Aeroplanes and Dirigibles of War
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Frederick A. Talbot >> Aeroplanes and Dirigibles of War
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Furthermore it is stated to be fitted with a small gyroscope in
the manner of the torpedo used in the seas, for the purpose of
maintaining direction during flight, but upon this point there is
considerable divergence of opinion among technicians, the general
idea being that the torpedo depends upon an application of the
principle of the ordinary rocket rather than upon a small engine
such as is fitted to the ordinary torpedo. The employment of a
slow combustible ensures the maintenance of the missile in the
air for a period exceeding that of the ordinary shell. It is
claimed by the Germans that this projectile will keep aloft for
half-an-hour or more, but this is a phantasy. Its maintenance of
flight is merely a matter of minutes.
The belated appearance of this much-lauded projectile and its
restricted use suggest that it is unreliable, and perhaps no more
effective than the aerial torpedo which appeared in the United
States during the Spanish-American War, and proved a complete
failure. An effective and reliable means of combating or
frustrating a dirigible attack, other than by gun-fire or resort
to the drastic remedy of ramming the enemy, has yet to be
devised.
CHAPTER XVII
WIRELESS IN AVIATION
In a previous chapter the various methods of signalling between
the ground and the airman aloft have been described. Seeing that
wireless telegraphy has made such enormous strides and has
advanced to such a degree of perfection, one naturally would
conclude that it constitutes an ideal system of communication
under such conditions in military operations.
But this is not the case. Wireless is utilised only to a very
limited extent. This is due to two causes. The one is of a
technical, the other of a strategical character.
The uninitiated, bearing in mind the comparative ease with which
wireless installations may be established at a relatively small
expense, would not unreasonably think that no serious
difficulties of a technical character could arise: at least none
which would defy solution. But these difficulties exist in two
or three different fields, each of which is peculiarly complex
and demands individual treatment.
In the first place, there is the weight of the necessary
installation. In the case of the dirigible this may be a
secondary consideration, but with the aeroplane it is a matter of
primary and vital importance. Again, under present conditions,
the noise of the motor is apt to render the intelligent
deciphering of messages while aloft a matter of extreme
difficulty, especially as these are communicated in code. The
engine noise might be effectively overcome by the use of a
muffler such as, is used with automobiles, but then there is the
further difficulty of vibration.
This problem is being attacked in an ingenious manner. It is
proposed to substitute for audible signals visual
interpretations, by the aid of an electric lamp, the fluctuations
in which would correspond to the dots and dashes of the Morse
code. Thus the airman would read his messages by sight instead
of by sound.
This method, however, is quite in its infancy, and although
attractive in theory and fascinating as a laboratory experiment
or when conducted under experimental conditions, it has not
proved reliable or effective in aeronautical operations. But at
the same time it indicates a promising line of research and
development.
Then there are the problems of weight and the aerial. So far as
present knowledge goes, the most satisfactory form of aerial yet
exploited is that known as the trailing wire. From 300 to 700
feet of wire are coiled upon a reel, and when aloft this wire is
paid out so that it hangs below the aeroplane. As a matter of
fact,when the machine is travelling at high speed it trails
horizontally astern, but this is immaterial. One investigator,
who strongly disapproves of the trailing aerial, has carried out
experiments with a network of wires laid upon and attached to the
surface of the aeroplane's wings. But the trailing wire is
generally preferred, and certainly up to the present has proved
more satisfactory.
The greatest obstacle, however, is the necessary apparatus. The
average aeroplane designed for military duty is already loaded to
the maximum. As a rule it carries the pilot and an observer, and
invariably includes a light arm for defence against an aerial
enemy, together with an adequate supply of ammunition, while
unless short sharp flights are to be made, the fuel supply
represents an appreciable load. Under these circumstances the
item of weight is a vital consideration. It must be kept within
a limit of 100 pounds, and the less the equipment weighs the more
satisfactory it is likely to prove, other things being equal.
The two most successful systems yet exploited are the Dubilier
and the Rouget. The former is an American invention, the latter
is of French origin. Both have been tested by the British
Military Aeronautical Department, and the French authorities
have subjected the French system to rigorous trials. Both
systems, within their limitations, have proved satisfactory.
