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A History of Aeronautics by E. Charles Vivian

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adhered to the non-rigid type; his first dirigible made its
first flight on September 18th, 1898, starting from the Jardin
d'Acclimatation to the west of Paris; he calculated that his 3
horse-power engine would yield sufficient power to enable him to
steer clear of the trees with which the starting-point was
surrounded, but, yielding to the advice of professional
aeronauts who were present, with regard to the placing of the
dirigible for his start, he tore the envelope against the trees.
Two days later, having repaired the balloon, he made an ascent of
1,300 feet. In descending, the hydrogen left in the balloon
contracted, and Santos-Dumont narrowly escaped a serious accident
in coming to the ground.

His second machine, built in the early spring of 1899, held over
7,000 cubic feet of gas and gave a further 44 lbs. of ascensional
force. The balloon envelope was very long and very narrow; the
first attempt at flight was made in wind and rain, and the
weather caused sufficient contraction of the hydrogen for a wind
gust to double the machine up and toss it into the trees near its
starting-point. The inventor immediately set about the
construction of 'Santos-Dumont No. 3,' on which he made a number
of successful flights, beginning on November 13th, 1899. On the
last of his flights, he lost the rudder of the machine and made a
fortunate landing at Ivry. He did not repair the balloon,
considering it too clumsy in form and its motor too small.
Consequently No. 4 was constructed, being finished on the 1st,
August, 1900. It had a cubic capacity of 14,800 feet, a length
of 129 feet and greatest diameter of 16.7 feet, the power
plant being a 7 horse-power Buchet motor. Santos-Dumont sat on
a bicycle saddle fixed to the long bar suspended under the
machine, which also supported motor propeller, ballast; and
fuel. The experiment of placing the propeller at the stem
instead of at the stern was tried, and the motor gave it a speed
of 100 revolutions per minute. Professor Langley witnessed the
trials of the machine, which proved before the members of the
International Congress of Aeronautics, on September 19th, that
it was capable of holding its own against a strong wind.

Finding that the cords with which his dirigible balloon cars were
suspended offered almost as much resistance to the air as did
the balloon itself, Santos-Dumont substituted piano wire and
found that the alteration constituted greater progress than many
a more showy device. He altered the shape and size of his No. 4
to a certain extent and fitted a motor of 12 horse-power.
Gravity was controlled by shifting weights worked by a cord;
rudder and propeller were both placed at the stern. In
Santos-Dumont's book there is a certain amount of confusion
between the No. 4 and No. 5 airships, until he explains that
'No. 5' is the reconstructed 'No. 4.' It was with No. 5 that
he won the Encouragement Prize presented by the Scientific
Commission of the Paris Aero Club. This he devoted to the first
aeronaut who between May and October of 1900 should start from
St Cloud, round the Eiffel Tower, and return. If not won in
that year, the prize was to remain open the following year from
May 1st to October 1st, and so on annually until won. This was a
simplification of the conditions of the Deutsch Prize itself, the
winning of which involved a journey of 11 kilometres in 30
minutes.

The Santos-Dumont No. 5, which was in reality the modified No. 4
with new keel, motor, and propeller, did the course of the
Deutsch Prize, but with it Santos-Dumont made no attempt to win
the prize until July of 1901, when he completed the course in 40
minutes, but tore his balloon in landing. On the 8th August,
with his balloon leaking, he made a second attempt, and narrowly
escaped disaster, the airship being entirely wrecked. Thereupon
he built No. 6 with a cubic capacity of 22,239 feet and a lifting
power of 1,518 lbs.

With this machine he won the Deutsch Prize on October 19th,
1901, starting with the disadvantage of a side wind of 20 feet
per second. He reached the Eiffel Tower in 9 minutes and,
through miscalculating his turn, only just missed colliding
with it. He got No. 6 under control again and succeeded in
getting back to his starting-point in 29 1/2 minutes, thus
winning the 125,000 francs which constituted the Deutsch Prize,
together with a similar sum granted to him by the Brazilian
Government for the exploit. The greater part of this money was
given by Santos-Dumont to charities.

He went on building after this until he had made fourteen
non-rigid dirigibles; of these No. 12 was placed at the disposal
of the military authorities, while the rest, except for one that
was sold to an American and made only one trip, were matters of
experiment for their maker. His conclusions from his experiments
may be gathered from his own work:--

'On Friday, 31st July, 1903, Commandant Hirschauer and
Lieutenant-Colonel Bourdeaux spent the afternoon with me at my
airship station at Neuilly St James, where I had my three newest
airships--the racing 'No. 7,' the omnibus 'No. 10,' and the
runabout 'No. 9'--ready for their study. Briefly, I may say
that the opinions expressed by the representatives of the
Minister of War were so unreservedly favourable that a practical
test of a novel character was decided to be made. Should the
airship chosen pass successfully through it the result will be
conclusive of its military value.

'Now that these particular experiments are leaving my exclusively
private control I will say no more of them than what has been
already published in the French press. The test will probably
consist of an attempt to enter one of the French frontier towns,
such as Belfort or Nancy, on the same day that the airship
leaves Paris. It will not, of course, be necessary to make the
whole journey in the airship. A military railway wagon may be
assigned to carry it, with its balloon uninflated, with tubes of
hydrogen to fill it, and with all the necessary machinery and
instruments arranged beside it. At some station a short
distance from the town to be entered the wagon may be uncoupled
from the train, and a sufficient number of soldiers accompanying
the officers will unload the airship and its appliances,
transport the whole to the nearest open space, and at once begin
inflating the balloon. Within two hours from quitting the train
the airship may be ready for its flight to the interior of the
technically-besieged town.

'Such may be the outline of the task--a task presented
imperiously to French balloonists by the events of 1870-1, and
which all the devotion and science of the Tissandier brothers
failed to accomplish. To-day the problem may be set with better
hope of success. All the essential difficulties may be revived
by the marking out of a hostile zone around the town that must
be entered; from beyond the outer edge of this zone, then, the
airship will rise and take its flight--across it.

'Will the airship be able to rise out of rifle range? I have
always been the first to insist that the normal place of the
airship is in low altitudes, and I shall have written this book
to little purpose if I have not shown the reader the real
dangers attending any brusque vertical mounting to considerable
heights. For this we have the terrible Severo accident before
our eyes. In particular, I have expressed astonishment at
hearing of experimenters rising to these altitudes without
adequate purpose in their early stages of experience with
dirigible balloons. All this is very different, however, from a
reasoned, cautious mounting, whose necessity has been foreseen
and prepared for.'

Probably owing to the fact that his engines were not of
sufficient power, Santos-Dumont cannot be said to have solved
the problem of the military airship, although the French
Government bought one of his vessels. At the same time, he
accomplished much in furthering and inciting experiment with
dirigible airships, and he will always rank high among the
pioneers of aerostation. His experiments might have gone
further had not the Wright brothers' success in America and
French interest in the problem of the heavier-than-air machine
turned him from the study of dirigibles to that of the
aeroplane, in which also he takes high rank among the pioneers,
leaving the construction of a successful military dirigible to
such men as the Lebaudy brothers, Major Parseval, and Zeppelin.

IV. THE MILITARY DIRIGIBLE

Although French and German experiment in connection with the
production of an airship which should be suitable for military
purposes proceeded side by side, it is necessary to outline the
development in the two countries separately, owing to the
differing character of the work carried out. So far as France
is concerned, experiment began with the Lebaudy brothers,
originally sugar refiners, who turned their energies to airship
construction in 1899. Three years of work went to the production
of their first vessel, which was launched in 1902, having been
constructed by them together with a balloon manufacturer named
Surcouf and an engineer, Julliot. The Lebaudy airships were
what is known as semi-rigids, having a spar which ran
practically the full length of the gas bag to which it was
attached in such a way as to distribute the load evenly. The
car was suspended from the spar, at the rear end of which both
horizontal and vertical rudders were fixed, whilst stabilising
fins were provided at the stern of the gas envelope itself. The
first of the Lebaudy vessels was named the 'Jaune'; its length
was 183 feet and its maximum diameter 30 feet, while the cubic
capacity was 80,000 feet. The power unit was a 40 horse-power
Daimler motor, driving two propellers and giving a maximum speed
of 26 miles per hour. This vessel made 29 trips, the last of
which took place in November, 1902, when the airship was wrecked
through collision with a tree.

The second airship of Lebaudy construction was 7 feet longer
than the first, and had a capacity of 94,000 cubic feet of gas
with a triple air bag of 17,500 cubic feet to compensate for
loss of gas; this latter was kept inflated by a rotary fan. The
vessel was eventually taken over by the French Government and
may be counted the first dirigible airship considered fit on its
tests for military service.

Later vessels of the Lebaudy type were the 'Patrie' and
'Republique,' in which both size and method of construction
surpassed those of the two first attempts. The 'Patrie' was
fitted with a 60 horse-power engine which gave a speed of 28
miles an hour, while the vessel had a radius of 280 miles,
carrying a crew of nine. In the winter of 1907 the 'Patrie' was
anchored at Verdun, and encountered a gale which broke her hold
on her mooring-ropes. She drifted derelict westward across
France, the Channel, and the British Isles, and was lost in the
Atlantic.

The 'Republique' had an 80 horse-power motor, which, however,
only gave her the same speed as the 'Patrie.' She was launched
in July, 1908, and within three months came to an end which
constituted a tragedy for France. A propeller burst while the
vessel was in the air, and one blade, flying toward the
envelope, tore in it a great gash; the airship crashed to earth,
and the two officers and two non-commissioned officers who were
in the car were instantaneously killed.

The Clement Bayard, and subsequently the Astra-Torres,
non-rigids, followed on the early Lebaudys and carried French
dirigible construction up to 1912. The Clement Bayard was a
simple non-rigid having four lobes at the stern end to assist
stability. These were found to retard the speed of the airship,
which in the second and more successful construction was driven
by a Clement Bayard motor of l00 horse-power at a speed of 30
miles an hour. On August 23rd, 1909, while being tried for
acceptance by the military authorities, this vessel achieved a
record by flying at a height of 5,000 feet for two hours. The
Astra-Torres non-rigids were designed by a Spaniard, Senor
Torres, and built by the Astra Company. The envelope was of
trefoil shape, this being due to the interior rigging from the
suspension band; the exterior appearance is that of two lobes
side by side, overlaid by a third. The interior rigging, which
was adopted with a view to decreasing air resistance, supports a
low-hung car from the centre of the envelope; steering is
accomplished by means of horizontal planes fixed on the envelope
at the stern, and vertical planes depending beneath the envelope,
also at the stern end.

One of the most successful of French pre-war dirigibles was a
Clement Bayard built in 1912. In this twin propellers were
placed at the front and horizontal and vertical rudders in a
sort of box formation under the envelope at the stern. The
envelope was stream-lined, while the car of the machine was
placed well forward with horizontal controlling planes above it
and immediately behind the propellers. This airship, which was
named 'Dupuy de Lome,' may be ranked as about the most
successful non-rigid dirigible constructed prior to the War.

Experiments with non-rigids in Germany was mainly carried on by
Major Parseval, who produced his first vessel in 1906. The main
feature of this airship consisted in variation in length of the
suspension cables at the will of the operator, so that the
envelope could be given an upward tilt while the car remained
horizontal in order to give the vessel greater efficiency in
climbing. In this machine, the propeller was placed above and
forward of the car, and the controlling planes were fixed
directly to the envelope near the forward end. A second vessel
differed from the first mainly in the matter of its larger size,
variable suspension being again employed, together with a similar
method of control. The vessel was moderately successful, and
under Major Parseval's direction a third was constructed for
passenger carrying, with two engines of 120 horsepower, each
driving propellers of 13 feet diameter. This was the most
successful of the early German dirigibles; it made a number of
voyages with a dozen passengers in addition to its crew, as well
as proving its value for military purposes by use as a scout
machine in manoeuvres. Later Parsevals were constructed of
stream-line form, about 300 feet in length, and with engines
sufficiently powerful to give them speeds up to 50 miles an hour.

