square feet, without taking 
into consideration the numerous knots, splices, pulleys, and ropes 
employed in the working of the vessels, air tubes communicating 
with the air balloonets, and the like. Add to this equivalent area 
that of the passengers, the air pump, other transverse members 
and exposed surfaces, and the total will be found equivalent to a 
quarter or even a third of the transverse section of the balloon itself. 

To insure the permanently horizontal position of the ship 
under the combined action of the motor and the air resistance, a 
position of the propeller at a point about one-third of the diameter 
of the balloon below its horizontal axis will be necessary. Without 
employing a rigid frame like that of the Zeppelin and the Pax, 
however, such a location of the shaft is a difficult matter for 
constructional reasons. Consequently, it has become customary to 
apply the driving effort to the car itself, as no other solution of 
the problem is apparent. This accounts for the tendency common 
in the dirigible to "float high forward," and this tilting becomes 
more pronounced in proportion to the distance the car is hung 
beneath the balloon. The term "deviation" is employed to 
describe this tilting effect produced by the action of the propeller. 
Conflicting requirements are met with in attempting to reduce this 
by bringing the car closer to the balloon as this approximation is 
limited by the danger of operating the gasoline motor too close 
to the huge volume of inflammable gas. The importance of this 
factor may be appreciated from the fact that if the car were 
placed too far from the balloon, the propulsive effect would tend to 
hold the latter at an angle without advancing much, owing to the 
vastly increased air resistance of the much larger surface thus 
presented. 

**Relations of Speed and Radius of Travel.** The various factors 
influencing the speed of a dirigible have already been referred to, 
but it will be apparent that the radius of action is of equally great 
importance. It is likewise something that has a very direct 
bearing upon the speed and, in consequence, upon the design as a 
whole. It will be apparent that to be of any great value for 
military or other purposes, the dirigible must possess not only 
sufficient speed to enable it to travel to any point of the compass 
under ordinarily prevailing conditions of wind and weather but also 
to enable it to remain in the air for some time and cover 
considerable distance under its own power. 

*Total Weight per Horsepower Hour.* As is the case in almost 
every point in the design of the dirigible, conflicting conditions 
must be reconciled in order to provide it with a power plant 
affording sufficient speed with ample radius of action. It has 
already been pointed out that power requirements increase as the 
*cube of the speed*, making a tremendous addition necessary to the 
amount of power to obtain a disproportionately small increase 
in velocity. In this connection there is a phase of the motor 
question that has not received the attention it merits up to the 
present time. The struggle to reduce weight to the attainable 
minimum has made weight per horsepower apparently the paramount 
consideration—a factor to which other things could be sacrificed. 
And this is quite as true of aeroplane motors as those designed for 
use in the dirigible. But it is quite as important to make the 
machine go as it is to make it rise in the air, so that the question 
of *total weight per horsepower hour* has led to the abandonment of 
extremely light engines requiring a great deal of fuel. 

Speed is quite as costly in an airship as it is in an Atlantic 
liner. To double it, the motor power must be multiplied by 8, and 
the machine must carry 8 times as much fuel. But by cutting the 
power in half, the speed is reduced only one-fifth. The problem 
of long voyages in the dirigible is, accordingly, how to reconcile 
best the minimum speed which will enable it to make way 
effectively against the prevailing winds, with the reduction in power 
necessary to cut the fuel consumption down to a point that will 
insure a long period of running. 

When the speed of the dirigible is greater than that of the 
prevailing wind, it may travel in any direction; when it is 
considerably less, it can travel only with the wind; when it is equal to the 
speed of the latter, it may travel at an angle with the wind—in other 
words, tack, as a ship does, utilizing the pressure of the contrary 
wind to force the ship against it. But as the air does not offer 
to the hull of the airship, the same hold that water does to that 
of the seagoing ship, the amount of leeway or drift in such a 
manoeuver is excessive. This applies quite as much to the 
aeroplane as it does to the dirigible. 

