MILITARY AND CROSS-COUNTRY FLYING
Aerial scouting--Types of machines used--The
high-speed monoplane--Steering across country--An
airman’s map and compass.
When they could fly in high winds, and their motors were reliable, it
was seen that aircraft would become vital factors in time of war; so
vital, indeed, that no army or navy could afford to be without them.
Successful aeroplane builders, consequently, such as the brothers Farman
and Louis Bleriot, became busy with the construction of military craft.
France threw herself with enthusiasm into the creation of an aerial
fleet. Germany, more methodical, studied cautiously and yet thoroughly
the problems involved; while in England, for several years, the subject
received scant attention.
It was in the autumn of 1910, when one or two aeroplanes were used in
the manœuvres in France, that interest was first focussed upon their
power as scouts. These machines were not built specially for military
work, and there was little organisation or foresight in their use; but
observers accompanied the pilots upon long cross-country flights,
during which they hovered above the enemy, and noted the location and
movements of troops. By being able to pass through the air, and evade
the enemy’s patrols, these observers brought back news it would have
been impossible to obtain by use of cavalry scouts; and, owing to the
speed of their flight, they were able to glean such reports, and fly
back with them to headquarters, in a far shorter time than would have
been possible by any other means. These first observers were officers,
who sat behind the pilots as passengers. They carried with them
field-glasses and notebooks, and the pilot obeyed their orders as to the
direction in which he should fly. Peering down upon the land that lay
below, an observer made rough notes of all he saw; then, upon returning
to his starting-point, he prepared and handed in such a report as is
printed below:
5.56 a.m.--At ---- a cyclist company.
5.59 a.m. ----, sixteen squadrons of cavalry and six
batteries at the south-west entrance to ----.
6.5 a.m.--South-west of ----, at the north point of ----
Wood, a company of two batteries of artillery.
6.7 a.m.--Northern entrance to the village of ----, one
company of infantry to the right and one to the left
of the wood; one company at point 188; one company in
the village of ----.
6.9 a.m.--At the cross roads to ----, a squadron of
dragoons concealed behind the edge of the wood.
6.14 a.m.--On the road south of ----, a squadron on the
march towards ----, and a troop in the village of ----.
6.16 a.m.--On the ---- road a squadron and two machine
guns marching towards ----.
6.19 a.m.--South-west entrance to ----, three regiments
of cavalry, including cuirassiers, and six batteries
of artillery in assembly formation.
[Illustration: _Photo, F. N. Birkett._
PLATE X.--MAURICE FARMAN BIPLANE.
Mr. Grahame-White is seen in the driving-seat of the machine he often
flies at Hendon. Behind him are the passengers’ seat, fuel tanks,
engine, and propeller. In front of the pilot will be observed a screen,
which protects him from the rush of wind when in flight.]
[Illustration: MACHINE SEEN FROM ABOVE,
showing shape and spread of planes and tail, and position of pilot and
passenger.
VIEW FROM IN FRONT,
showing the position of the body and the construction of the landing
gear.
A. Covered-in body, with seats for pilot and passenger; B. Motor (to
minimise wind resistance, only the lower cylinders are exposed to the
air); C. Propeller; D.D. Main-planes; E. Rudder; F. Elevator; G. Landing
gear.
FIG. 60.--Grahame-White Military Biplane.]
This report was one actually prepared, after an early morning flight, by
an officer-observer in the French manœuvres of 1910, and it shows how
successfully an air-scout may detect a movement of troops. The report
has an additional significance. Before he sent out his aeroplanes, on
this particular morning, the Commander-in-Chief had assumed, but could
not substantiate, the theory that his opponent was retreating. And now
this report by aeroplane, showing that nothing save cavalry and
rear-guards had been seen over a specific tract of country, served to
confirm the rumour that the enemy was giving ground.
