A History of Aeronautics
by
E. Charles Vivian
Part 5 out of 8
newspaper and a third flight was undertaken with a Handley-Page
machine under the auspices of the Daily Telegraph. The Air
Ministry had already prepared the route by means of three survey
parties which cleared the aerodromes and landing grounds,
dividing their journey into stages of 200 miles or less. Not
one of the competitors completed the course, but in both this
and Ross-Smith's flight valuable data was gained in respect of
reliability of machines and engines, together with a mass of
meteorological information.
The Handley-Page Company announced in the early months of 1920
that they had perfected a new design of wing which brought about
a twenty to forty per cent improvement in lift rate in the year.
When the nature of the design was made public, it was seen to
consist of a division of the wing into small sections, each with
its separate lift. A few days later, Fokker, the Dutch
inventor, announced the construction of a machine in which all
external bracing wires are obviated, the wings being of a very
deep section and self-supporting. The value of these two
inventions remains to be seen so far as commercial flying is
concerned.
The value of air work in war, especially so far as the Colonial
campaigns in which British troops are constantly being engaged is
in question, was very thoroughly demonstrated in a report issued
early in 1920 with reference to the successful termination of the
Somaliland campaign through the intervention of the Royal Air
Force, which between January 21st and the 31st practically
destroyed the Dervish force under the Mullah, which had been a
thorn in the side of Britain since 1907. Bombs and machine-guns
did the work, destroying fortifications and bringing about the
surrender of all the Mullah's following, with the exception of
about seventy who made their escape.
Certain records both in construction and performance had
characterised the post-war years, though as design advances and
comes nearer to perfection, it is obvious that records must get
fewer and farther between. The record aeroplane as regards size
at the time of its construction was the Tarrant triplane, which
made its first--and last--flight on May 28th, 1919. The total
loaded weight was 30 tons, and the machine was fitted with six
400 horse-power engines; almost immediately after the trial
flight began, the machine pitched forward on its nose and was
wrecked, causing fatal injuries to Captains Dunn and Rawlings,
who were aboard the machine. A second accident of similar
character was that which befell the giant seaplane known as the
Felixstowe Fury, in a trial flight. This latter machine was
intended to be flown to Australia, but was crashed over the
water.
On May 4th, 1920, a British record for flight duration and
useful load was established by a commercial type Handley-Page
biplane, which, carrying a load of 3,690 lbs., rose to a height
of 13,999 feet and remained in the air for 1 hour 20 minutes.
On May 27th the French pilot, Fronval, flying at Villacoublay in
a Morane-Saulnier type of biplane with Le Rhone motor, put up an
extraordinary type of record by looping the loop 962 times in 3
hours 52 minutes 10 seconds. Another record of the year of
similar nature was that of two French fliers, Boussotrot and
Bernard, who achieved a continuous flight of 24 hours 19 minutes
7 seconds, beating the pre-war record of 21 hours 48 3/4 seconds
set up by the German pilot, Landemann. Both these records are
likely to stand, being in the nature of freaks, which demonstrate
little beyond the reliability of the machine and the capacity for
endurance on the part of its pilots.
Meanwhile, on February 14th, Lieuts. Masiero and Ferrarin left
Rome on S.V.A. Ansaldo V. machines fitted with 220 horse-power
S.V.A. motors. On May 30th they arrived at Tokio, having flown
by way of Bagdad, Karachi, Canton, Pekin, and Osaka. Several
other competitors started, two of whom were shot down by Arabs in
Mesopotamia.
Considered in a general way, the first two years after the
termination of the Great European War form a period of transition
in which the commercial type of aeroplane was gradually evolved
from the fighting machine which was perfected in the four
preceding years. There was about this period no sense of
finality, but it was as experimental, in its own way, as were the
years of progressing design which preceded the war period. Such
commercial schemes as were inaugurated call for no more note than
has been given here; they have been experimental, and, with the
possible exception of the United States Government mail service,
have not been planned and executed on a sufficiently large scale
to furnish reliable data on which to forecast the prospects of
commercial aviation. And there is a school rapidly growing up
which asserts that the day of aeroplanes is nearly over. The
construction of the giant airships of to-day and the successful
return flight of R34 across the Atlantic seem to point to the
eventual triumph, in spite of its disadvantages, of the dirigible
airship.
This is a hard saying for such of the aeroplane industry as
survived the War period and consolidated itself, and it is but
the saying of a section which bases its belief on the fact that,
as was noted in the very early years of the century, the
aeroplane is primarily a war machine. Moreover, the experience
of the War period tended to discredit the dirigible, since,
before the introduction of helium gas, the inflammability of its
buoyant factor placed it at an immense disadvantage beside the
machine dependent on the atmosphere itself for its lift.
As life runs to-day, it is a long time since Kipling wrote his
story of the airways of a future world and thrust out a prophecy
that the bulk of the world's air traffic would be carried by
gas-bag vessels. If the school which inclines to belief in the
dirigible is right in its belief, as it well may be, then the
foresight was uncannily correct, not only in the matter of the
main assumption, but in the detail with which the writer
embroidered it.
On the constructional side, the history of the aeroplane is
still so much in the making that any attempt at a critical
history would be unwise, and it is possible only to record fact,
leaving it to the future for judgment to be passed. But, in a
general way, criticism may be advanced with regard to the place
that aeronautics takes in civilisation. In the past hundred
years, the world has made miraculously rapid strides materially,
but moral development has not kept abreast. Conception of the
responsibilities of humanity remains virtually in a position of
a hundred years ago; given a higher conception of life and its
responsibilities, the aeroplane becomes the crowning achievement
of that long series which James Watt inaugurated, the last step
in intercommunication, the chain with which all nations are
bound in a growing prosperity, surely based on moral wellbeing.
Without such conception of the duties as well as the rights of
life, this last achievement of science may yet prove the weapon
that shall end civilisation as men know it to-day, and bring
this ultra-material age to a phase of ruin on which saner people
can build a world more reasonable and less given to groping
after purely material advancement.
PART II
1903-1920: PROGRESS IN DESIGN
BY LIEUT.-COL. W. LOCKWOOD MARSH
I. THE BEGINNINGS
Although the first actual flight of an aeroplane was made by the
Wrights on December 17th 1903, it is necessary, in considering
the progress of design between that period and the present day,
to go back to the earlier days of their experiments with
'gliders,' which show the alterations in design made by them in
their step-bystep progress to a flying machine proper, and give
a clear idea of the stage at which they had arrived in the art
of aeroplane design at the time of their first flights.
They started by carefully surveying the work of previous
experimenters, such as Lilienthal and Chanute, and from the
lesson of some of the failures of these pioneers evolved certain
new principles which were embodied in their first glider, built
in 1900. In the first place, instead of relying upon the
shifting of the operator's body to obtain balance, which had
proved too slow to be reliable, they fitted in front of the main
supporting surfaces what we now call an 'elevator,' which could
be flexed, to control the longitudinal balance, from where the
operator lay prone upon the main supporting surfaces. The second
main innovation which they incorporated in this first glider, and
the principle of which is still used in every aeroplane in
existence, was the attainment of lateral balance by warping the
extremities of the main planes. The effect of warping or pulling
down the extremity of the wing on one side was to increase its
lift and so cause that side to rise. In the first two gliders
this control was also used for steering to right and left. Both
these methods of control were novel for other than model work, as
previous experimenters, such as Lilienthal and Pilcher, had
relied entirely upon moving the legs or shifting the position of
the body to control the longitudinal and lateral motions of their
gliders. For the main supporting surfaces of the glider the
biplane system of Chanute's gliders was adopted with certain
modifications, while the curve of the wings was founded upon the
calculations of Lilienthal as to wind pressure and consequent
lift of the plane.
This first glider was tested on the Kill Devil Hill sand-hills
in North Carolina in the summer of 1900 and proved at any
rate the correctness of the principles of the front elevator and
warping wings, though its designers were puzzled by the fact
that the lift was less than they expected; whilst the 'drag'(as
we call it), or resistance, was also considerably lower than
their predictions. The 1901 machine was, in consequence, nearly
doubled in area--the lifting surface being increased from 165 to
308 square feet--the first trial taking place on July 27th,
1901, again at Kill Devil Hill. It immediately appeared that
something was wrong, as the machine dived straight to the
ground, and it was only after the operator's position had been
moved nearly a foot back from what had been calculated as the
correct position that the machine would glide--and even then the
elevator had to be used far more strongly than in the previous
year's glider. After a good deal of thought the apparent
solution of the trouble was finally found.
This consisted in the fact that with curved surfaces, while at
large angles the centre of pressure moves forward as the angle
decreases, when a certain limit of angle is reached it travels
suddenly backwards and causes the machine to dive. The Wrights
had known of this tendency from Lilienthal's researches, but had
imagined that the phenomenon would disappear if they used a
fairly lightly cambered--or curved--surface with a very abrupt
curve at the front. Having discovered what appeared to be the
cause they surmounted the difficulty by 'trussing down' the
camber of the wings, with the result that they at once got back
to the old conditions of the previous year and could control the
machine readily with small movements of the elevator, even being
able to follow undulations in the ground. They still found,
however, that the lift was not as great as it should have been;
while the drag remained, as in the previous glider, surprisingly
small. This threw doubt on previous figures as to wind
resistance and pressure on curved surfaces; but at the same time
confirmed (and this was a most important result) Lilienthal's
previously questioned theory that at small angles the pressure
on a curved surface instead of being normal, or at right angles
to, the chord is in fact inclined in front of the perpendicular.
The result of this is that the pressure actually tends to draw
the machine forward into the wind--hence the small amount of
drag, which had puzzled Wilbur and Orville Wright.
Another lesson which was learnt from these first two years of
experiment, was that where, as in a biplane, two surfaces are
superposed one above the other, each of them has somewhat less
lift than it would have if used alone. The experimenters were
also still in doubt as to the efficiency of the warping method
of controlling the lateral balance as it gave rise to certain
phenomena which puzzled them, the machine turning towards the
wing having the greater angle, which seemed also to touch the
ground first, contrary to their expectations. Accordingly, on
returning to Dayton towards the end of 1901, they set
themselves to solve the various problems which had appeared and
started on a lengthy series of experiments to check the previous
figures as to wind resistance and lift of curved surfaces,
besides setting themselves to grapple with the difficulty of
lateral control. They accordingly constructed for themselves at
their home in Dayton a wind tunnel 16 inches square by 6 feet
long in which they measured the lift and 'drag' of more than two
hundred miniature wings. In the course of these tests they for
the first time produced comparative results of the lift of
oblong and square surfaces, with the result that they
re-discovered the importance of 'aspect ratio'--the ratio of
length to breadth of planes. As a result, in the next year's
glider the aspect ration of the wings was increased from the
three to one of the earliest model to about six to one, which is
approximately the same as that used in the machines of to-day.
Further than that, they discussed the question of lateral
stability, and came to the conclusion that the cause of the
trouble was that the effect of warping down one wing was to
increase the resistance of, and consequently slow down, that
wing to such an extent that its lift was reduced sufficiently to
wipe out the anticipated increase in lift resulting from the
warping. From this they deduced that if the speed of the warped
wing could be controlled the advantage of increasing the angle
by warping could be utilised as they originally intended. They
therefore decided to fit a vertical fin at the rear which, if the
machine attempted to turn, would be exposed more and more to the
wind and so stop the turning motion by offering increased
resistance.
