[Illustration: FRENCH MONOPLANE
(From _Aircraft_)]
It is easily possible to compute the areas, angles, and positions
of auxiliary planes to give desired controlling or stabilizing
effects; but the computation involves the use of accurate data as to
positions of the various weights, and on the whole it is simpler to
correct preliminary calculations by actually supporting the machine
at suitable points and observing its balance. Stability is especially
uncertain at very small angles of inclination, and such angles are
to be avoided whether in ordinary operation or in descent. The
necessity for rotating main planes in order to produce ascent is
disadvantageous on this ground; but the proposed use of sliding or
jockey weights for supplementary balancing appears to be open to
objections no less serious. Steering may be perceptibly assisted, in
as delicately a balanced device as the aeroplane, by the inclination
of the body of the operator, just as in a bicycle. The direction of
the wind in relation to the required course may seriously influence
the steering power. Suppose the course to be northeast, the wind east,
the independent speed of the machine and that of the wind being the
same. The car will head due north. By bringing the rudder in position
(_a_), the course may be changed to north, or nearly so, the wind
exerting a powerful pressure on the rudder; but if a more easterly or
east-northeast course be desired, and the rudder be thrown into the
usual position therefor (_b_), it will exert no influence whatever,
because it is moving before the wind and precisely at the speed of the
wind.
[Illustration: A PROBLEM IN STEERING]
It might be thought that, following analogies of marine engineering,
the center of gravity of an aeroplane should be kept low. The effect
of any unbalanced pressure or force against the widely extended sails
of the machine is to rotate the whole apparatus about its center of
gravity. The further the force from the center of gravity, the
more powerful is the force in producing rotation. The defect in most
aeroplanes (especially biplanes) is that the center of gravity is _too_
low. If it could be made to coincide with the center of disturbing
pressure, there would be no unbalancing effect from the latter. It is
claimed that the steadiest machines are those having a high center of
gravity; and the claim, from these considerations, appears reasonable.
[Illustration: LEJEUNE BIPLANE (385 LBS., 10-12 HP.)]