The outstanding feature of the Dubilier system is the production
of sine waves of musical frequency from continuous current, thus
dispensing with the rotary converter. The operating principle is
the obtaining of a series of unidirectional impulses by a
condenser discharge, the pulsating currents following one another
at regular intervals at a frequency of 500 impulses per second,
which may be augmented up to 1,000 impulses per second. The
complete weight of such an apparatus is 40 pounds; the electric
generator, which is no larger than the motor used for driving the
ordinary table ventilating fan, accounts for 16 pounds of this
total. Under test at sea, upon the deck of a ship, a range of
250 miles has been obtained. The British Government carried out
a series of experiments with this system, using a small plant
weighing about 30 pounds, with which communication was maintained
up to about 20 miles.
In the French system the Reuget transmitter is employed. The
apparatus, including the dynamo, which is extremely small, weighs
in all 70 pounds. A small alternator of 200 watts and 100 volts
is coupled direct to the aeroplane motor, a new clutch coupler
being employed for this purpose. By means of a small transformer
the voltage is raised to 30,000 volts, at which the condenser is
charged. In this instance the musical spark method is employed.
The whole of the high tension wiring is placed within a small
space so as not to endanger the pilot, while the transformer is
hermetically sealed in a box with paraffin. The aerial comprises
a trailing wire 100 feet in length, which, however, can be
wound in upon its reel within 15 seconds. This reeled antenna,
moreover, is fitted with a safety device whereby the wire can be
cut adrift in the event of an accident befalling the aeroplane
and necessitating an abrupt descent. With this apparatus the
French authorities have been able to maintain communication over
a distance of 30 miles.
In maintaining ethereal communication with aeroplanes, however, a
portable or mobile station upon the ground is requisite, and this
station must be within the radius of the aerial transmitter, if
messages are to be received from aloft with any degree of
accuracy and reliability. Thus it will be recognised that the
land station is as important as the aeroplane equipment, and
demands similar consideration.
A wide variety of systems have been employed to meet these
conditions. There is the travelling automobile station, in which
the installation is mounted upon a motor-car. In this instance
the whole equipment is carried upon a single vehicle, while the
antenna is stowed upon the roof and can be raised or lowered
within a few seconds. If motor traction is unavailable, then
animal haulage may be employed, but in this instance the
installation is divided between two vehicles, one carrying the
transmitting and receiving apparatus and the generating plant,
the other the fuel supplies and the aerial, together with spare
parts.
The motive power is supplied by a small air cooled petrol or
gasoline motor developing eight horse-power, and coupled direct
to a 2-kilo watt alternator. At one end of the shaft of the
latter the disk discharger is mounted, its function being to
break up the train of waves into groups of waves, so as to impart
a musical sound to the note produced in the receiver. A flexible
cable transmits the electric current from the generator to the
wagon containing the instruments. The aerial is built up of
masts carried in sections.
The Germans employ a mobile apparatus which is very similar, but
in this instance the mast is telescopic. When closed it occupies
but little space. By turning the winch handle the mast is
extended, and can be carried to any height up to a maximum of
about 100 feet. The capacity of these mobile stations varies
within wide limits, the range of the largest and most powerful
installations being about 200 miles. The disadvantage of these
systems, however, is that they are condemned to territories where
the ground at the utmost is gently undulating, and where there
are roads on which four-wheeled vehicles can travel.
For operation in hilly districts, where only trails are to be
found, the Marconi Company, has perfected what may be described
as "pack" and "knapsack" installations respectively. In the
first named the whole of the installation is mounted upon the
backs of four horses. The first carries the generator set, the
second the transmitting instruments, the third the receiving
equipment, and the fourth the detachable mast and stays.
