anything of value in the machine itself, except
that it incidentally has destroyed the largely
vaunted claim that concaved wings for supporting
surfaces are necessary.

HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.--
When flying "upside down," the convex
side of the plane takes the pressure of the air,
and maintains, so it is asserted, the weight of the
machine. This is true during that period when
the loop is being made. The evolution is made
by first darting down, as shown in Fig. 31, from
the horizontal position, 1, to the position 2, where
the turn begins.

_Fig. 31. Flying upside down._

TURNING MOVEMENT.--Now note the characteristic
angles of the tail, which is the controlling
factor. In position 1 the tail is practically
horizontal. In fact, in all machines, at
high flight, the tail is elevated so as to give little
positive angle of incidence to the supporting
planes.

In position No. 2, the tail is turned to an angle
of incidence to make the downward plunge, and
when the machine has assumed the vertical, as in
position 3, the tail is again reversed to assume
the angle, as in 1, when flying horizontally.