FRENCH DIRIGIBLES
`````````````````

**The First Lebaudy.** The interest evidenced by the German 
War Department in Zeppelin’s airship was more than duplicated 
by that aroused in French military circles by the success of the 
Lebaudy Brothers. Since 1900 these two brothers had been 
experimenting with dirigible balloons. Their first dirigible—built by the 
engineer Juillot—made thirty flights, in all but two of which it 
succeeded in returning to its starting point. This machine was 
somewhat similar to the later types built by Santos-Dumont and 
carried a 40-horsepower Daimler motor. A speed of 36 feet per 
second, or about 25 miles per hour, was obtained. During tests 
in the summer of 1904, the balloon was dashed against a tree and 
almost entirely destroyed. 

**Lebaudy 1904.** The next year the "Lebaudy 1904" appeared. 
This was 190 feet long and had a capacity of 94,000 cubic feet of 
gas. The air bag was divided into three parts and contained 
17,600 cubic feet of air. It was supplied with air from a fan 
driven by the engine, and an auxiliary electric motor and storage 
battery were carried to drive the fan when the gas engine was not 
working. The storage battery was also used to furnish electric lights 
for the airship. A horizontal sail of silk was stretched between the 
car and the gas bag, which had an area of something over 1,000 
square feet, and a sort of keel of silk was stretched below it. A 
horizontal rudder, shaped like a pigeon’s tail, was used at the rear, 
and immediately behind it were two V-shaped vertical rudders. 
A small vertical sail was carried, which could be used to assist in 
guiding the airship. The car was 16 feet long and was rigidly hung 
10 feet below the bag. It was provided with an inverted pyramid 
of steel tubes meeting at an apex below the car to prevent injury in 
alighting. Sixty-three ascents were made in 1904 with this balloon, 
all of them comparatively successful, the longest being a journey of 
60 miles in two hours and forty-five minutes. 

.. figure:: images/Image9.jpg
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   :alt: Fig. 9. La Patrie, French War Dirigible 
   
   Fig. 9. La Patrie, French War Dirigible 

The next year a new and larger balloon equipped with a more 
powerful motor was used. Many flights were made in tests for the 
French War Department. 

**La Patrie.** La Patrie was then built for the French 
government by the Lebaudy Brothers and was of the same design as their 
earlier airships. In speed it was nearly equal to Zeppelin’s, and its 
dirigibility was nearly perfect. Fig. 9 shows a view of this airship 
in flight. 

It was 200 feet long, and the 70-horsepower engine drove two 
propellers. It could carry seven people and one-half ton of ballast. 
It carried four people at a speed of 30 miles per hour. On its last 
trip it covered 175 miles in seven hours. A few days afterward, a 
heavy wind tore it away from its moorings and it was blown out 
to sea and lost. 

**La Republique and Le Jaune.** Two more airships of the same 
type, La Republique and Le Jaune, followed this. These were 
tried by the French government, in 1908, and both proved 
successful. La Republique is illustrated in Fig. 10. The shape and 
equipment of the car are shown in Fig. 11. The automobile type of 
radiator may be seen attached to the side of the car. During a 
flight in the fall of 1909, a propeller blade broke and was thrown 
clear through the balloon envelope, causing the balloon to fall from 
a height of 500 feet. The four officers who formed the crew of the 
dirigible were killed instantly. 

**Clement-Bayard II.** The numerous factors that must be 
considered in the design of a successful dirigible balloon as well as the 
many conflicting conditions that must be reconciled have already 
been referred to in detail. How these are carried out in practice 
may best be made clear by a description of what may be 
considered as an advanced type of dirigible, the Clement-Bayard II, 
Fig. 12, of French design, and the most successful of the French 
military air fleet. Its predecessor, the Clement-Bayard I, Fig. 13, 
made thirty voyages, some of them of considerable distances, 
without suffering any damage, but a study of its shortcomings led 
to their elimination in the following model. 

.. figure:: images/Image10.jpg
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   :alt: Fig. 10. La Republique, French War Dirigible 
   
   Fig. 10. La Republique, French War Dirigible 

.. figure:: images/Image11.jpg
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   :alt: Fig. 11. Car of La Republique 
   
   Fig. 11. Car of La Republique 

The pisciform shape of the first Clement-Bayard was retained 
but given more taper, the dimensions being 248.6 feet overall 
by 42.9 greatest diameter, this being but a short distance back of the 
bow. This gives it a ratio of length to diameter of 5.76. The gas 
balloonet stabilizers were eliminated altogether, Fig. 12. The total 
gas capacity is approximately 80,000 cubic feet. Like all French 
dirigibles it is of the true flexible type, the only rigid construction 
being that of the framework of the car itself. To the latter are 
attached all rudders and stabilizing devices, instead of making them 
a part of the envelope as formerly. The latter is made of 
continental rubber cloth. 

.. figure:: images/Image12.jpg
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   :alt: Fig. 12. Clement-Bayard II, French Dirigible 
   
   Fig. 12. Clement-Bayard II, French Dirigible 

Light steel and aluminum tubing are employed in the 
construction of the frame supplemented by numerous piano-wire stays. 
This frame extends almost the entire length of the envelope and 
carries at its rear end a cellular, or box-kite, type of stabilizing 
rudder, instead of the former gas balloonets employed on the 
Clement-Bayard I, Fig. 13. This cellular rudder is in two parts, 
consisting of two units of four cells each, the two groups being 
joined at the top, with a space between them. In addition to 
acting as a stabilizer, this is also the direction rudder, its leverage 
being increased by making the end planes somewhat larger than 
the partitions of the cells. Between the cellular stabilizing rudder 
and the envelope is placed the horizontal rudder for ascending or 
descending. In the illustration this appears to be a flag, but it 
is in reality a long rectangular plane, which may be tilted on its 
longitudinal axis, the latter being at right angles to that of the 
balloon. There are two air balloonets of about one-third the total 
capacity of the balloon itself, and they are designed to be inflated 
by large aluminum centrifugal blowers driven from the main 
engines themselves. 

.. figure:: images/Image13.jpg
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   :alt: Fig. 13. Clement-Bayard I 
   
   Fig. 13. Clement-Bayard I 

There are two motors, each of 125 horsepower, both being of 
the same conventional design, *i.e.*, four cylinder four cycle vertical 
water cooled. In fact, they are merely light automobile motors. 
The cylinders have separate copper water jackets and the motors 
themselves are muffled, which is a departure from the usual custom. 
Each drives a separate propeller carried on top of the main frame 
through bevel gearing. 

The Clement-Bayard II made itself famous by its rapid and 
successful flight from the suburbs of Paris across the Channel to 
London, in October, 1910. 

**Astra-Torres.** In reviewing the specifications of any of the 
big dirigibles, the observer cannot fail to be struck by the excessive 
amount of power necessary to drive them at speeds which are 
lower than the minimum, or landing speeds, of many aeroplanes. 
When a speed of 45 miles per hour was first reached by a dirigible, 
it was acclaimed as a great feat. But this comparatively moderate 
rate of travel was surpassed only by increasing the number of 
motors and their horsepower until the fuel consumption became 
exceedingly high. This necessitated the carrying of a great weight 
of fuel and cut down correspondingly the useful load that the 
dirigible was capable of lifting as well as restricted its radius of 
flight at full speed. Until aerodynamic research had 
demonstrated the contrary, the necessity 
for such a tremendous amount of 
power was considered necessary to 
overcome the head resistance of the 
balloon itself. Research brought 
out in a striking manner how great 
a proportion of the total head 
resistance of an aeroplane was due 
to the struts and bracing wires. 
In the construction of the different 
types of airships illustrated, it will 
be noted that the gear provided 
for suspending the car or cars below 
the balloon requires a great number 
of cables. Later developments showed that by eliminating the 
great amount of head resistance caused by these numerous surfaces, 
the speed of a dirigible could be increased by over 50 per cent with 
the same amount of power. 

.. figure:: images/Image14.jpg
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   :alt: Fig. 14. Section of Astra-Torres, Illustrating Method of Suspension.
   
   Fig. 14. Section of Astra-Torres, Illustrating Method of Suspension. *CB*, Bracing of Heavy Fabric Bands; *SR* and *A*, Suspension Ropes and Cable Passing through Envelope; *S*, Expansion Sleeve in Envelope; *CC'*, Ropes to Sides of Car; *E*, Envelope 

*Improved Suspension.* The shortcoming of the dirigible with 
reference to suspension was realized more than ten years previous 
by a Spaniard—Torres—but owing to lack of financial support, he 
was unable to put his idea into execution. The principle he evolved 
is made clear by Fig. 14, which gives a section of an Astra-Torres 
dirigible illustrating the method of suspension. Instead of the 
ropes *SR* used to suspend the car being attached to bands passing 
around the envelope, these reinforcing bands *CB* and also the ropes 
fastened to them are placed inside the envelope, thus eliminating 
head resistance from those sources. 

*Performance.* Failing to obtain any encouragement in Spain, 
Torres finally succeeded in interesting the French Astra Company, 
which built a vedette, or scouting airship, of a little over 50,000 
cubic feet capacity. It was pitted against the Colonel Renard, at 
that time the leading unit in the French aerial navy and the 
fastest airship in commission. The small Torres dirigible so 
completely outclassed its huge competitor that another of close to 
300,000 cubic feet capacity was built and tried against the Parseval 
with similar results. An Astra-Torres dirigible built for the 
British government showed a speed in excess of 50 miles per hour. 
This particular dirigible has been at the front in France almost 
since the outbreak of hostilities and has rendered considerable 
valuable service. Its success led the French Government to order 
a huge replica of it, having a capacity of over 800,000 cubic feet 
and with motors developing 1,000 horsepower, which would give 
it an indicated speed of 60 miles per hour. So confident were its 
builders of attaining or even exceeding this, that an order for a 
second and even larger airship of the Astra-Torres design was 
placed before the first one was finished. This is also fitted with 
motors aggregating 1,000 horsepower and displaces 38 tons, making 
it larger than any Zeppelin that had been constructed up to the 
time it was built. As its construction and trials were undertaken 
during the war, no details have been published, but it is said on 
good authority that its speed exceeds 60 miles per hour, so that it 
is faster than any of the German dirigibles. 

*Construction.* Unlike the German dirigibles, the larger types 
of which have been characterized by a rigid frame, the Astra-Torres 
is a flexible airship and, owing to its method of suspension, its 
external appearance is decidedly unconventional, since the envelope 
instead of being of the usual cigar shape is more like a triangular 
bundle of three cigars with the third one on top. At the point 
where the three envelopes join, as shown in section, Fig. 14, heavy 
cloth bands *CB* are stretched across the arcs, forming a chord 
across each arc, the three chords comprising an inverted triangle. 
The suspension ropes *SR* are attached to the opposite ends of the 
base of this inverted triangle and converge in straight lines 
downward through the gas space, so that the air resistance offered by 
the ropes is practically eliminated since only a very small part of 
the suspension system appears outside the envelope. This external 
part consists of vertical cables *A* attached to the collecting rings 
of the bracing system and extending downward through special 
accordion sleeves *S* which permit the free play necessary at the 
points where they pass through the outer wall of the envelope. 
These sleeves also have another function—that of permitting the 
escape of gas under the pressure of expansion. A short distance 
below the envelope *E* each of these cables splits into two parts *C* 
and *C'* attached to opposite sides of the car. 

The British airship mentioned is provided with but one car, 
but the larger French ships have two placed tandem, each of which 
carries a 500-horsepower motor driving two two-bladed propellers 
of large diameter. While the form of envelope made necessary by 
this construction increases the frictional resistance, this is negligible 
in comparison with the great saving in power effected by the method 
of suspension, not to mention the greater simplicity of construction. 

GERMAN DIRIGIBLES
````````````````` 

**Early Zeppelin Airships.** At the same time that Santos-Dumont 
was carrying on his hazardous experiments, the problem was being 
attacked along slightly different lines by Count Zeppelin. 

It will be remembered that Dumont experienced much trouble 
on account of the envelope of his balloon being too flexible, causing 
it to crumple in the middle and to become distorted in shape from 
the pressure of the air. His efforts to overcome this by the 
employment of air bags did not meet with great success, even in his later 
types. 

.. figure:: images/Image15.jpg
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   :alt: Fig. 15. Zeppelin Dirigible Rising from Lake Constance 
   
   Fig. 15. Zeppelin Dirigible Rising from Lake Constance 

*Construction.* Zeppelin employed a very rigid construction. 
His first balloon, which was built in 1898, was the largest which 
had ever been made. It is illustrated in Fig. 15, which shows his 
first design slightly improved. It was about 40 feet in diameter 
and 420 feet long—an air craft as large as many an ocean vessel. 
The envelope consisted of two distinct bags, an outer and an inner 
one, with an air space between. The air space between the inner 
and outer envelopes acted as a heat insulator and prevented the 
gas within from being affected by rapid changes of temperature. 
The inner bag contained the gas, and the outer one served as a 
protective covering. In the construction of this outer bag lies the 
novelty of Zeppelin’s design. A rigid framework of strongly braced 
aluminum rings was provided and this was covered with linen and 
silk which had been specially treated to prevent leakage of gas. 
The inner envelope consisted of seventeen gas-tight compartments 
which could be filled or emptied separately. In the event of the 
puncture of one of them, the balloon would remain afloat. An 
aluminum keel was provided to further increase the rigidity. A 
sliding weight could be moved backward or forward along the keel 
and cause the nose of the airship to point upward or downward as 
desired. This would make the craft move upward or downward 
without throwing out ballast or losing gas. Lender each end of the 
balloon a light aluminum car was rigidly fastened and in each was 
a 16-horsepower Daimler gasoline engine. The two engines could 
be worked either independently of each other or together. Each 
engine drove a vertical and horizontal propeller. The propellers 
each had four aluminum blades. As will be seen from Fig. 15, the 
ears were too far apart for ordinary means of communication and so 
speaking tubes, electric bells, and an electric telegraph system were 
installed. 