Once the value of aerial reconnaissance had been proved, France
proceeded to the development of a scouting aeroplane; and the need, in
such a machine, is that the observer shall have a clear view ahead and
below. The construction of machines was, for this reason, modified. The
front elevating plane was moved to the rear, where it was fitted in the
form of a flap--as in the case of monoplanes--and the pilot and observer
placed in a covered-in body, which projected in front of the
main-planes, as shown in Fig. 60. By placing the body before the planes,
the observer has a clear view ahead and on either side; and even when
he leans over the side, and looks directly downward, there is no surface
to obstruct him.
[Illustration: FIG. 61.--Single-seated Air Scout.
A. Propeller; B. Motor (partly hidden by shield); C. Pilot’s seat; D.
Sustaining plane; E. Rudder; F. Elevating-plane; G. Chassis.]
This scouting biplane is intended for detailed reconnaissance; for a
careful flight above an enemy’s position, that is to say, in which every
movement of troops is observed and noted. Another machine becomes
necessary for the making of a quick and general survey--such, for
instance, as that in which a pilot would be asked to fly to some
definite point, and see whether a body of troops is stationary or on the
march. Speed, for such a task, is the chief requirement. Hence there is
a type of fast scouting monoplane, in which a pilot can ascend alone,
and fly at 100 miles an hour. With such a craft, sweeping rapidly above
an enemy’s position, the pilot-observer can return with his information
at surprising speed. In Fig. 61 an air-scout of this type is seen. The
tapering, covered-in body will be observed; this is to reduce wind
resistance as the machine rushes through the air. The Gnome engine is,
for the same reason, covered by an aluminium shield, which only allows
the lower cylinders to project; they must, of course, be exposed in some
way to the air, or they would not cool themselves. The landing-carriage
has been reduced to its simplest form; this, again, is to reduce wind
resistance; and the pilot, sitting deep in the body, shows only his head
as the machine flies. Here, again, apart from the greater comfort in
being so shielded, the placing of the pilot within the machine spells a
lessening of pressure. This question of the resistance of the air is
vital in the designing of high-speed craft. Every projecting surface
must be “stream-lined,” as it is called; it must, that is to say, have
such a tapering shape as will offer least resistance as it passes
through the air. The atmosphere is viscous--or, to use a commoner word,
“sticky.” It clings to anything that is passed quickly through it, as
treacle might adhere to the back of a knife; therefore the body of an
aeroplane--like the hull of an airship--slopes away to a point astern,
so that friction may be minimised.
What the pressure of the wind may mean, when high speeds are reached,
one may prove by holding a hand from the window of an express, say while
it is running at 60 miles an hour. The rush is so fierce that the arm
will ache from the mere effort of holding it outstretched. Whereas the
train is running at 60 miles an hour, a monoplane may be flying at more
than 100 miles an hour. Therefore the thrust of the wind against wires,
struts, and body may be imagined; it reaches the violence of a
hurricane. Even the pilot, glancing above the wind-screen to steer his
course, finds the pressure so tremendous that, in some racing machines,
he is provided with a padded rest against which he can lean his head.
In the development of speed, some remarkable craft are built. Each year
there is an international air race for the possession of the
Gordon-Bennett trophy, and to win this designers build special craft. In
tiny monoplanes, engines of high power are installed; and the sustaining
wings are so reduced, to give a maximum speed, that the machines appear
more like projectiles than flying craft. A purely racing-type monoplane
is seen in Fig. 62. It represents a Deperdussin, which, with an engine
of 160 horse-power, reached a speed of 130 miles an hour. How small this
machine was, in relation to its engine-power, will be realised from the
fact that the sustaining surface of its wings amounted to only 104
square feet--far less lifting area, in fact, than Lilienthal used in his
gliders. Wires and struts are reduced to a minimum; the body is tapered
and smoothed. Such a machine, although it carries speed to an extreme,
and is in reality a “freak,” teaches useful lessons. But though it
provides data for the construction of high-speed scouts, a monoplane of
this type would be useless for cross-country flying; and for the reason
that it cannot be manœuvred, prior to an ascent, upon anything save the
smoothest of ground. Its wings being so small, to ensure a maximum of
speed, the machine will not rise until it has run forward a long
distance across the ground; and during this run it attains a speed of
nearly 90 miles an hour. At such a pace, unless the ground below its
wheels was level, it would leap, swerve, and probably overturn. When
alighting from a flight, also, again owing to the smallness of its
wings, the craft has to plane down so fast that its pilot could not land
safely unless he had below him a surface that was absolutely smooth.
