orward
stabilizing surface, in order to secure a longitudinal dihedral. The
defect of such design lies in the fact that the main surface must have
a certain angle to lift the weight--say 5 degrees. Then, in order to
secure a sufficiency of longitudinal stability, it is necessary to
set the forward stabilizer at about 15 degrees. Such a large angle of
incidence results in a very poor lift-drift ratio (and consequently
great loss of efficiency), except at very low velocities compared with
the speed of modern aeroplanes. At the time such aeroplanes were built
velocities were comparatively low, and this defect was; for that reason,
not sufficiently appreciated. In the end it killed the "canard" or
"tail-first" design.

Aeroplanes of the Dunne and similar types possess no stabilizing surface
distinct from the main surface, but they have a longitudinal dihedral
which renders them stable.

The main surface towards the wing-tips is given a decreasing angle
of incidence and corresponding camber. The wing-tips then act as
longitudinal stabilizers.

This design of aeroplane, while very interesting, has not proved very
practicable, owing to the following disadvantages: (1) The plan design
is not, from a mechanical point of view, so sound as that of the
ordinary aeroplane surface, which is, in plan, a parallelogram. It is,
then, necessary to make the strength of construction greater than would
otherwise be the case. That means extra weight. (2) The plan of the
surface area is such that the aspect ratio is not so high as if the
surface was arranged with its leading edges at right angles to the
direction of motion. The lower the aspect ratio, then, the less the
lift. This design, then, produces less lift for weight of surface than
would the same surface if arranged as a parallelogram. (3) In order to
secure the longitudinal dihedral, the angle of incidence has to be very
much decreased towards the wing-tips. Then, in order that the lift-drift
ratio may be preserved, there must be a corresponding decrease in the
camber. That calls for surface ribs of varying cambers, and results in
an expensive and lengthy job for the builder. (4) In order to secure
directional stability, the surface is, in the centre, arranged to dip
down in the form of a V, pointing towards the direction of motion.
Should the aeroplane turn off its course, then its momentum in the
direction of its first course causes it to move in a direction the
resultant of the