*First Trials.* Very little was known as to the effects of 
alighting on the ground with such a rigid affair as this vessel, therefore 
the cars were made like boats so that the airship could alight and 
float on the water. The first trials were made over Lake Constance 
in July, 1900. The mammoth craft was housed in a huge floating 
shed, and the vessel emerged from it with the gas bag floating 
above and the two cars touching the water. She rose easily from 
the water, and then began a series of mishaps such as usually fall 
to the lot of experimenters. The upper cross stay proved too 
weak for the long body of the balloon and bent upward about 
10 inches during the flight. This prevented the propeller shafts 
from working properly. Then the winch which worked the sliding 
weight was broken and, finally, the steering ropes to the rudders 
became entangled. In spite of all this, a speed of 13 feet per 
second, or about 9 miles per hour, was obtained. These breakages 
made it necessary to descend to the lake for repairs and in 
alighting the framework was further damaged by running into a pile 
in the lake. The airship was repaired and another flight was made 
later in the year, during which a speed of 30 feet per second, or 
20 miles per hour, was obtained. 

*Second Airship.* Zeppelin had sunk his own private fortune 
and that of his supporters in his first venture, and it was not till 
five years later that he succeeded in raising enough money to 
construct a second airship. No radical changes in construction 
were made in the new model, but there were slight improvements 
made in all its details. The balloon was about 8 feet shorter than 
the original and the propellers were enlarged. Three vertical 
rudders were placed in front and three behind the balloon, and below 
the end of the craft horizontal rudders were installed to assist in 
steering upward or downward. The steering was taken care of 
from the front car. 

The most important change was made possible by the 
improvement in gasoline engines during the preceding five years. Where, 
in the earlier model, he had two 16-horsepower engines, he now 
used an 85-horsepower engine in each car, with practically the same 
weight. In fact, the total weight of the vessel was only 9 tons, 
while his first airship weighed 10 tons. 

His new craft made many successful flights. One was made 
at the rate of 38 miles per hour and continued for seven hours, 
covering a total distance of 266 miles. 

**Later Zeppelins.** The later Zeppelins embody no remarkable 
changes in design, the principal alteration being in size. One of 
these is illustrated in Fig. 16. In this the gas bag was increased 
to 446 feet in length and it held over 460,000 cubic feet of gas. 
This gave it a total lifting power of 16 tons. With this, Zeppelin 
made a voyage of over 375 miles. He was in the air for twenty 
hours on this trip and carried eleven passengers with him. 

.. figure:: images/Image16.jpg
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   :alt: Fig. 16. Zeppelin Airship in Flight 
   
   Fig. 16. Zeppelin Airship in Flight 

In August, 1908, the Zeppelin left its great iron house at 
Friedrichshafen and sailed in a great circle over Lake Constance. The 
day after it started, however, it was destroyed by a storm, and sudden 
destruction from one cause or another has ended the existence of 
practically every one of the Zeppelins built since, usually after a 
very brief period of service. 

**Shape and Framing.** In the early days of dirigible design 
the data upon which the shape and proportions of the envelope 
were based were purely empirical. Schwartz, Germany’s pioneer 
in this field, adopted the projectile as representing the form 
offering the least air resistance and accordingly designed his envelope 
with a sharply pointed bow and a rounded-off stern, giving it 
a length four times its diameter. Zeppelin did not agree with 
these conclusions and adopted a pencil form, rounded at the nose 
and tapering to a sharp point at the stern, making the length 
nine to ten times the diameter. Subsequent research work in the 
aerodynamic laboratory has demonstrated that the most efficient 
form for air penetration is one having a length six times its 
maximum diameter with the latter situated at a point four-tenths of 
the total length from the bow. It has likewise been proved that 
an ellipse is more efficient than either the projectile or pencil form 
and that tapering to a sharp point at the stern offers no particular 
advantage. As a result, the most approved form resembles the 
shape of a perfecto cigar, the nose being somewhat blunter than 
the after end. This form is likewise that of the swiftest-swimming 
fishes and has been shown to have the least head resistance as 
well as the minimum skin friction; it results in a section to which 
the term *stream-line* has been applied, and it is now employed on 
all exposed non-supporting surfaces on aeroplanes, such as the struts 
and even the bracing cables. Laboratory research has 
demonstrated that it is worth while to reduce the head resistance of even 
such apparently negligible surfaces as those presented by these wires 
and cables and, therefore, they are stream-lined by attaching recessed 
triangular strips of wood to their forward sides. 

*Framing Details.* Despite this, the builders of the Zeppelins 
have adhered to the original pencil shape with but slight 
modifications at the bow and stern, probably because that shape is 
much easier to build and assemble from standard girders. The 
form of girder employed is shown in Fig. 17, while the complete 
assembly of the frame is illustrated in Fig. 18. The girders form 
the longerons, or longitudinal beams, running the entire length of 
the rigid frame and supported at equidistant points by ring 
members built of similar girder sections. The fourth ring from the 
nose and each alternate ring after that are further braced by being 
trussed to the longitudinal beams around their entire circumferences, 
as shown in Fig. 18. The larger V-shaped truss at the bottom 
forms the gangway, which is now placed inside the envelope 
instead of being suspended beneath it, as formerly. This is done 
to eliminate the head resistance set up by the additional surface 
thus exposed. In the first instance in which this gangway was 
incorporated in the envelope, no provision was made for 
ventilation, and the ship was wrecked by a gas explosion. Regardless of 
how tight the fabric is made, gas is always oozing out through it 
to a greater or less extent. This fact is now met by providing 
ventilating shafts leading from the gangway to the upper surface 
of the envelope. Additional shafts through the envelope lead to 
gun platforms, forward, amidships, and aft, and are reached by 
aluminum ladders. 

.. figure:: images/Image17.jpg
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   :alt: Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin Frame 
   
   Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin Frame 

.. figure:: images/Image18.jpg
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   :alt: Fig. 18. Aluminum Frame Construction of Zeppelin Hull 
   
   Fig. 18. Aluminum Frame Construction of Zeppelin Hull 

*Framing of Schutte-Lanz Type.* It has become customary to 
refer to all large German airships as Zeppelins, but many of those 
used during the past three years have been of the Schutte-Lanz 
build, which is also a rigid frame type of dirigible but has been 
designed with a view of overcoming some of the disadvantages of 
the aluminum frame construction encountered in the use of the 
Zeppelin. The length and diameter of the latter airships are such 
that, no matter how rigidly the framing is assembled, there is more 
or less sag. When the sag exceeds a certain amount, the frame 
is apt to buckle at the point where it occurs, involving expensive 
repairs or wrecking the airship altogether. To overcome this 
difficulty, the Schutte-Lanz type employs a rigid frame of flexible 
material, namely, laminated wood in strip form, held together at 
joints and crossings by aluminum fittings and braced inside by 
cables. As shown by Fig. 19, no rigid longitudinal beams are 
employed, the only girders used being rings, to which a network 
built of the wood strips is attached. Starting at the nose, each 
continuous strip follows an open spiral path such as would be 
traced in the air by a screw of very large pitch, in fact, 
approximating the rifling of a gun barrel. It will also be noted from the 
illustration that the form of the Schutte-Lanz airship is the 
cigar-shape, which laboratory research has shown to be the most efficient. 

.. figure:: images/Image19.jpg
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   :alt: Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum Fittings 
   
   Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum Fittings 

The use of wood in conjunction with the spiral construction of 
the supporting members of the framing affords the maximum degree 
of flexibility, since the displacement of any of these members under 
stresses of either tension or compression would have to be very 
great to cause damage to the frame as a whole. The frame not 
being rigid, strictly speaking, either as units or as a complete 
assembly, stress at any particular point would simply cause all the 
members near that point to give in the direction of the strain, 
and the rest of the frame would accommodate itself to their change 
of position by either elongating or shortening slightly. In addition 
to these advantages, the Schutte-Lanz type of construction is said 
to be lighter than the Zeppelin for an airship of the same 
load-carrying capacity. 

**Power Plant.** Compared with their successors of war times, 
the early Zeppelins were mere pigmies where power is concerned. 
Many of these pioneers were driven by less than 100 horsepower 
all told, whereas in the later types no single motor unit as small as 
this total has been employed. The motors used most largely 
have been the 160-horsepower Mercedes and the 200-horsepower 
Maybach, both of which are described in detail under the title 
"Aviation Motors." From five to ten of these units have been 
used on a single ship, giving an aggregate in some of the latest 
types of close to 2,000 horsepower. Power has been applied 
through five or six propellers to limit their diameter and to guard 
against the breakdown of any one of the units putting the power 
plant out of commission as a whole. To distribute the weight of 
the engines equally and to insure each propeller a position in which 
it can work in undisturbed air, the engines have been placed at 
widely separated points on the airship and in different planes so 
that no two are coaxial. The main engine room is usually located 
in a cabin just back of the operating bridge and wireless room, 
while the remaining motors are suspended in independent gondolas 
at different points along the sides. Where more than 1,000 
horsepower has been used, each of these gondolas' has been fitted with 
two motors placed side by side and so coupled that either one or 
both may be employed to drive the single propeller carried by the 
propelling car. All the more recent propellers have been of the 
two-bladed type. 

