THE CONTROLLING OF LATEST-TYPE CRAFT
People are puzzled, often, when they try to explain to themselves how
it is that an aeroplane, which is so much heavier than air, manages to
leave the ground and to soar in flight. When balloons or airships
ascend, it is realised of course that the gas, imprisoned within their
envelopes, draws them upward. But the aeroplane--weighing with pilot,
passenger, and fuel perhaps several thousand pounds--rises without the
aid of a gas-bag and with nothing to sustain it but narrow planes; and
these do not beat, like the wings of a bird, but are fixed rigidly on
either side of its body. How is the weight of machine and man borne
through this element we cannot see, and which appears intangible?
The secret is speed--the sheer pace at which an aeroplane passes
through the air. As a craft stands on the ground, its planes are
inoperative. Power lies dormant in the air, but only when it is in
motion, or when some object or apparatus is propelled through it at
high speed. Have you stood on a height, in a gale, and felt an air
wave strike powerfully against your body? The blow is invisible; but
you yield a step, gasping; and, had you wings at such a moment, you
would not doubt the power of the wind to sweep you upward. This is the
force the aeroplane utilises.
If, on a calm day, you accelerate your motor-car to 60 miles an hour,
the air sweeps past you in a powerful stream; just as it would if you
were standing still, and there was a gale of wind. Instead of the wind
possessing the speed, in this instance, it is you who provide it. The
motor of an aeroplane, driving the propeller of the machine, turns
this at 1000 or more revolutions a minute, and causes its curved
blades to screw forward through the air as they turn, like those of a
ship's propeller through water--or a gimlet into wood. The propeller,
as it bores its way into the air, draws or pushes the aeroplane across
the ground; and the speed grows rapidly until the air, sweeping with
an increasing pressure beneath the planes, becomes sufficient to bear
the craft in flight.
But the wing of an aeroplane would not sustain its load unless
designed specially to act upon the air. A man, if he is unlucky enough
to fall from a tall building, passes through the air at a high speed.
His body obtains no support from the air; so he crashes to the ground.
This is because his body is heavy, and presents only a small surface
to the air. To secure a lifting influence from the air, it must be
struck swiftly with a large, light surface.
Men go to Nature when building wings for aeroplanes, and imitate the
birds. The wing of a bird arches upward from front to back, most of
the curve occurring near the forward edge; and this shape, when
applied to an aeroplane wing, is known as its camber. With an
aeroplane wing, if its curve is adjusted precisely, the air not only
thrusts up from below as a machine passes through it, but has a
lifting influence also from above; an effect that is secured by the
downward slope of the plane towards its rear edge. The air, sweeping
above the raised front section of the plane, is deflected upward, and
with such force that it cannot descend again immediately and follow
the downward curve of the surface. So, between this swiftly-moving air
stream, and the slope to the rear of the plane, a partial vacuum is
formed, and this sucks powerfully upward. With a single wing,
therefore, it is possible to gain a double lifting influence--one
above and one below.
The building of aeroplanes, once their wing lift is known, becomes a
matter of precision. According to the speed at which they fly, and the
size and curve of their planes, machines will sustain varying loads.
In some machines, as a general illustration--craft which fly fast--the
planes may bear a load equal to 10 lbs. per square foot. In others the
loading may be less than 3 lbs. per square foot.
Apart from raising a craft into the air, by the lifting power of its
wings, there is the problem of controlling it when in flight. The air
is treacherous, quickly moving. Gusts of abnormal strength, sweeping
up as they do invisibly, may threaten to overturn a machine and dash
it to earth. Eddies are formed between layers of warm and cold air.
There are, as a craft flies, constant increases or lessenings of
pressure in the air-stream that is sweeping under and over its wings;
and all these fluctuations influence its equilibrium. Unless,
therefore, a machine is automatically stable--and with craft of this
type we shall deal later--the pilot must be ready, by a movement of
the surfaces which govern the flight of the machine, to counteract
quickly, with a suitable action of his levers, the overturning
influence that may be exercised by a gust of wind. Here lies the art
of flying. A man is given a machine which, by the action of its motor
and propeller, will raise itself into the air; and it is his task,
when the craft is once aloft, to manipulate it accurately and without
accident, and to bring it to earth safely after he has made a flight.
In the description of controlling movements which follows we shall,
for the sake of convenience, and for the sake also of brevity, deal
only with the type of "pusher" biplane to which reference has been
made already, and on which large numbers of pupils have been, and are
being, trained to fly. This casts no aspersion whatever on tractor
machines or on monoplanes. On either, if he has an inclination, a
pupil can undergo his instruction, and do so usually with success. But
explanation is rendered more easy, and there is less likelihood of a
dispersal of interest, if one machine is selected for illustration;
and our reasons for the choice of a "pusher" biplane, regarded from
the point of view of tuition, have been explained already.
First, therefore, one may deal with raising the craft into the air,
and causing it to descend. In the photograph of the school machine
shown facing this page, it will be seen that the control surfaces are
indicated by lettering. In front of the biplane, on outriggers, is the
plane "A." This surface (aided in its action by a rear plane) governs
the rise or descent of the machine. When the motor is started, and the
propeller drives the biplane across the ground on its chassis B, the
machine would, if this lifting plane was held in a negative position,
continue to move forward on the earth and would make no attempt to
rise. In order to leave the ground, when the speed of the machine is
sufficient for its main-planes (C.C.) to become operative, and bear
its weight through the air, the pilot draws back slightly towards him
a lever, which is placed just to the right of his driving-seat and is
held with the right hand. A photograph which shows this lever, and the
other controls, appears facing page 36, the lever to which we are
referring being indicated by the figure 1. The effect on the aircraft
when the pilot draws back this lever--the motion being slight and made
gently--is to tilt up the elevating plane A, and this in its turn,
owing to the pressure of air upon it, raises the front of the machine.