[Illustration: A. Propeller; B. Shield to lessen wind resistance; C.
Sloping shield which encloses engine (also to minimise wind-pressure).
Air passes between the shields B and C to cool the motor. D. Pilot’s
seat; E. Padded projection against which, when at high speed, the pilot
rests his head, F. Sustaining-plane, very slightly cambered; G. Rudder;
H. Elevating-plane; I. Landing wheels.
SEEN FROM THE BOW,
showing the “stream-line” effect which is gained by tapering the body,
also the simplification of the landing chassis, and the use of a minimum
of wires.
VIEWED FROM ABOVE.
The shape of main-planes and tail are shown also the exact position of
the pilot’s seat.
FIG. 62.--Racing Deperdussin Monoplane (160 h.p.).]
What is needed, in the high-speed machine, is a power to vary its pace.
If it will fly slowly, as well as at high speed, landing difficulties
are overcome; and as a scouting machine it has the added advantage that,
should he be passing over a spot where he wishes to make careful notes,
the pilot can reduce his speed and so gain leisure in which to survey.
In the provision of variable speed, aeroplane designers have achieved
already a striking success. By constructing a machine lightly,
increasing the efficiency of its planes, and reducing head resistance to
a minimum, and at the same time by fitting an engine of ample
horse-power, the modern builder has, in some instances, produced a craft
which will fly at 90 miles an hour as its high speed, and at 30 miles an
hour for a low, when its engine is throttled down.
Contributing to this efficiency, there is the study that has been made
of the curve of planes. It will be remembered that, according to early
experiments, there was a pressure below a cambered plane, and a vacuum
or lifting influence upon the top. The first students of plane-curves
reckoned that the pressure from below was the more important of the two.
But modern and scientific research has shown that top suction is the
really powerful influence. It has been proved that the upper part of a
plane will yield a lifting effect which is from three to five times as
great as the pressure from below. Hence, in the latest type of machine,
the planes are given two separate curves or cambers. The one on the
lower surface is designed to obtain a maximum up-thrust; while on the
upper surface the plane is so shaped that, according to scientific
research, it will extract the strongest possible up-lift as it passes
through the air. The “hump” or arch, as advised by Phillips, is still
preserved; but in many cases it is less pronounced, and is continued
farther towards the rear of the plane. What modern builders do is to
design a wing-curve, and then send it to a laboratory to be tested. Here
it is put in a wind tunnel--a tube through which a current of air is
driven by a fan--and its lifting influence tested by instruments of
precision.
The pilot slackens his speed when flying by throttling down his motor,
and so reducing the pull or thrust of his propeller; or he sets his
engine at full power, and so attains his maximum speed. For military
work such variation is, as has been said, of great importance. An
air-scout needs to reach a given point quickly, and return to
headquarters at high speed. Every moment’s delay in bringing the
Commander-in-Chief some vital piece of news, may spell the difference
between victory or defeat. It is here, in fact, that cavalry scouts have
failed. They may obtain important tidings, but before they can make
their way to headquarters and report, the aspect of affairs has changed,
perhaps, and their news--which would have been valuable had it been
received at once--has lost its significance through delay. An air-scout
who can vary his speed will fly fast till he needs to make an
observation; then he will slow down and study what lies below him; and,
his survey completed, he will return at top speed to headquarters.
Wireless telegraphy, for communicating between an aeroplane in flight
and its headquarters, is now adopted for urgent reports--a cypher being
used to prevent messages being “tapped” by an enemy. At first poor
results were obtained, signals being audible on the ground, when sent
from a machine flying low, at a distance of only about a mile. This was
due to the difficulty of producing a sufficiently light apparatus; but
now, with transmitting mechanism weighing from 70 to 80 lbs., messages
may be dispatched from an aeroplane to a land station 100 miles away,
although problems still remain to be solved in regard to the tapping and
jamming of signals. The dynamo generating the electric current is driven
by a small petrol motor, which develops about 2-3/4 horse-power; and the
antenna or aerial wire, by means of which the message is sent forth--a
wave length of from 200 to 500 metres being adopted--may be arranged
between the planes and tail, or unwound from a reel below the landing
chassis when a machine is in flight, and allowed to trail earthward.
