So much has been said and written concerning the Zeppelin airship,
particularly in its military aspect, that all other developments in
this field have sunk into insignificance so far as the general public is
concerned. The Zeppelin dirigible has come to be generally regarded as
the one and only form of practical lighter-than-air type of aircraft.
Moreover, the name has been driven home with such effect that it is
regarded as the generic term for all German airships.
These are grievous fallacies. The Zeppelin is merely one of a variety of
types, even in Germany, although at the moment it probably ranks as
the solitary survivor of the rigid system of construction. At one time,
owing to the earnestness with which the advantages of this form of
design were discussed, and in view of the fact that the Zeppelin
certainly appeared to triumph when all other designs failed, Great
Britain was tempted to embrace the rigid form of construction. The
building of an immense vessel of this class was actively supported
and it was aptly christened the "May-fly." Opponents of the movement
tempered their emphatic condemnatory criticism so far as to remark that
it MAY FLY, but as events proved it never did. The colossal craft
broke its back before it ever ventured into the air, and this solitary
experience proving so disastrous, the rigid form of construction was
abandoned once and for all. The venture was not in vain; it brought home
to the British authorities more convincingly than anything else that
the Zeppelin was a mechanical monstrosity. The French never even
contemplated the construction of such a craft at that time, estimating
it at its true value, and the British failure certainly served to
support French antagonism to the idea. Subsequently, however, an attempt
at rigid construction was made in France with the "Spiess" airship,
mainly as a concession to public clamour.
Even in Germany itself the defects of the Zeppelin were recognised and
a decided effort to eliminate them was made by Professor Schutte in
co-operation with a manufacturer of Mannheim named Lanz. The joint
product of their ambitions, the Schutte-Lanz, is declared to be superior
to the Zeppelin, but so far it has failed to justify any of the claims
of its designers. This vessel, which also favours the colossal, is
likewise of the rigid type, but realising the inherent dangers accruing
from the employment of metal for the framework, its constructors have
used wood, reinforced and strengthened where necessary by metallic
angle-iron, plates, and bracing; this utilisation of metal is, however,
carried out very sparingly. The first vessel of this class was a huge
failure, while subsequent craft have not proved much more successful.
In fact, one of the largest German airships ever designed, L4, is, or
rather was, a Schutte-Lanz, with a capacity of 918,000 cubic feet, but
over 6,000 pounds lighter than a Zeppelin of almost similar dimensions.
I say "was" since L4 is no more. The pride of its creators evinced a
stronger preference for Davy Jones' Locker than its designed realm. Yet
several craft of this type have been built and have been mistaken for
Zeppelins owing to the similarity of the broad principles of design and
their huge dimensions. In one vital respect they are decidedly inferior
to their contemporary--they are not so speedy.
The most successful of the German lighter-than-air machines are those
known respectively as the semi rigid and non-rigid types, the best
examples of which are the Gross and Parseval craft. Virtually they are
Teutonic editions of the successful French craft of identical design by
which they were anticipated. The Lebaudy is possibly the most famous of
the French efforts in this direction. The gas-bag has an asymmetrical
shape, and is pointed at both ends, although the prow is blunter or
rounder than the stem. The gas-bag comprises a single chamber for the
inflating agent, the distended shape of the envelope being sustained by
means of an air-ballonet. By varying the contents of the latter through
the agency of a pump the tension of the gas in the lifting envelope can
be maintained, and the shape of the inflated balloon preserved under all
conditions.
Beneath the gas-bag is a long strengthened girder, and from this in turn
the car is suspended. It is the introduction of this rigid girder which
is responsible for the descriptive generic term of "semi-rigid." On the
other hand the "non-rigid" type may be roughly described as a pisciform
balloon fitted with propelling machinery, inasmuch as the car containing
the driving machinery is suspended from the balloon in the manner of
the car in the ordinary drifting vessel. So far as the French effort is
concerned the Bayard-Clement type is the best example of the non-rigid
system; it is represented in Germany by the Parseval class.
The Gross airship has been definitely adopted as a military machine
by the German authorities, and figures in the "M" class. The "M-IV"
completed in 1913 is the largest of this type, and differs from its
prototypes in that it carries two cars, each fitted with motors, whereas
the earlier machines were equipped with a single gondola after the
French pattern. This vessel measures 320 feet in length, has a maximum
diameter of 44 1/2 feet, displaces 13 tons, and is fitted with motors
developing 450 horse-power, which is sufficient to give it a speed of
47 miles per hour. This vessel represents a huge advance upon its
predecessors of this design, inasmuch as the latter were about 245 feet
in length by 36 1/4 feet in diameter, and displaced only six tons,
while the single car was provided with a motor developing only 150
horse-power, the speed being 28 miles per hour. Thus it will be seen
that a huge development has suddenly taken place, a result due no doubt
to the co-operation of the well-known engineer Basenach. The "M-IV"
is essentially an experiment and great secrecy has been maintained
in regard to the trials which have been carried out therewith, the
authorities merely vouchsafing the fact that the airship has proved
completely successful in every respect; conclusive testimony of this
is offered by the inclusion of the vessel in the active aerial fleet of
Germany.
