turning a circle, which tends to swing the wheels
and frame outwardly, and thereby still further
elevating the outer end of the plane.

THE WARPING PLANES.--The only remedy to
meet this condition is expressed in the mechanism
which wraps or twists the outer ends of the planes,
as constructed in the Wright machine, or the
ailerons, or small wings at the rear margins of the
planes, as illustrated by the Farman machine.
The object of this arrangement is to decrease the
angle of incidence at the rising end, and increase
the angle at the depressed end, and thus, by manually-
operated means keep the machine on an even
keel.



CHAPTER IV

FORE AND AFT CONTROL


THERE is no phase of the art of flying more important
than the fore and aft control of an airship.
Lateral stability is secondary to this feature, for
reasons which will appear as we develop the
subject.

THE BIRD TYPE OF FORE AND AFT CONTROL.--