Apparatus weighing 20 lbs., is also being tested, by means of
which--using a magnifying receiver--an operator in an aeroplane may
receive a message as well as send one. This allows communication, not
only between a machine and an earth-station, but also between two craft
when in flight.
Another ingenious system of signalling, from an aeroplane to its
headquarters, when the former is flying within view, is by means of
smoke signals from the exhaust of the engine. As the exhaust gases are
shot forth into the air they are rendered black by the mixing with them
of a powder, the admission of which to the exhaust pipes the pilot can
regulate by a lever. In this way he is able to send black puffs of smoke
into the air, and spell out a message in the Morse code, which an
observer on the ground can read with field-glasses. A more simple
method, when an observer wishes to communicate with those below, and yet
avoid the delay of a descent, is to drop a written message in a little
bag, to which a flag and a weight are attached. This is seen as it
falls, and is retrieved and carried to headquarters.
[Illustration: FIG. 63.--Sopwith Military Biplane.
A. Propeller; B. Motor, partly hidden by shield; C.C. Main-planes; D.
Pilot’s seat; E. Observer’s seat; F. Outlook windows in side of hull; G.
Rudder; H. Elevating-plane; I. Landing gear.]
A machine that has achieved success, owing to its power of varying
speed, is the Sopwith military biplane, as shown in Fig. 63. Adopting a
practice that has become general, its wings are fitted upon what is
practically a monoplane body. Tail-planes and rudder are the same as in
a monoplane. The top main-plane, as will be seen, is set slightly in
advance of the lower. The system is called “staggering”; and the idea is
that, by placing the upper plane ahead of the lower, the total lifting
power will be increased. It has been proved a disadvantage of the
biplane that, when the main-planes are placed one above another, there
is a slight loss of lift owing to the fact that, acting upon the air as
they do quite close to each other, a certain amount of interference
occurs between them--one tending to disturb the air-stream in which the
other moves. By “staggering” the two planes this interference is
overcome; but some makers regard it as a small consideration, and build
their planes in the ordinary way, allowing as large a gap as possible
between them. In the Sopwith military machine, engine and propeller are
in front of the main-planes; then come the places for pilot and
observer. The pilot sits first, and the body of the machine is so high
that only his head appears above it, while just in front of his face, to
deflect the wind-rush from the propeller, there is a raised section of
the hull which acts as a screen. Behind the pilot, sitting in a second
opening in the hull, is the observer. He has a view forward, rendered
the better by setting back the lower-plane; while at the point at which
it joins the body of the machine, immediately below him, this plane is
hollowed out, so that he can look directly upon the earth below. Small
windows are also fitted upon either side of the hull. Through those in
front the pilot may glance when descending from a flight, so as to judge
his distance from the ground, while the others are utilised by the
observer, as he turns to look from side to side. This biplane, and many
others, is balanced against sideway roll by ailerons, and not by warping
the wings. Constant warping, such as is necessary in the everyday use of
machines, has been declared to strain a plane and render it weak;
therefore the use of ailerons is now favoured.
[Illustration: FIG. 64.--Scouting Monoplane, with occupants below the
wings.
A. Engine and propeller; B. Plane raised above hull; C. Seats for pilot
and passenger; D. Rudder; E. Elevating-plane.]
To meet the demand for a purely scouting machine, in which pilot and
passenger shall have a clear field for observation, both above and
below, a monoplane has been designed which is called the “parasol.” This
machine, a Morane-Saulnier, is shown in Fig. 64. The two sustaining
wings, forming a single surface, are raised above the body so that its
occupants have nothing to impede their view earthward; and they can also
see above them--an advantage of course in time of war, seeing that an
enemy might be hovering overhead.