Major Von Gross, commander of a Balloon Battalion, produced
semi-rigid dirigibles from 1907 onward. The second of these,
driven by two 75 horse-power Daimler motors, was capable of a
speed of 27 miles an hour; in September of 1908 she made a trip
from and back to Berlin which lasted 13 hours, in which period
she covered 176 miles with four passengers and reached a height
of 4,000 feet. Her successor, launched in April of 1909,
carried a wireless installation, and the next to this, driven by
four motors of 75 horse-power each, reached a speed of 45 miles
an hour. As this vessel was constructed for military purposes,
very few details either of its speed or method of construction
were made public.

Practically all these vessels were discounted by the work of
Ferdinand von Zeppelin, who set out from the first with the idea
of constructing a rigid dirigible. Beginning in 1898, he built a
balloon on an aluminium framework covered with linen and silk,
and divided into interior compartments holding linen bags which
were capable of containing nearly 400,000 cubic feet of
hydrogen. The total length of this first Zeppelin airship was
420 feet and the diameter 38 feet. Two cars were rigidly
attached to the envelope, each carrying a 16 horse-power motor,
driving propellers which were rigidly connected to the aluminium
framework of the balloon. Vertical and horizontal screws were
used for lifting and forward driving and a sliding weight was
used to raise or lower the stem of the vessel out of the
horizontal in order to rise or descend without altering the load
by loss of ballast or the lift by loss of gas.

The first trial of this vessel was made in July of 1900, and was
singularly unfortunate. The winch by which the sliding weight
was operated broke, and the balloon was so bent that the working
of the propellers was interfered with, as was the steering. A
speed of 13 feet per second was attained, but on descending, the
airship ran against some piles and was further damaged. Repairs
were completed by the end of September, 1900, and on a second
trial flight made on October 21st a speed of 30 feet per second
was reached.

Zeppelin was far from satisfied with the performance of this
vessel, and he therefore set about collecting funds for the
construction of a second, which was completed in 1905. By this
time the internal combustion engine had been greatly improved,
and without any increase of weight, Zeppelin was able to instal
two motors of 85 horse-power each. The total capacity was
367,000 cubic feet of hydrogen, carried in 16 gas bags inside
the framework, and the weight of the whole construction was 9
tons--a ton less than that of the first Zeppelin airship. Three
vertical planes at front and rear controlled horizontal
steering, while rise and fall was controlled by horizontal
planes arranged in box form. Accident attended the first trial
of this second airship, which took place over the Bodensee on
November 30th, 1905, 'It had been intended to tow the raft, to
which it was anchored, further from the shore against the wind.
But the water was too low to allow the use of the raft. The
balloon was therefore mounted on pontoons, pulled out into the
lake, and taken in tow by a motor-boat. It was caught by a
strong wind which was blowing from the shore, and driven ahead
at such a rate that it overtook the motor-boat. The tow rope
was therefore at once cut, but it unexpectedly formed into knots
and became entangled with the airship, pulling the front end
down into the water. The balloon was then caught by the wind
and lifted into the air, when the propellers were set in motion.
The front end was at this instant pointing in a downward
direction, and consequently it shot into the water, where it was
found necessary to open the valves.'[*]

[*] Hildebrandt, Airships Past and Present.

The damage done was repaired within six weeks, and the second
trial was made on January 17th, 1906. The lifting force was too
great for the weight, and the dirigible jumped immediately to
1,500 feet. The propellers were started, and the dirigible
brought to a lower level, when it was found possible to drive
against the wind. The steering arrangements were found too
sensitive, and the motors were stopped, when the vessel was
carried by the wind until it was over land--it had been intended
that the trial should be completed over water. A descent was
successfully accomplished and the dirigible was anchored for the
night, but a gale caused it so much damage that it had to be
broken up. It had achieved a speed of 30 feet per second with
the motors developing only 36 horse-power and, gathering from
this what speed might have been accomplished with the full 170
horse-power, Zeppelin set about the construction of No. 3, with
which a number of successful voyages were made, proving the value
of the type for military purposes.

No. 4 was the most notable of the early Zeppelins, as much on
account of its disastrous end as by reason of any superior merit
in comparison with No. 3. The main innovation consisted in
attaching a triangular keel to the under side of the envelope,
with two gaps beneath which the cars were suspended. Two Daimler
Mercedes motors of 110 horse-power each were placed one in each
car, and the vessel carried sufficient fuel for a 60-hour cruise
with the motors running at full speed. Each motor drove a pair
of three-bladed metal propellers rigidly attached to the
framework of the envelope and about 15 feet in diameter. There
was a vertical rudder at the stern of the envelope and horizontal
controlling planes were fixed on the sides of the envelope. The
best performances and the end of this dirigible were summarised
as follows by Major Squier:--

'Its best performances were two long trips performed during the
summer of 1908. The first, on July 4th, lasted exactly 12
hours, during which time it covered a distance of 235 miles,
crossing the mountains to Lucerne and Zurich, and returning to
the balloon-house near Friedrichshafen, on Lake Constance. The
average speed on this trip was 32 miles per hour. On August
4th, this airship attempted a 24-hour flight, which was one of
the requirements made for its acceptance by the Government. It
left Friedrichshafen in the morning with the intention of
following the Rhine as far as Mainz, and then returning to its
starting-point, straight across the country. A stop of 3 hours
30 minutes was made in the afternoon of the first day on the
Rhine, to repair the engine. On the return, a second stop was
found necessary near Stuttgart, due to difficulties with the
motors, and some loss of gas. While anchored to the ground, a
storm arose which broke loose the anchorage, and, as the balloon
rose in the air, it exploded and took fire (due to causes which
have never been actually determined and published) and fell to
the ground, where it was completely destroyed. On this journey,
which lasted in all 31 hours 15 minutes, the airship was in the
air 20 hours 45 minutes, and covered a total distance of 378
miles.

'The patriotism of the German nation was aroused. Subscriptions
were immediately started, and in a short space of time a quarter
of a million pounds had been raised. A Zeppelin Society was
formed to direct the expenditure of this fund. Seventeen
thousand pounds has been expended in purchasing land near
Friedrichshafen; workshops were erected, and it was announced
that within one year the construction of eight airships of the
Zeppelin type would be completed. Since the disaster to
'Zeppelin IV.' the Crown Prince of Germany made a trip in
'Zeppelin No. 3,' which had been called back into service, and
within a very few days the German Emperor visited Friedrichshafen
for the purpose of seeing the airship in flight. He decorated
Count Zeppelin with the order of the Black Eagle. German
patriotism and enthusiasm has gone further, and the "German
Association for an Aerial Fleet" has been organised in
sections throughout the country. It announces its intention of
building 50 garages (hangars) for housing airships.'

By January of 1909, with well over a quarter of a million in
hand for the construction of Zeppelin airships, No. 3 was again
brought out, probably in order to maintain public enthusiasm in
respect of the possible new engine of war. In March of that
year No. 3 made a voyage which lasted for 4 hours over and in
the vicinity of Lake Constance; it carried 26 passengers for a
distance of nearly 150 miles.

Before the end of March, Count Zeppelin determined to voyage
from Friedrichshafen to Munich, together with the crew of the
airship and four military officers. Starting at four in the
morning and ascertaining their route from the lights of railway
stations and the ringing of bells in the towns passed over, the
journey was completed by nine o'clock, but a strong south-west
gale prevented the intended landing. The airship was driven
before the wind until three o'clock in the afternoon, when it
landed safely near Dingolfing; by the next morning the wind had
fallen considerably and the airship returned to Munich and
landed on the parade ground as originally intended. At about
3.30 in the afternoon, the homeward journey was begun,
Friedrichshafen being reached at about 7.30.

These trials demonstrated that sufficient progress had been made
to justify the construction of Zeppelin airships for use with
the German army. No. 3 had been manoeuvred safely if not
successfully in half a gale of wind, and henceforth it was known
as 'SMS. Zeppelin I.,' at the bidding of the German Emperor,
while the construction of 'SMS. Zeppelin II.' was rapidly
proceeded with. The fifth construction of Count Zeppelin's was
446 feet in length, 42 1/2 feet in diameter, and contained
530,000 cubic feet of hydrogen gas in 17 separate compartments.
Trial flights were made on the 26th May, 1909, and a week later
she made a record voyage of 940 miles, the route being from Lake
Constance over Ulm, Nuremberg, Leipzig, Bitterfeld, Weimar,
Heilbronn, and Stuttgart, descending near Goppingen; the time
occupied in the flight was upwards of 38 hours.

In landing, the airship collided with a pear-tree, which damaged
the bows and tore open two sections of the envelope, but repairs
on the spot enabled the return journey to Friedrichshafen to be
begun 24 hours later. In spite of the mishap the Zeppelin had
once more proved itself as a possible engine of war, and
thenceforth Germany pinned its faith to the dirigible, only
developing the aeroplane to such an extent as to keep abreast of
other nations. By the outbreak of war, nearly 30 Zeppelins had
been constructed; considerably more than half of these were
destroyed in various ways, but the experiments carried on with
each example of the type permitted of improvements being made.
The first fatality occurred in September, 1913, when the
fourteenth Zeppelin to be constructed, known as Naval Zeppelin
L.1, was wrecked in the North Sea by a sudden storm and her
crew of thirteen were drowned. About three weeks after this,
Naval Zeppelin L.2, the eighteenth in order of building,
exploded in mid-air while manoeuvring over Johannisthal. She
was carrying a crew of 25, who were all killed.

By 1912 the success of the Zeppelin type brought imitators.
Chief among them was the Schutte-Lanz, a Mannheim firm, which
produced a rigid dirigible with a wooden framework, wire braced.
This was not a cylinder like the Zeppelin, but reverted to the
cigar shape and contained about the same amount of gas as the
Zeppelin type. The Schutte-Lanz was made with two gondolas
rigidly attached to the envelope in which the gas bags were
placed. The method of construction involved greater weight than
was the case with the Zeppelin, but the second of these vessels,
built with three gondolas containing engines, and a navigating
cabin built into the hull of the airship itself, proved quite
successful as a naval scout until wrecked on the islands off the
coast of Denmark late in 1914. The last Schutte-Lanz to be
constructed was used by the Germans for raiding England, and was
eventually brought down in flames at Cowley.

V. BRITISH AIRSHIP DESIGN

As was the case with the aeroplane, Great Britain left France
and Germany to make the running in the early days of airship
construction; the balloon section of the Royal Engineers was
compelled to confine its energies to work with balloons pure and
simple until well after the twentieth century had dawned, and
such experiments as were made in England were done by private
initiative. As far back as 1900 Doctor Barton built an airship
at the Alexandra Palace and voyaged across London in it. Four
years later Mr E. T. Willows of Cardiff produced the first
successful British dirigible, a semi-rigid 74 feet in length and
18 feet in diameter, engined with a 7 horse-power Peugot
twin-cylindered motor. This drove a two-bladed propeller at the
stern for propulsion, and also actuated a pair of auxiliary
propellers at the front which could be varied in their direction
so as to control the right and left movements of the airship.
This device was patented and the patent was taken over by the
British Government, which by 1908 found Mr Willow's work of
sufficient interest to regard it as furnishing data for
experiment at the balloon factory at Farnborough. In 1909,
Willows steered one of his dirigibles to London from Cardiff in
a little less than ten hours, making an average speed of over 14
miles an hour. The best speed accomplished was probably
considerably greater than this, for at intervals of a few miles,
Willows descended near the earth to ascertain his whereabouts
with the help of a megaphone. It must be added that he carried
a compass in addition to his megaphone. He set out for Paris in
November of 1910, reached the French coast, and landed near
Douai. Some damage was sustained in this landing, but, after
repair, the trip to Paris was completed.

