th the aeroplanes 1 and 2; but its
rear edge may be moved upward or downward, so as to be above or below
the normal plane of said rudder through the mechanism provided for that
purpose. It will be seen that the springs 36 will resist any tendency of
the forward edge of the rudder to move in either direction, so that when
force is applied to the rear edge of said rudder the longitudinal ribs
35 bend, and the rudder thus presents a concave surface to the action of
the wind either above or below its normal plane, said surface presenting
a small angle of incidence at its forward portion and said angle of
incidence rapidly increasing toward the rear. This greatly increases the
efficiency of the rudder as compared with a plane surface of equal area.
By regulating the pressure on the upper and lower sides of the rudder
through changes of angle and curvature in the manner described a
turning movement of the main structure around its transverse axis may be
effected, and the course of the machine may thus be directed upward
or downward at the will of the operator and the longitudinal balance
thereof maintained.

Contrary to the usual custom, we place the horizontal rudder in front of
the aeroplanes at a negative angle and employ no horizontal tail at all.
By this arrangement we obtain a forward surface which is almost entirely
free from pressure under ordinary conditions of flight, but which even
if not moved at all from its original position becomes an efficient
lifting-surface whenever the speed of the machine is accidentally
reduced very much below the normal, and thus largely counteracts that
backward travel of the centre of pressure on the aeroplanes which has
frequently been productive of serious injuries by causing the machine
to turn downward and forward and strike the ground head-on. We are aware
that a forward horizontal rudder of different construction has been used
in combination with a supporting surface and a rear horizontal-rudder;
but this combination was not intended to effect and does not effect the
object which we obtain by the arrangement hereinbefore described.

We have used the term 'aeroplane' in this specification and the appended
claims to indicate the supporting surface or supporting surfaces by
means of which the machine is sustained in the air, and by this term we
wish to be understood as including any suitable supporting surface which
normally is substantially flat, although. Of course, when construct