The generator is carried upon the horse's saddle, and is fitted
with a pair of legs on each side. On one side of the saddle is
mounted a small highspeed explosion motor, while on the opposite
side, in axial alignment with the motor, is a small dynamo. When
it is desired to erect the installation the saddle carrying this
set is removed from the horse's back and placed upon the ground,
the legs acting as the support. A length of shaft is then
slipped into sockets at the inner ends of the motor and dynamo
shafts respectively, thus coupling them directly, while the
current is transmitted through a short length of flexible cable
to the instruments. The mast itself is made in lengths of about
four feet, which are slipped together in the manner of the
sections of a fishing rod, and erected, being supported by means
of wire guys. In this manner an antenna from 40 to 50 feet in
height may be obtained.
The feature of this set is its compactness, the equal division of
the sections of the installation, and the celerity with which the
station may be set up and dismantled in extremely mountainous
country such as the Vosges, where it is even difficult for a
pack-horse to climb to commanding or suitable positions, there is
still another set which has been perfected by the Marconi
Company. This is the "knapsack" set, in which the whole of the
installation, necessarily light, small, and compact, is divided
among four men, and carried in the manner of knapsacks upon their
backs. Although necessarily of limited radius, such an
installation is adequate for communication within the restricted
range of air-craft.
Greater difficulties have to be overcome in the mounting of a
wireless installation upon a dirigible. When the Zeppelin was
finally accepted by the German Government, the military
authorities emphasised the great part which wireless telegraphy
was destined to play in connection with such craft. But have
these anticipations been fulfilled? By no means, as a little
reflection will suffice to prove.
In the first place, a wireless outfit is about the most dangerous
piece of equipment which could be carried by such a craft as the
Zeppelin unless it is exceptionally well protected. As is well
known the rigidity of this type of airship is dependent upon a
large and complicated network of aluminium, which constitutes the
frame. Such a huge mass of metal constitutes an excellent
collector of electricity from the atmosphere; it becomes charged
to the maximum with electricity.
In this manner a formidable contributory source of danger to the
airship is formed. In fact, this was the reason why "Z-IV"
vanished suddenly in smoke and flame upon falling foul of the
branches of trees during its descent. At the time the Zeppelin
was a highly charged electrical machine or battery as it were,
insulated by the surrounding air. Directly the airship touched
the trees a short circuit was established, and the resultant
spark sufficed to fire the gas, which is continuously exuding
from the gas bags.
After this accident minute calculations were made and it was
ascertained that a potential difference of no less than 100,00
volts existed between the framework of the dirigible and the
trees. This tension sufficed to produce a spark 4 inches in
length. It is not surprising that the establishment of the
electric equilibrium by contact with the trees, which produced
such a spark should fire the hydrogen inflation charge. In fact
the heat generated was so intense that the aluminium metallic
framework was fused. The measurements which were made proved
that the gas was consumed within 15 seconds and the envelope
destroyed within 20 seconds.
As a result of this disaster endeavours were made to persuade
Count Zeppelin to abandon the use of aluminium for the framework
of his balloon but they were fruitless, a result no doubt due to
the fact that the inventor of the airship of this name has but a
superficial knowledge of the various sciences which bear upon
aeronautics, and fully illustrates the truth of the old adage
that "a little learning is a dangerous thing." Count Zeppelin
continues to work upon his original lines, but the danger of his
system of construction was not lost upon another German
investigator, Professor Schiitte, who forthwith embarked upon the
construction of another rigid system, similar to that of
Zeppelin, at Lanz. In this vessel aluminium was completely
abandoned in favour of a framework of ash and poplar.
The fact that the aluminium constituted a dangerous collector of
electricity rendered the installation of wireless upon the
Zeppelin not only perilous but difficult. Very serious
disturbances of an electrical nature were set up, with the result
that wireless communication between the travelling dirigible and
the ground below was rendered extremely uncertain. In fact, it
has never yet been possible to communicate over distances
exceeding about 150 miles. Apart from this defect, the danger of
operating the wireless is obvious, and it is generally believed
in technical circles that the majority of the Zeppelin disasters
from fire have been directly attributable to this, especially
those disasters which have occurred when the vessel has suddenly
exploded before coming into contact with terrestrial
obstructions.