Meanwhile the Government balloon factory at Farnborough began
airship construction in 1907; Colonel Capper, R.E., and S. F.
Cody were jointly concerned in the production of a semi-rigid.
Fifteen thicknesses of goldbeaters' skin--about the most
expensive covering obtainable--were used for the envelope, which
was 25 feet in diameter. A slight shower of rain in which the
airship was caught led to its wreckage, owing to the absorbent
quality of the goldbeaters' skin, whereupon Capper and Cody set
to work to reproduce the airship and its defects on a larger
scale. The first had been named 'Nulli Secundus' and the second
was named 'Nulli Secundus II.' Punch very appropriately
suggested that the first vessel ought to have been named 'Nulli
Primus,' while a possible third should be christened 'Nulli
Tertius.' 'Nulli Secundus II.' was fitted with a 100 horse-power
engine and had an envelope of 42 feet in diameter, the
goldbeaters' skin being covered in fabric and the car being
suspended by four bands which encircled the balloon envelope.
In October of 1907, 'Nulli Secundus II.' made a trial flight
from Farnborough to London and was anchored at the Crystal
Palace. The wind sprung up and took the vessel away from its
mooring ropes, wrecking it after the one flight.

Stagnation followed until early in 1909, when a small airship
fitted with two 12 horse-power motors and named the 'Baby' was
turned out from the balloon factory. This was almost
egg-shaped, the blunt end being forward, and three inflated fins
being placed at the tail as control members. A long car with
rudder and elevator at its rear-end carried the engines and
crew; the 'Baby' made some fairly successful flights and gave a
good deal of useful data for the construction of later vessels.

Next to this was 'Army Airship 2A 'launched early in 1910 and
larger, longer, and narrower in design than the Baby. The
engine was an 80 horse-power Green motor which drove two pairs
of propellers; small inflated control members were fitted at the
stern end of the envelope, which was 154 feet in length. The
suspended car was 84 feet long, carrying both engines and crew,
and the Willows idea of swivelling propellers for governing the
direction was used in this vessel. In June of that year a new,
small-type dirigible, the 'Beta,' was produced, driven by a 30
horse-power Green engine with which she flew over 3,000 miles.
She was the most successful British dirigible constructed up to
that time, and her successor, the 'Gamma,' was built on similar
lines. The 'Gamma' was a larger vessel, however, produced in
1912, with flat, controlling fins and rudder at the rear end of
the envelope, and with the conventional long car suspended at
some distance beneath the gas bag. By this time, the mooring
mast, carrying a cap of which the concave side fitted over the
convex nose of the airship, had been originated. The cap was
swivelled, and, when attached to it, an airship was held nose on
to the wind, thus reducing by more than half the dangers
attendant on mooring dirigibles in the open.

Private subscription under the auspices of the Morning Post got
together sufficient funds in 1910 for the purchase of a Lebaudy
airship, which was built in France, flown across the Channel, and
presented to the Army Airship Fleet. This dirigible was 337 feet
long, and was driven by two 135 horse-power Panhard motors, each
of which actuated two propellers. The journey from Moisson to
Aldershot was completed at a speed of 36 miles an hour, but the
airship was damaged while being towed into its shed. On May of
the following year, the Lebaudy was brought out for a flight,
but, in landing, the guide rope fouled in trees and sheds and
brought the airship broadside on to the wind; she was driven into
some trees and wrecked to such an exteent that rebuilding was
considered an impossibility. A Clement Bayard, bought by the
army airship section, became scrap after even less flying than
had been accomplished by the Lebaudy.

In April of 1910,, the Admiralty determined on a naval air
service, and set about the production of rigid airships which
should be able to compete with Zeppelins as naval scouts. The
construction was entrusted to Vickers, Ltd., who set about the
task at their Barrow works and built something which, when tested
after a year's work, was found incapable of lifting its own
weight. This defect was remedied by a series of alterations, and
meanwhile the unofficial title of 'Mayfly' was given to the
vessel.

Taken over by the Admiralty before she had passed any flying
tests, the 'Mayfly' was brought out on September 24th, 1911, for
a trial trip, being towed out from her shed by a tug. When ha]f
out from the shed, the envelope was caught by a light
cross-wind, and, in spite of the pull from the tug, the great
fabric broke in half, nearly drowning the crew, who had to dive
in order to get clear of the wreckage.

There was considerable similarity in form, though not in
performance, between the Mayfly and the prewar Zeppelin. The
former was 510 feet in length, cylindrical in form, with a
diameter of 48 feet, and divided into 19 gas-bag compartments.
The motive power consisted of two 200 horse-power Wolseley
engines. After its failure, the Naval Air Service bought an
Astra-Torres airship from France and a Parseval from Germany,
both of which proved very useful in the early days of the War,
doing patrol work over the Channel before the Blimps came into
being.

Early in 1915 the 'Blimp' or 'S.S.' type of coastal airship
was evolved in response to the demand for a vessel which could
be turned out quickly and in quantities. There was urgent
demand, voiced by Lord Fisher, for a type of vessel capable of
maintaining anti-submarine patrol off the British coasts, and
the first S.S. airships were made by combining a gasbag with
the most available type of aeroplane fuselage and engine, and
fitting steering gear. The 'Blimp' consisted of a B.E. fuselage
with engine and geared-down propeller, and seating for pilot and
observer, attached to an envelope about 150 feet in length.
With a speed of between 35 and 40 miles an hour, the 'Blimp' had
a cruising capacity of about ten hours; it was fitted with
wireless set, camera, machine-gun, and bombs, and for submarine
spotting and patrol work generally it proved invaluable, though
owing to low engine power and comparatively small size, its uses
were restricted to reasonably fair weather. For work farther out
at sea and in all weathers, airships known as the coast patrol
type, and more commonly as 'coastals,' were built, and later the
'N.S.' or North Sea type, still larger and more weather-worthy,
followed. By the time the last year of the War came, Britain
led the world in the design of non-rigid and semi-rigid
dirigibles. The 'S.S.' or 'Blimp' had been improved to a speed
of 50 miles an hour, carrying a crew of three, and the endurance
record for the type was 18 1/2 hours, while one of them had
reached a height of 10,000 feet. The North Sea type of
non-rigid was capable of travelling over 20 hours at full speed,
or forty hours at cruising speed, and the number of non-rigids
belonging to the British Navy exceeded that of any other
country.

It was owing to the incapacity--apparent or real-- of the
British military or naval designers to produce a satisfactory
rigid airship that the 'N.S.' airship was evolved. The first of
this type was produced in 1916, and on her trials she was voted
an unqualified success, in consequence of which the building of
several more was pushed on. The envelope, of 360,000 cubic feet
capacity, was made on the Astra-Torres principle of three lobes,
giving a trefoil section. The ship carried four fins, to three
of which the elevator and rudder flaps were attached; petrol
tanks were placed inside the envelope, under which was rigged a
long covered-in car, built up of a light steel tubular framework
35 feet in length. The forward portion was covered with
duralumin sheeting, an aluminium alloy which, unlike aluminium
itself, is not affected by the action of sea air and water, and
the remainder with fabric laced to the framework. Windows and
port-holes were provided to give light to the crew, and the
controls and navigating instruments were placed forward, with the
sleeping accommodation aft. The engines were mounted in a power
unit structure, separate from the car and connected by wooden
gang ways supported by wire cables. A complete electrical
installation of two dynamos and batteries for lights, signalling
lamps, wireless, telephones, etc., was carried, and the motive
power consisted of either two 250 horse-power Rolls-Royce engines
or two 240 horse-power Fiat engines. The principal dimensions of
this type are length 262 feet, horizontal diameter 56 feet 9
inches, vertical diameter 69 feet 3 inches. The gross lift is
24,300 lbs. and the disposable lift without crew, petrol, oil,
and ballast 8,500 lbs. The normal crew carried for patrol work
was ten officers and men. This type holds the record of 101
hours continuous flight on patrol duty.

In the matter of rigid design it was not until 1913 that the
British Admiralty got over the fact that the 'Mayfly' would not,
and decided on a further attempt at the construction of a rigid
dirigible. The contract for this was signed in March of 1914;
work was suspended in the following February and begun again in
July, 1915, but it was not until January of 1917 that the
ship was finished, while her trials were not completed until
March of 1917, when she was taken over by the Admiralty. The
details of the construction and trial of this vessel, known as
'No. 9,' go to show that she did not quite fill the contract
requirements in respect of disposable lift until a number of
alterations had been made. The contract specified that a speed
of at least 45 miles per hour was to be attained at full engine
power, while a minimum disposable lift of 5 tons was to be
available for movable weights, and the airship was to be capable
of rising to a height of 2,000 feet. Driven by four Wolseley
Maybach engines of 180 horse-power each, the lift of the vessel
was not sufficient, so it was decided to remove the two engines
in the after car and replace them by a single engine of 250
horsepower. With this the vessel reached the contract speed of
45 miles per hour with a cruising radius of 18 hours, equivalent
to 800 miles when the engines were running at full speed. The
vessel served admirably as a training airship, for, by the time
she was completed, the No. 23 class of rigid airship had come to
being, and thus No. 9 was already out of date.

Three of the 23 class were completed by the end of 1917; it was
stipulated that they should be built with a speed of at least 55
miles per hour, a minimum disposable lift of 8 tons, and a
capability of rising at an average rate of not less than 1,000
feet per minute to a height of 3,000 feet. The motive power
consisted of four 250 horse-power Rolls-Royce engines, one in
each of the forward and after cars and two in a centre car.
Four-bladed propellers were used throughout the ship.

A 23X type followed on the 23 class, but by the time two ships
had been completed, this was practically obsolete. The No. 31
class followed the 23X; it was built on Schutte-Lanz lines, 615
feet in length, 66 feet diameter, and a million and a half cubic
feet capacity. The hull was similar to the later types of
Zeppelin in shape, with a tapering stern and a bluff, rounded
bow. Five cars each carrying a 250 horse-power Rolls-Royce
engine, driving a single fixed propeller, were fitted, and on
her trials R.31 performed well, especially in the matter of
speed. But the experiment of constructing in wood in the
Schutte-Lanz way adopted with this vessel resulted in failure
eventually, and the type was abandoned.

Meanwhile, Germany had been pushing forward Zeppelin design and
straining every nerve in the improvement of rigid dirigible
construction, until L.33 was evolved; she was generally known as
a super-Zeppelin, and on September 24th, 1916, six weeks
after her launching, she was damaged by gun-fire in a raid over
London, being eventually compelled to come to earth at Little
Wigborough in Essex. The crew gave themselves up after having
set fire to the ship, and though the fabric was totally
destroyed, the structure of the hull remained intact, so that
just as Germany was able to evolve the Gotha bomber from the
HandleyPage delivered at Lille, British naval constructors were
able to evolve the R.33 type of airship from the Zeppelin
framework delivered at Little Wigborough. Two vessels, R.33 and
R.34, were laid down for completion; three others were also put
down for construction, but, while R.33 and R.34 were built
almost entirely from the data gathered from the wrecked L.33,
the three later vessels embody more modern design, including a
number of improvements, and more especially greater disposable
lift. It has been commented that while the British authorities
were building R.33 and R.34, Germany constructed 30 Zeppelins on
4 slips, for which reason it may be reckoned a matter for
congratulation that the rigid airship did not decide the fate of
the War. The following particulars of construction of the R.33
and R.34 types are as given by Major Whale in his survey of
British Airships:--

'In all its main features the hull structure of R.33 and R.34
follows the design of the wrecked German Zeppelin airship L.33.
'The hull follows more nearly a true stream-line shape than in
the previous ships constructed of duralumin, in which a greater
proportion of the greater length was parallel-sided. The
Germans adopted this new shape from the Schutte-Lanz design and
have not departed from this practice. This consists of a short,
parallel body with a long, rounded bow and a long tapering stem
culminating in a point. The overall length of the ship is 643
feet with a diameter of 79 feet and an extreme height of 92
feet.