As a result of this laboratory research work the third Wright
glider, which was taken to Kill Devil Hill in September, 1902,
was far more efficient aerodynamically than either of its two
predecessors, and was fitted with a fixed vertical fin at the
rear in addition to the movable elevator in front. According to
Mr Griffith Brewer,[*] this third glider contained 305 square
feet of surface; though there may possibly be a mistake here, as
he states[**] the surface of the previous year's glider to have
been only 290 square feet, whereas Wilbur Wright himself[***]
states it to have been 308 square feet. The matter is not,
perhaps, save historically, of much importance, except that the
gliders are believed to have been progressively larger, and
therefore if we accept Wilbur Wright's own figure of the surface
of the second glider, the third must have had a greater area
than that given by Mr Griffith Brewer. Unfortunately, no
evidence of the Wright Brothers themselves on this point is
available.
[*] Fourth Wilbur Wright Memorial Lecture, Aeronautical Journal,
Vol. XX, No. 79, page 75.
[**] Ibid. page 73.
[***] Ibid. pp. 91 and 102.
The first glide of the 1902, season was made on September 17th
of that year, and the new machine at once showed itself an
improvement on its predecessors, though subsequent trials showed
that the difficulty of lateral balance had not been entirely
overcome. It was decided, therefore, to turn the vertical fin
at the rear into a rudder by making it movable. At the same
time it was realised that there was a definite relation between
lateral balance and directional control, and the rudder controls
and wing-warping wires were accordingly connected This ended the
pioneer gliding experiments of Wilbur and Orville Wright--though
further glides were made in subsequent years--as the following
year, 1903, saw the first power-driven machine leave the ground.
To recapitulate--in the course of these original experiments the
Wrights confirmed Lilienthal's theory of the reversal of the
centre of pressure on cambered surfaces at small angles of
incidence: they confirmed the importance of high aspect ratio
in respect to lift: they had evolved new and more accurate
tables of lift and pressure on cambered surfaces: they were the
first to use a movable horizontal elevator for controlling
height: they were the first to adjust the wings to different
angles of incidence to maintain lateral balance: and they were
the first to use the movable rudder and adjustable wings in
combination.
They now considered that they had gone far enough to justify
them in building a power-driven 'flier,' as they called their
first aeroplane. They could find no suitable engine and so
proceeded to build for themselves an internal combustion engine,
which was designed to give 8 horse-power, but when completed
actually developed about 12-15 horse-power and weighed 240 lbs.
The complete machine weighed about 750 lbs. Further details of
the first Wright aeroplane are difficult to obtain, and even
those here given should be received with some caution. The
first flight was made on December 17th 1903, and lasted 12
seconds. Others followed immediately, and the fourth lasted 59
seconds, a distance of 852 feet being covered against a 20-mile
wind.
The following year they transferred operations to a field
outside Dayton, Ohio (their home), and there they flew a
somewhat larger and heavier machine with which on September 20th
1904, they completed the first circle in the air. In this
machine for the first time the pilot had a seat; all the
previous experiments having been carried out with the operator
lying prone on the lower wing. This was followed next year by
another still larger machine, and on it they carried out many
flights. During the course of these flights they satisfied
themselves as to the cause of a phenomenon which had puzzled
them during the previous year and caused them to fear that they
had not solved the problem of lateral control. They found that
on occasions--always when on a turn--the machine began to slide
down towards the ground and that no amount of warping could stop
it. Finally it was found that if the nose of the machine was
tilted down a recovery could be effected; from which they
concluded that what actually happened was that the machine,
'owing to the increased load caused by centrifugal force,' had
insufficient power to maintain itself in the air and therefore
lost speed until a point was reached at which the controls
became inoperative. In other words, this was the first
experience of 'stalling on a turn,' which is a danger against
which all embryo pilots have to guard in the early stages of
their training.
The 1905 machine was, like its predecessors, a biplane with a
biplane elevator in front and a double vertical rudder in rear.
The span was 40 feet, the chord of the wings being 6 feet and
the gap between them about the same. The total area was about
600 square feet which supported a total weight of 925 lbs.;
while the motor was 12 to 15 horse-power driving two propellers
on each side behind the main planes through chains and giving
the machine a speed of about 30 m.p.h. one of these chains was
crossed so that the propellers revolved in opposite directions
to avoid the torque which it was feared would be set up if they
both revolved the same way. The machine was not fitted with a
wheeled undercarriage but was carried on two skids, which also
acted as outriggers to carry the elevator. Consequently, a
mechanical method of launching had to be evolved and the machine
received initial velocity from a rail, along which it was drawn
by the impetus provided by the falling of a weight from a wooden
tower or 'pylon.' As a result of this the Wright aeroplane in
its original form had to be taken back to its starting rail
after each flight, and could not restart from the point of
alighting. Perhaps, in comparison with French machines of more
or less contemporary date (evolved on independent lines in
ignorance of the Americans' work), the chief feature of the
Wright biplane of 1905 was that it relied entirely upon the
skill of the operator for its stability; whereas in France some
attempt was being made, although perhaps not very successfully,
to make the machine automatically stable laterally. The
performance of the Wrights in carrying a loading of some 60 lbs.
per horse-power is one which should not be overlooked. The wing
loading was about 1 1/2 lbs. per square foot.
About the same time that the Wrights were carrying out their
power-driven experiments, a band of pioneers was quite
independently beginning to approach success in France. In
practically every case, however, they started from a somewhat
different standpoint and took as their basic idea the cellular
(or box) kite. This form of kite, consisting of two superposed
surfaces connected at each end by a vertical panel or curtain of
fabric, had proved extremely successful for man-carrying
purposes, and, therefore, it was little wonder that several minds
conceived the idea of attempting to fly by fitting a series of
box-kites with an engine. The first to achieve success was M.
Santos-Dumont, the famous Brazilian pioneer-designer of airships,
who, on November 12th, 1906, made several flights, the last of
which covered a little over 700 feet. Santos-Dumont's machine
consisted essentially of two box-kites, forming the main wings,
one on each side of the body, in which the pilot stood, and at
the front extremity of which was another movable box-kite to act
as elevator and rudder. The curtains at the ends were intended
to give lateral stability, which was further ensured by setting
the wings slightly inclined upwards from the centre, so that when
seen from the front they formed a wide V. This feature is still
to be found in many aeroplanes to-day and has come to be known
as the 'dihedral.' The motor was at first of 24 horse-power, for
which later a 50 horse-power Antoinette engine was substituted;
whilst a three-wheeled undercarriage was provided, so that the
machine could start without external mechanical aid. The
machine was constructed of bamboo and steel, the weight being as
low as 352 lbs. The span was 40 feet, the length being 33 feet,
with a total surface of main planes of 860 square feet. It will
thus be seen--for comparison with the Wright machine--that the
weight per horse-power (with the 50 horse-power engine) was only
7 lbs., while the wing loading was equally low at 1/2 lb. per
square foot.
The main features of the Santos-Dumont machine were the box-kite
form of construction, with a dihedral angle on the main planes,
and the forward elevator which could be moved in any direction
and therefore acted in the same way as the rudder at the rear of
the Wright biplane. It had a single propeller revolving in the
centre behind the wings and was fitted with an undercarriage
incorporated in the machine.
The other chief French experimenters at this period were the
Voisin Freres, whose first two machines--identical in
form--were sold to Delagrange and H. Farman, which has sometimes
caused confusion, the two purchasers being credited with the
design they bought. The Voisins, like the Wrights, based their
designs largely on the experimental work of Lilienthal, Langley,
Chanute, and others, though they also carried out tests on the
lifting properties of aerofoils in a wind tunnel of their own.
Their first machines, like those of Santos-Dumont, showed the
effects of experimenting with box-kites, some of which they had
built for M. Ernest Archdeacon in 1904. In their case the
machine, which was again a biplane, had, like both the others
previously mentioned, an elevator in front--though in this case
of monoplane form--and, as in the Wright, a rudder was fitted in
rear of the main planes. The Voisins, however, fitted a fixed
biplane horizontal 'tail'--in an effort to obtain a measure of
automatic longitudinal stability--between the two surfaces of
which the single rudder worked. For lateral stability they
depended entirely on end curtains between the upper and lower
surfaces of both the main planes and biplane tail surfaces.
They, like Santos-Dumont, fitted a wheeled undercarriage, so
that the machine was self-contained. The Voisin machine, then,
was intended to be automatically stable in both senses; whereas
the Wrights deliberately produced a machine which was entirely
dependent upon the pilot's skill for its stability. The
dimensions of the Voisin may be given for comparative purposes,
and were as follows: Span 33 feet with a chord (width from back
to front) of main planes of 6 1/2 feet, giving a total area of
430 square feet. The 50 horse-power Antoinette engine, which was
enclosed in the body (or 'nacelle ') in the front of which the
pilot sat, drove a propeller behind, revolving between the
outriggers carrying the tail. The total weight, including Farman
as pilot, is given as 1,540 lbs., so that the machine was much
heavier than either of the others; the weight per horse-power
being midway between the Santos-Dumont and the Wright at 31 lbs.
per square foot, while the wing loading was considerably greater
than either at 3 1/2 lbs. per square foot. The Voisin machine
was
experimented with by Farman and Delagrange from about June 1907
onwards, and was in the subsequent years developed by Farman; and
right up to the commencement of the War upheld the principles of
the box-kite method of construction for training purposes. The
chief modification of the original design was the addition of
flaps (or ailerons) at the rear extremities of the main planes to
give lateral control, in a manner analogous to the wing-warping
method invented by the Wrights, as a result of which the end
curtains between the planes were abolished. An additional
elevator was fitted at the rear of the fixed biplane tail, which
eventually led to the discarding of the front elevator
altogether. During the same period the Wright machine came into
line with the others by the fitting of a wheeled undercarriage
integral with the machine. A fixed horizontal tail was also
added to the rear rudder, to which a movable elevator was later
attached; and, finally, the front elevator was done away with.
It will thus be seen that having started from the very different
standpoints of automatic stability and complete control by the
pilot, the Voisin (as developed in the Farman) and Wright
machines, through gradual evolution finally resulted in
aeroplanes of similar characteristics embodying a modicum of
both features.
Before proceeding to the next stage of progress mention should
be made of the experimental work of Captain Ferber in France.
This officer carried out a large number of experiments with
gliders contemporarily with the Wrights, adopting--like
them--the Chanute biplane principle. He adopted the front
elevator from the Wrights, but immediately went a step farther
by also fitting a fixed tail in rear, which did not become a
feature of the Wright machine until some seven or eight years
later. He built and appeared to have flown a machine fitted
with a motor in 1905, and was commissioned to go to America by
the French War Office on a secret mission to the Wrights.
Unfortunately, no complete account of his experiments appears to
exist, though it can be said that his work was at least as
important as that of any of the other pioneers mentioned.
II. MULTIPLICITY OF IDEAS
In a review of progress such as this, it is obviously
impossible, when a certain stage of development has been
reached, owing to the very multiplicity of experimenters, to
continue dealing in anything approaching detail with all the
different types of machines; and it is proposed, therefore, from
this point to deal only with tendencies, and to mention
individuals merely as examples of a class of thought rather than
as personalities, as it is often difficult fairly to allocate
the responsibility for any particular innovation.