**Control Surfaces.** The numerous expedients formerly resorted 
to by various designers in providing for stabilizing, steering, and 
elevating surfaces have been abandoned for forms that are 
practically a duplication of aeroplane practice. Experience demonstrated 
that the different types of multiplane rudders, elevators, and 
stabilizing surfaces employed in earlier days not only offered no operating 
advantages but were actually detrimental, in that they increased 
the head resistance unnecessarily. Moreover, their complication 
meant increased weight and weaker construction. They have 
accordingly been displaced by monoplane surfaces which are of 
exactly the same type of construction as those used on the 
aeroplane and the location and proportions of which are very 
evidently based on aeroplane practice. Both the horizontal and 
vertical stabilizers are of approximately triangular form and have 
the steering and elevating surfaces hinged to them at their after 
ends, so that, except for the pointed extremity of the envelope 
which extends beyond them, the tail unit of the later Zeppelins is 
practically the same as the empennage of an aeroplane. The 
horizontal surfaces are apparently depended on entirely to effect 
the ascent and descent, there being no evidence of swiveling 
propellers by means of which the power of the engines could be 
employed to draw the airship up or down. The great weight of 
ballast carried is, of course, in the form of water, but this is 
discarded in order to ascend only when the power of the engines 
exerted against the elevating planes is no longer capable of keeping 
the airship at the altitude desired. In the low temperatures 
encountered in night flights, however, the contraction of the 
hydrogen gas is so great that the crew has found it necessary to reduce 
the weight by discarding not only every pound of ballast but, as 
far as possible, everything portable. Despite this, several airships 
have fallen when their fuel supply was exhausted, one coming to the 
ground in Scotland, two dropping into the North Sea, and three 
or four falling in France. 

**Operating Controls.** All the operating controls are centered at 
the navigating bridge, which is inclosed to form the commander’s 
cabin. By means of push buttons, switches, levers, and wheels 
every operating function required is set into motion from this 
central point. Whether auxiliary motors are carried for the 
purpose of pumping air into the balloonets or this is one of the duties 
of the main engine just back of the wireless room does not appear, 
but with the aid of a push button board the amount of air in any 
of the balloonets may be increased or decreased at will. There is 
a control button for each operation, or two for each balloonet, 
which fact necessitates a rather forbidding looking board, since the 
more recent Zeppelins have seventeen to nineteen gas bags within 
each of which is incorporated an air balloonet. 

The amount of fuel supplied to any one of the motor units 
can likewise be controlled from a central board, and this is also 
true of the ballast release apparatus, so that water can be emptied 
from any one of the ballast tanks at will, thus facilitating ascent 
or descent by lightening one end or the other. Elevating and 
steering surfaces are operated by small hand-steering wheels with 
cables passing around their drums, a member of the crew being 
stationed at each of these controlling wheels. Owing to the 
number of motors used, the instrument board is the most formidable 
appearing piece of apparatus on the bridge, since there is a 
revolution counter for each power unit in addition to the numerous 
other instruments required. Some of these instruments are the 
aneroid barometer for indicating the altitude, transverse and 
longitudinal clinometers to show the amount of heel and the angle 
at which the airship is traveling with relation to the horizontal, 
the anemometer, or air-speed indicator, manometers, or pressure 
gauges, for each one of the gas bags, fuel and ballast supply 
gauges, drift indicators, electric bomb releasers, mileage recorders, 
and the like. In addition to these, there are a large chart and a 
compass, so the navigating bridge of a Zeppelin combines in small 
space all the instruments to be found in the engine room and on 
the bridge of an ocean liner besides several which the latter does 
not require. That the proper coordination of all the functions 
mentioned is an exceedingly difficult task for one man seems evident 
from the numerous Zeppelins that have apparently wrecked 
themselves. 

**Crew Carried.** In the various Zeppelins that have been 
captured or shot down by the British or French, the personnel has 
varied from fifteen to thirty men but in the majority of instances 
has not exceeded twenty. The positions and duties are about as 
follows: The commander, lieutenant-commander, and chief 
engineer, and possibly a navigating officer are stationed at the bridge. 
Two or three of the crew are also stationed there to work the 
manually operated controls. In the cabin just back of the bridge 
are two wireless operators and one or two engine attendants for 
the motors in the engine room behind the wireless room. A 
similar number of engine attendants are stationed in the after 
engine room and there is at least one attendant for each of the 
other motor units. One man is stationed at each machine gun, of 
which there are three to five on the "roof" and two in each car, 
and at least as many bombers are needed to load the "droppers." 
As a reserve there are usually an additional gun pointer for each 
gun and an extra engine attendant, since to run continuously most 
of the crew would have to stand watch and watch as in marine 
practice. The sleeping accommodations consist of canvas hammocks 
slung in the gangway. 

**Explosives Carried.** In addition to a liberal supply of 
ammunition for the machine guns, a large weight of bombs is carried, 
though the quantity as well as the size of the bombs themselves 
has been exaggerated in the same or even greater ratio than that 
which has proved characteristic of the German military 
press-agency service. The bombs are carried suspended in racks 
amidships, and the bomb droppers are also located at that part of the 
ship so that the release of the bombs will not upset the longitudinal 
equilibrium of the craft. The bomb-dropping apparatus is 
controlled electrically from the navigating bridge but may also be 
operated by hand from the same point. It has been reported by 
the Germans that their latest types of Zeppelins are capable of 
dropping bombs weighing 1 ton each. In view of the effect that 
the sudden release of a weight of 1 ton would have on the airship 
itself, this is manifestly very much of an exaggeration. Zeppelin 
bombs that have failed to explode have never exceeded 200 to 300 
pounds and many of those employed are doubtless still lighter. 
So far as the total amount carried is concerned, many of the later 
airships doubtless are capable of transporting 2 to 3 tons and still 
carrying sufficient fuel, though adverse conditions would prevent 
their return, as has frequently happened. 

BRITISH WAR DIRIGIBLES
`````````````````````` 

**Adoption of Small Type.** German designers have continued 
to pin their faith blindly to the huge rigid type, despite the fact 
that prior to the war almost a dozen of these costly machines met 
with disaster as fast as they could be turned out. Since the 
war started, their destruction has kept pace pretty closely with 
their building without their accomplishing anything of military 
value. The British naval aeronautic service, on the other hand, 
appreciated the futility of such tremendous and unwieldy 
construction and, after a single demonstration of its uselessness, abandoned 
it altogether. This single attempt was the ill-fated Mayfly, which 
was most appropriately named, since its performance resolved into 
a certainty the doubt expressed by its title. In being taken out 
of its shed, the framing of the airship was damaged, and it 
collapsed a few minutes later so that it never did fly. One of the 
early types of small British dirigibles is shown in Fig. 20. 

Attention has since been concentrated in most part on the 
construction of aeroplanes in constantly increasing numbers, although 
the dirigible has not been given up altogether. However, its restricted 
usefulness as well as the necessary limitations of its effective size 
has been recognized. Early in the war Great Britain planned the 
construction of fifty small dirigibles, of both the rigid and nonrigid 
types, all of which have undoubtedly since been completed. They 
are small airships designed chiefly for scouting and short-range 
bombing raids over camps when in army service and for coast 
patrol and submarine hunting as an aid to the naval forces. While 
no specifications are available, the cubic capacity of these patrol 
airships probably does not exceed 50,000 to 75,000 cubic feet, their 
over-all length being approximately 100 to 125 feet. 

.. figure:: images/Image20.jpg
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   :alt: Fig. 20. An Early Type of Small British Dirigible
   
   Fig. 20. An Early Type of Small British Dirigible

**Aeroplane Features.** To simplify the construction and at the 
same time minimize the amount of head resistance, the car consists 
of an aeroplane fuselage of the tractor type, fitted with a 
comparatively small motor—under 100 horsepower—and having 
accommodations for a pilot and an observer in two cockpits, placed tandem. 
The control surfaces are also similar to those used in aeroplane 
construction. Despite their low power, these dirigibles can make 
40 miles an hour, owing to their greatly reduced head resistance. 
Instead of employing either an auxiliary blowing motor or a 
blower driven by the motor itself, the supply duct to the air 
balloonet is made rigid and is sloped forward so that its open end 
comes directly in the slip stream of the propeller; thus the latter 
serves to inflate the balloonet as well as to drive the dirigible. 
The desired amount of inflation is controlled by a valve. 

.. figure:: images/Image21.jpg
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   :alt: Fig. 21. Side and End Views of British Astra-Torres Dirigible Used for Anti-Submarine Patrol Service 
   
   Fig. 21. Side and End Views of British Astra-Torres Dirigible Used for Anti-Submarine Patrol Service 

**Use in Locating Submarines.** Many of these small scouting 
and naval-patrol dirigibles have given a good account of 
themselves and comparatively few have met with accident or have been 
destroyed by the enemy. On frequent occasions they have been 
very successful in locating submarines below the surface, since the 
body of the under-water boat is readily detected from an altitude 
of a thousand feet or more, even 
though submerged to a great 
depth and despite a heavy ripple 
on the surface that makes the 
water absolutely opaque when 
viewed from the deck of a ship. 
Doubtless they will be employed 
to an increasing extent as the 
hunt for the submarine becomes 
more and more intensive, though 
their use is very much restricted 
during the winter months, owing 
to the frequent and severe storms 
encountered. 

**British Astra-Torres.** A 
number of comparatively small 
Astra-Torres dirigibles have also been 
built in Great Britain for coast 
patrol and anti-submarine work. 
The line drawing at the left of 
Fig. 21 illustrates the general 
design and construction of these 
small airships, while the various 
letters indicate the different parts 
of the gas container, air 
balloonets, suspension and car, and the 
end view at the right of the 
figure shows the small amount 
of head resistance offered by the 
suspension of this type as 
compared with that of the usual form 
of nonrigid dirigible. *A* is the 
balloon itself, or main gas 
container, the pressure relief valve 
for which is located at *M*. *BB* 
are the air balloonets connected 
with the blower *H* in the car. In 
the illustration these balloonets are 
shown fully inflated as they would be after the gas bag had lost 
a considerable proportion of its original contents through leakage 
or expansion. At the beginning of a flight, when the gas bag is 
fully inflated with hydrogen, they lie perfectly flat along the lower 
side of the envelope, being brought into service only as they are 
needed to keep the envelope distended to its full volume. 

The novel method of suspension to which this type of dirigible 
owes its greater speed and fuel economy, because of the reduction 
of the head resistance, is shown by the numerous supporting ropes 
*O-O-O*, which terminate in a comparatively few cables attached 
to the car. In the small British airships referred to here, there is 
but one small car designed to carry a crew of two men and the 
engine is of comparatively low power, driving a propeller at 
either end of the car, but in the large French dirigibles of the 
same type, two large cars are placed tandem some distance apart 
and are fitted with 500-horsepower motors. The various parts 
indicated by the letters are: *CC* propellers, *D* motor, *F* space for 
pilot and crew, *G* fuel and oil tanks, *J* guide rope, *K* gas valve, 
*LL* air valves, *NN* balloonet cable, *P* rudder, *Q* stabilizer, *RR*
bracing cables, and *S* the car itself. 

MILITARY USES OF ZEPPELINS
`````````````````````````` 