'The type of girders in this class has been much altered from
those in previous ships. The hull is fitted with an internal
triangular keel throughout practically the entire length. This
forms the main corridor of the ship, and is fitted with a
footway down the centre for its entire length. It contains water
ballast and petrol tanks, bomb storage and crew accommodation,
and the various control wires, petrol pipes, and electric leads
are carried along the lower part.

'Throughout this internal corridor runs a bridge girder, from
which the petrol and water ballast tanks are supported. These
tanks are so arranged that they can be dropped clear of the
ship. Amidships is the cabin space with sufficient room for a
crew of twenty-five. Hammocks can be swung from the bridge
girder before mentioned.

'In accordance with the latest Zeppelin practice, monoplane
rudders and elevators are fitted to the horizontal and vertical
fins.

'The ship is supported in the air by nineteen gas bags, which
give a total capacity of approximately two million cubic feet of
gas. The gross lift works out at approximately 59 1/2 tons, of
which the total fixed weight is 33 tons, giving a disposable
lift of 26 1/2 tons.

'The arrangement of cars is as follows: At the forward end the
control car is slung, which contains all navigating instruments
and the various controls. Adjoining this is the wireless cabin,
which is also fitted for wireless telephony. Immediately aft of
this is the forward power car containing one engine, which gives
the appearance that the whole is one large car.

'Amidships are two wing cars, each containing a single engine.
These are small and just accommodate the engines with sufficient
room for mechanics to attend to them. Further aft is another
larger car which contains an auxiliary control position and two
engines.

'It will thus be seen that five engines are installed in the
ship; these are all of the same type and horsepower, namely, 250
horse-power Sunbeam. R.33 was constructed by Messrs Armstrong,
Whitworth, Ltd.; while her sister ship R.34 was built by Messrs
Beardmore on the Clyde.'

Of the two vessels, R.34 appeared rather more airworthy than her
sister ship; the lift of the ship justified the carrying of a
greater quantity of fuel than had been provided for, and, as she
was considered suitable for making a Transatlantic crossing,
extra petrol tanks were fitted in the hull and a new type of
outer cover was fitted with a view to her making the Atlantic
crossing. She made a 21-hour cruise over the North of England
and the South of Scotland at the end of May, 1919, and
subsequently went for a longer cruise over Denmark, the Baltic,
and the north coast of Germany, remaining in the air for 56 hours
in spite of very bad weather conditions. Finally, July 2nd was
selected as the starting date for the cross Atlantic flight; the
vessel was commanded by Major G. H. Scott, A.F.C., with Captain
G. S. Greenland as first officer, Second-Lieut. H. F. Luck as
second officer, and Lieut. J. D. Shotter as engineer officer.
There were also on board Brig.-Gen. E. P. Maitland, representing
the Air Ministry, Major J. E. M. Pritchard, representing the
Admiralty, and Lieut.-Col. W. H. Hemsley of the Army Aviation
Department. In addition to eight tons of petrol, R.34 carried a
total number of 30 persons from East Fortune to Long Island, N.Y.

There being no shed in America capable of accommodating the
airship, she had to be moored in the open for refilling with fuel
and gas, and to make the return journey almost immediately.

Brig.-Gen. Maitland's account of the flight, in itself a record
as interesting as valuable, divides the outward journey into two
main stages, the first from East Fortune to Trinity Bay,
Newfoundland, a distance of 2,050 sea miles, and the second and
more difficult stage to Mineola Field, Long Island, 1,080 sea
miles. An easy journey was experienced until Newfoundland was
reached, but then storms and electrical disturbances rendered it
necessary to alter the course, in consequence of which petrol
began to run short. Head winds rendered the shortage still more
acute, and on Saturday, July 5th, a wireless signal was sent out
asking for destroyers to stand by to tow. However, after an
anxious night, R.33 landed safely at Mineola Field at 9.55 a.m.
on July 6th, having accomplished the journey in 108 hours 12
minutes.

She remained at Mineola until midnight of July 9th, when,
although it had been intended that a start should be made by
daylight for the benefit of New York spectators, an approaching
storm caused preparations to be advanced for immediate
departure. She set out at 5.57 a.m. by British summer time,
and flew over New York in the full glare of hundreds of
searchlights before heading out over the Atlantic. A following
wind assisted the return voyage, and on July 13th, at 7.57 a.m.,
R.34 anchored at Pulham, Norfolk, having made the return journey
in 75 hours 3 minutes, and proved the suitability of the
dirigible for Transatlantic commercial work. R.80, launched on
July 19th, 1920, afforded further proof, if this were needed.

It is to be noted that nearly all the disasters to airships have
been caused by launching and landing-- the type is safe enough
in the air, under its own power, but its bulk renders it
unwieldy for ground handling. The German system of handling
Zeppelins in and out of their sheds is, so far, the best
devised: this consists of heavy trucks running on rails through
the sheds and out at either end; on descending, the trucks are
run out, and the airship is securely attached to them outside
the shed; the trucks are then run back into the shed, taking the
airship with them, and preventing any possibility of the wind
driving the envelope against the side of the shed before it is
safely housed; the reverse process is adopted in launching,
which is thus rendered as simple as it is safe.

VI. THE AIRSHIP COMMERCIALLY

Prior to the war period, between the years 1910 and 1914, a
German undertaking called the Deutsche Luftfahrt Actien
Gesellschaft conducted a commercial Zeppelin service in which
four airships known as the Sachsan, Hansa, Victoria Louise, and
Schwaben were used. During the four years of its work, the
company carried over 17,000 passengers, and over 100,000 miles
were flown without incurring one fatality and with only minor
and unavoidable accidents to the vessels composing the service.
Although a number of English notabilities made voyages in these
airships, the success of this only experiment in commercial
aerostation seems to have been forgotten since the war. There
was beyond doubt a military aim in this apparently peaceful use
of Zeppelin airships; it is past question now that all Germany's
mechanical development in respect of land sea, and air transport
in the years immediately preceding the war, was accomplished
with the ulterior aim of military conquest, but, at the same
time, the running of this service afforded proof of the
possibility of establishing a dirigible service for peaceful
ends, and afforded proof too, of the value of the dirigible as a
vessel of purely commercial utility.

In considering the possibility of a commercial dirigible
service, it is necessary always to bear in mind the
disadvantages of first cost and upkeep as compared with the
aeroplane. The building of a modern rigid is an exceedingly
costly undertaking, and the provision of an efficient supply of
hydrogen gas to keep its compartments filled is a very large
item in upkeep of which the heavier-than-air machine goes free.
Yet the future of commercial aeronautics so far would seem to
lie with the dirigible where very long voyages are in question.
No matter how the aeroplane may be improved, the possibility of
engine failure always remains as a danger for work over water.
In seaplane or flying boat form, the danger is still present in
a rough sea, though in the American Transatlantic flight, N.C.3,
taxi-ing 300 miles to the Azores after having fallen to the
water, proved that this danger is not so acute as is generally
assumed. Yet the multiple-engined rigid, as R.34 showed on her
return voyage, may have part of her power plant put out of
action altogether and still complete her voyage very
successfully, which, in the case of mail carrying and services
run strictly to time, gives her an enormous advantage over the
heavier-than-air machine.

'For commercial purposes,' General Sykes has remarked, 'the
airship is eminently adapted for long distance journeys
involving non-stop flights. It has this inherent advantage over
the aeroplane, that while there appears to be a limit to the
range of the aeroplane as at present constructed, there is
practically no limit whatever to that of the airship, as this
can be overcome by merely increasing the size. It thus appears
that for such journeys as crossing the Atlantic, or crossing the
Pacific from the west coast of America to Australia or Japan,
the airship will be peculiarly suitable. It having been
conceded that the scope of the airship is long distance travel,
the only type which need be considered for this purpose is the
rigid. The rigid airship is still in an embryonic state, but
sufficient has already been accomplished in this country, and
more particularly in Germany, to show that with increased
capacity there is no reason why, within a few years' time,
airships should not be built capable of completing the circuit
of the globe and of conveying sufficient passengers and
merchandise to render such an undertaking a paying proposition.'

The British R.38 class, embodying the latest improvements in
airship design outside Germany, gives a gross lift per airship
of 85 tons and a net lift of about 45 tons. The capacity of
the gas bags is about two and three-quarter million cubic feet,
and, travelling at the rate of 45 miles per hour, the cruising
range of the vessel is estimated at 8.8 days. Six engines, each
of 350 horse-power, admit of an extreme speed of 70 miles per
hour if necessary.

The last word in German design is exemplified in the rigids L.70
and L.71, together with the commercial airship 'Bodensee.'
Previous to the construction of these, the L.65 type is
noteworthy as being the first Zeppelin in which direct drive of
the propeller was introduced, together with an improved and
lighter type of car. L.70 built in 1918 and destroyed by the
British naval forces, had a speed of about 75 miles per hour;
L.71 had a maximum speed of 72 miles per hour, a gas bag
capacity of 2,420,000 cubic feet, and a length of 743 feet,
while the total lift was 73 tons. Progress in design is best
shown by the progress in useful load; in the L.70 and L.71
class, this has been increased to 58.3 per cent, while in the
Bodensee it was ever higher.

As was shown in R.34's American flight, the main problem in
connection with the commercial use of dirigibles is that of
mooring in the open. The nearest to a solution of this problem,
so far, consists in the mast carrying a swivelling cap; this has
been tried in the British service with a non-rigid airship,
which was attached to a mast in open country in a gale of 52
miles an hour without the slightest damage to the airship. In
its commercial form, the mast would probably take the form of a
tower, at the top of which the cap would revolve so that the
airship should always face the wind, the tower being used for
embarkation and disembarkation of passengers and the provision
of fuel and gas. Such a system would render sheds unnecessary
except in case of repairs, and would enormously decrease the
establishment charges of any commercial airship.

All this, however, is hypothetical. Remains the airship of
to-day, developed far beyond the promise of five years ago,
capable, as has been proved by its achievements both in Britain
and in Germany, of undertaking practically any given voyage with
success.

VII. KITE BALLOONS

As far back as the period of the Napoleonic wars, the balloon
was given a place in warfare, but up to the Franco-Prussian
Prussian War of 1870-71 its use was intermittent. The Federal
forces made use of balloons to a small extent in the American
Civil War; they came to great prominence in the siege of Paris,
carrying out upwards of three million letters and sundry carrier
pigeons which took back messages into the besieged city.
Meanwhile, as captive balloons, the German and other armies used
them for observation and the direction of artillery fire. In
this work the ordinary spherical balloon was at a grave
disadvantage; if a gust of wind struck it, the balloon was blown
downward and down wind, generally twirling in the air and
upsetting any calculations and estimates that might be made by
the observers, while in a wind of 25 miles an hour it could not
rise at all. The rotatory movement caused by wind was stopped
by an experimenter in the Russo-Japanese war, who fixed to the
captive observation balloons a fin which acted as a rudder. This
did not stop the balloon from being blown downward and away from
its mooring station, but this tendency was overcome by a
modification designed in Germany by the Parseval-Siegsfield
Company, which originated what has since become familiar as the
'Sausage' or kite balloon. This is so arranged that the forward
end is tilted up into the wind, and the underside of the gas
bag, acting as a plane, gives the balloon a lifting tendency in
a wind, thus counteracting the tendency of the wind to blow it
downward and away from its mooring station. Smaller bags are
fitted at the lower and rear end of the balloon with openings
that face into the wind; these are thus kept inflated, and they
serve the purpose of a rudder, keeping the kite balloon steady
in the air.