During 1907 and 1908 a new type of machine, in the monoplane,
began to appear from the workshops of Louis Bleriot, Robert
Esnault-Pelterie, and others, which was destined to give rise to
long and bitter controversies on the relative advantages of the
two types, into which it is not proposed to enter here; though
the rumblings of the conflict are still to be heard by
discerning ears. Bleriot's early monoplanes had certain new
features, such as the location of the pilot, and in some cases
the engine, below the wing; but in general his monoplanes,
particularly the famous No. XI on which the first Channel
crossing was made on July 25th, 1909, embodied the main
principles of the Wright and Voisin types, except that the
propeller was in front of instead of behind the supporting
surfaces, and was, therefore, what is called a 'tractor' in
place of the then more conventional 'pusher.' Bleriot aimed at
lateral balance by having the tip of each wing pivoted, though he
soon fell into line with the Wrights and adopted the warping
system. The main features of the design of Esnault-Pelterie's
monoplane was the inverted dihedral (or kathedral as this was
called in Mr S. F. Cody's British Army Biplane of 1907) on the
wings, whereby the tips were considerably lower than the roots at
the body. This was designed to give automatic lateral stability,
but, here again, conventional practice was soon adopted and the
R.E.P. monoplanes, which became well-known in this country
through their adoption in the early days by Messrs Vickers, were
of the ordinary monoplane design, consisting of a tractor
propeller with wire-stayed wings, the pilot being in an enclosed
fuselage containing the engine in front and carrying at its rear
extremity fixed horizontal and vertical surfaces combined with
movable elevators and rudder. Constructionally, the R.E.P.
monoplane was of extreme interest as the body was constructed of
steel. The Antoinette monoplane, so ably flown by Latham, was
another very famous machine of the 1909-1910 period, though its
performance were frequently marred by engine failure; which was
indeed the bugbear of all these early experimenters, and it is
difficult to say, after this lapse of time, how far in many cases
the failures which occurred, both in performances and even in the
actual ability to rise from the ground, were due to defects in
design or merely faults in the primitive engines available. The
Antoinette aroused admiration chiefly through its graceful,
birdlike lines, which have probably never been equalled; but its
chief interest for our present purpose lies in the novel method
of wing-staying which was employed. Contemporary monoplanes
practically all had their wings stayed by wires to a post in the
centre above the fuselage, and, usually, to the undercarriage
below. In the Antoinette, however, a king post was introduced
half-way along the wing, from which wires were carried to the
ends of the wings and the body. This was intended to give
increased strength and permitted of a greater wing-spread and
consequently improved aspect ratio. The same system of
construction was adopted in the British Martinsyde monoplanes of
two or three years later.
This period also saw the production of the first triplane, which
was built by A. V. Roe in England and was fitted with a J.A.P.
engine of only 9 horse-power--an amazing performance which
remains to this day unequalled. Mr Roe's triplane was chiefly
interesting otherwise for the method of maintaining longitudinal
control, which was achieved by pivoting the whole of the three
main planes so that their angle of incidence could be altered.
This was the direct converse of the universal practice of
elevating by means of a subsidiary surface either in front or
rear of the main planes.
Recollection of the various flying meetings and exhibitions
which one attended during the years from 1909 to 1911, or even
1912 are chiefly notable for the fact that the first thought on
seeing any new type of machine was not as to what its
'performance'--in speed, lift, or what not--would be; but
speculation as to whether it would leave the ground at all when
eventually tried. This is perhaps the best indication of the
outstanding characteristic of that interim period between the
time of the first actual flights and the later period,
commencing about 1912, when ideas had become settled and it
was at last becoming possible to forecast on the drawing-board
the performance of the completed machine in the air. Without
going into details, for which there is no space here, it is
difficult to convey the correct impression of the chaotic state
which existed as to even the elementary principles of aeroplane
design. All the exhibitions contained large numbers--one had
almost written a majority--of machines which embodied the most
unusual features and which never could, and in practice never
did, leave the ground. At the same time, there were few who
were sufficiently hardy to say certainly that this or that
innovation was wrong; and consequently dozens of inventors in
every country were conducting isolated experiments on both good
and bad lines. All kinds of devices, mechanical and otherwise,
were claimed as the solution of the problem of stability, and
there was even controversy as to whether any measure of
stability was not undesirable; one school maintaining that the
only safety lay in the pilot having the sole say in the attitude
of the machine at any given moment, and fearing danger from the
machine having any mind of its own, so to speak. There was, as
in most controversies, some right on both sides, and when we
come to consider the more settled period from 1912 to the
outbreak of the War in 1914 we shall find how a compromise was
gradually effected.
At the same time, however, though it was at the time difficult
to pick out, there was very real progress being made, and,
though a number of 'freak' machines fell out by the wayside, the
pioneer designers of those days learnt by a process of trial and
error the right principles to follow and gradually succeeded in
getting their ideas crystallised.
In connection with stability mention must be made of a machine
which was evolved in the utmost secrecy by Mr J. W. Dunne in a
remote part of Scotland under subsidy from the War office. This
type, which was constructed in both monoplane and biplane form,
showed that it was in fact possible in 1910 and 1911 to design an
aeroplane which could definitely be left to fly itself in the
air. One of the Dunne machines was, for example flown from
Farnborough to Salisbury Plain without any control other than the
rudder being touched; and on another occasion it flew a complete
circle with all controls locked automatically assuming the
correct bank for the radius of turn. The peculiar form of wing
used, the camber of which varied from the root to the tip, gave
rise however, to a certain loss in efficiency, and there was also
a difficulty in the pilot assuming adequate control when desired.
Other machines designed to be stable--such as the German Etrich
and the British Weiss gliders and Handley-Page monoplanes--were
based on the analogy of a wing attached to a certain seed found
in Nature (the 'Zanonia' leaf), on the righting effect of
back-sloped wings combined with upturned (or 'negative') tips.
Generally speaking, however, the machines of the 1909-1912 period
relied for what automatic stability they had on the principle of
the dihedral angle, or flat V, both longitudinally and laterally.
Longitudinally this was obtained by setting the tail at a
slightly smaller angle than the main planes.
The question of reducing the resistance by adopting 'stream-line'
forms, along which the air could flow uninterruptedly without the
formation of eddies, was not at first properly realised, though
credit should be given to Edouard Nieuport, who in 1909 produced
a monoplane with a very large body which almost completely
enclosed the pilot and made the machine very fast, for those
days, with low horse-power. On one of these machines C. T.
Weyman won the Gordon-Bennett Cup for America in 1911 and
another put up a fine performance in the same race with only a 30
horse-power engine. The subject, was however, early taken up by
the British Advisory Committee for Aeronautics, which was
established by the Government in 1909, and designers began to
realise the importance of streamline struts and fuselages towards
the end of this transition period. These efforts were at first
not always successful and showed at times a lack of understanding
of the problems involved, but there was a very marked improvement
during the year 1912. At the Paris Aero Salon held early in that
year there was a notable variety of ideas on the subject; whereas
by the time of the one held in October designs had considerably
settled down, more than one exhibitor showing what were called
'monocoque' fuselages completely circular in shape and having
very low resistance, while the same show saw the introduction of
rotating cowls over the propeller bosses, or 'spinners,' as they
came to be called during the War. A particularly fine example of
stream-lining was to be found in the Deperdussin monoplane on
which Vedrines won back the Gordon-Bennett Aviation Cup from
America at a speed of 105.5 m.p.h.--a considerable improvement on
the 78 m.p.h. of the preceding year, which was by no means
accounted for by the mere increase in engine power from 100
horse-power to 140 horse-power. This machine was the first in
which the refinement of 'stream-lining' the pilot's head, which
became a feature of subsequent racing machines, was introduced.
This consisted of a circular padded excresence above the cockpit
immediately behind the pilot's head, which gradually tapered off
into the top surface of the fuselage. The object was to give the
air an uninterrupted flow instead of allowing it to be broken up
into eddies behind the head of the pilot, and it also provided a
support against the enormous wind-pressure encountered. This
true stream-line form of fuselage owed its introduction to the
Paulhan-Tatin 'Torpille' monoplane of the Paris Salon of early
1917. Altogether the end of the year 1912 began to see the
disappearance of 'freak' machines with all sorts of original
ideas for the increase of stability and performance. Designs had
by then gradually become to a considerable extent standardised,
and it had become unusual to find a machine built which would
fail to fly. The Gnome engine held the field owing to its
advantages, as the first of the rotary type, in lightness and
ease of fitting into the nose of a fuselage. The majority of
machines were tractors (propeller in front) although a
preference, which died down subsequently, was still shown for the
monoplane over the biplane. This year also saw a great increase
in the number of seaplanes, although the 'flying boat' type had
only appeared at intervals and the vast majority were of the
ordinary aeroplane type fitted with floats in place of the land
undercarriage; which type was at that time commonly called
'hydro-aeroplane.' The usual horse power was 50--that of the
smallest Gnome engine--although engines of 100 to 140 horse-power
were also fitted occasionally. The average weight per
horse-power varied from 18 to 25 lbs., while the wing-loading was
usually in the neighbourhood of 5 to 6 lbs. per square foot. The
average speed ranged from 65-75 miles per hour.
III. PROGRESS ON STANDARDISED LINES
In the last section an attempt has been made to show how, during
what was from the design standpoint perhaps the most critical
period, order gradually became evident out of chaos,
ill-considered ideas dropped out through failure to make good,
and, though there was still plenty of room for improvement in
details, the bulk of the aeroplanes showed a general similarity
in form and conception. There was still a great deal to be
learnt in finding the best form of wing section, and performances
were still low; but it had become definitely possible to say that
flying had emerged from the chrysalis stage and had become a
science. The period which now began was one of scientific
development and improvement--in performance, manoeuvrability,
and general airworthiness and stability.
The British Military Aeroplane Competition held in the summer of
1912 had done much to show the requirements in design by giving
possibly the first opportunity for a definite comparison of the
performance of different machines as measured by impartial
observers on standard lines--albeit the methods of measuring were
crude. These showed that a high speed--for those days--of 75
miles an hour or so was attended by disadvantages in the form of
an equally fast low speed, of 50 miles per hour or more, and
generally may be said to have given designers an idea what to aim
for and in what direction improvements were required. In fact,
the most noticeable point perhaps of the machines of this time
was the marked manner in which a machine that was good in one
respect would be found to be wanting in others. It had not yet
been possible to combine several desirable attributes in one
machine. The nearest approach to this was perhaps to be found
in the much discussed Government B.E.2 machine, which was
produced from the Royal Aircraft Factory at Farnborough, in the
summer of 1912. Though considerably criticized from many points
of view it was perhaps the nearest approach to a machine of
all-round efficiency that had up to that date appeared. The
climbing rate, which subsequently proved so important for
military purposes, was still low, seldom, if ever, exceeding 400
feet per minute; while gliding angles (ratio of descent to
forward travel over the ground with engine stopped) little
exceeded 1 in 8.
The year 1912 and 1913 saw the subsequently all-conquering
tractor biplane begin to come into its own. This type, which
probably originated in England, and at any rate attained to its
greatest excellence prior to the War from the drawing offices of
the Avro Bristol and Sopwith firms, dealt a blow at the monoplane
from which the latter never recovered.