[Illustration: FIG. 65.--The Control of a Biplane.
A. Pilot’s seat; B. Hand-wheel (pushed forward or backward operates
elevator; twisted sideways works ailerons); C. Foot-bar actuating
rudder; D. Compass; E. Dial showing number of revolutions per minute
that engine is making; F. Gauge showing pressure in petrol tank; G.
Speed indicator; H. Dial showing altitude; I. Clock; J. Switch for
cutting off ignition.]
The driver of a modern-type aeroplane, sitting snugly within its hull,
has a wheel and instrument-board before him, as sketched in Fig. 65. As
he flies across country he has many things to think of. Holding the
control-wheel in both hands, his feet resting upon the rudder-bar, his
eyes rove constantly among the instruments on the dashboard before him.
He glances at the compass often, for it is by this that he steers; and
when the air is clear, and the earth below plainly seen, he will every
now and then glance over the side of the hull, so as to be on the
look-out for a landmark that may tell him he is on his course.
But sometimes, when the air is thick and misty, or there are low-lying
clouds and the earth is shrouded in a fog, the pilot flies in an empty
void. Nothing is to be seen above, below, or on either hand; he must
rely entirely upon his instruments. The altitude meter tells him whether
he is rising or descending; his compass tells him he is flying
accurately to his goal; while his own ear, and the tell-tale dial of the
engine indicator, informs him that his motor is doing its work. So he
sits within the hull of his craft, perhaps 5000 feet above the
earth--unseen by those below, and himself seeing nothing of the land
over which he flies. Should the wind be steady, he has little to do save
keep an eye upon his instruments, and listen to the beat of his engine.
But if there are gusts and eddies his hand-wheel is busy; each lurch
must be corrected by a movement of the ailerons, each dive checked by a
pull upon the elevator.
The aeroplane compass, nowadays, has been made accurate and reliable;
but pioneers found it a dangerous instrument. Vibrations from the
engine, and the nearness to the compass of such large masses of metal as
the motor and its fittings, made the needle deviate and give false
readings. Once, when upon a cross-Channel flight and out of sight of
land, a pilot glanced down at his compass and saw that the needle,
instead of pointing northward, was spinning slowly round and round; and
so it continued until he had by guesswork groped his way to land. But
experience showed how a compass may be mounted upon rubber
shock-absorbers to guard it against vibration; how fittings that are
near it, such as the steering-column and rudder-bar, can be made of
brass, or some other non-magnetic metal; while, as to the attraction of
the motor, the compass is corrected against this by introducing scraps
of metal into its case, so that the needle can be drawn back to an
accurate reading from any deviation it may show.
But, even with an accurate compass, the cross-country airman may have
anxiety in his mind. He may be flying in a side wind; and this, should
it be strong and steady, will have an insidious effect upon his path,
tending always to drift him sideways even while he keeps his bow upon a
compass course. Fig. 66 should make this clear. The airman seeks to fly
from A to B, a distance say of 60 miles; so he sets his course due east
and passes steadily across country at the rate of 60 miles an hour, the
bow of his machine always upon its compass line. But while he is flying,
a southerly wind blowing at the rate of 20 miles an hour is pushing him
sideways; and, unless he corrects this leeway, he will find himself
after an hour’s flying, not at the point B, towards which he imagined he
had been making, but at C, 20 miles north of the spot at which he had
wished to alight. The wind, blowing at 20 miles an hour across his
course, has pushed him these 20 miles to the north, although he has
steered accurately eastward.
[Illustration: PLATE XI.--AN AIRMAN’S POINT OF VIEW.
Sheets of water are excellent guides when flying. Trees show up clearly,
too; also roads--as may be seen from the one curving at the extreme
right of this photograph, which was taken from a biplane piloted by Mr.
Grahame-White.]