Various types of kite balloon have been introduced; the original
German Parseval-Siegsfield had a single air bag at the stern
end, which was modified to two, three, or more lobes in later
varieties, while an American experimental design attempted to do
away with the attached lobes altogether by stringing out a
series of small air bags, kite fashion, in rear of the main
envelope. At the beginning of the War, Germany alone had kite
balloons, for the authorities of the Allied armies con-sidered
that the bulk of such a vessel rendered it too conspicuous a
mark to permit of its being serviceable. The Belgian arm alone
possessed two which, on being put into service, were found
extremely useful. The French followed by constructing kite
balloons at Chalais Meudon, and then, after some months of
hostilities and with the example of the Royal Naval Air Service
to encourage them, the British military authorities finally took
up the construction and use of kite balloons for
artillery-spotting and general observation purposes. Although
many were brought down by gun-fire, their uses far outweighed
their disadvantages, and toward the end of the War, hardly a
mile of front was without its 'Sausage.'

For naval work, kite balloons were carried in a specially
constructed hold in the forepart of certain vessels; when
required for use, the covering of the hold was removed, the
kite balloon inflated and released to the required height by
means of winches as in the case of the land work. The
perfecting of the 'Coastal' and N.S. types of airship, together
with the extension of wireless telephony between airship and
cruiser or other warship, in all probability will render the use
of the kite balloon unnecessary in connection with naval
scouting. But, during the War, neither wireless telephony nor
naval airships had developed sufficiently to render the Navy
independent of any means that might come to hand, and the
fitting of kite balloons in this fashion filled a need of the
times.

A necessary accessory of the kite balloon is the parachute,
which has a long history. Da Vinci and Veranzio appear to have
been the first exponents, the first in the theory and the latter
in the practice of parachuting. Montgolfier experimented at
Annonay before he constructed his first hot air-balloon, and in
1783 a certain Lenormand dropped from a tree in a parachute.
Blanchard the balloonist made a spectacle of parachuting, and
made it a financial success; Cocking, in 1836, attempted to use
an inverted form of parachute; taken up to a height of 3,000
feet, he was cut adrift, when the framework of the parachute
collapsed and Cocking was killed.

The rate of fall is slow in parachuting to the ground. Frau
Poitevin, making a descent from a height of 6,000 feet, took 45
minutes to reach the ground, and, when she alighted, her
husband, who had taken her up, had nearly got his balloon packed
up. Robertson, another parachutist is said to have descended
from a height of 10,000 feet in 35 minutes, or at a rate of
nearly 5 feet per second. During the War Brigadier-General
Maitland made a parachute descent from a height of 10,000 feet,
the time taken being about 20 minutes.

The parachute was developed considerably during the War period,
the main requirement, that of certainty in opening, being
considerably developed. Considered a necessary accessory for
kite balloons, the parachute was also partially adopted for use
with aeroplanes in the later War period, when it was contended
that if a machine were shot down in flames, its occupants would
be given a far better chance of escape if they had parachutes.
Various trials were made to demonstrate the extreme efficiency
of the parachute in modern form, one of them being a descent
from the upper ways of the Tower Bridge to the waters of the
Thames, in which short distance the 'Guardian Angel' type of
parachute opened and cushioned the descent for its user.

For dirigibles, balloons, and kite balloons the parachute is
an essential. It would seem to be equally essential in the case
of heavier-than-air machines, but this point is still debated.
Certainly it affords the occupant of a falling aeroplane a
chance, no matter how slender, of reaching the ground in safety,
and, for that reason, it would seem to have a place in aviation
as well as in aerostation.

PART IV. ENGINE DEVELOPMENT

I. THE VERTICAL TYPE

The balloon was but a year old when the brothers Robert, in 1784
attempted propulsion of an aerial vehicle by hand-power,
and succeeded, to a certain extent, since they were able to make
progress when there was only a slight wind to counteract their
work. But, as may be easily understood, the manual power
provided gave but a very slow speed, and in any wind it all the
would-be airship became an uncontrolled balloon.

Henson and Stringfellow, with their light steam engines, were
first to attempt conquest of the problem of mechanical
propulsion in the air; their work in this direction is so fully
linked up with their constructed models that it has been
outlined in the section dealing with the development of the
aeroplane. But, very shortly after these two began, there came
into the field a Monsieur Henri Giffard, who first achieved
success in the propulsion by mechanical means of dirigible
balloons, for his was the first airship to fly against the wind.
He employed a small steam-engine developing about 3 horse-power
and weighing 350 lbs. with boiler, fitting the whole in a car
suspended from the gas-bag of his dirigible. The propeller which
this engine worked was 11 feet in diameter, and the inventor, who
made several flights, obtained a speed of 6 miles an hour against
a slight wind. The power was not sufficient to render the
invention practicable, as the dirigible could only be used in
calm weather, but Giffard was sufficiently encouraged by his
results to get out plans for immense dirigibles, which through
lack of funds he was unable to construct. When, later, his
invention of the steam-injector gave him the means he desired, he
became blind, and in 1882 died, having built but the one famous
dirigible.

This appears to have been the only instance of a steam engine
being fitted to a dirigible; the inherent disadvantage of this
form of motive power is that a boiler to generate the steam must
be carried, and this, together with the weight of water and
fuel, renders the steam engine uneconomical in relation to the
lift either of plane or gas-bag. Again, even if the weight
could be brought down to a reasonable amount, the attention
required by steam plant renders it undesirable as a motive power
for aircraft when compared with the internal combustion engine.

Maxim, in Artificial and Natural Flight, details the engine
which he constructed for use with his giant experimental flying
machine, and his description is worthy of reproduction since it
is that of the only steam engine besides Giffard's, and apart
from those used for the propulsion of models, designed for
driving an aeroplane. 'In 1889,' Maxim says, 'I had my
attention drawn to some very thin, strong, and comparatively
cheap tubes which were being made in France, and it was only
after I had seen these tubes that I seriously considered the
question of making a flying machine. I obtained a large
quantity of them and found that they were very light, that they
would stand enormously high pressures, and generate a very large
quantity of steam. Upon going into a mathematical calculation of
the whole subject, I found that it would be possible to make a
machine on the aeroplane system, driven by a steam engine, which
would be sufficiently strong to lift itself into the air. I
first made drawings of a steam engine, and a pair of these
engines was afterwards made. These engines are constructed, for
the most part, of a very high grade of cast steel, the cylinders
being only 3/32 of an inch thick, the crank shafts hollow, and
every part as strong and light as possible. They are compound,
each having a high-pressure piston with an area of 20 square
inches, a low-pressure piston of 50.26 square inches, and a
common stroke of 1 foot. When first finished they were found to
weigh 300 lbs. each; but after putting on the oil cups, felting,
painting, and making some slight alterations, the weight was
brought up to 320 lbs. each, or a total of 640 lbs. for the
two engines, which have since developed 362 horsepower with a
steam pressure of 320 lbs. per square inch.'

The result is remarkable, being less than 2 lbs. weight per
horse-power, especially when one considers the state of
development to which the steam engine had attained at the time
these experiments were made. The fining down of the internal
combustion engine, which has done so much to solve the problems
of power in relation to weight for use with aircraft, had not
then been begun, and Maxim had nothing to guide him, so far as
work on the part of his predecessors was concerned, save the
experimental engines of Stringfellow, which, being constructed
on so small a scale in comparison with his own, afforded little
guidance. Concerning the factor of power, he says: 'When first
designing this engine, I did not know how much power I might
require from it. I thought that in some cases it might be
necessary to allow the high-pressure steam to enter the
low-pressure cylinder direct, but as this would involve a
considerable loss, I constructed a species of injector. This
injector may be so adjusted (hat when the steam in the boiler
rises above a certain predetermined point, say 300 lbs., to the
square inch, it opens a valve and escapes past the high-pressure
cylinder instead of blowing off at the safety valve. In
escaping through this valve, a fall of about 200 lbs. pressure
per square inch is made to do work on the surrounding steam and
drive it forward in the pipe, producing a pressure on the
low-pressure piston considerably higher than the back-pressure
on the high-pressure piston. In this way a portion of the work
which would otherwise be lost is utilised, and it is possible,
with an unlimited supply of steam, to cause the engines to
develop an enormous amount of power.'

With regard to boilers, Maxim writes,

'The first boiler which I made was constructed something on the
Herreshof principle, but instead of having one simple pipe in
one very long coil, I used a series of very small and light
pipes, connected in such a manner that there was a rapid
circulation through the whole--the tubes increasing in size and
number as the steam was generated. I intended that there should
be a pressure of about 100 lbs. more on the feed water end of
the series than on the steam end, and I believed that this
difference in pressure would be sufficient to ensure direct and
positive circulation through every tube in the series. The first
boiler was exceedingly light, but the workmanship, as far as
putting the tubes together was concerned, was very bad, and it
was found impossible to so adjust the supply of water as to make
dry steam without overheating and destroying the tubes.

'Before making another boiler I obtained a quantity of copper
tubes, about 8 feet long, 3/8 inch external diameter, and 1/50 of
an inch thick. I subjected about 100 of these tubes to an
internal pressure of 1 ton per square inch of cold kerosene oil,
and as none of them leaked I did not test any more, but
commenced my experiments by placing some of them in a white-hot
petroleum fire. I found that I could evaporate as much as 26
1/2 lbs. of water per square foot of heating surface per hour,
and that with a forced circulation, although the quantity of
water passing was very small but positive, there was no danger
of overheating. I conducted many experiments with a pressure of
over 400 lbs. per square inch, but none of the tubes failed.
I then mounted a single tube in a white-hot furnace, also with a
water circulation, and found that it only burst under steam at a
pressure of 1,650 lbs. per square inch. A large boiler,
having about 800 square feet of heating surface, including the
feed-water heater, was then constructed. This boiler is about 4
1/2 feet wide at the bottom, 8 feet long and 6 feet high. It
weighs, with the casing, the dome, and the smoke stack and
connections, a little less than 1,000 lbs. The water first
passes through a system of small tubes--1/4 inch in diameter and
1/60 inch thick--which were placed at the top of the boiler and
immediately over the large tubes.... This feed-water heater is
found to be very effective. It utilises the heat of the
products of combustion after they have passed through the boiler
proper and greatly reduces their temperature, while the
feed-water enters the boiler at a temperature of about 250 F. A
forced circulation is maintained in the boiler, the feed-water
entering through a spring valve, the spring valve being adjusted
in such a manner that the pressure on the water is always 30
lbs. per square inch in excess of the boiler pressure. This
fall of 30 lbs. in pressure acts upon the surrounding hot water
which has already passed through the tubes, and drives it down
through a vertical outside tube, thus ensuring a positive and
rapid circulation through all the tubes. This apparatus is
found to act extremely well.'

Thus Maxim, who with this engine as power for his large
aeroplane achieved free flight once, as a matter of experiment,
though for what distance or time the machine was actually off
the ground is matter for debate, since it only got free by
tearing up the rails which were to have held it down in the
experiment. Here, however, was a steam engine which was
practicable for use in the air, obviously, and only the rapid
success of the internal combustion engine prevented the
steam-producing type from being developed toward perfection.