In the later vessels of this type the wireless installation is
housed in a well insulated compartment. This insulation has been
carried, to an extreme degree, which indicates that at last the
authorities have recognised the serious menace that wireless
offers to the safety of the craft, with the result that every
protective device to avoid disaster from this cause has been
freely adopted.
The fact that it is not possible to maintain cornmunication over
a distance exceeding some 20 miles is a severe handicap to the
progressive development of wireless telegraphy in this field. It
is a totally inadequate radius when the operations of the present
war are borne in mind. A round journey of 200, or even more
miles is considered a mere jaunt; it is the long distance flight
which counts, and which contributes to the value of an airman's
observations. The general impression is that the fighting line
or zone comprises merely two or three successive stretches of
trenches and other defences, representing a belt five miles or so
in width, but this is a fallacy. The fighting zone is at least
20 miles in width; that is to say, the occupied territory in
which vital movements take place represents a distance of 20
miles from the foremost line of trenches to the extreme rear,
and then comes the secondary zone, which may be a further 10
miles or more in depth. Consequently the airman must fly at
least 30 miles in a bee-line to cover the transverse belt of the
enemy's field of operations. Upon the German and Russian sides
this zone is of far greater depth, ranging up to 50 miles or so
in width. In these circumstances the difficulties of ethereal
communication 'twixt air and earth may be realised under the
present limitations of radius from which it is possible to
transmit.
But there are reasons still more cogent to explain why wireless
telegraphy has not been used upon a more extensive scale during
the present campaign. Wireless communication is not secretive.
In other words, its messages may be picked up by friend and foe
alike with equal facility. True, the messages are sent in code,
which may be unintelligible to the enemy. In this event the
opponent endeavours to render the communications undecipherable
to one and all by what is known as "jambing." That is to say, he
sends out an aimless string of signals for the purpose of
confusing senders and receivers, and this is continued without
cessation and at a rapid rate. The result is that messages
become blurred and undecipherable.
But there is another danger attending the use of wireless upon
the battlefield. The fact that the stations are of limited range
is well known to the opposing forces, and they are equally well
aware of the fact that aerial craft cannot communicate over long
distances. For instance, A sends his airmen aloft and
conversation begins between the clouds and the ground. Presently
the receivers of B begin to record faint signals. They fluctuate
in intensity, but within a few seconds B gathers that an
aeroplane is aloft and communicating with its base. By the aid
of the field telephone B gets into touch with his whole string of
wireless stations and orders a keen look-out and a listening ear
to ascertain whether they have heard the same signals. Some
report that the signals are quite distinct and growing louder,
while others declare that the signals are growing fainter and
intermittent. In this manner B is able to deduce in which
direction the aeroplane is flying. Thus if those to the east
report that signals are growing stronger, while the stations on
the west state that they are diminishing, it is obvious that the
aeroplane is flying west to east, and vice versa when the west
hears more plainly at the expense of the east. If, however, both
should report that signals are growing stronger, then it is
obvious that the aircraft is advancing directly towards them.
It was this ability to deduce direction from the sound of the
signals which led to the location of the Zeppelin which came down
at Lun6ville some months previous to the war, and which
threatened to develop into a diplomatic incident of serious
importance. The French wireless stations running south-east to
north-west were vigilant, and the outer station on the north-west
side picked up the Zeppelin's conversation. It maintained a
discreet silence, but communicated by telephone to its colleagues
behind.
Presently No. 2 station came within range, followed by Nos. 3, 4,
5, 6, and so on in turn. Thus the track of the Zeppelin was
dogged silently through the air by its wireless conversation as
easily and as positively as if its flight had been followed by
the naked eye. The Zeppelin travellers were quite ignorant of
this action upon the part of the French and were surprised when
they were rounded-up to learn that they had been tracked so
ruthlessly. Every message which the wireless of the Zeppelin had
transmitted had been received and filed by the French.
Under these circumstances it is doubtful whether wireless
telegraphy between aircraft and the forces beneath will be
adopted extensively during the present campaign. Of course,
should some radical improvement be perfected, whereby
communication may be rendered absolutely secretive, while no
intimation is conveyed to the enemy that ethereal conversation is
in progress, then the whole situation will be changed, and there
may be remarkable developments.
