e when finished and equipped.

Second--Area of the supporting surface required.

Third--Amount of power that will be necessary to secure the desired
speed and lifting capacity.

Fourth--Exact dimensions of the main framework and of the auxiliary
parts.

Fifth--Size, speed and character of the propeller.

In deciding upon these it will be well to take into consideration
the experience of expert aviators regarding these features as given
elsewhere. (See Chapter X.)

Estimating the Weights Involved.

In fixing upon the probable approximate weight in advance of
construction much, of course, must be assumed. This means that it will
be a matter of advance estimating. If a two-passenger machine is to be
built we will start by assuming the maximum combined weight of the two
people to be 350 pounds. Most of the professional aviators are lighter
than this. Taking the medium between the weights of the Curtiss and
Wright machines we have a net average of 850 pounds for the framework,
motor, propeller, etc. This, with the two passengers, amounts to 1,190
pounds. As the machines quoted are in successful operation it will be
reasonable to assume that this will be a safe basis to operate on.

What the Novice Must Avoid.

This does not mean, however, that it will be safe to follow these
weights exactly in construction, but that they will serve merely as
a basis to start from. Because an expert can turn out a machine,
thoroughly equipped, of 850 pounds weight, it does not follow that a
novice can do the same thing. The expert's work is the result of years
of experience, and he has learned how to construct frames and motor
plants of the utmost lightness and strength.

It will be safer for the novice to assume that he can not duplicate the
work of such men as Wright and Curtiss without adding materially to the
gross weight of the framework and equipment minus passengers.

How to Distribute the Weight.

Let us take 1,030 pounds as the net weight of the machine as against the
same average in the Wright and Curtiss machines. Now comes the question
of distributing this weight between the framework, motor, and other
equipment. As a general proposition the framework should weigh about
twice as much as the complete power plant (this is for amateur work).

The word "framework" indicates not only the wooden frames of the main
planes, auxiliary planes, rudders, etc., but the cloth coverings as
well--everything in fact except the engi