**Limitations of Use.** Nothing excites the Teutonic imagination 
so strongly as things military to which the characteristic German 
adjective *kolossal* can be enthusiastically applied. It was for this 
reason that, despite its uniform record of tragic disaster for years 
before the war, the Germans pinned their faith to the Zeppelin as 
a weapon that could not fail to strike terror to the hearts of the 
British and French and make them hasten "to sue for peace." 
However, apart from its reputed employment on the single 
occasion that the German grand fleet left the security of the Kiel 
Canal, it is not known to have been used in any purely military 
operation. The aeroplane has been developed to a point that, 
in spite of the ability of the Zeppelin to ascend rapidly when hard 
pressed, would make it suicidal for one of the huge gas bags to 
sally forth in daylight, unless attended by a large number of 
battle planes to prevent enemy flying machines from attacking it. 
No such use of the Zeppelin has been recorded thus far. 
Consequently, it has been used only in nocturnal bomb-dropping 
expeditions, chiefly directed against London and only undertaken 
when weather conditions made detection difficult. In order to 
carry these out, it has been necessary to establish stations in 
Belgium, since the fuel consumption of the Zeppelin is so great 
that, even with its tremendous fuel supply of 3 to 5 tons, a flight 
to London and return to points well within the German border is 
impracticable. The first raids of this character were carried out 
successfully, but subsequent attempts were marked by the loss 
of one or two airships on each occasion, so that the practice was 
abandoned as being too expensive for the results attained and 
aeroplanes were substituted. 

**Number Built.** Taking it for granted that the numbering of 
the German airships has been consecutive, the total number built 
during the first three and one-half years of the war by the Germans 
would be between eighty and one hundred. All large German 
airships have come to be commonly termed Zeppelins, but a number 
of them were of the Schutte-Lanz type, almost equally large and 
also characterized by rigid construction, which, however, was of 
wood with aluminum fittings instead of being all metal, as it was 
found that the huge metal frame accumulated a static charge of 
high potential that was responsible for igniting the gas in one or 
two instances. 

**Weakness of Type.** The L-I (*Luftschiff*, or airship), the first of 
the German airships designed for purely military purposes, was a 
Zeppelin 525 feet long by 50 feet in diameter, of 777,000 cubic 
feet capacity, and 22 tons displacement. Its three sets of motors 
developed 500 horsepower and it had a speed of 52 miles per 
hour. It was launched at Friedrichshafen in 1912, and after a 
number of successful cross-country trips, it was tried in 
connection with naval maneuvers off Heligoland. Before the trial had 
proceeded very far, a sudden squall broke the backbone of the 
huge gas bag and hurled it into the sea, drowning fifteen out of 
the crew of twenty-two. It is a striking commentary on the 
frailness of these aerial monsters that every one of the big airships 
built up to that time had met disaster in an equally sudden 
manner but from a totally different cause in each instance. The 
L-II was slightly shorter but had 5 feet longer beam and 
displaced 27 tons. She was designed particularly for naval use, had 
four sets of motors developing 900 horsepower, and was fitted with 
a navigating bridge like that of a ship. It was confidently thought 
that all possible shortcomings had been remedied and success 
finally achieved in the L-II, but before there was any opportunity 
to demonstrate its efficiency, the airship exploded in mid-air, killing 
its entire crew. 

*Effectiveness Grossly Overrated.* Despite this unbroken chain 
of disasters, the German official press bureau spread broadcast 
the prowess of the Zeppelin, its magnificent ability, and its 
remarkable achievements as an engine of war—in theory, since this was a 
year or two prior to the outbreak of hostilities. Had it not been 
for the forced descent of the Zeppelin IV at Luneville, where it 
was taken possession of by the French, these tales might have 
been accepted at their face value. But the log of the commander 
of this airship showed that its maximum speed was but 45 miles 
per hour, the load 10,560 pounds, and the ascensional effort 45,100 
pounds. The fuel consumption averaged 297 pounds per hour 
while the fuel capacity was only sufficient for a flight of seven 
hours. During its flight, it had reached an altitude of only 6,250 
feet, to accomplish which over 3 tons of ballast had to be dropped. 
It was also shown that the critical flying height of these huge 
airships is between 3,500 and 4,000 feet, Zeppelin himself declaring 
that his machines were useless above 5,000 feet. This probably 
accounts for the fact that the early raids on English towns were 
carried out at a height but slightly in excess of 2,000 feet. Later 
types, however, are said to have reached high altitudes. 

.. figure:: images/Image22.jpg
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   :alt: Fig. 22. Zeppelin L-49 Brought Down Intact by a French Airman
   
   Fig. 22. Zeppelin L-49 Brought Down Intact by a French Airman, Resting on Hillside near Bourbon-Les-Baines 
   *Copyright by Underwood and Underwood, New York*

Shortly before the outbreak of the war the L-5 was completed. 
This had a capacity of about 1,000,000 cubic feet, motors 
aggregating 1,000 horsepower or over, and a reputed speed of 65 miles 
per hour. Just what was the fate of this particular ship did not 
become known, since information of a military character has not 
been permitted to leak out of Germany from that time on. But 
capture or destruction has accounted for many of the intermediate 
numbers of the series; big German airships have been brought 
down in England, in the North Sea, in France, and at Saloniki, 
their loss culminating in the disaster to four out of the fleet of five 
that attempted a raid over London but were caught by adverse 
winds which exhausted their fuel supply so that they were blown 
out of control, toward the south of France. French anti-aircraft 
batteries or aeroplanes accounted for three of these, while the 
fourth, the L-49, was captured intact. 

.. figure:: images/Image23.jpg
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   :alt: Fig. 23. Nose of Giant L-49 and Group of Sightseers
   
   Fig. 23. Nose of Giant L-49 and Group of Sightseers 
   *Copyright by Underwood and Underwood, New York*

**L-49.** An essential part of the equipment of every form of 
German military apparatus is a means of destroying it in case of 
capture. In the case of the big airships, the officers are provided 
with revolvers loaded with incendiary bullets, which are fired into 
the gas bag, so that until the L-49 was forced to descend in the 
south of France by the activities of a battle plane, plus a lack of 
fuel, no airship of a recent type had ever been captured intact. 
In this case, the commander fired his pistol at the balloon but 
missed and was prevented from firing again by a French peasant 
who "covered" him with a shotgun. The wireless operator 
succeeded in using a sledge hammer on some of the apparatus of the 
very completely equipped wireless cabin before he was captured 
but did not do sufficient damage to prevent reassembly of the 
parts with little trouble. With the exception of the earlier type 
of Zeppelin that was forced to descend at Luneville prior to the 
war, the L-49 was the first that was ever known to have landed 
undamaged in hostile territory, as practically all the others were 
destroyed in the air, most of them having been wrecked either by 
aeroplane or anti-aircraft fire. Fig. 22 shows the L-49 as it rested 
on a hillside at Bourbon-les-Baines, France, and Fig. 23 shows a 
close view of the nose of the monster. 