The two-seater tractor biplane produced by Sopwith and piloted
by H. G. Hawker, showed that it was possible to produce a
biplane with at least equal speed to the best monoplanes, whilst
having the advantage of greater strength and lower landing
speeds. The Sopwith machine had a top speed of over 80 miles an
hour while landing as slowly as little more than 30 miles an
hour; and also proved that it was possible to carry 3 passengers
with fuel for 4 hours' flight with a motive power of only 80
horse-power. This increase in efficiency was due to careful
attention to detail in every part, improved wing sections, clean
fuselage-lines, and simplified undercarriages. At the same
time, in the early part of 1913 a tendency manifested itself
towards the four-wheeled undercarriage, a pair of smaller wheels
being added in front of the main wheels to prevent overturning
while running on the ground; and several designs of
oleo-pneumatic and steel-spring undercarriages were produced in
place of the rubber shock-absorber type which had up till then
been almost universal.
These two statements as to undercarriage designs may appear to
be contradictory, but in reality they do not conflict as they
both showed a greater attention to the importance of good
springing, combined with a desire to avoid complication and a
mass of struts and wires which increased head resistance.
The Olympia Aero Show of March, 1913, also produced a machine
which, although the type was not destined to prove the best for
the purpose for which it was designed, was of interest as being
the first to be designed specially for war purposes. This was
the Vickers 'Gun-bus,' a 'pusher' machine, with the propeller
revolving behind the main planes between the outriggers carrying
the tail, with a seat right in front for a gunner who was
provided with a machine gun on a swivelling mount which had a
free field of fire in every direction forward. The device which
proved the death-blow for this type of aircraft during the war
will be dealt with in the appropriate place later, but the
machine should not go unrecorded.
As a result of a number of accidents to monoplanes the
Government appointed a Committee at the end of 1912 to inquire
into the causes of these. The report which was presented in
March, 1913, exonerated the monoplane by coming to the
conclusion that the accidents were not caused by conditions
peculiar to monoplanes, but pointed out certain desiderata in
aeroplane design generally which are worth recording. They
recommended that the wings of aeroplanes should be so internally
braced as to have sufficient strength in themselves not to
collapse if the external bracing wires should give way. The
practice, more common in monoplanes than biplanes, of carrying
important bracing wires from the wings to the undercarriage was
condemned owing to the liability of damage from frequent
landings. They also pointed out the desirability of duplicating
all main wires and their attachments, and of using stranded
cable for control wires. Owing to the suspicion that one
accident at least had been caused through the tearing of the
fabric away from the wing, it was recommended that fabric should
be more securely fastened to the ribs of the wings, and that
devices for preventing the spreading of tears should be
considered. In the last connection it is interesting to note
that the French Deperdussin firm produced a fabric wing-covering
with extra strong threads run at right-angles through the fabric
at intervals in order to limit the tearing to a defined area.
In spite, however, of the whitewashing of the monoplane by the
Government Committee just mentioned, considerable stir was
occasioned later in the year by the decision of the War office
not to order any more monoplanes; and from this time forward
until the War period the British Army was provided exclusively
with biplanes. Even prior to this the popularity of the
monoplane had begun to wane. At the Olympia Aero Show in March,
1913, biplanes for the first time outnumbered the
'single-deckers'(as the Germans call monoplanes); which had the
effect of reducing the wing-loading. In the case of the
biplanes exhibited this averaged about 4 1/2 lbs. per square
foot, while in the case of the monoplanes in the same exhibition
the lowest was 5 1/2 lbs., and the highest over 8 1/2 lbs. per
square foot of area. It may here be mentioned that it was not
until the War period that the importance of loading per
horse-power was recognised as the true criterion of aeroplane
efficiency, far greater interest being displayed in the amount
of weight borne per unit area of wing.
An idea of the state of development arrived at about this time
may be gained from the fact that the Commandant of the Military
Wing of the Royal Flying Corps in a lecture before the Royal
Aeronautical Society read in February, 1913, asked for
single-seater scout aeroplanes with a speed of 90 miles an hour
and a landing speed of 45 miles an hour--a performance which
even two years later would have been considered modest in the
extreme. It serves to show that, although higher performances
were put up by individual machines on occasion, the general
development had not yet reached the stage when such performances
could be obtained in machines suitable for military purposes.
So far as seaplanes were concerned, up to the beginning of 1913
little attempt had been made to study the novel problems
involved, and the bulk of the machines at the Monaco Meeting in
April, 1913, for instance, consisted of land machines fitted with
floats, in many cases of a most primitive nature, without other
alterations. Most of those which succeeded in leaving the water
did so through sheer pull of engine power; while practically all
were incapable of getting off except in a fair sea, which enabled
the pilot to jump the machine into the air across the trough
between two waves. Stability problems had not yet been
considered, and in only one or two cases was fin area added at
the rear high up, to counterbalance the effect of the floats low
down in front. Both twin and single-float machines were used,
while the flying boat was only just beginning to come into being
from the workshops of Sopwith in Great Britain, Borel-Denhaut in
France, and Curtiss in America. In view of the approaching
importance of amphibious seaplanes, mention should be made of the
flying boat (or 'bat boat' as it was called, following Rudyard
Kipling) which was built by Sopwith in 1913 with a wheeled
landing-carriage which could be wound up above the bottom surface
of the boat so as to be out of the way when alighting on water.
During 1913 the (at one time almost universal) practice
originated by the Wright Brothers, of warping the wings for
lateral stability, began to die out and the bulk of aeroplanes
began to be fitted with flaps (or 'ailerons') instead. This
was a distinct change for the better, as continually warping the
wings by bending down the extremities of the rear spars was
bound in time to produce 'fatigue' in that member and lead to
breakage; and the practice became completely obsolete during the
next two or three years.
The Gordon-Bennett race of September, 1913, was again won by
a Deperdussin machine, somewhat similar to that of the previous
year, but with exceedingly small wings, only 107 square feet in
area. The shape of these wings was instructive as showing how
what, from the general utility point of view, may be
disadvantageous can, for a special purpose, be turned to
account. With a span of 21 feet, the chord was 5 feet, giving
the inefficient 'aspect ratio' of slightly over 4 to 1 only.
The object of this was to reduce the lift, and therefore the
resistance, to as low a point as possible. The total weight was
1,500 lbs., giving a wing-loading of 14 lbs. per square foot--a
hitherto undreamt-of figure. The result was that the machine
took an enormously long run before starting; and after touching
the ground on landing ran for nearly a mile before stopping; but
she beat all records by attaining a speed of 126 miles per
hour. Where this performance is mainly interesting is in
contrast to the machines of 1920, which with an even higher
speed capacity would yet be able to land at not more than 40 or
50 miles per hour, and would be thoroughly efficient flying
machines.
The Rheims Aviation Meeting, at which the Gordon-Bennett race
was flown, also saw the first appearance of the Morane 'Parasol'
monoplane. The Morane monoplane had been for some time an
interesting machine as being the only type which had no fixed
surface in rear to give automatic stability, the movable
elevator being balanced through being hinged about one-third of
the way back from the front edge. This made the machine
difficult to fly except in the hands of experts, but it was very
quick and handy on the controls and therefore useful for racing
purposes. In the 'Parasol' the modification was introduced of
raising the wing above the body, the pilot looking out beneath
it, in order to give as good a view as possible.
Before passing to the year 1914 mention should be made of the
feat performed by Nesteroff, a Russian, and Pegoud, a French
pilot, who were the first to demonstrate the possibilities of
flying upside-down and looping the loop. Though perhaps not
coming strictly within the purview of a chapter on design
(though certain alterations were made to the top wing-bracing of
the machine for this purpose) this performance was of extreme
importance to the development of aviation by showing the
possibility of recovering, given reasonable height, from any
position in the air; which led designers to consider the extra
stresses to which an aeroplane might be subjected and to take
steps to provide for them by increasing strength where
necessary.
When the year 1914 opened a speed of 126 miles per hour had been
attained and a height of 19,600 feet had been reached. The
Sopwith and Avro (the forerunner of the famous training machine
of the War period) were probably the two leading tractor
biplanes of the world, both two-seaters with a speed variation
from 40 miles per hour up to some 90 miles per hour with 80
horse-power engines. The French were still pinning their faith
mainly to monoplanes, while the Germans were beginning to come
into prominence with both monoplanes and biplanes of the 'Taube'
type. These had wings swept backward and also upturned at the
wing-tips which, though it gave a certain measure of automatic
stability, rendered the machine somewhat clumsy in the air, and
their performances were not on the whole as high as those of
either France or Great Britain.
Early in 1914 it became known that the experimental work of
Edward Busk--who was so lamentably killed during an experimental
flight later in the year--following upon the researches of
Bairstow and others had resulted in the production at the Royal
Aircraft Factory at Farnborough of a truly automatically stable
aeroplane. This was the 'R.E.' (Reconnaissance Experimental), a
development of the B.E. which has already been referred to. The
remarkable feature of this design was that there was no
particular device to which one could point out as the cause of
the stability. The stable result was attained simply by detailed
design of each part of the aeroplane, with due regard to its
relation to, and effect on, other parts in the air. Weights and
areas were so nicely arranged that under practically any
conditions the machine tended to right itself. It did not,
therefore, claim to be a machine which it was impossible to
upset, but one which if left to itself would tend to right itself
from whatever direction a gust might come. When the principles
were extended to the 'B.E. 2c' type (largely used at the outbreak
of the War) the latter machine, if the engine were switched of f
at a height of not less than 1,000 feet above the ground, would
after a few moments assume its correct gliding angle and glide
down to the ground.
The Paris Aero Salon of December, 1913, had been remarkable
chiefly for the large number of machines of which the chassis and
bodywork had been constructed of steel-tubing; for the excess of
monoplanes over biplanes; and (in the latter) predominance of
'pusher' machines (with propeller in rear of the main planes)
compared with the growing British preference for 'tractors' (with
air screw in front). Incidentally, the Maurice Farman, the last
relic of the old type box-kite with elevator in front appeared
shorn of this prefix, and became known as the 'short-horn' in
contradistinction to its front-elevatored predecessor which,
owing to its general reliability and easy flying capabilities,
had long been affectionately called the 'mechanical cow.' The
1913 Salon also saw some lingering attempts at attaining
automatic stability by pendulum and other freak devices.