When flying above land, the making of leeway may be nothing more than an
annoyance; but should the pilot be passing above the sea, between coasts
many miles apart, this side sweep of the wind may be a peril. One of the
grim tragedies of aviation is attributed to leeway in a wind. Leaving
France on a flight to England, Mr. Cecil Grace was driven from his
course by a wind which blew up Channel towards the North Sea. There was
fog, too; and as the pilot was using an early type compass, it may have
failed to register accurately. At all events, he never reached
the English shore. Seen once while in flight--and this by a
fishing-smack--he was lost in the mist, flew wide of his course, and
passed out to the North Sea instead of towards the cliffs at Dover. From
that day to this his fate has been a mystery, although it is true that
not long after he vanished his flying cap and goggles were washed upon
the beach near Ostend--mute but tragic witnesses to the ending of his
flight. But of the airman’s body, or of the wreckage of his machine,
nothing was ever found.
[Illustration: FIG. 66.--Effect of a side wind.
A. Starting-point; B. Point steered for; C. Point actually reached; D.
The course flown by the machine, owing to the pressure of a southerly
wind.]
It is possible, with a modern-type compass, to make an allowance for
leeway. The airman studies a gauge before he ascends, ascertaining the
strength at which the wind is blowing. Then he sets a pointer upon his
compass by which he may correct, even while passing through the air, the
sideway thrust of the wind; that is to say, should he be flying to some
point due east of his starting-point, as was assumed in Fig. 66, and
should the wind--blowing from the south across his path--tend to force
him towards the north, then he would set his pointer so that he was
steering not due east, but to a point a certain number of miles south of
east. In this way, with the wind driving him always north, he would
arrive not at the imaginary destination towards which he steered, but at
the real point due east which he desired to make. The drawback of the
method may be this: should the pilot leave ground in a 10-mile-an-hour
wind, and should the strength of this wind increase say to 20 miles an
hour, his allowance for leeway would be insufficient; but against this
may be set the fact that the airman, becoming aware probably, by the
increased rolling of his machine, that the wind was tending to
strengthen, would steer still wider of his goal. Compasses are being
tested, also, which allow pilots to make an accurate and mechanical
allowance, even while in flight, for risings or fallings of a side wind.
There is one, a form of transparent compass, made so that the airman can
look down through it, and see the ground passing away below. Selecting
landmarks with his eye which are a little distance apart, he is able to
note--by contrasting his compass-course with that his machine makes when
in relation with these objects--just how much drift he should allow
for. Then he alters his leeway indicator and makes another observation
later on, should he think the wind has changed again.
[Illustration: FIG. 67.--An Airman’s Map.]
Vital to the equipment of a pilot is his map. In the infancy of flying,
when airmen first began to venture upon journeys between cities, they
had neither maps nor compasses, and contented themselves as a rule with
following a railway--the metals of which, gleaming below and appearing
as though ruled across the country, provided an excellent guide. But
soon, making longer flights and passing perhaps over districts where
there were no railways, pilots found they needed a map; but not an
ordinary map, such as a tourist upon the earth might use. Flying
thousands of feet high, the airman’s view of the land is bird-like. The
country stretches away on all sides below, apparently almost flat, and
with its hills so dwarfed that they hardly catch the eye (see Plates XI
and XII).
A river, or a sheet of water, is a conspicuous guide, and must figure
plainly upon the airman’s map. Main roads, too, are clearly
seen--stretching like white ribbons across the country. Railways also,
and woods; while churches, chimneys, and isolated buildings may be seen
from great distances when a voyager is in the air.
So the airman’s map is made up of landmarks that are likely to catch his
eye, remembering always his point of view from above--and remembering
also that as he rushes through the air at a speed faster than an express
train, he needs to identify quickly any feature of the landscape below.
A sketch showing what an airman’s map is like, will be seen in Fig. 67.
Here we have railways, roads, rivers, lakes, and woods all made to show
plainly, and with a large building or chimney indicated here and there.
With such maps, and aided by a compass, a pilot will fly for hours
without losing his way. When long flights are undertaken, and it would
be inconvenient for an airman to change from one map section to another,
he uses a narrow strip-map, mounted upon a couple of rollers, and fitted
in a case with a transparent cover. As he passes across country he
unrolls his map, section by section, so that the district he is
traversing lies always before his eye.