The result of this alteration in the angle of the craft is that it
presents its main-planes at a steeper angle to the air. Their lifting
influence is increased, with the result that--at an angle governed by
the pilot with his movement of the elevating plane--they bear the
machine from the ground into the air.
[Illustration: GRAHAME-WHITE SCHOOL BIPLANE (TYPE XV.) _Photo by
Topical Press Agency._
A.--The front elevating plane, which acts in conjunction with the
rear-plane marked A1; B.--The landing-chassis; C.C.--The main-planes;
D.D.--The ailerons; E.E.--The rudders; F.--Engine (a 60-h.p. Le Rhone)
and propeller.]
A reverse movement of the elevator reduces the lift of the main-planes;
hence, when an aviator wishes to descend, he tilts down his elevator,
bringing his machine at such an angle that it is inclined towards the
ground. Then, switching off his engine so as to moderate the speed of
his descent, and by such manipulations as may be necessary of his
elevator, he pilots his craft to earth in a vol-plane, during which
gravity takes the place of his motor, and he is able--by steadying his
machine and bringing it into a horizontal position just at the right
moment--to make a gentle contact with the ground.
A pilot must be able to do more than cause his aeroplane to ascend and
to alight: he must have means to check the lateral movements which,
under the influence of wind gusts, may develop while the biplane is in
flight. At the rear extremities of the main-planes as illustrated in
the photograph facing page 34--and marked D.D.--are flaps, or ailerons,
which are hinged so that they may be either raised or lowered. These
ailerons are operated, through the medium of wires, by the same
hand-lever which governs the movement of the elevator. This lever is
mounted on a universal joint, and can be moved from side to side as
well as to and fro. Should the biplane tilt, while flying, say towards
the left, the pilot moves his hand-lever sideways towards the right.
This is a natural movement, the instinct being to move the lever away
from the direction in which the machine is heeling. This movement of
the lever has the effect of drawing down the ailerons on the left-hand
side of the machine; on the side, that is to say, which is tilted down;
and the depression of these auxiliary surfaces, increasing suddenly
as they do the lifting influence of the main-planes to which they are
attached, tend to thrust up the down-tilted wings, and so restore the
equilibrium of the machine.
In the operation of his ailerons, combined with the use of his
elevator, a pilot is given means to balance his craft while in flight.
One should not gain the impression that an aeroplane is threatening
ceaselessly to heel this way and that. This is not so. The machine has
a large measure of stability, apart from any manipulation of its
controls, and needs balancing only when some disturbance of the
atmosphere affects its equilibrium. Under favourable conditions, such
as a pupil will experience in his first flights, nothing more is
necessary with the hand-lever than a very slight but fairly constant
action; a similar motion, in a way, as is made by the driver of a
motor-car when he maintains, by his "feel" on the wheel, his sense of
control over the machine. In the controlling actions of an
aeroplane--and this is a fact which tends sometimes to the confusion
of the novice--nothing more is required, normally, than the most
delicate of movements. The difference say between ascending, and
skimming along the ground, is represented by a movement of the
hand-lever of only a few inches. Delicate, sure, quick, and firm; such
is the touch needed with an aeroplane.
With the one hand-lever, as we have shown, it is possible for a pilot
to control the rise and descent, and also the lateral movements of his
machine; and there remains only the steering to be effected--the
movement from side to side, from right to left, or vice-versa. At the
rear of the biplane, as shown facing page 34, will be seen two
vertical planes, E.E. These, being hinged, will swing from side to
side; and they exercise a sufficient influence, when working in the
strong current of air that blows upon them when a machine is in flight,
to steer it accurately in any direction. The pilot, to operate this
rudder, rests his feet on a conveniently-placed bar, which is mounted
on a central swivel, and allows the bar to be swung by a pressure of
either foot. When the pilot needs to make a turn say to the left, as
he is flying, he presses his left foot forward. This swings the bar in
same direction; and, by a simple connection of wires running to the
tail of the machine, the rudders are made to swing over to the left
also, and the machine turns in response to them. A similar movement to
the right produces a right-hand turn. This foot rudder bar, being
numbered 2, is shown in the picture facing page 36.
[Illustration: THE CONTROLS OF A SCHOOL BIPLANE. _Photo by Topical
Press Agency._
1.--The upright lever which, working on a universal joint, operates
the elevator and ailerons; 2.--The bar, actuated by the pilot's feet,
which operates the rudders of the machine; 3.--The pilot's seat;
4.--The passenger's seat.]
Apart from the movements we have described, which are extremely simple,
a pilot needs also to maintain control over his motor. Near his left
hand, fixed to the framework just at one side of his seat, are levers
which govern the speed of the engine, also the petrol supply; while
close to them is the switch by which the ignition can be switched on
or off.
A final word is necessary here, perhaps, and it is this: the glamour
and mystery which, in the early days, clung to the handling of an
aeroplane has now been dispelled almost entirely. A well-constructed
machine, flying under favourable conditions, requires surprisingly
little control; what it does, one may almost say, is to fly itself.