asy to construct one within this limit. This implies,
of course, that due care will be taken to eliminate all superfluous
weight by using the lightest material compatible with strength and
safety.

This plan will admit of 686 pounds weight in the frame work, coverings,
etc., and 344 for the motor, propeller, etc., which will be ample. Just
how to distribute the weight of the planes is a matter which must be
left to the ingenuity of the builder.

Comparison of Bird Power.

There is an interesting study in the accompanying illustration. Note
that the surface area of the albatross is much smaller than that of the
vulture, although the wing spread is about the same. Despite this the
albatross accomplishes fully as much in the way of flight and soaring as
the vulture. Why? Because the albaboss is quicker and more powerful in
action. It is the application of this same principle in flying machines
which enables those of great speed and power to get along with less
supporting surface than those of slower movement.

Measurements of Curtiss Machine.

Some idea of framework proportion may be had from the following
description of the Curtiss machine. The main planes have a spread
(width) of 29 feet, and are 4 1/2 feet deep. The front double surface
horizontal rudder is 6x2 feet, with an area of 24 square feet. To the
rear of the main planes is a single surface horizontal plane 6x2 feet,
with an area of 12 square feet. In connection with this is a vertical
rudder 2 1/2 feet square. Two movable ailerons, or balancing planes, are
placed at the extreme ends of the upper planes. These are 6x2 feet,
and have a combined area of 24 square feet. There is also a triangular
shaped vertical steadying surface in connection with the front rudder.

Thus we have a total of 195 square feet, but as the official figures are
258, and the size of the triangular-shaped steadying surface is unknown,
we must take it for granted that this makes up the difference. In
the matter of proportion the horizontal double-plane rudder is about
one-tenth the size of the main plane, counting the surface area of
only one plane, the vertical rudder one-fortieth, and the ailerons
one-twentieth.

CHAPTER XI. PLANE AND RUDDER CONTROL.

Having constructed and equipped your machine, the next thing is to
decide upon the method of controlling the various rudders and auxiliary
planes by which the direction and equilibrium and ascending and
descending of the machin