Apart from the appearance of 'R.E.1,' perhaps the most notable
development towards the end of 1913 was the appearance of the
Sopwith 'Tabloid 'tractor biplane. This single-seater machine,
evolved from the two-seater previously referred to, fitted with a
Gnome engine of 80 horse-power, had the, for those days,
remarkable speed of 92 miles an hour; while a still more
notable feature was that it could remain in level flight at not
more than 37 miles per hour. This machine is of particular
importance because it was the prototype and forerunner of the
successive designs of single-seater scout fighting machines
which were used so extensively from 1914 to 1918. It was also
probably the first machine to be capable of reaching a height of
1,000 feet within one minute. It was closely followed by the
'Bristol Bullet,' which was exhibited at the Olympia Aero Show
of March, 1914. This last pre-war show was mainly remarkable
for the good workmanship displayed--rather than for any distinct
advance in design. In fact, there was a notable diversity in
the types displayed, but in detailed design considerable
improvements were to be seen, such as the general adoption of
stranded steel cable in place of piano wire for the mail bracing
IV. THE WAR PERIOD
Up to this point an attempt has been made to give some idea of
the progress that was made during the eleven years that had
elapsed since the days of the Wrights' first flights. Much
advance had been made and aeroplanes had settled down,
superficially at any rate, into more or less standardised forms
in three main types--tractor monoplanes, tractor biplanes, and
pusher biplanes. Through the application of the results of
experiments with models in wind tunnels to full-scale machines,
considerable improvements had been made in the design of wing
sections, which had greatly increased the efficiency of
aeroplanes by raising the amount of 'lift' obtained from the
wing compared with the 'drag' (or resistance to forward motion)
which the same wing would cause. In the same way the shape of
bodies, interplane struts, etc., had been improved to be of
better stream-line shape, for the further reduction of
resistance; while the problems of stability were beginning to be
tolerably well understood. Records (for what they are worth)
stood at 21,000 feet as far as height was concerned, 126 miles
per hour for speed, and 24 hours duration. That there was
considerable room for development is, however, evidenced by a
statement made by the late B. C. Hucks (the famous pilot) in
the course of an address delivered before the Royal Aeronautical
Society in July, 1914. 'I consider,' he said, 'that the present
day standard of flying is due far more to the improvement in
piloting than to the improvement in machines.... I consider
those (early 1914) machines are only slight improvements on the
machines of three years ago, and yet they are put through
evolutions which, at that time, were not even dreamed of. I can
take a good example of the way improvement in piloting has
outdistanced improvement in machines--in the case of myself, my
'looping' Bleriot. Most of you know that there is very little
difference between that machine and the 50 horse-power Bleriot
of three years ago.' This statement was, of course, to some
extent an exaggeration and was by no means agreed with by
designers, but there was at the same time a germ of truth in it.
There is at any rate little doubt that the theory and practice
of aeroplane design made far greater strides towards becoming an
exact science during the four years of War than it had done
during the six or seven years preceding it.
It is impossible in the space at disposal to treat of this
development even with the meagre amount of detail that has been
possible while covering the 'settling down' period from 1911 to
1914, and it is proposed, therefore, to indicate the improvements
by sketching briefly the more noticeable difference in various
respects between the average machine of 1914 and a similar
machine of 1918.
In the first place, it was soon found that it was possible to
obtain greater efficiency and, in particular, higher speeds,
from tractor machines than from pusher machines with the air
screw behind the main planes. This was for a variety of reasons
connected with the efficiency of propellers and the possibility
of reducing resistance to a greater extent in tractor machines
by using a 'stream-line' fuselage (or body) to connect the main
planes with the tail. Full advantage of this could not be
taken, however, owing to the difficulty of fixing a machine-gun
in a forward direction owing to the presence of the propeller.
This was finally overcome by an ingenious device (known as an
'Interrupter gear') which allowed the gun to fire only when
none of the propeller blades was passing in front of the muzzle.
The monoplane gradually fell into desuetude, mainly owing to the
difficulty of making that type adequately strong without it
becoming prohibitively heavy, and also because of its high
landing speed and general lack of manoeuvrability. The triplane
was also little used except in one or two instances, and,
practically speaking, every machine was of the biplane tractor
type.
A careful consideration of the salient features leading to
maximum efficiency in aeroplanes--particularly in regard to
speed and climb, which were the two most important military
requirements--showed that a vital feature was the reduction in
the amount of weight lifted per horse-power employed; which in
1914 averaged from 20 to 25 lbs. This was effected both by
gradual increase in the power and size of the engines used and
by great improvement in their detailed design (by increasing
compression ratio and saving weight whenever possible); with the
result that the motive power of single-seater aeroplanes rose
from 80 and 100 horse-power in 1914 to an average of 200 to 300
horse-power, while the actual weight of the engine fell from 3
1/2-4 lbs. per horse-power to an average of 2 1/2 lbs. per
horse-power. This meant that while a pre-war engine of 100
horse-power would weigh some 400 lbs., the 1918 engine developing
three times the power would have less than double the weight.
The result of this improvement was that a scout aeroplane at the
time of the Armistice would have 1 horse-power for every 8 lbs.
of weight lifted, compared with the 20 or 25 lbs. of its 1914
predecessors. This produced a considerable increase in the rate
of climb, a good postwar machine being able to reach 10,000 feet
in about 5 minutes and 20,000 feet in under half an hour. The
loading per square foot was also considerably increased; this
being rendered possible both by improvement in the design of wing
sections and by more scientific construction giving increased
strength. It will be remembered that in the machine of the very
early period each square foot of surface had only to lift a
weight of some 1 1/2 to 2 lbs., which by 1914 had been increased
to about 4 lbs. By 1918 aeroplanes habitually had a loading of 8
lbs. or more per square foot of area; which resulted in great
increase in speed. Although a speed of 126 miles per hour had
been attained by a specially designed racing machine over a short
distance in 1914, the average at that period little exceeded, if
at all, 100 miles per hour; whereas in 1918 speeds of 130 miles
per hour had become a commonplace, and shortly afterwards a speed
of over 166 miles an hour was achieved.
In another direction, also, that of size, great developments
were made. Before the War a few machines fitted with more than
one engine had been built (the first being a triple
Gnome-engined biplane built by Messrs Short Bros. at Eastchurch
in 1913), but none of large size had been successfully produced,
the total weight probably in no case exceeding about 2 tons. In
1916, however, the twin engine Handley-Page biplane was
produced, to be followed by others both in this country and
abroad, which represented a very great increase in size and,
consequently, load-carrying capacity. By the end of the War
period several types were in existence weighing a total of 10
tons when fully loaded, of which some 4 tons or more represented
'useful load' available for crew, fuel, and bombs or passengers.
This was attained through very careful attention to detailed
design, which showed that the material could be employed more
efficiently as size increased, and was also due to the fact that
a large machine was not liable to be put through the same
evolutions as a small machine, and therefore could safely be
built with a lower factor of safety. Owing to the fact that a
wing section which is adopted for carrying heavy loads usually
has also a somewhat low lift to drag ratio, and is not therefore
productive of high speed, these machines are not as fast as
light scouts; but, nevertheless, they proved themselves capable
of achieving speeds of 100 miles an hour or more in some cases;
which was faster than the average small machine of 1914.
In one respect the development during the War may perhaps have
proved to be somewhat disappointing, as it might have been
expected that great improvements would be effected in metal
construction, leading almost to the abolition of wooden
structures. Although, however, a good deal of experimental work
was done which resulted in overcoming at any rate the worst of
the difficulties, metal-built machines were little used (except
to a certain extent in Germany) chiefly on account of the need
for rapid production and the danger of delay resulting from
switching over from known and tried methods to experimental
types of construction. The Germans constructed some large
machines, such as the giant Siemens-Schukhert machine, entirely
of metal except for the wing covering, while the Fokker and
Junker firms about the time of the Armistice in 1918 both
produced monoplanes with very deep all-metal wings (including
the covering) which were entirely unstayed externally, depending
for their strength on internal bracing. In Great Britain cable
bracing gave place to a great extent to 'stream-line wires,'
which are steel rods rolled to a more or less oval section,
while tie-rods were also extensively used for the internal
bracing of the wings. Great developments in the economical use
of material were also made in the direction of using built-up
main spars for the wings and interplane struts; spars composed
of a series of layers (or 'laminations') of different pieces of
wood also being used.
Apart from the metallic construction of aeroplanes an enormous
amount of work was done in the testing of different steels and
light alloys for use in engines, and by the end of the War
period a number of aircraft engines were in use of which the
pistons and other parts were of such alloys; the chief
difficulty having been not so much in the design as in the
successful heat-treatment and casting of the metal.
An important development in connection with the inspection and
testing of aircraft parts, particularly in the case of metal,
was the experimental application of X-ray photography, which
showed up latent defects, both in the material and in
manufacture, which would otherwise have passed unnoticed. This
method was also used to test the penetration of glue into the
wood on each side of joints, so giving a measure of the
strength; and for the effect of 'doping' the wings, dope being a
film (of cellulose acetate dissolved in acetone with other
chemicals) applied to the covering of wings and bodies to render
the linen taut and weatherproof, besides giving it a smooth
surface for the lessening of 'skin friction' when passing rapidly
through the air.
An important result of this experimental work was that it in
many cases enabled designers to produce aeroplane parts from
less costly material than had previously been considered
necessary, without impairing the strength. It may be mentioned
that it was found undesirable to use welded joints on aircraft
in any part where the material is subjectto a tensile or bending
load, owing to the danger resulting from bad workmanship causing
the material to become brittle--an effect which cannot be
discovered except by cutting through the weld, which, of course,
involves a test to destruction. Written, as it has been, in
August, 1920, it is impossible in this chapter to give any
conception of how the developments of War will be applied to
commercial aeroplanes, as few truly commercial machines have yet
been designed, and even those still show distinct traces of the
survival of war mentality. When, however, the inevitable
recasting of ideas arrives, it will become evident, whatever the
apparent modification in the relative importance of different
aspects of design, that enormous advances were made under the
impetus of War which have left an indelible mark on progress.
We have, during the seventeen years since aeroplanes first took
the air, seen them grow from tentative experimental structures
of unknown and unknowable performance to highly scientific
products, of which not only the performances (in speed,
load-carrying capacity, and climb) are known, but of which the
precise strength and degree of stability can be forecast with
some accuracy on the drawing board. For the rest, with the
future lies--apart from some revolutionary change in fundamental
design--the steady development of a now well-tried and well-found
engineering structure.
PART III
AEROSTATICS
I. BEGINNINGS
Francesco Lana, with his 'aerial ship,' stands as one of the
first great exponents of aerostatics; up to the time of the
Montgolfier and Charles balloon experiments, aerostatic and
aerodynamic research are so inextricably intermingled that it
has been thought well to treat of them as one, and thus the work
of Lana, Veranzio and his parachute, Guzman's frauds, and the
like, have already been sketched. In connection with Guzman,
Hildebrandt states in his Airships Past and Present, a fairly
exhaustive treatise on the subject up to 1906, the year of its
publication, that there were two inventors--or
charlatans--Lorenzo de Guzman and a monk Bartolemeo Laurenzo,
the former of whom constructed an unsuccessful airship out of a
wooden basket covered with paper, while the latter made certain
experiments with a machine of which no description remains. A
third de Guzman, some twenty-five years later, announced that he
had constructed a flying machine, with which he proposed to fly
from a tower to prove his success to the public. The lack of
record of any fatal accident overtaking him about that time
seems to show that the experiment was not carried out.
Galien, a French monk, published a book L'art de naviguer dans
l'air in 1757, in which it was conjectured that the air at high
levels was lighter than that immediately over the surface of
the earth. Galien proposed to bring down the upper layers of
air and with them fill a vessel, which by Archimidean principle
would rise through the heavier atmosphere. If one went high
enough, said Galien, the air would be two thousand times as
light as water, and it would be possible to construct an
airship, with this light air as lifting factor, which should be
as large as the town of Avignon, and carry four million
passengers with their baggage. How this high air was to be
obtained is matter for conjecture--Galien seems to have thought
in a vicious circle, in which the vessel that must rise to
obtain the light air must first be filled with it in order to
rise.
Cavendish's discovery of hydrogen in 1776 set men thinking, and
soon a certain Doctor Black was suggesting that vessels might be
filled with hydrogen, in order that they might rise in the air.