The first designers of internal combustion engines, knowing
nothing of the petrol of these days, constructed their examples
with a view to using gas as fuel. As far back as 1872 Herr Paul
Haenlein obtained a speed of about 10 miles an hour with a
balloon propelled by an internal combustion engine, of which the
fuel was gas obtained from the balloon itself. The engine in
this case was of the Lenoir type, developing some 6 horse-power,
and, obviously, Haenlein's flights were purely experimental and
of short duration, since he used the gas that sustained him and
decreased the lifting power of his balloon with every stroke of
the piston of his engine. No further progress appears to have
been made with the gas-consuming type of internal combustion
engine for work with aircraft; this type has the disadvantage of
requiring either a gas-producer or a large storage capacity for
the gas, either of which makes the total weight of the power
plant much greater than that of a petrol engine. The latter type
also requires less attention when working, and the fuel is more
convenient both for carrying and in the matter of carburation.

The first airship propelled by the present-day type of internal
combustion engine was constructed by Baumgarten and Wolfert in
1879 at Leipzig, the engine being made by Daimler with a view to
working on benzine--petrol as a fuel had not then come to its
own. The construction of this engine is interesting since it was
one of the first of Daimler's make, and it was the development
brought about by the experimental series of which this engine
was one that led to the success of the motor-car in very few
years, incidentally leading to that fining down of the internal
combustion engine which has facilitated the development of the
aeroplane with such remarkable rapidity. Owing to the faulty
construction of the airship no useful information was obtained
from Daimler's pioneer installation, as the vessel got out of
control immediately after it was first launched for flight, and
was wrecked. Subsequent attempts at mechanically-propelled
flight by Wolfert ended, in 1897, in the balloon being set on
fire by an explosion of benzine vapour, resulting in the death
of both the aeronauts.

Daimler, from 1882 onward, devoted his attention to the
perfecting of the small, high-speed petrol engine for motor-car
work, and owing to his efforts, together with those of other
pioneer engine-builders, the motorcar was made a success. In a
few years the weight of this type of engine was reduced from near
on a hundred pounds per horse-power to less than a tenth of that
weight, but considerable further improvement had to be made
before an engine suitable for use with aircraft was evolved.

The increase in power of the engines fitted to airships has made
steady progress from the outset; Haenlein's engine developed
about 6 horse-power; the Santos-Dumont airship of 1898 was
propelled by a motor of 4 horse-power; in 1902 the Lebaudy
airship was fitted with an engine of 40 horse-power, while, in
1910, the Lebaudy brothers fitted an engine of nearly 300
horsepower to the airship they were then constructing--1,400
horse-power was common in the airships of the War period, and
the later British rigids developed yet more.

Before passing on to consideration of the petrol-driven type of
engine, it is necessary to accord brief mention to the dirigible
constructed in 1884 by Gaston and Albert Tissandier, who at
Grenelle, France, achieved a directed flight in a wind of 8
miles an hour, obtaining their power for the propeller from 1 1/3
horse-power Siemens electric motor, which weighed 121 lbs. and
took its current from a bichromate battery weighing 496 lbs. A
two-bladed propeller, 9 feet in diameter, was used, and the
horse-power output was estimated to have run up to 1 1/2 as the
dirigible successfully described a semicircle in a wind of 8
miles an hour, subsequently making headway transversely to a wind
of 7 miles an hour. The dirigible with which this motor was used
was of the conventional pointed-end type, with a length of 92
feet, diameter of 30 feet, and capacity of 37,440 cubic feet of
gas. Commandant Renard, of the French army balloon corps,
followed up Tissandier's attempt in the next year--1885--making a
trip from Chalais-Meudon to Paris and returning to the point of
departure quite successfully. In this case the motive power was
derived from an electric plant of the type used by the
Tissandiers, weighing altogether 1,174 lbs., and developing 9
horsepower. A speed of 14 miles an hour was attained with this
dirigible, which had a length of 165 feet, diameter of 27 feet,
and capacity of 65,836 cubic feet of gas.

Reverting to the petrol-fed type again, it is to be noted that
Santos-Dumont was practically the first to develop the use of
the ordinary automobile engine for air work--his work is of such
importance that it has been considered best to treat of it as
one whole, and details of the power plants are included in the
account of his experiments. Coming to the Lebaudy brothers and
their work, their engine of 1902 was a 40 horse-power Daimler,
four-cylindered; it was virtually a large edition of the Daimler
car engine, the arrangement of the various details being on the
lines usually adopted for the standard Daimler type of that
period. The cylinders were fully water-jacketed, and no special
attempt toward securing lightness for air work appears to have
been made.

The fining down of detail that brought weight to such limits as
would fit the engine for work with heavier-than-air craft
appears to have waited for the brothers Wright. Toward the end
of 1903 they fitted to their first practicable flying machine the
engine which made the historic first aeroplane flight; this
engine developed 30 horse-power, and weighed only about 7 lbs.
per horse-power developed, its design and workmanship being far
ahead of any previous design in this respect, with the exception
of the remarkable engine, designed by Manly, installed in
Langley's ill-fated aeroplane--or 'aerodrome,' as he preferred to
call it--tried in 1903.

The light weight of the Wright brothers' engine did not
necessitate a high number of revolutions per minute to get the
requisite power; the speed was only 1,300 revolutions per
minute, which, with a piston stroke of 3.94 inches, was quite
moderate. Four cylinders were used, the cylinder diameter being
4.42 inches; the engine was of the vertical type, arranged to
drive two propellers at a rate of about 350 revolutions per
minute, gearing being accomplished by means of chain drive from
crank-shaft end to propeller spindle.

The methods adopted by the Wrights for obtaining a light-weight
engine were of considerable interest, in view of the fact that
the honour of first achieving flight by means of the driven plane
belongs to them--unless Ader actually flew as he claimed. The
cylinders of this first Wright engine were separate castings of
steel, and only the barrels were jacketed, this being done by
fixing loose, thin aluminium covers round the outside of each
cylinder. The combustion head and valve pockets were cast
together with the cylinder barrel, and were not water cooled.
The inlet valves were of the automatic type, arranged on the tops
of the cylinders, while the exhaust valves were also overhead,
operated by rockers and push-rods. The pistons and piston rings
were of the ordinary type, made of cast-iron, and the connecting
rods were circular in form, with a hole drilled down the middle
of each to reduce the weight.

Necessity for increasing power and ever lighter weight in
relation to the power produced has led to the evolution of a
number of different designs of internal combustion engines. It
was quickly realised that increasing the number of cylinders on
an engine was a better way of getting more power than that of
increasing the cylinder diameter, as the greater number of
cylinders gives better torque-even turning effect--as well as
keeping down the weight--this latter because the bigger
cylinders must be more stoutly constructed than the small sizes;
this fact has led to the construction of engines having as many
as eighteen cylinders, arranged in three parallel rows in order
to keep the length of crankshaft within reasonable limits. The
aero engine of to-day may, roughly, be divided into four
classes: these are the V type, in which two rows of cylinders
are set parallel at a certain angle to each other; the radial
type, which consists of cylinders arranged radially and
remaining stationary while the crankshaft revolves; the rotary,
where the cylinders are disposed round a common centre and
revolve round a stationary shaft, and the vertical type, of four
or six cylinders--seldom more than this--arranged in one row. A
modification of the V type is the eighteen-cylindered engine--
the Sunbeam is one of the best examples--in which three rows of
cylinders are set parallel to each other, working on a common
crankshaft. The development these four types started with that
of the vertical--the simplest of all; the V, radial, and rotary
types came after the vertical, in the order given.

The evolution of the motor-car led to the adoption of the
vertical type of internal combustion engine in preference to any
other, and it followed naturally that vertical engines should be
first used for aeroplane propulsion, as by taking an engine that
had been developed to some extent, and adapting it to its new
work, the problem of mechanical flight was rendered easier than
if a totally new type had had to be evolved. It was quickly
realised--by the Wrights, in fact-that the minimum of weight per
horse-power was the prime requirement for the successful
development of heavier-than-air machines, and at the same time
it was equally apparent that the utmost reliability had to be
obtained from the engine, while a third requisite was economy,
in order to reduce the weight of petrol necessary for flight.

Daimler, working steadily toward the improvement of the internal
combustion engine, had made considerable progress by the end of
last century. His two-cylinder engine of 1897 was approaching
to the present-day type, except as regards the method of
ignition; the cylinders had 3.55 inch diameter, with a 4.75 inch
piston stroke, and the engine was rated at 4.5 brake horse-power,
though it probably developed more than this in actual running at
its rated speed of 800 revolutions per minute. Power was limited
by the inlet and exhaust passages, which, compared with
present-day practice, were very small. The heavy castings of
which the engine was made up are accounted for by the necessity
for considering foundry practice of the time, for in 1897
castings were far below the present-day standard. The crank-case
of this two-cylinder vertical Daimler engine was the only part
made of aluminium, and even with this no attempt was made to
attain lightness, for a circular flange was cast at the bottom to
form a stand for the engine during machining and erection. The
general design can be followed from the sectional views, and
these will show, too, that ignition was by means of a hot tube on
the cylinder head, which had to be heated with a blow-lamp before
starting the engine. With all its well known and hated troubles,
at that time tube ignition had an advantage over the magneto, and
the coil and accumulator system, in reliability; sparking plugs,
too, were not so reliable then as they are now. Daimler fitted a
very simple type of carburettor to this engine, consisting only
of a float with a single jet placed in the air passage. It may
be said that this twin-cylindered vertical was the first of the
series from which has been evolved the Mercedes-Daimler car and
airship engines, built in sizes up to and even beyond 240
horse-power.

In 1901 the development of the petrol engine was still so slight
that it did not admit of the construction, by any European
maker, of an engine weighing less than 12 lbs. per horse-power.
Manly, working at the instance of Professor Langley, produced a
five-cylindered radial type engine, in which both the design and
workmanship showed a remarkable advance in construction. At 950
revolutions per minute it developed 52.4 horse-power, weighing
only 2.4 pounds per horse-power; it was a very remarkable
achievement in engine design, considering the power developed in
relation to the total weight, and it was, too, an interruption
in the development of the vertical type which showed that there
were other equally great possibilities in design.

In England, the first vertical aero-engine of note was that
designed by Green, the cylinder dimensions being 4.15 inch
diameter by 4.75 stroke--a fairly complete idea of this engine
can be obtained from the accompanying diagrams. At a speed of
1,160 revolutions per minute it developed 35 brake horse-power,
and by accelerating up to 1,220 revolutions per minute a maximum
of 40 brake horse-power could be obtained--the first-mentioned
was the rated working speed of the engine for continuous runs.
A flywheel, weighing 23.5 lbs., was fitted to the engine, and
this, together with the ignition system, brought the weight up
to 188 lbs., giving 5.4 lbs. per horse-power. In comparison with
the engine fitted to the Wrights' aeroplane a greater power was
obtained from approximately the same cylinder volume, and an
appreciable saving in weight had also been effected. The
illustration shows the arrangement of the vertical valves at the
top of the cylinder and the overhead cam shaft, while the
position of the carburettor and inlet pipes can be also seen.
The water jackets were formed by thin copper casings, each
cylinder being separate and having its independent jacket rigidly
fastened to the cylinder at the top only, thus allowing for free
expansion of the casing; the joint at the bottom end was formed
by sliding the jacket over a rubber ring. Each cylinder was
bolted to the crank-case and set out of line with the crankshaft,
so that the crank has passed over the upper dead centre by the
time that the piston is at the top of its stroke when receiving
the full force of fuel explosion. The advantage of this
desaxe setting is that the pressure in the cylinder acts on the
crank-pin with a more effective leverage during that part of the
stroke when that pressure is highest, and in addition the side
pressure of the piston on the cylinder wall, due to the thrust of
the connecting rod, is reduced. Possibly the charging of the
cylinder is also more complete by this arrangement, owing to the
slower movement of the piston at the bottom of its stroke
allowing time for an increased charge of mixture to enter the
cylinder.