*Standardized Parts.* Comparing the L-49 with many of its 
predecessors led to the conclusion that it was one of the latest 
types, but an inspection of its construction revealed the use of 
many parts produced in quantities from standard patterns as well 
as a lack of the finish that has always characterized airship 
construction. Appearance and comfort had both been sacrificed with 
a view to saving the last ounce of superfluous weight in order to 
carry more fuel and ammunition. Evidently the production of 
these large airships has been reduced to a manufacturing basis and 
they are constructed in series in much the same manner as motor 
cars, though on a reduced scale. 

*General Design.* In its general construction the L-49 was 
along the same lines that have characterized the Zeppelin since its 
inception, the outer envelope being stretched over a rigid frame of 
aluminum girders, inclosing a large number of independent balloons 
inflated with the usual hydrogen gas, no trace being discovered of 
the non-inflammable gas, the discovery of which had been hailed 
by the German press. The commander’s cabin was suspended 
well forward with the wireless room directly behind it, while a 
V-shaped gangway, recessed in the envelope proper so as to present 
no additional head resistance, ran back from the latter the whole 
length of the ship. This and the gun platform on top, mounting 
two machine guns and reached by a ladder suspended in a well 
amidships, have been familiar features of all the recent Zeppelins. 
The main envelope contained nineteen independent gas bags, each of 
which was made integral with an air balloonet to take care of the 
expansion and contraction of the hydrogen with varying altitudes 
and temperatures. Distributed along the lower part of the frame 
inside the envelope were a series of 50-gallon water-ballast tanks. 

*Power Plant.* No less than nine large motors were employed 
to drive the huge gas bag, the maximum horsepower probably 
aggregating 1,600 to 2,000. The motors were distributed in five 
different locations, the largest being suspended just abaft the 
wireless room. The remainder were placed in self-contained units 
in the form of gondolas suspended from the sides of the frame, as 
shown in Fig. 24, the outline being that of a blunt-nosed fish. 
Each of these gondolas carried two motors placed side by side 
and coupled up so that either one or both could be employed to 
drive the single propeller. For cruising speeds one motor in each 
gondola supplied sufficient power or in some gondolas both motors 
could remain idle. No accommodation was provided for attendants 
in the gondolas, any of which could easily be reached by light 
ladders from the inclosed gangway. 

To insure greater safety, the fuel supply was divided among 
sixteen tanks, all of which were interconnected with each other 
and the engines so that gasoline from any tank or tanks could be 
diverted to any particular engine. The supply of lubricating oil 
for each engine was carried in a tank in the gondola itself. 

*Control.* Vertical and horizontal stabilizing surfaces of 
conventional form were built on the sharply tapering rear end of the 
frame, the elevator and rudder being similar to those used in 
aeroplane construction, except that the rudder was in two sections, 
the larger of which was placed on top of the envelope. The 
control of these surfaces, the operation of all the engines, the control 
of the water ballast, the air supply to the balloonets, and the fuel 
supply to the motors were all concentrated at a panel board in the 
commander’s cabin, the forward end of which bore a close 
resemblance to the bridge of a man-of-war. By means of thirty-eight 
push buttons, half red and half white, air could be released from 
or pumped into the balloonets, while in a similar manner the 
contents of any one of the water-ballast tanks could be emptied. 
Elaborate controls were provided for the power plant, it being 
possible to vary the speed or stop any one or more of the motors 
from the bridge. The rudder and elevators were operated by 
means of small hand wheels, similar to a marine steering wheel. 
One of the most prominent features of the operating cabin was a 
huge chart frame, capable of carrying a large scale map covering a 
considerable area, as well as an ample supply of maps. Few 
instruments were found in the captured ship and it is thought 
highly probable that everything not fastened in place had been 
dumped overboard at the last to increase its lifting power. 

.. figure:: images/Image24.jpg
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   :alt: Fig. 24. One of Six Gondolas, or Power Units of the Zeppelin L-49
   
   Fig. 24. One of Six Gondolas, or Power Units of the Zeppelin L-49 
   *Copyright by Underwood and Underwood, New York*

Apart from the use of standardized fittings and parts and the 
employment of a great deal more power in a slightly different 
manner than had characterized the earlier types of Zeppelins, the 
L-49 revealed nothing of unusual importance in airship design and 
certainly none of the world-beating features that German 
propaganda had been heralding for some time previous. 

**Destruction of Zeppelins.** Mention has already been made of 
the fact that practically the only use made by Germany of her 
huge airships has been the bombardment of open cities, and that 
always at night. From the first of September, 1914, up to the 
end of 1917, between thirty and forty had met disaster, but only 
two were captured intact. The first of these was discovered by a 
Russian cavalry patrol while at anchor and its crew of thirty men 
were made prisoners. This was at an early period in the war, 
while the second one to be captured was the L-49, already referred 
to, which formed one of a squadron of five evidently sent out on 
a bombing expedition against London. Owing to adverse winds, 
they never reached their destination and four of them were known 
to have been put out of action, all except the L-49 being destroyed 
in the air. Not a few of these big airships have fallen victims to 
their own weakness and succumbed to the elements, in one instance 
a high wind tearing the airship loose from its moorings while the 
crew was not aboard. This was at Kiel, and after traveling a 
number of miles unguided, the big bag fell into the North Sea. 
In quite a number of other cases head winds have prevented the 
return of the raiders to their base and they have either been 
destroyed by their crews or wrecked at sea in attempting to return. 
In still other instances the unwieldy monsters have been wrecked 
by high winds when attempting to land, as was so frequently the 
case prior to the war. 

*Aeroplane and Anti-Aircraft Fire Effective.* Before the war 
broke out the ability of either the aeroplane or the anti-aircraft 
gun to overcome the Zeppelin was purely theoretical, but actual 
experience has demonstrated that much of the theory was well 
founded. At least three Zeppelins have been destroyed by British 
aviators in mid-air, all or most of the crews being killed, while 
probably an equal number have been accounted for by French 
aviators in open battle. The war had not been under way a 
month before French anti-aircraft gunners showed their skill by 
bringing down-a "Zep," while only a week later a Russian battery 
accomplished the same feat, in this instance killing the entire crew. 
In 1916, British and French gunners succeeded in either "winging" 
or setting on fire three or four, while two dropped into the North 
Sea and one was blown up by its crew, having run out of fuel 
while raiding Scotch towns. 

*Bombing Raids against Zeppelin Sheds.* Not the least of the 
disadvantages from which such huge and unwieldy craft suffer is 
the fact that the correspondingly large structures required to 
house them make exceedingly easy marks for the raiding aviator. 
Bombing, however, is such an uncertain art that even such large 
buildings as these cannot be struck from any altitude with a fair 
degree of accuracy. Consequently, in the number of raids that 
have been carried out against Zeppelin sheds, success has been due 
very largely to the temerity of the aviators, who have descended 
within a few hundred feet of their mark despite the fire directed 
at them from all quarters. At least three and probably more of 
the big airships have been destroyed in this manner by British 
aviators, who have made flights of several hundred miles to reach 
their destination, while the destruction of as many more has been 
ascribed by the Germans to the "accidental" explosion of a bomb 
in the shed. In view of the great precautions taken against 
accident from the explosion of the bombs carried by the airship 
itself, it is not considered at all likely that there was anything 
accidental about the wrecking of these craft. 

One of the earliest attempts against Zeppelin headquarters at 
Friedrichshafen on Lake Constance, which resulted in the 
destruction of the L-31, is typical of the plan followed in attacks of 
this kind. Two British aviators flew from their base in France, 
about 250 miles distant, at a high altitude. They became 
separated before reaching their destination owing to a mist. This, 
however, prevented their discovery until they had dropped within 
a few hundred feet of the surface of the lake, which it was 
necessary to do to obtain a view of the airship sheds. The first pilot 
dropped his cargo of bombs from a height of only 100 feet or so 
over the shed and was rewarded by seeing it catch fire. He had 
hardly straightened out on his return course before he heard the 
attack of his companion. The latter was not so fortunate in 
escaping unscathed, as a bullet pierced his fuel tank and compelled 
him to descend. In the majority of instances, however, the raiders 
have succeeded not only in carrying out their task but in escaping 
undamaged as well. 