Black, however, did not get beyond suggestion; it was Leo
Cavallo who first made experiments with hydrogen, beginning with
filling soap bubbles, and passing on to bladders and special
paper bags. In these latter the gas escaped, and Cavallo was
about to try goldbeaters' skin at the time that the Montgolfiers
came into the field with their hot air balloon.
Joseph and Stephen Montgolfier, sons of a wealthy French paper
manufacturer, carried out many experiments in physics, and
Joseph interested himself in the study of aeronautics some time
before the first balloon was constructed by the brothers--he is
said to have made a parachute descent from the roof of his house
as early as 1771, but of this there is no proof. Galien's idea,
together with study of the movement of clouds, gave Joseph some
hope of achieving aerostation through Galien's schemes, and the
first experiments were made by passing steam into a receiver,
which, of course, tended to rise--but the rapid condensation of
the steam prevented the receiver from more than threatening
ascent. The experiments were continued with smoke, which
produced only a slightly better effect, and, moreover, the paper
bag into which the smoke was induced permitted of escape through
its pores; finding this method a failure the brothers desisted
until Priestley's work became known to them, and they conceived
the use of hydrogen as a lifting factor. Trying this with paper
bags, they found that the hydrogen escaped through the pores of
the paper.
Their first balloon, made of paper, reverted to the hot-air
principle; they lighted a fire of wool and wet straw under the
balloon--and as a matter of course the balloon took fire after
very little experiment; thereupon they constructed a second,
having a capacity of 700 cubic feet, and this rose to a height
of over 1,000 feet. Such a success gave them confidence, and
they gave their first public exhibition on June 5th, 1783, with
a balloon constructed of paper and of a circumference of 112
feet. A fire was lighted under this balloon, which, after
rising to a height of 1,000 feet, descended through the cooling
of the air inside a matter of ten minutes. At this the Academie
des Sciences invited the brothers to conduct experiments in
Paris.
The Montgolfiers were undoubtedly first to send up balloons, but
other experimenters were not far behind them, and before they
could get to Paris in response to their invitation, Charles, a
prominent physicist of those days, had constructed a balloon of
silk, which he proofed against escape of gas with rubber--the
Roberts had just succeeded in dissolving this substance to
permit of making a suitable coating for the silk. With a
quarter of a ton of sulphuric acid, and half a ton of iron
filings and turnings, sufficient hydrogen was generated in four
days to fill Charles's balloon, which went up on August 28th,
1783. Although the day was wet, Paris turned out to the number
of over 300,000 in the Champs de Mars, and cannon were fired to
announce the ascent of the balloon. This, rising very rapidly,
disappeared amid the rain clouds, but, probably bursting through
no outlet being provided to compensate for the escape of gas,
fell soon in the neighbourhood of Paris. Here peasants,
ascribing evil supernatural influence to the fall of such a
thing from nowhere, went at it with the implements of their
craft--forks, hoes, and the like--and maltreated it severely,
finally attaching it to a horse's tail and dragging it about
until it was mere rag and scrap.
Meanwhile, Joseph Montgolfier, having come to Paris, set about
the construction of a balloon out of linen; this was in three
diverse sections, the top being a cone 30 feet in depth, the
middle a cylinder 42 feet in diameter by 26 feet in depth, and
the bottom another cone 20 feet in depth from junction with the
cylindrical portion to its point. The balloon was both lined
and covered with paper, decorated in blue and gold. Before ever
an ascent could be attempted this ambitious balloon was caught
in a heavy rainstorm which reduced its paper covering to pulp
and tore the linen at its seams, so that a supervening strong
wind tore the whole thing to shreds.
Montgolfier's next balloon was spherical, having a capacity of
52,000 cubic feet. It was made from waterproofed linen, and on
September 19th, 1783, it made an ascent for the palace courtyard
at Versailles, taking up as passengers a cock, a sheep, and a
duck. A rent at the top of the balloon caused it to descend
within eight minutes, and the duck and sheep were found none the
worse for being the first living things to leave the earth in a
balloon, but the cock, evidently suffering, was thought to have
been affected by the rarefaction of the atmosphere at the
tremendous height reached--for at that time the general opinion
was that the atmosphere did not extend more than four or five
miles above the earth's surface. It transpired later that the
sheep had trampled on the cock, causing more solid injury than
any that might be inflicted by rarefied air in an eight-minute
ascent and descent of a balloon.
For achieving this flight Joseph Montgolfier received from the
King of France a pension of of L40, while Stephen was given
the order of St Michael, and a patent of nobility was granted to
their father. They were made members of the Legion d'Honneur,
and a scientific deputation, of which Faujas de Saint-Fond, who
had raised the funds with which Charles's hydrogen balloon was
constructed, presented to Stephen Montgolfier a gold medal
struck in honour of his aerial conquest. Since Joseph appears
to have had quite as much share in the success as Stephen, the
presentation of the medal to one brother only was in
questionable taste, unless it was intended to balance Joseph's
pension.
Once aerostation had been proved possible, many people began the
construction of small balloons--the wholehole thing was regarded
as a matter of spectacles and a form of amusement by the great
majority. A certain Baron de Beaumanoir made the first balloon
of goldbeaters' skin, this being eighteen inches in diameter, and
using hydrogen as a lifting factor. Few people saw any
possibilities in aerostation, in spite of the adventures of the
duck and sheep and cock; voyages to the moon were talked and
written, and there was more of levity than seriousness over
ballooning as a rule. The classic retort of Benjamin Franklin
stands as an exception to the general rule: asked what was the
use of ballooning--'What's the use of a baby?' he countered, and
the spirit of that reply brought both the dirigible and the
aeroplane to being, later.
The next noteworthy balloon was one by Stephen Montgolfier,
designed to take up passengers, and therefore of rather large
dimensions, as these things went then. The capacity was 100,000
cubic feet, the depth being 85 feet, and the exterior was very
gaily decorated. A short, cylindrical opening was made at the
lower extremity, and under this a fire-pan was suspended, above
the passenger car of the balloon. On October 15th, 1783,
Pilatre de Rozier made the first balloon ascent--but the balloon
was held captive, and only allowed to rise to a height of 80
feet. But, a little later in 1783, Rozier secured the honour
of making the first ascent in a free balloon, taking up with him
the Marquis d'Arlandes. It had been originally intended that
two criminals, condemned to death, should risk their lives in
the perilous venture, with the prospect of a free pardon if they
made a safe descent, but d'Arlandes got the royal consent to
accompany Rozier, and the criminals lost their chance. Rozier
and d'Arlandes made a voyage lasting for twenty-five minutes,
and, on landing, the balloon collapsed with such rapidity as
almost to suffocate Rozier, who, however, was dragged out to
safety by d'Arlandes. This first aerostatic journey took place
on November 21st, 1783.
Some seven months later, on June 4th, 1784, a Madame Thible
ascended in a free balloon, reaching a height of 9,000 feet, and
making a journey which lasted for forty-five minutes--the great
King Gustavus of Sweden witnessed this ascent. France grew used
to balloon ascents in the course of a few months, in spite of
the brewing of such a storm as might have been calculated to
wipe out all but purely political interests. Meanwhile,
interest in the new discovery spread across the Channel, and on
September 15th, 1784, one Vincent Lunardi made the first balloon
voyage in England, starting from the Artillery Ground at
Chelsea, with a cat and dog as passengers, and landing in a
field in the parish of Standon, near Ware. There is a rather
rare book which gives a very detailed account of this first
ascent in England, one copy of which is in the library of the
Royal Aeronautical Society; the venturesome Lunardi won a
greater measure of fame through his exploit than did Cody for
his infinitely more courageous and--from a scientific point of
view--valuable first aeroplane ascent in this country.
The Montgolfier type of balloon, depending on hot air for its
lifting power, was soon realised as having dangerous
limitations. There was always a possibility of the balloon
catching fire while it was being filled, and on landing there
was further danger from the hot pan which kept up the supply of
hot air on the voyage --the collapsing balloon fell on the pan,
inevitably. The scientist Saussure, observing the filling of
the balloons very carefully, ascertained that it was rarefaction
of the air which was responsible for the lifting power, and not
the heat in itself, and, owing to the rarefaction of the air at
normal temperature at great heights above the earth, the limit
of ascent for a balloon of the Montgolfier type was estimated by
him at under 9,000 feet. Moreover, since the amount of fuel
that could be carried for maintaining the heat of the balloon
after inflation was subject to definite limits, prescribed by
the carrying capacity of the balloon, the duration of the
journey was necessarily limited just as strictly.
These considerations tended to turn the minds of those
interested in aerostation to consideration of the hydrogen
balloon evolved by Professor Charles. Certain improvements had
been made by Charles since his first construction; he employed
rubber-coated silk in the construction of a balloon of 30 feet
diameter, and provided a net for distributing the pressure
uniformly over the surface of the envelope; this net covered the
top half of the balloon, and from its lower edge dependent ropes
hung to join on a wooden ring, from which the car of the balloon
was suspended--apart from the extension of the net so as to
cover in the whole of the envelope, the spherical balloon of
to-day is virtually identical with that of Charles in its method
of construction. He introduced the valve at the top of the
balloon, by which escape of gas could be controlled, operating
his valve by means of ropes which depended to the car of the
balloon, and he also inserted a tube, of about 7 inches
diameter, at the bottom of the balloon, not only for purposes of
inflation, but also to provide a means of escape for gas in case
of expansion due to atmospheric conditions.
Sulphuric acid and iron filings were used by Charles for filling
his balloon, which required three days and three nights for the
generation of its 14,000 cubic feet of hydrogen gas. The
inflation was completed on December 1st, 1783, and the fittings
carried included a barometer and a grapnel form of anchor. In
addition to this, Charles provided the first 'ballon sonde' in
the form of a small pilot balloon which he handed to Montgolfier
to launch before his own ascent, in order to determine the
direction and velocity of the wind. It was a graceful compliment
to his rival, and indicated that, although they were both working
to the one end, their rivalry was not a matter of bitterness.
Ascending on December 1st, 1783, Charles took with him one of
the brothers Robert, and with him made the record journey up to
that date, covering a period of three and three-quarter hours,
in which time they journeyed some forty miles. Robert then
landed, and Charles ascended again alone, reaching such a height
as to feel the effects of the rarefaction of the air, this very
largely due to the rapidity of his ascent. Opening the valve at
the top of the balloon, he descended thirty-five minutes after
leaving Robert behind, and came to earth a few miles from the
point of the first descent. His discomfort over the rapid
ascent was mainly due to the fact that, when Robert landed, he
forgot to compensate for the reduction of weight by taking in
further ballast, but the ascent proved the value of the tube at
the bottom of the balloon envelope, for the gas escaped very
rapidly in that second ascent, and, but for the tube, the
balloon must inevitably have burst in the air, with fatal
results for Charles.