CHAPTER XVIII
AIRCRAFT AND NAVAL OPERATIONS
When once the flying machine had indicated its possibilities in
connection with land operations it was only natural that
endeavours should be made to adapt it to the more rigorous
requirements of the naval service. But the conditions are so
vastly dissimilar that only a meagre measure of success has been
recorded. Bomb-throwing from aloft upon the decks of battleships
appeals vividly to the popular imagination, and the widespread
destruction which may be caused by dropping such an agent down
the funnel of a vessel into the boiler-room is a favourite theme
among writers of fiction and artists. But hitting such an
objective while it is tearing at high speed through the water,
from a height of several thousand feet is a vastly different task
from throwing sticks and balls at an Aunt Sally on terra firma:
the target is so small and elusive.
Practically it is impossible to employ the flying machine,
whether it be a dirigible or an aeroplane, in this field. Many
factors militate against such an application. In the first place
there is a very wide difference between dry land and a stretch of
water as an area over which to manoeuvre. So far as the land is
concerned descent is practicable at any time and almost anywhere.
But an attempt to descend upon the open sea even when the latter
is as calm as the proverbial mill-pond is fraught with
considerable danger. The air-currents immediately above the
water differ radically from those prevailing above the surface of
the land. Solar radiation also plays a very vital part. In fact
the dirigible dare not venture to make such a landing even if it
be provided with floats. The chances are a thousand to one that
the cars will become water-logged, rendering re-ascent a matter
of extreme difficulty, if not absolutely impossible. On the
other hand, the aeroplane when equipped with floats, is able to
alight upon the water, and to rest thereon for a time. It may
even take in a new supply of fuel if the elements be propitious,
and may be able to re-ascend, but the occasions are rare when
such operations can be carried out successfully.
In operations over water the airman is confronted with one
serious danger--the risk of losing his bearings and his way. For
instance, many attempts have been made to cross the North Sea by
aeroplane, but only one has proved successful so far. The
intrepid aviator did succeed in passing from the shore of Britain
to the coast of Scandinavia. Many people suppose that because an
airman is equipped with a compass he must be able to find his
way, but this is a fallacy. The aviator is in the same plight as
a mariner who is compelled from circumstances to rely upon his
compass alone, and who is debarred by inclement weather from
deciding his precise position by taking the sun. A ship
ploughing the waters has to contend against the action of cross
currents, the speed of which varies considerably, as well as
adverse winds. Unless absolute correction for these influences
can be made the ship will wander considerably from its course.
The airman is placed in a worse position. He has no means of
determining the direction and velocity of the currents prevailing
in the atmosphere, and his compass cannot give him any help in
this connection, because it merely indicates direction.
Unless the airman has some means of determining his position,
such as landmarks, he fails to realise the fact that he is
drifting, or, even if he becomes aware of this fact, it is by no
means a simple straightforward matter for him to make adequate
allowance for the factor. Side-drift is the aviator's greatest
enemy. It cannot be determined with any degree of accuracy. If
the compass were an infallible guide the airman would be able to
complete a given journey in dense fog just as easily as in clear
weather. It is the action of the cross currents and the
unconscious drift which render movement in the air during fog as
impracticable with safety as manoeuvring through the water under
similar conditions. More than one bold and skilful aviator has
essayed the crossing of the English Channel and, being overtaken
by fog, has failed to make the opposite coast. His compass has
given him the proper direction, but the side-drift has proved his
undoing, with the result that he has missed his objective.
The fickle character of the winds over the water, especially over
such expanses as the North Sea, constitutes another and seriously
adverse factor. Storms, squalls, gales, and, in winter,
blizzards, spring up with magical suddenness, and are so severe
that no aircraft could hope to live in them. But such
visitations are more to be dreaded by the lighter-than-air than
by the heavier-than-air machines. The former offers a
considerable area of resistance to the tempest and is caught up
by the whirlwind before the pilot fully grasps the significant
chance of the natural phenomenon. Once a dirigible is swept out
of the hands of its pilot its doom is sealed.
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