CAPTIVE BALLOONS 
````````````````

**Military Value.** As an aid to military operations, the use of 
the captive balloon dates back many years. It was extensively 
employed in the Civil war and more recently in the Boer war, 
but with the advent of both the dirigible and the aeroplane, it 
was generally considered outside of Germany that its reason for 
existence had passed away. The German military plans included 
a large number of balloons for artillery observation purposes and 
they were used right from the start. It was only when the 
fighting settled down to trench warfare, however, that they came into 
prominence and the aid that they rendered the German batteries 
put their opponents at a serious disadvantage. Like the bayonet, 
which was also generally considered to have been relegated to 
military operations of the past, the captive balloon is now playing 
a very important role, particularly on the western front. In 
favorable weather, anywhere from ten to forty of these aerial observation 
posts will be visible from a single point on the line. 

**Spherical Type Defective.** The captive balloon of the present 
day, however, bears no resemblance to its predecessors. From a 
sphere, it has been developed into a form that more nearly resembles 
the dirigible and at the same time, it embodies some of the features 
of the aeroplane. The old spherical balloon was always at the mercy 
of the wind, which not only governed the altitude to which the balloon 
would rise but also made things extremely uncomfortable as well as 
dangerous for the observers. With 1,000 feet of cable out, such a 
balloon rises to an equivalent height on a perfectly, calm day. But 
even a light wind cuts this height down by 100 or 200 feet, while 
if a strong wind is blowing, the balloon is held down to within a 
few hundred feet of the ground regardless of the length of cable 
paid out. Every strong gust beats it over at a perilous angle and 
the resulting shocks to the basket are so severe that its occupants 
can have little thought for anything but their own safety. Strong 
cross gusts set both the bag and basket to spinning and jumping in 
a manner that would make the results of the severest storm at sea 
seem mild by comparison, since the movements of the basket are 
executed with such rapidity that they seem to be in almost every 
plane simultaneously. As a result, the old type of captive balloon 
was available for service only in the calmest weather. 

**Modern Kite Balloon.** It should not be supposed that the 
improved type of observation balloon now in use in such large 
numbers provides any unusual amount of ease or comfort, since 
it is also prey to the wind and does a great deal of swinging about 
as well as jerking when the wind is more than 15 or 20 miles an 
hour. But it has been improved to a point where the wind not 
only serves to elevate, instead of depressing it, but also to steady 
it. The new type. Fig. 25, is technically known as a kite balloon, 
because, in addition to the appendages attached to the bag itself for 
steadying purposes, it is equipped with a tail to assist in keeping 
it heading into the wind. This consists of a number of 
bucket-shaped pieces of heavy canvas attached to the tail cable by 
bridles so as to catch the wind and hold it, thus placing a heavy 
strain on the cable and preventing the balloon from swinging 
violently. As is the case with practically everything used at the 
front, the technical name of the new type of balloon is prominent 
by its absence. It is a *Drache* (kite) to the Germans and a "blimp" 
to Tommy Atkins. Both its shape and attitude when aloft bear a 
close resemblance to a huge sausage, so that the term "sausage" is 
used by all the belligerents in common to a large extent. A side 
view of an American type is shown in Fig. 26. 

.. figure:: images/Image25.jpg
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   :alt: Fig. 25. Head-On View of Modern Kite Balloon, Showing Details of Tail Buckets
   
   Fig. 25. Head-On View of Modern Kite Balloon, Showing Details of Tail Buckets 
   *Copyright by Central News Service, New York City*

It will be noted from Figs. 25 and 26 that the suspension of 
the basket and the appendages attached to the balloon at the rear 
hold it in a position which is roughly the equivalent on a large scale 
of the curve of an aeroplane wing. It has both camber and an angle 
of incidence, so that the wind serves to elevate it instead of 
beating it down. This lifting effect is further increased by tubes of 
large diameter, open at the forward end only and curving around 
the end of the gas bag at the rear. (It is also equipped with an 
air balloonet, the same as a dirigible.) The wind enters the lower 
end of this tubular member, which is in a line with the 
longitudinal axis of the balloon, but it must pass around the curve at 
the end of the gas bag before it can fully inflate it, so that it 
performs the double function of increasing the lift and steadying 
the balloon, though the latter is its chief purpose. The basket is 
suspended quite a distance below the gas bag and has 
accommodation for two observers. Like scores of other inventions that the 
Germans were the first to utilize on a large scale in the present war, 
the kite balloon was not a German creation but was originally 
developed in France. 

.. figure:: images/Image26.jpg
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   :alt: Fig. 26. American Kite Balloon of Latest Type Ascending
   
   Fig. 26. American Kite Balloon of Latest Type Ascending 
   *Copyright by Committee on Public Information, Washington, D C.*

**Methods of Inflation.** The average capacity of the kite 
balloons used for observation purposes is 28,000 cubic feet. They 
are inflated with hydrogen either from a portable generating plant 
forming part of the equipment of the balloon company or from a 
supply carried under high pressure in heavy steel "bottles" similar 
to those used for transporting oxygen or carbonic acid gas intended 
for industrial use. Since the balloon companies are stationed about 
4 miles back of the firing line, the use of the portable plant is 
practical, but it has been found more economical and more 
convenient to generate the gas on a large scale at special 
establishments in France and England and send it to the front in containers. 
With a portable plant, several hours are necessary to inflate the 
gas bag, whereas with a large supply of the gas at hand under 
high pressure, the operation may be carried out in less than an hour. 

The balloon naturally works under the same difficulties as 
all lighter-than-air craft, that is, there is a constant leakage of 
the hydrogen through the fabric in addition to that lost by the 
expansion of the gas on warm days when the summer sun beats 
down directly on the gas bag. Where a field generating plant is 
employed, quick inflation of a new balloon or replacement of loss 
is accomplished by the used of several "nurses", Fig. 27. These are 
simply large gas bags which are kept replenished by the gas plant 
working constantly, in other words, they are storage tanks, and 
when it is necessary to inflate the balloon quickly, their contents 
are simply transferred to it. 

.. figure:: images/Image27.jpg
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   :alt: Fig. 27. Landing Big Kite Balloon at Training Station "Somewhere in England."
   
   Fig. 27. Landing Big Kite Balloon at Training Station "Somewhere in England." "Nurse" in Background 
   *Copyright by Underwood and Underwood, New York*

**Balloon Company.** Though aeronautical in character, the kite 
balloon service is actually a branch of the artillery, to which it is 
directly attached. A balloon company accordingly consists of 
twelve to twenty artillery officers of varying ranks and about 120 
to 130 men. Of the officers, six to eight are artillery lieutenants or 
captains and go aloft as observers, this number being necessary 
because the strain of watching constantly is very great and the 
observers must be relieved at frequent intervals, the balloon 
otherwise being kept up continuously, both day and night. There are 
also a number of sergeants, each of whom is in charge of a 
different branch of the work, such as the inflation, transport, telephone 
service, and winding machine. No less than fifteen 3-ton to 5-ton 
motor trucks are necessary for each balloon company besides two 
or more motorcycle messengers, the care of the machines usually 
being entrusted to the corporals of the company. The remainder 
of the company are practically laborers, whose chief duties are to 
attach the ballast bags to the ropes when it is intended to hold 
the balloon on the ground for any length of time and to utilize 
their own weight for the same purpose when the balloon is about 
to go aloft or is only on the ground temporarily. In addition, 
every company has its surgeon and assistants, quartermaster, cooks, 
company clerk, and other attaches necessary to complete its 
organization, since a balloon company serves as an independent unit. 

**Equipment.** The paraphernalia required is quite as elaborate 
as that necessary to keep several aeroplanes aloft, though naturally 
of a different nature. It must all be readily portable, for a balloon 
company has to change camp more or less frequently, or as often 
as the enemy artillery happens to discover its range. To secure 
mobility is the purpose of the great number of motor trucks 
employed. One of these is equipped with a hoisting winch and a 
large drum capable of holding 3,000 or 4,000 feet of about 3/8-inch 
steel cable. The winch is driven by the same engine that propels 
the truck, and in case of emergency the engine may be applied to 
the two purposes alternately within a short space of time. For 
instance, in case of attack either by shrapnel from an enemy 
battery or by a hostile aviator, it may be used to quickly haul in 
or let out cable to change the altitude of the balloon, or it may be 
employed to drive the truck to another and more favorable 
location with the balloon in tow. 

Another truck houses a complete telephone exchange, since the 
observers in the balloon may wish to communicate with any one 
of a number of batteries which they are serving. Telephone 
communication is established by means of an insulated wire which 
forms the core of the cable, while the steel cable itself acts as the 
return wire to complete the circuit. In some cases, a separate 
copper cable is employed, using the steel cable as the return half 
of the circuit. In addition there is a truck for transporting the 
balloons, for the company must always have duplicate equipment 
at hand in case of the destruction of the balloon it is using or, as 
more frequently happens, damage of a nature that requires hours or 
days to repair. In addition to the balloon itself, there are covers 
and the ground cloth, as in inflating a balloon no part of its fabric 
must be allowed to touch the ground because of the danger of stones 
or sticks tearing rents in it. The balloon proper and its immediate 
accessories utilize at least one and sometimes two motor trucks. 

To hold the balloon on the ground when out of service, there 
are eighty sacks of sand weighing 25 pounds each, or an aggregate 
of 1 ton of ballast, in addition to which there are necessary a 