As in the case of aeroplane flight, as soon as the balloon was
proved practicable the flight across the English Channel was
talked of, and Rozier, who had the honour of the first flight,
announced his intention of being first to cross. But Blanchard,
who had an idea for a 'flying car,' anticipated him, and made a
start from Dover on January 7th, 1785, taking with him an
American doctor named Jeffries. Blanchard fitted out his craft
for the journey very thoroughly, taking provisions, oars, and
even wings, for propulsion in case of need. He took so much, in
fact, that as soon as the balloon lifted clear of the ground the
whole of the ballast had to be jettisoned, lest the balloon
should drop into the sea. Half-way across the Channel the
sinking of the balloon warned Blanchard that he had to part with
more than ballast to accomplish the journey, and all the
equipment went, together with certain books and papers that were
on board the car. The balloon looked perilously like
collapsing, and both Blanchard and Jeffries began to undress in
order further to lighten their craft--Jeffries even proposed a
heroic dive to save the situation, but suddenly the balloon rose
sufficiently to clear the French coast, and the two voyagers
landed at a point near Calais in the Forest of Gaines, where a
marble column was subsequently erected to commemorate the great
feat.
Rozier, although not first across, determined to be second, and
for that purpose he constructed a balloon which was to owe its
buoyancy to a combination of the hydrogen and hot air
principles. There was a spherical hydrogen balloon above, and
beneath it a cylindrical container which could be filled with
hot air, thus compensating for the leakage of gas from the
hydrogen portion of the balloon--regulating the heat of his
fire, he thought, would give him perfect control in the matter of
ascending and descending.
On July 6th, 1785, a favourable breeze gave Rozier his
opportunity of starting from the French coast, and with a
passenger aboard he cast off in his balloon, which he had named
the 'Aero-Montgolfiere.' There was a rapid rise at first, and
then for a time the balloon remained stationary over the land,
after which a cloud suddenly appeared round the balloon,
denoting that an explosion had taken place. Both Rozier and his
companion were killed in the fall, so that he, first to leave
the earth by balloon, was also first victim to the art of
aerostation.
There followed, naturally, a lull in the enthusiasm with which
ballooning had been taken up, so far as France was concerned.
In Italy, however, Count Zambeccari took up hot-air ballooning,
using a spirit lamp to give him buoyancy, and on the first
occasion when the balloon car was set on fire Zambeccari let
down his passenger by means of the anchor rope, and managed to
extinguish the fire while in the air. This reduced the buoyancy
of the balloon to such an extent that it fell into the Adriatic
and was totally wrecked, Zambeccari being rescued by fishermen.
He continued to experiment up to 1812, when he attempted to
ascend at Bologna; the spirit in his lamp was upset by the
collision of the car with a tree, and the car was again set on
fire. Zambeccari jumped from the car when it was over fifty feet
above level ground, and was killed. With him the Rozier type of
balloon, combining the hydrogen and hot air principles,
disappeared; the combination was obviously too dangerous to be
practical.
The brothers Robert were first to note how the heat of the sun
acted on the gases within a balloon envelope, and it has since
been ascertained that sun rays will heat the gas in a balloon to
as much as 80 degrees Fahrenheit greater temperature than the
surrounding atmosphere; hydrogen, being less affected by change
of temperature than coal gas, is the most suitable filling
element, and coal gas comes next as the medium of buoyancy. This
for the free and non-navigable balloon, though for the airship,
carrying means of combustion, and in military work liable to
ignition by explosives, the gas helium seems likely to replace
hydrogen, being non-combustible.
In spite of the development of the dirigible airship, there
remains work for the free, spherical type of balloon in the
scientific field. Blanchard's companion on the first Channel
crossing by balloon, Dr Jeffries, was the first balloonist to
ascend for purely scientific purposes; as early as 1784 he made
an ascent to a height of 9,000 feet, and observed a fall in
temperature of from degrees--at the level of London, where he
began his ascent--to 29 degrees at the maximum height reached.
He took up an electrometer, a hydrometer, a compass, a
thermometer, and a Toricelli barometer, together with bottles of
water, in order to collect samples of the air at different
heights. In 1785 he made a second ascent, when trigonometrical
observations of the height of the balloon were made from the
French coast, giving an altitude of 4,800 feet.
The matter was taken up on its scientific side very early in
America, experiments in Philadelphia being almost simultaneous
with those of the Montgolfiers in France. The flight of Rozier
and d'Arlandes inspired two members of the Philadelphia
Philosophical Academy to construct a balloon or series of
balloons of their own design; they made a machine which consisted
of no less than 47 small hydrogen balloons attached to a wicker
car, and made certain preliminary trials, using animals as
passengers. This was followed by a captive ascent with a man as
passenger, and eventually by the first free ascent in America,
which was undertaken by one James Wilcox, a carpenter, on
December 28th, 1783. Wilcox, fearful of falling into a river,
attempted to regulate his landing by cutting slits in some of the
supporting balloons, which was the method adopted for regulating
ascent or descent in this machine. He first cut three, and then,
finding that the effect produced was not sufficient, cut three
more, and then another five--eleven out of the forty-seven. The
result was so swift a descent that he dislocated his wrist on
landing.
A NOTE ON BALLONETS OR AIR BAGS.
Meusnier, toward the end of the eighteenth century, was first to
conceive the idea of compensating for the loss of gas due to
expansion by fitting to the interior of a free balloon a
ballonet, or air bag, which could be pumped full of air so as to
retain the shape and rigidity of the envelope.
The ballonet became particularly valuable as soon as airship
construction became general, and it was in the course of advance
in Astra Torres design that the project was introduced of using
the ballonets in order to give inclination from the horizontal.
In the earlier Astra Torres, trimming was accomplished by moving
the car fore and aft--this in itself was an advance on the
separate 'sliding weigh' principle--and this was the method
followed in the Astra Torres bought by the British Government
from France in 1912 for training airship pilots. Subsequently,
the two ballonets fitted inside the envelope were made to serve
for trimming by the extent of their inflation, and this method of
securing inclination proved the best until exterior rudders, and
greater engine power, supplanted it, as in the Zeppelin and, in
fact, all rigid types.
In the kite balloon, the ballonet serves the purpose of a
rudder, filling itself through the opening being kept pointed
toward the wind--there is an ingenious type of air scoop with
non-return valve which assures perfect inflation. In the S.S.
type of airship, two ballonets are provided, the supply of air
being taken from the propeller draught by a slanting aluminium
tube to the underside of the envelope, where it meets a
longitudinal fabric hose which connects the two ballonet air
inlets. In this hose the non-return air valves, known as
'crab-pots,' are fitted, on either side of the junction with the
air-scoop. Two automatic air valves, one for each ballonet, are
fitted in the underside of the envelope, and, as the air
pressure tends to open these instead of keeping them shut, the
spring of the valve is set inside the envelope. Each spring is
set to open at a pressure of 25 to 28 mm.
II. THE FIRST DIRIGIBLES
Having got off the earth, the very early balloonists set about
the task of finding a means of navigating the air but, lacking
steam or other accessory power to human muscle, they failed to
solve the problem. Joseph Montgolfier speedily exploded the
idea of propelling a balloon either by means of oars or sails,
pointing out that even in a dead calm a speed of five miles an
hour would be the limit achieved. Still, sailing balloons were
constructed, even up to the time of Andree, the explorer, who
proposed to retard the speed of the balloon by ropes dragging on
the ground, and then to spread a sail which should catch the
wind and permit of deviation of the course. It has been proved
that slight divergences from the course of the wind can be
obtained by this means, but no real navigation of the air could
be thus accomplished.
Professor Wellner, of Brunn, brought up the idea of a sailing
balloon in more practical fashion in 1883. He observed that
surfaces inclined to the horizontal have a slight lateral motion
in rising and falling, and deduced that by alternate lowering
and raising of such surfaces he would be able to navigate the
air, regulating ascent and descent by increasing or decreasing
the temperature of his buoyant medium in the balloon. He
calculated that a balloon, 50 feet in diameter and 150 feet in
length, with a vertical surface in front and a horizontal
surface behind, might be navigated at a speed of ten miles per
hour, and in actual tests at Brunn he proved that a single rise
and fall moved the balloon three miles against the wind. His
ideas were further developed by Lebaudy in the construction of
the early French dirigibles.
According to Hildebrandt,[*] the first sailing balloon was built
in 1784 by Guyot, who made his balloon egg-shaped, with the
smaller end at the back and the longer axis horizontal; oars
were intended to propel the craft, and naturally it was a
failure. Carra proposed the use of paddle wheels, a step in the
right direction, by mounting them on the sides of the car, but
the improvement was only slight. Guyton de Morveau, entrusted
by the Academy of Dijon with the building of a sailing balloon,
first used a vertical rudder at the rear end of his
construction--it survives in the modern dirigible. His
construction included sails and oars, but, lacking steam or
other than human propulsive power, the airship was a failure
equally with Guyot's.
[*] Airships Past and Present.
Two priests, Miollan and Janinet, proposed to drive balloons
through the air by the forcible expulsion of the hot air in the
envelope from the rear of the balloon. An opening was made
about half-way up the envelope, through which the hot air was to
escape, buoyancy being maintained by a pan of combustibles in
the car. Unfortunately, this development of the Montgolfier type
never got a trial, for those who were to be spectators of the
first flight grew exasperated at successive delays, and in the
end, thinking that the balloon would never rise, they destroyed
it.
Meusnier, a French general, first conceived the idea of
compensating for loss of gas by carrying an air bag inside the
balloon, in order to maintain the full expansion of the
envelope. The brothers Robert constructed the first balloon in
which this was tried and placed the air bag near the neck of the
balloon which was intended to be driven by oars, and steered by
a rudder. A violent swirl of wind which was encountered on the
first ascent tore away the oars and rudder and broke the ropes
which held the air bag in position; the bag fell into the
opening of the neck and stopped it up, preventing the escape of
gas under expansion. The Duc de Chartres, who was aboard,
realised the extreme danger of the envelope bursting as the
balloon ascended, and at 16,000 feet he thrust a staff through
the envelope--another account says that he slit it with his
sword--and thus prevented disaster. The descent after this rip
in the fabric was swift, but the passengers got off without
injury in the landing.
Meusnier, experimenting in various ways, experimented with
regard to the resistance offered by various shapes to the air,
and found that an elliptical shape was best; he proposed to make
the car boat--shaped, in order further to decrease the
resistance, and he advocated an entirely rigid connection
between the car and the body of the balloon, as indispensable to
a dirigible.[*] He suggested using three propellers, which were
to be driven by hand by means of pulleys, and calculated that a
crew of eighty would be required to furnish sufficient motive
power. Horizontal fins were to be used to assure stability, and
Meusnier thoroughly investigated the pressures exerted by gases,
in order to ascertain the stresses to which the envelope would be
subjected. More important still, he went into detail with
regard to the use of air bags, in order to retain the shape of
the balloon under varying pressures of gas due to expansion and
consequent losses; he proposed two separate envelopes, the inner
one containing gas, and the space between it and the outer one
being filled with air. Further, by compressing the air inside
the air bag, the rate of ascent or descent could be regulated.
Lebaudy, acting on this principle, found it possible to pump air
at the rate of 35 cubic feet per second, thus making good loss
of ballast which had to be thrown overboard.
[*] Hildebrandt.
Meusnier's balloon, of course, was never constructed, but his
ideas have been of value to aerostation up to the present time.
His career ended in the revolutionary army in 1793, when he was
killed in the fighting before Mayence, and the King of Prussia
ordered all firing to cease until Meusnier had been buried. No
other genius came forward to carry on his work, and it was
realised that human muscle could not drive a balloon with
certainty through the air; experiment in this direction was
abandoned for nearly sixty years, until in 1852 Giffard
brought the first practicable power-driven dirigible to being.
