great circle.

As the machine nears the earth it is caused to
change the angle of flight by the control mechanism
so that it will dart upwardly at an angle, or downwardly,
and thus enable the pilot to sail to another
point beyond where he may safely land.
This changing the course of the machine so that
it will glide upwardly, means that the incidence
of the planes has been changed to a positive
angle.

ANGLE OF INCIDENCE.--In aviation this is a term
given to the position of a plane, relative to the
air against which it impinges. If, for instance,
an aeroplane is moving through the air with the
front margin of the planes higher than their rear
margins, it is said to have the planes at a positive
angle of incidence. If the rear margins are
higher than the front, then the planes have a negative
angle of incidence.

The word incidence really means, a falling
upon, or against; and it will be seen, therefore,
that the angle of incidence means the tilt of the
planes in relation to the air which strikes it.

Having in view, therefore, that the two qualities,
namely, speed and surface, bear an intimate
relation with each other, it may be understood