large number of steel screw stakes, spare ropes and parts, ladders 
and the like, besides the basket and its equipment. The stakes 
are employed to hold the balloon down in a heavy wind by 
"pegging" it in the same manner as a tent. Three or four trucks are 
required to carry the large supply of hydrogen necessary, which 
entails the transportation of 130 to 150 containers. Each container 
holds several thousand cubic feet of gas under high pressure, which 
is released through a reducing valve. Some of the other 
transportation units required are the "cook wagon," quartermaster’s stores 
truck, truck for carrying tents, blankets, and other impediments for 
the men, and the "doctor’s wagon" (ambulance). 

**Advantages of Kite Balloon.** It became a necessity to 
resurrect the captive balloon and bring it up to date, not simply 
because the Germans were employing it in numbers, but because 
experience demonstrated that it possessed numerous advantages 
over the aeroplane for artillery observation. The observer in an 
aeroplane is carried back and forth over and around the location 
he wishes to watch, at high speed and at a constantly varying 
altitude. He must communicate by means of either signals or 
wireless, and it is not always possible for him in either case to 
know whether his signals have been received and understood, 
since it is possible to transmit messages by wireless from an 
aeroplane but a very difficult matter to receive. The observers in 
a kite balloon, on the other hand, have the advantage of being 
able to scrutinize a certain sector constantly with the aid of 
powerful glasses. With a few weeks of experience in observing a given 
terrain they become so familiar with it that any changes or the 
movements of troops or supplies are quickly distinguished. The 
greatest advantage, however, is that the information thus acquired 
may be instantly transmitted not merely to one but to any one 
or all of a group of batteries extending over a mile or two of 
front in either direction, the balloons being stationed 4 to 6 
miles apart. The observers are fitted with portable head sets so 
that they speak directly into their telephones without the 
necessity of removing the glasses from their eyes, which enables 
them to watch the fall of the shells and tell the battery 
attendant in the dugout alongside the gun whether a shell fell "short", 
"over," "left," or "right," and the amount of correction needed 
before the smoke from the explosion has cleared away. With 
the aid of close corrections of this nature the battery 
commander is in a position to get the range exactly without the 
great expenditure of ammunition that firing entirely by map or 
with the assistance of aeroplane observers entails. Instances are 
recorded in which a 9.5-inch shell has been landed right in a 
concrete "pill-box" not over 15 feet square from a distance of 
3 miles after six trial shots had been fired to obtain the range. 
Such a shot is reported back to the battery by the balloon 
observer as a "direct hit," and it is only necessary to fire the gun 
at the same range and direction to score as often as necessary. 

**Duties of Balloon Crew.** Each kite balloon carries aloft two 
observers, Fig. 28, both of whom can concentrate their entire 
attention on the work of "spotting," since they have nothing to do with 
the control of the balloon itself, except to give orders. Their chief 
duties consist of "counter-battery" observation, that is, spotting 
the location of enemy batteries, and being constantly alert to 
detect any suspicious movements back of the enemy’s lines, such 
as movements of troops, ammunition, or supplies. The batteries 
controlled from observation balloons are the "heavies," which are 
located 1 mile or more back of the front line trenches and to the 
gunners of which the objects they are firing at are never visible. 
Some of the heaviest guns mounted on specially constructed 
railway trucks are often fired from points 5 miles or more back of 
the lines. In fact, when balked in their attempt to take Calais, the 
Germans bombarded the town with the aid of long-range naval 
guns from a distance of over 15 miles and every shot dropped 
into either some part of the city or its outskirts. Buildings, hills, 
or specially constructed and concealed observation towers are 
frequently utilized in conjunction with captive balloons to serve 
as auxiliary observation posts, so that the base line connecting the 
two may be used to triangulate distances and thus calculate them 
more accurately than is possible by direct observation from a 
single point. 

.. figure:: images/Image28.jpg
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   :alt: Fig. 28. French Kite Balloon Observers about to Ascend
   
   Fig. 28. French Kite Balloon Observers about to Ascend 
   *Copyright by Committee on Public Information, Washington, D.C.*

**Risks Incurred.** *Enemy Fire.* While the observers in a kite 
balloon are not subjected to all the risks that the aviator must 
encounter when he goes aloft or, at least, not to the same extent, 
their lot is far from being free from danger. One of the duties 
of the reconnoitering aviator is to destroy observation balloons by 
means of incendiary bombs equipped with fishhooks which catch 
in the fabric or by the use of his machine gun. Enemy batteries 
may also succeed in getting the range of the balloon and fire at it 
with large caliber shrapnel, which spreads its fragments over an 
area 100 yards or more in diameter when it bursts. So many of 
the German balloons were downed by French and British aviators 
in the early part of the war—and the Germans retaliated in 
kind—that a battle plane is now always detailed to keep watch above the 
balloon to ward off attacks by aeroplanes. 

*Escape of Balloon.* In addition to the risk of being shot down, 
there is the ever-present danger of the balloon being wrecked by a 
sudden squall or of its breaking away from its windlass through the 
parting of the cable and floating over the enemy lines. Balloons 
have been lost through both causes in a number of instances. Each 
of the two observers wears a heavy harness to which is attached a 
parachute suspended by a light cord from the rigging of the balloon, 
so that in case of emergency they may save themselves by jumping 
without having to make any preparations for their sudden drop. 

In case of the breakage of the cable, which usually results 
from a strong wind coming up suddenly and putting a terrific 
strain on the steel line by jerking it, the observers are guided 
in their actions by the direction in which the balloon moves. 
When it is carrying them back over their own territory, they 
navigate in the same manner as a free balloon, coming to the ground 
as soon as a favorable landing place can be reached. Instruction in 
free ballooning is accordingly an important part of the curriculum 
that the kite balloon observers must go through. Should the 
wind be in the opposite direction, however, as only too often proves 
to be the case, all instruments, papers, and maps are immediately 
thrown over the side and the observers promptly follow suit in 
their parachutes, abandoning the balloon to its fate. As the 
balloon travels with the speed of the wind, once it is released, 
and the parachute of the descending observer is carried in the same 
direction, prompt action is vital to prevent coming to the ground 
in the enemy’s territory. In a 30-mile wind, for example, only 
eight minutes would elapse from the moment that the balloon 
broke away until it traversed the 4 miles intervening between its 
station and the enemy’s lines. On some occasions, kite balloons 
which were not fit for further service have been loaded with 
explosives and released from a height that would cause them 
to land well within the enemy’s territory with disastrous results 
to the men detailed to capture them. 

**Marine Service.** The kite balloon was first used by the 
British naval forces in their operations against the Dardanelles and 
proved so valuable that they have since been employed in fleet 
expeditions in the North Sea as well as for anti-submarine work. 
In the latter form of service, they have the same superiority over 
the aeroplane for observation that they possess in land operations. 
The ship naturally cannot run the risk of remaining stationary, 
but as the speed of the balloon is the same as that of the ship 
towing it, the observers do not pass over a given area with 
anything like the velocity of an aeroplane, while their elevated 
position affords the same advantages for detecting the presence of the 
submerged submarine or the approach of enemy vessels. 

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    EXAMINATION PAPER 

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    DIRIGIBLE BALLOONS

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**Read Carefully:** Place your name and full address at the head of the 
paper. Any cheap, light paper like the sample previously sent you may be 
used. Do not crowd your work, but arrange it neatly and legibly. *Do not 
copy the answers from the Instruction Paper; use your own words, so that we 
may be sure you understand the subject.* 

1. What essential features of design did Meusnier’s first dirigible incorporate? 

2. Describe the difference between rigid, semi-rigid, and flexible types of dirigibles. 

3. State the laws governing the increase of resistance with speed, the increase of power necessary for a given increase of speed, and the ratio in which the volume and area of the gas bag increase with increased dimensions. 

4. What provides the lifting power of the dirigible and how is this lifting power utilized? Why should this lifting power be so much less at night than in the daytime? What is net lifting power? 

5. What are air balloonets? How and for what purpose are they used? 

6. What is the most efficient form of envelope for the dirigible, and why? 

7. Why cannot the ordinary spherical balloon be propelled as a dirigible? 

8. Is the form of the stern as important as the bow? 

9. What is longitudinal stability and how is it obtained? 

10. How is stability of direction obtained? What are stabilizing planes? 

11. Why must a form of suspension for the car that cannot be accidentally displaced with relation to the balloon be provided? 

12. Theoretically, where should the propulsive effort be applied to a dirigible? What factors affect the placing of the propeller and 
what has been proved to be the most practical solution of the problem? 

13. Discuss the advantages of the kite balloon over the aeroplane for observation. 

14. What is the effect of the wind on a modern kite balloon? 

15. What is the difference between "pounds per horsepower" and "pounds per horsepower hour" as applied to the motor of a dirigible? Which is more important? 

10. Sketch and explain the Astra-Torres suspension. 

17. What differences exist between a Zeppelin and a Schutte-Lanz dirigible? 

18. Describe the "L-49", discussing power plant and control. 

19. Define static and dynamic equilibrium as applied to the dirigible. 

20. Is the Zeppelin effective? Discuss fully. 

**After completing the work, add and sign the following statement:**

I hereby certify that the above work is entirely my own. 

(Signed) 

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