But it is the Parseval which is regarded as the finest type of airship
flying the German flag. This vessel is the product of slow evolution,
for it is admitted to be a power-driven balloon. Even the broad lines
of the latter are preserved, the shape being that of a cylinder with
rounded ends. It is the direct outcome of the "Drachen-Balloon,"
perfected by Parseval and Siegsfeld, the captive balloon which is an
indispensable part of the German military equipment.
The complete success of the suspension system in this captive balloon
prompted Parseval to continue his researches and experiments in regard
to the application of power to the vessel, so as to induce it to move
independently of the wind. The suspension system and the car are the
outstanding features of the craft. It is non-rigid in the strictest
interpretation of the term, although, owing to the incorporation of
the steadying hollow "mattress" (as it is called by its inventor), the
strength of the suspension system, and the substantial character of the
car, it conveys an impression of great solidity. The thinnest rope,
both manilla and steel, in the suspension system is as thick as a man's
finger, while the car, measuring 30 feet in length by 6 feet in width,
carried out in wood, is a striking example of the maximum of strength
with the minimum of weight, being as steady and as solid as a boat's
deck. The propellers are collapsible, although in the latest craft of
this class they are semi-rigid.
The mechanical equipment is also interesting. There are two propellers,
and two motors, each nominally driving one propeller. But should one
motor break down, or motives of economy, such as husbanding of fuel,
render it advisable to run upon one engine, then the two propellers may
be driven by either of the motors.
The inventor has perfected an ingenious, simple, and highly efficient
coupling device to attain this end, but to ensure that the propeller
output is of the maximum efficiency in relation to the engine, the pitch
of the propellers may be altered and even reversed while the engine is
running. When one motor only is being used, the pitch is lowered until
the propellers revolve at the speed which they would attain if both
engines were in operation. This adjustment of the propeller pitch to the
most economical engine revolutions is a distinctive characteristic, and
contributes to the efficiency and reliability of the Parseval dirigible
to a very pronounced degree.
Steering in the vertical plane is also carried out upon distinctive
lines. There are no planes for vertical steering, but movement is
accomplished by tilting the craft and thus driving the gas from one end
of the balloon to the other. This is effected by the manipulation of the
air-ballonets, one of which is placed at the prow and stem of the gas
bag respectively. If it is desired to descend the gas is driven from the
forward to the after end of the envelope, merely by inflating the bow
ballonet with air by means of a pump placed in the car. If ascent is
required, the after-ballonet is inflated, thereby driving the gas to the
forward end of the balloon, the buoyancy of which is thus increased.
The outstanding feature of the "Drachen-Balloon" is incorporated in
the airship. This is the automatic operation of the safety valve on the
gas-bag directly by the air ballonets. If these ballonets empty owing
to the pressure of the gas within the envelope, a rope system disposed
within the balloon and connecting the ballonets and the gas-valve at the
top is stretched taut, thereby opening the gas-valve. In this manner the
gas-pressure becomes reduced until the ballonets are enabled to exercise
their intended function. This is a safety precaution of inestimable
value.
The Parseval is probably the easiest dirigible to handle, inasmuch as it
involves no more skill or knowledge than that required for an ordinary
free balloon. Its movements in the vertical plane are not dissimilar
to those of the aeroplane, inasmuch as ascent and descent are normally
conducted in a "screwing" manner, the only exception being of course
in abrupt descent caused by the ripping of the emergency-valve. On one
occasion, it is stated, one of the latest machines of this type,
when conducting experimental flights, absolutely refused to descend,
producing infinite amusement both among the crowd and those on board.
The development of the Parseval is directly attributable to the
influence and intimate interest of the Kaiser, and undoubtedly this
represents the wisest step he ever made in the realm of aeronautics. It
certainly has enabled the German military machine to become possessed of
a significant fleet of what may be described as a really efficient and
reliable type of dirigible. The exact number of military Parsevals in
commission is unknown, but there are several classes thereof, in the
nature of aerial cruisers and vedettes.
