CONTROLLING AN AEROPLANE
It need scarcely be said that the control of an aeroplane very greatly
depends upon the pilot. One pilot will perform marvels with a machine
which in the hands of another may produce a very different result.
There are, of course, rules which must be observed. But to the skilful
pilot an aeroplane may be said to be like a horse under the care of
a trained horseman. A light touch will achieve more than the most
strenuous efforts of the amateur, and out of the seemingly wayward
machine the expert aviator will make a docile and obedient servant.
The pilot has various rudders by which he steers parts of his machine
independently of the other parts. If he finds the left-hand side of his
machine dipping, he can steer the side up, or _vice versa_. In this way
he has at his command the means of correcting any tendency to ‘heel
over’ to one side or the other, or to ‘pitch skyward.’ But without a
natural tendency on the part of the machine to keep a safe angle, such
precautions would, of course, be futile.
It has been said that the bicycle affords a good illustration. ‘The
rider of a bicycle instinctively balances himself on his machine, but
it would be exceedingly difficult for him to do so were it not for
the fact that a rolling wheel tends of itself to keep upright.’ As
regards air pressure, a little thought will show that when a machine
is moving along horizontally in the air the upward pressure must
be equal to the downward pull of gravity. Consequently, a machine
travelling steadily through the air has been likened to a pendulum.
‘It is just as if the machine,’ writes Mr. Thomas Corbin, author of
_Aircraft_, ‘were suspended upon a point at the centre of pressure. And
just as a pendulum always hangs, when it is steady, with its centre
of gravity exactly under the point of support, so the flying machine
hangs with its centre of gravity exactly under the centre of pressure.’
The designer and user of an aeroplane have, therefore, so to arrange
surfaces and weights that when the machine is in the right position of
horizontal flight the centre of gravity and the centre of pressure
will be in the same vertical line.
Suppose, for instance, that the machine tips forward and tends to
dive downward; the centre of pressure is thrown forward, though of
course the centre of gravity remains still. In such a case the natural
righting tendencies of the machine come into operation, causing it to
steer upward and so right itself. On the other hand, if the machine
tries to deflect upward the very opposite happens. The only pose in
which the machine is stable is when it is moving horizontally.
As we turn from the horizontal to the vertical, the effective surface
of the plane diminishes, but when turning from the vertical towards
the horizontal it increases. When the machine tips to the left the
effective area of its right hand half diminishes, whilst that of
the left hand half increases. Similar action will take place if the
machine tips over to the other side, but whichever way it tips the
self-righting tendency brings it back. And so we see that an aeroplane
is far safer than is thought by many persons. But a great deal, as we
have seen, rests with the pilot; in his hands is the general system of
control.
One of the simplest methods consists in providing a universally pivoted
hand lever and pivoted foot lever. The latter operates the rudder
through two crossed cables which connect the rudder tiller with a cross
piece on the spindle of the rudder bar. Upon releasing the pressure on
the left foot, the machine turns to the left, and acting similarly with
the right foot the machine turns to the right.
The general method for controlling the elevators is by cross wires
which pass from their tillers to the ends of a fore and aft bar passing
through the centre of the universal action of the vertical centred
rod. One wire cables to the balancing flaps, or the warping cables are
attached to a horizontal crosspiece, whose axis is set transversely in
the machine and passes through the same centre of motion of the control
rod. In this the method is such that a forward or backward movement of
the rods rocks the fore and aft bar and pulls on the elevator cables
to make the machine go up or down. A side movement of the control rod
rocks the traverse bar and pulls on the warp or flap cables.
Another control system consists in replacing the universally pivoted
rod by a simple pivoted rod, the pivoting of which, fore and aft,
controls the elevators, and having a handwheel and drum upon which
the warp or flap cable is wound or unwound. The winding in and out of
the balancing cables has been likened to the wheel control system of
a motor boat or small steamer. By duplicating the cables on single
control the safety of the machine is enhanced, and by duplicating
the controls both the pilot and the passenger are given power. This
duplication is, of course, most useful in the event of the pilot
becoming incapacitated from action.
The experienced pilot, in virtue of his keen sense of touch, has an
almost infallible guide as to what the air is doing with his machine.
His hand is upon his lever, holding the elevator in the desired
position, and the slightest increase or decrease in the speed of the
air causes an increase or decrease of the lever’s pressure against his
hand. ‘He has his hand on the machine’s pulse, and feels instantly any
change in its conditions.’ In the event of the elevator pulling, he
knows that the wind is increasing and that there is a call for reducing
the ‘up-starring action’ of the elevator. If, on the contrary, the wind
slackens, his lever gives toward him and is drawn in a little, till
the normal tension is gained. The ‘feel’ of the lever tells him what to
do, and with practice the necessary correcting movements are made by
instinct.
We know how well our airmen have learnt their lesson. Many of them
have become competent pilots with astonishing rapidity. A writer in
the _Daily Chronicle_ (October 13, 1916) has told how ‘the British
Air Service is now a great army, 80 per cent. of whom, before the
war, had never even seen an aeroplane, much less been up in one—bank
clerks, young merchants, undergrads., doctors, lawyers, journalists,
all endowed with two sterling qualities required by the pilot of the
air, courage and levelheadedness.’ And how has this great miracle
been accomplished? August, 1914, found us lamentably short of both
personnel and material, but what little there was, was of the very
best. The already experienced pilots set to work with a will upon
the more than generous quantity of raw material that came to hand.
Within a few months their influence made itself felt. ‘They taught the
_quirks_—the airmen’s pet name for the novice—in their own simple
and undemonstrative manner, that the air is to be respected but never
feared, the aeroplane treated as a being of life and animation, with
quaint humours peculiarly its own, and not as a lifeless mass of metal
and woodwork.’ The usual method of training a new hand is to get him
used to the air. The beginner is taken up for several flights as a
passenger. In the initial flight the pilot will perform the most daring
manœuvres and precipitous turns, watching his passenger closely the
whole time for any signs of nervousness or fear. It is a most trying
ordeal that first trip up aloft, and the bravest hearts have been known
to quail.
‘Following the first flight,’ says the author of the article from
which we have quoted above, ‘there are numerous trips in dual-control
machines, that is to say, with the ordinary pilot’s control-stick
and steering-bar duplicated, and both couples working under the same
controls. Thus, gradually, the _quirk_ becomes used to the handling of
the craft and accustomed to the sudden drop of wind, until eventually,
without his knowledge, the instructor allows him to fly the machine
himself. Sufficient progress made, he is allowed to make flights alone,
and when he has learnt to bank left and right, and land the machine
in a safe and seemly manner, permission is given him to attempt
the Royal Aero Club’s certificate; for which an altitude flight, a
distance flight, and landing on a given spot are the only tests that
are necessary. This, let it be said, is but the starting-point of his
flying education. Flying fast machines, wireless operating, machine-gun
firing, bomb dropping, navigation and map reading are still to be
mastered. Only one who has been in the air and seen that queer panorama
of jumbled green, grey and blue, stretching away for miles on either
hand behind him, can appreciate the difficulties of an air pilot
endeavouring to make a true course from a mist-bound earth; or when
one’s hands are frozen to the bone, and the ice-cold wind whistles by
one’s ears, the extreme difficulty of manœuvring the control-stick and
working the machine gun at one and the same time.’
As for flying at night, ‘when sky and earth are alike
indistinguishable,’ that is a science needing far more than the average
degree of courage. Such flying is only entrusted to experienced
and skilful pilots. How few persons know the _full_ meaning of the
achievements of the heroic airmen who have attacked German airships and
caused them to fall flaming to the earth!