Giffard, inventor of the steam injector, had already made
balloon ascents when he turned to aeronautical propulsion, and
constructed a steam engine of 5 horsepower with a weight of only
100 lbs.--a great achievement for his day. Having got his
engine, he set about making the balloon which it was to drive;
this he built with the aid of two other enthusiasts, diverging
from Meusnier's ideas by making the ends pointed, and keeping the
body narrowed from Meusnier's ellipse to a shape more resembling
a rather fat cigar. The length was 144 feet, and the greatest
diameter only 40 feet, while the capacity was 88,000 cubic feet.
A net which covered the envelope of the balloon supported a
spar, 66 feet in length, at the end of which a triangular sail
was placed vertically to act as rudder. The car, slung 20 feet
below the spar, carried the engine and propeller. Engine and
boiler together weighed 350 lbs., and drove the 11 foot
propeller at 110 revolutions per minute.
As precaution against explosion, Giffard arranged wire gauze in
front of the stoke-hole of his boiler, and provided an exhaust
pipe which discharged the waste gases from the engine in a
downward direction. With this first dirigible he attained to a
speed of between 6 and 8 feet per second, thus proving that the
propulsion of a balloon was a possibility, now that steam had
come to supplement human effort.
Three years later he built a second dirigible, reducing the
diameter and increasing the length of the gas envelope, with a
view to reducing air resistance. The length of this was 230
feet, the diameter only 33 feet, and the capacity was 113,000
cubic feet, while the upper part of the envelope, to which the
covering net was attached, was specially covered to ensure a
stiffening effect. The car of this dirigible was dropped rather
lower than that of the first machine, in order to provide more
thoroughly against the danger of explosions. Giffard, with a
companion named Yon as passenger, took a trial trip on this
vessel, and made a journey against the wind, though slowly. In
commencing to descend, the nose of the envelope tilted upwards,
and the weight of the car and its contents caused the net to
slip, so that just before the dirigible reached the ground, the
envelope burst. Both Giffard and his companion escaped with very
slight injuries.
Plans were immediately made for the construction of a third
dirigible, which was to be 1,970 feet in length, 98 feet in
extreme diameter, and to have a capacity of 7,800,000 cubic feet
of gas. The engine of this giant was to have weighed 30 tons,
and with it Giffard expected to attain a speed of 40 miles per
hour. Cost prevented the scheme being carried out, and Giffard
went on designing small steam engines until his invention of the
steam injector gave him the funds to turn to dirigibles again.
He built a captive balloon for the great exhibition in London in
1868, at a cost of nearly L30,000, and designed a dirigible
balloon which was to have held a million and three quarters
cubic feet of gas, carry two boilers, and cost about L40,000.
The plans were thoroughly worked out, down to the last detail,
but the dirigible was never constructed. Giffard went blind, and
died in 1882--he stands as the great pioneer of dirigible
construction, more on the strength of the two vessels which he
actually built than on that of the ambitious later conceptions
of his brain.
In 1872 Dupuy de Lome, commissioned by the French government,
built a dirigible which he proposed to drive by man-power--it
was anticipated that the vessel would be of use in the siege of
Paris, but it was not actually tested till after the conclusion
of the war. The length of this vessel was 118 feet, its
greatest diameter 49 feet, the ends being pointed, and the
motive power was by a propeller which was revolved by the
efforts of eight men. The vessel attained to about the same
speed as Giffard's steam-driven airship; it was capable of
carrying fourteen men, who, apart from these engaged in driving
the propeller, had to manipulate the pumps which controlled the
air bags inside the gas envelope.
In the same year Paul Haenlein, working in Vienna, produced an
airship which was a direct forerunner of the Lebaudy type, 164
feet in length, 30 feet greatest diameter, and with a cubic
capacity of 85,000 feet. Semi-rigidity was attained by placing
the car as close to the envelope as possible, suspending it by
crossed ropes, and the motive power was a gas engine of the
Lenoir type, having four horizontal cylinders, and giving about
5 horse-power with a consumption of about 250 cubic feet of gas
per hour. This gas was sucked from the envelope of the balloon,
which was kept fully inflated by pumping in compensating air to
the air bags inside the main envelope. A propeller, 15 feet in
diameter, was driven by the Lenoir engine at 40 revolutions per
minute. This was the first instance of the use of an internal
combustion engine in connection with aeronautical experiments.
The envelope of this dirigible was rendered airtight by means of
internal rubber coating, with a thinner film on the outside.
Coal gas, used for inflation, formed a suitable fuel for the
engine, but limited the height to which the dirigible could
ascend. Such trials as were made were carried out with the
dirigible held captive, and a speed of I 5 feet per second was
attained. Full experiment was prevented through funds running
low, but Haenlein's work constituted a distinct advance on all
that had been done previously.
Two brothers, Albert and Gaston Tissandier, were next to enter
the field of dirigible construction; they had experimented with
balloons during the Franc-Prussian War, and had attempted to get
into Paris by balloon during the siege, but it was not until
1882 that they produced their dirigible.
This was 92 feet in length and 32 feet in greatest diameter,
with a cubic capacity of 37,500 feet, and the fabric used was
varnished cambric. The car was made of bamboo rods, and in
addition to its crew of three, it carried a Siemens dynamo, with
24 bichromate cells, each of which weighed 17 lbs. The motor
gave out 1 1/2 horse-power, which was sufficient to drive the
vessel at a speed of up to 10 feet per second. This was not so
good as Haenlein's previous attempt and, after L2,000 had been
spent, the Tissandier abandoned their experiments, since a 5-mile
breeze was sufficient to nullify the power of the motor.
Renard, a French officer who had studied the problem of
dirigible construction since 1878, associated himself first with
a brother officer named La Haye, and subsequently with another
officer, Krebs, in the construction of the second dirigible to
be electrically-propelled. La Haye first approached Colonel
Laussedat, in charge of the Engineers of the French Army, with a
view to obtaining funds, but was refused, in consequence of the
practical failure of all experiments since 1870. Renard, with
whom Krebs had now associated himself, thereupon went to
Gambetta, and succeeded in getting a promise of a grant of
L8,000 for the work; with this promise Renard and Krebs set to
work.
They built their airship in torpedo shape, 165 feet in length,
and of just over 27 feet greatest diameter--the greatest diameter
was at the front, and the cubic capacity was 66,000 feet. The
car itself was 108 feet in length, and 4 1/2 feet broad, covered
with silk over the bamboo framework. The 23 foot diameter
propeller was of wood, and was driven by an electric motor
connected to an accumulator, and yielding 8.5 horsepower. The
sweep of the propeller, which might have brought it in contact
with the ground in landing, was counteracted by rendering it
possible to raise the axis on which the blades were mounted, and
a guide rope was used to obviate damage altogether, in case of
rapid descent. There was also a 'sliding weight' which was
movable to any required position to shift the centre of gravity
as desired. Altogether, with passengers and ballast aboard, the
craft weighed two tons.
In the afternoon of August 8th, 1884, Renard and Krebs ascended
in the dirigible--which they had named 'La France,' from the
military ballooning ground at Chalais-Meudon, making a circular
flight of about five miles, the latter part of which was in the
face of a slight wind. They found that the vessel answered well
to her rudder, and the five-mile flight was made successfully in
a period of 23 minutes. Subsequent experimental flights
determined that the air speed of the dirigible was no less than
14 1/2 miles per hour, by far the best that had so far been
accomplished in dirigible flight. Seven flights in all were
made, and of these five were completely successful, the
dirigible returning to its starting point with no difficulty. On
the other two flights it had to be towed back.
Renard attempted to repeat his construction on a larger scale,
but funds would not permit, and the type was abandoned; the
motive power was not sufficient to permit of more than short
flights, and even to the present time electric motors, with
their necessary accumulators, are far too cumbrous to compete
with the self-contained internal combustion engine. France had
to wait for the Lebaudy brothers, just as Germany had to wait
for Zeppelin and Parseval.
Two German experimenters, Baumgarten and Wolfert, fitted a
Daimler motor to a dirigible balloon which made its first ascent
at Leipzig in 1880. This vessel had three cars, and placing a
passenger in one of the outer cars[*] distributed the load
unevenly, so that the whole vessel tilted over and crashed to
the earth, the occupants luckily escaping without injury. After
Baumgarten's death, Wolfert determined to carry on with his
experiments, and, having achieved a certain measure of success,
he announced an ascent to take place on the Tempelhofer Field,
near Berlin, on June 12th, 1897. The vessel, travelling with
the wind, reached a height of 600 feet, when the exhaust of the
motor communicated flame to the envelope of the balloon, and
Wolfert, together with a passenger he carried, was either killed
by the fall or burnt to death on the ground. Giffard had taken
special precautions to avoid an accident of this nature, and
Wolfert, failing to observe equal care, paid the full penalty.
[*] Hildebrandt.
Platz, a German soldier, attempting an ascent on the Tempelhofer
Field in the Schwartz airship in 1897, merely proved the
dirigible a failure. The vessel was of aluminium, 0.008 inch
in thickness, strengthened by an aluminium lattice work; the
motor was two-cylindered petrol-driven; at the first trial the
metal developed such leaks that the vessel came to the ground
within four miles of its starting point. Platz, who was aboard
alone as crew, succeeded in escaping by jumping clear before the
car touched earth, but the shock of alighting broke up the
balloon, and a following high wind completed the work of full
destruction. A second account says that Platz, finding the
propellers insufficient to drive the vessel against the wind,
opened the valve and descended too rapidly.
The envelope of this dirigible was 156 feet in length, and the
method of filling was that of pushing in bags, fill them with
gas, and then pulling them to pieces and tearing them out of the
body of the balloon. A second contemplated method of filling
was by placing a linen envelope inside the aluminium casing,
blowing it out with air, and then admitting the gas between the
linen and the aluminium outer casing. This would compress the
air out of the linen envelope, which was to be withdrawn when
the aluminium casing had been completely filled with gas.
All this, however, assumes that the Schwartz type--the first
rigid dirigible, by the way--would prove successful. As it
proved a failure on the first trial, the problem of filling it
did not arise again.
By this time Zeppelin, retired from the German army, had begun
to devote himself to the study of dirigible construction, and, a
year after Schwartz had made his experiment and had failed, he
got together sufficient funds for the formation of a
limitedliability company, and started on the construction of the
first of his series of airships. The age of tentative
experiment was over, and, forerunner of the success of the
heavier-than-air type of flying machine, successful dirigible
flight was accomplished by Zeppelin in Germany, and by
Santos-Dumont in France.
III. SANTOS-DUMONT
A Brazilian by birth, Santos-Dumont began in Paris in the year
1898 to make history, which he subsequently wrote. His book, My
Airships, is a record of his eight years of work on
lighter-than-air machines, a period in which he constructed no
less than fourteen dirigible balloons, beginning with a cubic
capacity of 6,350 feet, and an engine of 3 horse-power, and
rising to a cubic capacity of 71,000 feet on the tenth dirigible
he constructed, and an engine of 60 horse-power, which was
fitted to the seventh machine in order of construction, the one
which he built after winning the Deutsch Prize.
The student of dirigible construction is recommended to
Santos-Dumont's own book not only as a full record of his work,
but also as one of the best stories of aerial navigation that
has ever been written. Throughout all his experiments, he
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