The largest and most powerful class are those known as the B type,
measuring about 240 feet in length by 40 feet maximum diameter,
of 223,000 cubic feet capacity, and fitted with two motorsand two
propellers. This vessel carries about 10 passengers, can climb to a
maximum height of approximately 8,500 feet, and is capable of remaining
in the air for twenty hours upon a single fuel charge. While this is
the largest and most serviceable type of Parseval designed for
military duties, there is another, the A class, 200 feet in length with
accommodation for six passengers in addition to the crew of three, which
is capable of attaining a maximum altitude of 6,700 feet, and has an
endurance capacity of 15 hours. This class also is fitted with twin
propellers and motors. In addition there are the C and E classes,
carrying from four to eight passengers, while the vedettes are
represented by the D and F classes, which have a maximum altitude of
2,000 feet and can remain aloft for only five hours upon a single fuel
charge. These smaller vessels, however, have the advantage of requiring
only one or two men to handle them. The present military Parseval
dirigible is made in one of these five standardised classes, experience
having established their efficiency for the specified military services
for which they are built. In point of speed they compare favourably with
the latest types of Zeppelin, the speeds of the larger types ranging
from 32 to 48 miles per hour with a motor effort of 360 to 400
horse-power.
So far as the French airships of war are concerned, the fleet is
somewhat heterogeneous, although the non-rigid type prevails. The French
aerial navy is represented by the Bayard-Clement, Astra, Zodiac, and the
Government-built machines. Although the rigid type never has met with
favour in France, there is yet a solitary example of this system of
construction--the Spiess, which is 460 feet in length by 47 feet in
diameter and has a displacement of 20 tons. The semi-rigid craft are
represented by the Lebaudy type, the largest of which measures 293 feet
in length by 51 feet in diameter, and has a displacement of 10 tons.
One may feel disposed to wonder why the French should be apparently
backward in this form of aerial craft, but this may be explained by the
fact that the era of experiment had not been concluded at the time war
was declared, with the result that it has been somewhat difficult to
determine which type would meet the military requirements of the country
to the best advantage. Moreover, the French military authorities evinced
a certain disposition to relegate the dirigible to a minor position,
convinced that it had been superseded by the heavier-than-air machine.
Taken on the whole, the French airship fleet is inferior to the German
in point of speed, if not numerically, but this deficiency is more than
counterbalanced by the skill and ability of the men manning their craft,
who certainly are superior to their contemporaries in Germany, combined
with the proved character of such craft as are in service.
The same criticism may be said to apply to Great Britain. That
country was backward in matters pertaining to the airship, because its
experiments were carried out spasmodically while dependence was reposed
somewhat too much upon foreign effort. The British airships are small
and of low speed comparatively speaking. Here again it was the advance
of the aeroplane which was responsible for the manifestation of a
somewhat indifferent if not lethargic feeling towards the airship.
Undoubtedly the experiments carried out in Great Britain were somewhat
disappointing. The one and only attempt to out-Zeppelin the Zeppelin
resulted in disaster to the craft before she took to the air, while
the smaller craft carried out upon far less ambitious lines were
not inspiritingly successful. Latterly the non-rigid system has been
embraced exclusively, the craft being virtually mechanically driven
balloons. They have proved efficient and reliable so far as they go, but
it is the personal element in this instance also which has contributed
so materially to any successes achieved with them.
But although Great Britain and France apparently lagged behind the
Germans, appreciable enterprise was manifested in another direction.
The airship was not absolutely abandoned: vigilance was maintained for
a superior type of craft. It was an instance of weighing the advantages
against the disadvantages of the existing types and then evolving for a
design which should possess the former without any of the latter. This
end appears to be achieved with the Astra type of dirigible, the story
of the development of which offers an interesting chapter in the annals
of aeronautics.
In all lighter-than-air machines the resistance to the air offered
by the suspension ropes is considerable, and the reduction of this
resistance has proved one of the most perplexing problems in the
evolution of the dirigible. The air is broken up in such a manner by
the ropes that it is converted into a brake or drag with the inevitable
result that the speed undergoes a severe diminution. A full-rigged
airship such as the Parseval, for instance, may present a picturesque
appearance, but it is severely unscientific, inasmuch as if it were
possible to eliminateor to reduce the air-resistance offered by the
ropes, the speed efficiency might be raised by some sixty per cent and
that without any augmentation of the propelling effort. As a matter
of fact Zeppelin solved this vexatious problem unconsciously. In his
monster craft the resistance to the air is reduced to a remarkable
degree, which explains why these vessels, despite all their other
defects are able to show such a turn of speed.
It was this feature of the Zeppelin which induced Great Britain to
build the May-fly and which likewise induced the French Government to
stimulate dirigible design and construction among native manufacturers,
at the same time, however, insisting that such craft should be equal at
least in speed to the Zeppelins. The response to this invitation was the
Spiess, which with its speed of 45 miles per hour ranked, until 1914, as
one of the fastest dirigibles in the French service.