A 60 horse-power engine was also made, having four vertical
cylinders, each with a diameter of 5.5 inches and stroke of 5.75
inches, developing its rated power at 1,100 revolutions per
minute. By accelerating up to 1,200 revolutions per minute 70
brake horsepower could be obtained, and a maximum of 80 brake
horse-power was actually attained with the type. The flywheel,
fitted as with the original 35 horse-power engine, weighed 37
lbs.; with this and with the ignition system the total weight of
the engine was only 250 lbs., or 4.2 lbs. per horse-power at
the normal rating. In this design, however, low weight in
relation to power was not the ruling factor, for Green gave more
attention to reliability and economy of fuel consumption, which
latter was approximately 0.6 pint of petrol per brake
horse-power per hour. Both the oil for lubricating the bearings
and the water for cooling the cylinders were circulated by
pumps, and all parts of the valve gear, etc., were completely
enclosed for protection from dust.

A later development of the Green engine was a six-cylindered
vertical, cylinder dimensions being 5.5 inch diameter by 6 inch
stroke, developing 120 brake horsepower when running at 1,250
revolutions per minute. The total weight of the engine with
ignition system 398 was 440 lbs., or 3.66 lbs. per horse-power.
One of these engines was used on the machine which, in 1909, won
the prize of L1,000 for the first circular mile flight, and it
may be noted, too, that S. F. Cody, making the circuit of England
in 1911, used a four-cylinder Green engine. Again, it was a
Green engine that in 1914 won the L5,000 prize offered for the
best aero engine in the Naval and Military aeroplane engine
competition.

Manufacture of the Green engines, in the period of the War, had
standardised to the production of three types. Two of these were
six-cylinder models, giving respectively 100 and 150 brake
horse-power, and the third was a twelve-cylindered model rated
at 275 brake horse-power.

In 1910 J. S. Critchley compiled a list showing the types of
engine then being manufactured; twenty-two out of a total of
seventy-six were of the four-cylindered vertical type, and in
addition to these there were two six-cylindered verticals.
The sizes of the four-cylinder types ranged from 26 up to 118
brake horse-power; fourteen of them developed less than 50
horse-power, and only two developed over 100 horse-power.

It became apparent, even in the early stages of heavier-than-air
flying, that four-cylinder engines did not produce the even
torque that was required for the rotation of the power shaft,
even though a flywheel was fitted to the engine. With this type
of engine the breakage of air-screws was of frequent occurrence,
and an engine having a more regular rotation was sought, both
for this and to avoid the excessive vibration often experienced
with the four-cylinder type. Another, point that forced itself
on engine builders was that the increased power which was
becoming necessary for the propulsion of aircraft made an
increase in the number of cylinders essential, in order to obtain
a light engine. An instance of the weight reduction obtainable
in using six cylinders instead of four is shown in Critchley's
list, for one of the four-cylinder engines developed 118.5 brake
horse-power and weighed 1,100 lbs., whereas a six-cylinder engine
by the same manufacturer developed 117.5 brake horse-power with a
weight of 880 lbs., the respective cylinder dimensions being
7.48 diameter by 9.06 stroke for the four-cylinder engine, and
6.1 diameter by 7.28 stroke for the six-cylinder type.

A list of aeroplane engines, prepared in 1912 by Graham Clark,
showed that, out of the total number of 112 engines then
being manufactured, forty-two were of the vertical type, and of
this number twenty-four had four-cylinders while sixteen were
six-cylindered. The German aeroplane engine trials were held a
year later, and sixty-six engines entered the competition,
fourteen of these being made with air-cooled cylinders. All of
the ten engines that were chosen for the final trials were of
the water-cooled type, and the first place was won by a Benz
four-cylinder vertical engine which developed 102 brake
horse-power at 1,288 revolutions per minute. The cylinder
dimensions of this engine were 5.1 inch diameter by 7.1 inch
stroke, and the weight of the engine worked out at 3.4 lbs. per
brake horse-power. During the trials the full-load petrol
consumption was 0.53 pint per horse-power per hour, and the
amount of lubricating oil used was 0.0385 pint per brake
horse-power per hour. In general construction this Benz engine
was somewhat similar to the Green engine already described; the
overhead valves, fitted in the tops of the cylinders, were
similarly arranged, as was the cam-shaft; two springs were
fitted to each of the valves to guard against the possibility of
the engine being put out of action by breakage of one of the
springs, and ignition was obtained by two high-tension magnetos
giving simultaneous sparks in each cylinder by means of two
sparking plugs--this dual ignition reduced the possibility of
ignition troubles. The cylinder jackets were made of welded
sheet steel so fitted around the cylinder that the head was also
water-cooled, and the jackets were corrugated in the middle to
admit of independent expansion. Even the lubrication system was
duplicated, two sets of pumps being used, one to circulate the
main supply of lubricating oil, and the other to give a
continuous supply of fresh oil to the bearings, so that if the
supply from one pump failed the other could still maintain
effective lubrication.

Development of the early Daimler type brought about the
four-cylinder vertical Mercedes-Daimler engine of 85 horse-power,
with cylinders of 5.5 diameter with 5.9 inch stroke, the
cylinders being cast in two pairs. The overhead arrangement of
valves was adopted, and in later designs push-rods were
eliminated, the overhead cam-shaft being adopted in their place.
By 1914 the four-cylinder Mercedes-Daimler had been partially
displaced from favour by a six-cylindered model, made in two
sizes; the first of these gave a nominal brake horse-power of 80,
having cylinders of 4.1 inches diameter by 5.5 inches stroke; the
second type developed 100 horse-power with cylinders 4.7 inches
in diameter and 5.5 inches stroke, both types being run at 1,200
revolutions per minute. The cylinders of both these types were
cast in pairs, and, instead of the water jackets forming part of
the casting, as in the design of the original four-cylinder
Mercedes-Daimler engine, they were made of steel welded to
flanges on the cylinders. Steel pistons, fitted with cast-iron
rings, were used, and the overhead arrangement of valves and
cam-shaft was adopted. About 0.55 pint per brake horse-power per
hour was the usual fuel consumption necessary to full load
running, and the engine was also economical as regards the
consumption of lubricating oil, the lubricating system being
'forced' for all parts, including the cam-shaft. The shape of
these engines was very well suited for work with aircraft, being
narrow enough to admit of a streamline form being obtained, while
all the accessories could be so mounted as to produce little or
no wind resistance, and very little obstruction to the pilot's
view.

The eight-cylinder Mercedes-Daimler engine, used for airship
propulsion during the War, developed 240 brake horse-power at
1,100 revolutions per minute; the cylinder dimensions were 6.88
diameter by 6.5 stroke--one of the instances in which the short
stroke in relation to bore was very noticeable.

Other instances of successful vertical design-the types already
detailed are fully sufficient to give particulars of the type
generally--are the Panhard, Chenu, Maybach, N.A.G., Argus,
Mulag, and the well-known Austro-Daimler, which by 1917 was
being copied in every combatant country. There are also the
later Wright engines, and in America the Wisconsin six-cylinder
vertical, weighing well under 4 lbs. per horse-power, is
evidence of the progress made with this first type of aero
engine to develop.

II. THE VEE TYPE

An offshoot from the vertical type, doubling the power of this
with only a very slight--if any--increase in the length of
crankshaft, the Vee or diagonal type of aero engine leaped to
success through the insistent demand for greater power.
Although the design came after that of the vertical engine, by
1910, according to Critchley's list of aero engines, there
were more Vee type engines being made than any other type,
twenty-five sizes being given in the list, with an average
rating of 57.4 brake horse-power.

The arrangement of the cylinders in Vee form over the
crankshaft, enabling the pistons of each pair of opposite
cylinders to act upon the same crank pin, permits of a very
short, compact engine being built, and also permits of reduction
of the weight per horsepower, comparing this with that of the
vertical type of engine, with one row of cylinders. Further, at
the introduction of this type of engine it was seen that
crankshaft vibration, an evil of the early vertical engines, was
practically eliminated, as was the want of longitudinal
stiffness that characterised the higher-powered vertical
engines.

Of the Vee type engines shown in Critchley's list in 1910
nineteen different sizes were constructed with eight cylinders,
and with horse-powers ranging from thirty to just over the
hundred; the lightest of these weighed 2.9 lbs. per
horse-power--a considerable advance in design on the average
vertical engine, in this respect of weight per horse-power.
There were also two sixteen-cylinder engines of Vee design, the
larger of which developed 134 horse-power with a weight of only 2
lbs. per brake horse-power. Subsequent developments have
indicated that this type, with the further development from it of
the double-Vee, or engine with three rows of cylinders, is likely
to become the standard design of aero engine where high powers
are required. The construction permits of placing every part so
that it is easy of access, and the form of the engine implies
very little head resistance, while it can be placed on the
machine--supposing that machine to be of the single-engine
type--in such a way that the view of the pilot is very little
obstructed while in flight.

An even torque, or great uniformity of rotation, is transmitted
to the air-screw by these engines, while the design also permits
of such good balance of the engine itself that vibration is
practically eliminated. The angle between the two rows of
cylinders is varied according to the number of cylinders, in
order to give working impulses at equal angles of rotation and
thus provide even torque; this angle is determined by dividing
the number of degrees in a circle by the number of cylinders in
either row of the engine. In an eight-cylindered Vee type
engine, the angle between the cylinders is 90 degrees; if it is
a twelve-cylindered engine, the angle drops to 60 degrees.

One of the earliest of the British-built Vee type engines was an
eight-cylinder 50 horse-power by the Wolseley Company,
constructed in 1908 with a cylinder bore of 3.75 inches and
stroke of 5 inches, running at a normal speed of 1,350
revolutions per minute. With this engine, a gearing was
introduced to enable the propeller to run at a lower speed than
that of the engine, the slight loss of efficiency caused by the
friction of the gearing being compensated by the slower speed of
the air-screw, which had higher efficiency than would have been
the case if it had been run at the engine speed. The ratio of
the gearing--that is, the speed of the air-screw relatively to
that of the engine, could be chosen so as to suit exactly the
requirements of the air-screw, and the gearing itself, on this
engine, was accomplished on the half-speed shaft actuating the
valves.

Very soon after this first design had been tried out, a second
Vee type engine was produced which, at 1,200 revolutions per
minute, developed 60 horse-power; the size of this engine was
practically identical with that of its forerunner, the only
exception being an increase of half an inch in the cylinder
stroke--a very long stroke of piston in relation to the bore of
the cylinder. In the first of these two engines, which was
designed for airship propulsion, the weight had been about 8
lbs. per brake horse-power, no special attempt appearing to
have been made to fine down for extreme lightness; in this 60
horse-power design, the weight was reduced to 6.1 lbs. per
horse-power, counting the latter as normally rated; the
engine actually gave a maximum of 75 brake horse-power, reducing
the ratio of weight to power very considerably below the figure
given.

