n 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,