In the meantime a Spanish engineer, Senor Torres, had been quietly
working out a new idea. He realised the shortcomings of the prevailing
types of airships some eleven years ago, and unostentatiously and
painstakingly set out to eliminate them by the perfection of a new type
of craft. He perfected his idea, which was certainly novel, and then
sought the assistance of the Spanish Government. But his fatherland was
not adapted to the prosecution of the project. He strove to induce the
authorities to permit even a small vessel to be built, but in vain. He
then approached the French Astra Company. His ambition was to build a
vessel as large as the current Zeppelin, merely to emphasise the value
of his improvement upon a sufficiently large scale, and to enable
comparative data concerning the two designs to be obtained. But the
bogey of expense at first proved insuperable. However, the French
company, decided to give the invention a trial, and to this end a small
"vedette" of about 53,000 cubic feet displacement was built.
Although an unpretentious little vessel, it certainly served to
emphasise the importance of the Torres idea. It was pitted against the
"Colonel Renard," the finest ship at that time in the French aerial
service, which had proved the fastest airship in commission, and
which also was a product of the Astra Company. But this fine craft was
completely outclassed by the puny Astra-Torres.
The builders and the inventor were now additionally anxious to
illustrate more emphatically the features of this design and to build
a far larger vessel. The opportunity was offered by the British
Government, which had been following the experiments with the small
Astra-Torres in France. An order was given for a vessel of 282,500
cubic feet displacement; in this instance it was ranged against another
formidable rival--the Parseval. But the latter also failed to hold its
own against the Spanish invention, inasmuch as the Astra-Torres built
for the British authorities exceeded a speed of 50 miles per hour in the
official tests. This vessel is still doing valuable duty, being attached
to the British air-service in France.
The achievements of the British vessel were not lost upon the French
Government, which forthwith placed an order for a huge vessel of 812,200
cubic feet capacity, equipped with motors developing 1,000 horse-power,
which it was confidently expected would enable a speed of 60 miles per
hour to be attained. Thus France would be able to meet the Germans upon
fairly level terms, inasmuch as the speed of the latest Zeppelins does
not exceed 60 miles per hour. So confident were the authorities that a
second order for an even larger vessel was placed before the first large
craft was completed.
This latter vessel is larger than any Zeppelin yet built, seeing that
it displaces 38 tons, and is fitted with motors developing 1,000
horse-power. It has recently been completed, and although the results
of the trials, as well as the dimensions of the craft have not been
published, it is well known that the speed has exceeded 60 miles per
hour, so that France now possesses the speediest dirigible in the world.
The Torres invention has been described as wonderful, scientifically
perfect and extremely simple. The vessel belongs to the non-rigid class,
but the whole of the suspension system is placed within the gas-bag, so
that the air-resistance offered by ropes is virtually eliminated in its
entirety, for the simple reason that practically no ropes are placed
outside the envelope. The general principle of design may be gathered
from the accompanying diagram. It is as if three sausage-shaped
balloons were disposed pyramidally--two lying side by side with one
super-imposed, with the bags connected at the points where the circular
sections come into contact. Thus the external appearance of the envelope
is decidedly unusual, comprising three symmetrical ridges. At the points
where the three bags come into contact cloth bands are stretched across
the arcs, thereby forming a cord. The suspension system is attached to
the upper corners of the inverted triangle thus formed, and converges
in straight lines through the gas space. The bracing terminates in
collecting rings from which a short vertical cable extends downwards
through a special accordion sleeve to pass through the lower wall of the
envelope. These sleeves are of special design, the idea being to permit
the gas to escape under pressure arising from expansion and at the
same time to provide ample play for the cable which is necessary in a
flexible airship.
This cable emerges from the envelope only at the point or points where
the car or cars is or are placed. In the British airship of this type
there is only one car, but the larger French vessels are equipped
with two cars placed tandem-wise. The vertical cable, after extending
downwards a certain distance, is divided, one rope being attached
to one, and the second to the other side of the car. The two-bladed
propellers are disposed on either side of the car, in each of which a
500 horse-power motor is placed.
The Astra-Torres type of dirigible may be said to represent the latest
expression in airship design and construction. The invention has given
complete satisfaction, and has proved strikingly successful. The French
Government has completed arrangements for the acquisition of larger
and more powerful vessels of this design, being now in the position to
contest every step that is made by Germany in this field. The type has
also been embraced by the Russian military authorities. The Astra-Torres
airship has a rakish appearance, and although the lines of the gas-bag
are admitted to increase frictional resistance, this is regarded as a
minor defect, especially when the many advantages of the invention are
taken into consideration.