The accompanying diagram illustrates a later Wolseley model, end
elevation, the eight-cylindered 120 horse-power Vee type aero
engine of the early war period. With this engine, each crank
pin has two connecting rods bearing on it, these being placed
side by side and connected to the pistons of opposite cylinders
and the two cylinders of the pair are staggered by an amount
equal to the width of the connecting rod bearing, to afford
accommodation for the rods. The crankshaft was a nickel chrome
steel forging, machined hollow, with four crank pins set at 180
degrees to each other, and carried in three bearings lined with
anti-friction metal. The connecting rods were made of tubular
nickel chrome steel, and the pistons of drawn steel, each being
fitted with four piston rings. Of these the two rings nearest to
the piston head were of the ordinary cast-iron type, while the
others were of phosphor bronze, so arranged as to take the side
thrust of the piston. The cylinders were of steel, arranged in
two groups or rows of four, the angular distance between them
being 90 degrees. In the space above the crankshaft, between the
cylinder rows, was placed the valve-operating mechanism, together
with the carburettor and ignition system, thus rendering this a
very compact and accessible engine. The combustion heads of the
cylinders were made of cast-iron, screwed into the steel cylinder
barrels; the water-jacket was of spun aluminium, with one end
fitting over the combustion head and the other free to slide on
the cylinder; the water-joint at the lower end was made tight by
a Dermatine ring carried between small flanges formed on the
cylinder barrel. Overhead valves were adopted, and in order to
make these as large as possible the combustion chamber was made
slightly larger in diameter than the cylinder, and the valves set
at an angle. Dual ignition was fitted in each cylinder, coil and
accumulator being used for starting and as a reserve in case of
failure of the high-tension magneto system fitted for normal
running. There was a double set of lubricating pumps, ensuring
continuity of the oil supply to all the bearings of the engine.

The feature most noteworthy in connection with the running of
this type of engine was its flexibility; the normal output of
power was obtained with 1,150 revolutions per minute of the
crankshaft, but, by accelerating up to 1,400 revolutions, a
maximum of 147 brake horse-power could be obtained. The weight
was about 5 lbs. per horse-power, the cylinder dimensions being
5 inches bore by 7 inches stroke. Economy in running was
obtained, the fuel consumption being 0.58 pint per brake
horse-power per hour at full load, with an expenditure of about
0.075 pint of lubricating oil per brake horse-power per hour.

Another Wolseley Vee type that was standardised was a 90
horse-power eight-cylinder engine running at 1,800 revolutions
per minute, with a reducing gear introduced by fitting the air
screw on the half-speed shaft. First made semi-cooled--the
exhaust valve was left air-cooled, and then entirely
water-jacketed--this engine demonstrated the advantage of full
water cooling, for under the latter condition the same power was
developed with cylinders a quarter of an inch less in diameter
than in the semi-cooled pattern; at the same time the weight was
brought down to 4 1/2 lbs. per horsepower.

A different but equally efficient type of Vee design was the
Dorman engine, of which an end elevation is shown; this
developed 80 brake horse-power at a speed of 1,300 revolutions
per minute, with a cylinder bore of 5 inches; each cylinder was
made in cast-iron in one piece with the combustion chamber, the
barrel only being water-jacketed. Auxiliary exhaust ports were
adopted, the holes through the cylinder wall being uncovered by
the piston at the bottom of its stroke--the piston, 4.75 inches
in length, was longer than its stroke, so that these ports were
covered when it was at the top of the cylinder. The exhaust
discharged through the ports into a belt surrounding the
cylinder, the belts on the cylinders being connected so that the
exhaust gases were taken through a single pipe. The air was
drawn through the crank case, before reaching the carburettor,
this having the effect of cooling the oil in the crank case as
well as warming the air and thus assisting in vaporising the
petrol for each charge of the cylinders. The inlet and exhaust
valves were of the overhead type, as may be gathered from the
diagram, and in spite of cast-iron cylinders being employed a
light design was obtained, the total weight with radiator,
piping, and water being only 5.5 lbs. per horse-power.

Here was the antithesis of the Wolseley type in the matter of
bore in relation to stroke; from about 1907 up to the beginning
of the war, and even later, there was controversy as to which
type--that in which the bore exceeded the stroke, or vice
versa--gave greater efficiency. The short-stroke enthusiasts
pointed to the high piston speed of the long-stroke type, while
those who favoured the latter design contended that full power
could not be obtained from each explosion in the short-stroke
type of cylinder. It is now generally conceded that the
long-stroke engine yields higher efficiency, and in addition to
this, so far as car engines are concerned, the method of rating
horse-power in relation to bore without taking stroke into
account has given the long-stroke engine an advantage, actual
horse-power with a long stroke engine being in excess of the
nominal rating. This may have had some influence on aero engine
design, but, however this may have been, the long-stroke engine
has gradually come to favour, and its rival has taken second
place.

For some time pride of place among British Vee type engines was
held by the Sunbeam Company, which, owing to the genius of Louis
Coatalen, together with the very high standard of construction
maintained by the firm, achieved records and fame in the middle
and later periods of the war. Their 225 horse-power
twelve-cylinder engine ran at a normal speed of 2,000 revolutions
per minute; the air screw was driven through gearing at half this
speed, its shaft being separate from the timing gear and carried
in ball-bearings on the nose-piece of the engine. The cylinders
were of cast-iron, entirely water-cooled; a thin casing formed
the water-jacket, and a very light design was obtained, the
weight being only 3.2 lbs. per horse-power. The first engine of
Sunbeam design had eight cylinders and developed 150 horse-power
at 2,000 revolutions per minute; the final type of Vee design
produced during the war was twelve-cylindered, and yielded 310
horse-power with cylinders 4.3 inches bore by 6.4 inches stroke.
Evidence in favour of the long-stroke engine is afforded in this
type as regards economy of working; under full load, working at
2,000 revolutions per minute, the consumption was 0.55 pints of
fuel per brake horse-power per hour, which seems to indicate that
the long stroke permitted of full use being made of the power
resulting from each explosion, in spite of the high rate of speed
of the piston.

Developing from the Vee type, the eighteen-cylinder 475 brake
horse-power engine, designed during the war, represented
for a time the limit of power obtainable from a single plant.
It was water-cooled throughout, and the ignition to each
cylinder was duplicated; this engine proved fully efficient, and
economical in fuel consumption. It was largely used for
seaplane work, where reliability was fully as necessary as high
power.

The abnormal needs of the war period brought many British firms
into the ranks of Vee-type engine-builders, and, apart from
those mentioned, the most notable types produced are the
Rolls-Royce and the Napier. The first mentioned of these firms,
previous to 1914 had concentrated entirely on car engines, and
their very high standard of production in this department of
internal combustion engine work led, once they took up the
making of aero engines, to extreme efficiency both of design and
workmanship. The first experimental aero engine, of what became
known as the 'Eagle' type, was of Vee design--it was completed
in March of 1915--and was so successful that it was standardised
for quantity production. How far the original was from the
perfection subsequently ascertained is shown by the steady
increase in developed horse-power of the type; originally
designed to develop 200 horse-power, it was developed and
improved before its first practical trial in October of 1915,
when it developed 255 horsepower on a brake test. Research and
experiment produced still further improvements, for, without any
enlargement of the dimensions, or radical alteration in design,
the power of the engine was brought up to 266 horse-power by
March of 1916, the rate of revolutions of 1,800 per minute being
maintained throughout. July, 1916 gave 284 horse-power; by the
cud of the year this had been increased to 322 horse-power; by
September of 1917 the increase was to 350 horse-power, and by
February of 1918 then 'Eagle' type of engine was rated at 360
horse-power, at which standard it stayed. But there is no more
remarkable development in engine design than this, a 75 per cent
increase of power in the same engine in a period of less than
three years.

To meet the demand for a smaller type of engine for use on
training machines, the Rolls-Royce firm produced the 'Hawk'
Vee-type engine of 100 horsepower, and, intermediately between
this and the 'Eagle,' the 'Falcon' engine came to being with an
original rated horse-power of 205 at 1,800 revolutions per
minute, in April of 1916. Here was another case of growth of
power in the same engine through research, almost similar to
that of the 'Eagle' type, for by July of 1918 the 'Falcon' was
developing 285 horse-power with no radical alteration of
design. Finally, in response to the constant demand for
increase of power in a single plant, the Rolls-Royce company
designed and produced the 'Condor' type of engine, which yielded
600 horse-power on its first test in August of 1918. The
cessation of hostilities and consequent falling off in the
demand for extremely high-powered plants prevented the 'Condor'
being developed to its limit, as had been the 'Falcon' and
'Eagle' types.

The 'Eagle 'engine was fitted to the two Handley-Page
aeroplanes--which made flights from England to India--it was
virtually standard on the Handley-Page bombers of the later War
period, though to a certain extent the American 'Liberty' engine
was also used. Its chief record, however, is that of being the
type fitted to the Vickers-Vimy aeroplane which made the first
Atlantic flight, covering the distance of 1,880 miles at a speed
averaging 117 miles an hour.

The Napier Company specialised on one type of engine from the
outset, a power plant which became known as the 'Lion' engine,
giving 450 horse-power with twelve cylinders arranged in three
rows of four each. Considering the engine as 'dry,' or without
fuel and accessories, an abnormally light weight per
horse-power--only 1.89 lbs.--was attained when running at the
normal rate of revolution. The cylinders and water-jackets are
of steel, and there is fitted a detachable aluminium cylinder
head containing inlet and exhaust valves and valve actuating
mechanism; pistons are of aluminium alloy, and there are two
inlet and two exhaust valves to each cylinder, the whole of the
valve mechanism being enclosed in an oil-tight aluminium case.
Connecting rods and crankshaft are of steel, the latter being
machined from a solid steel forging and carried in five roller
bearings and one plain bearing at the forward end. The front end
of the crank-case encloses reduction gear for the propeller
shaft, together with the shaft and bearings. There are two
suction and one pressure type oil pumps driven through gears at
half-engine speed, and two 12 spark magnetos, giving 2 sparks in
each cylinder.

The cylinders are set with the central row vertical, and the two
side rows at angles of 60 degrees each; cylinder bore is 5 1/2
inches, and stroke 5 1/8 inches; the normal rate of revolution
is 1,350 per minute, and the reducing gear gives one revolution
of the propeller shaft to 1.52 revolutions of crankshaft. Fuel
consumption is 0.48lbs. of fuel per brake horse-power hour at
full load, and oil consumption is 0.020 lbs. per brake horsepower
hour. The dry weight of the engine, complete with propeller
boss, carburettors, and induction pipes, is 850 lbs., and the
gross weight in running order, with fuel and oil for six hours
working, is 2,671 lbs., exclusive of cooling water.

To this engine belongs an altitude record of 30,500 feet, made at
Martlesham, near Ipswich, on January 2nd, 1919, by Captain Lang,
R.A.F., the climb being accomplished in 66 minutes 15 seconds.
Previous to this, the altitude record was held by an Italian
pilot, who made 25,800 feet in an hour and 57 minutes in 1916.
Lang's climb was stopped through the pressure of air, at the
altitude he reached, being insufficient for driving the small
propellers on the machine which worked the petrol and oil pumps,
or he might have made the height said to have been attained by
Major Schroeder on February 27th, 1920, at Dayton, Ohio.
Schroeder is said to have reached an altitude of 36,020 feet on a
Napier biplane, and, owing to failure of the oxygen supply, to
have lost consciousness, fallen five miles, righted his machine
when 2,000 feet in the air, and alighted successfully. Major
Schroeder is an American.

Turning back a little, and considering other than British design
of Vee and double-Vee or 'Broad arrow' type of engine, the
Renault firm from the earliest days devoted considerable
attention to the development of this type, their air-cooled
engines having been notable examples from the earliest days of
heavier-than-air machines. In 1910 they were making three sizes
of eight-cylindered Vee-type engines, and by 1915 they had
increased to the manufacture of five sizes, ranging from 25 to
100 brake horse-power, the largest of the five sizes having
twelve cylinders but still retaining the air-cooled principle.
The De Dion firm, also, made Vee-type engines in 1914, being
represented by an 80 horse-power eight-cylindered engine,

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