ve of them, are 3 feet long by 11/4 x 1/2 inch.
For a 20-foot biplane about 20 yards of stout silk or unbleached muslin,
of standard one yard width, will be needed. The forty-one ribs are
each 4 feet long, and 1/2 inch square. A roll of No. 12 piano wire,
twenty-four sockets, a package of small copper tacks, a pot of glue, and
similar accessories will be required. The entire cost of this material
should not exceed $20. The wood and cloth will be the two largest
items, and these should not cost more than $10. This leaves $10 for the
varnish, wire, tacks, glue, and other incidentals. This estimate is
made for cost of materials only, it being taken for granted that the
experimenter will construct his own glider. Should the services of a
carpenter be required the total cost will probably approximate $60 or
$70.

Application of the Rudders.

The figures given also include the expense of rudders, but the details
of these have not been included as the glider is really complete without
them. Some of the best flights the writer ever saw were made by Mr. A.
M. Herring in a glider without a rudder, and yet there can be no doubt
that a rudder, properly proportioned and placed, especially a rear
rudder, is of great value to the aviator as it keeps the machine with
its head to the wind, which is the only safe position for a novice. For
initial educational purposes, however, a rudder is not essential as the
glides will, or should, be made on level ground, in moderate, steady
wind currents, and at a modest elevation. The addition of a rudder,
therefore, may well be left until the aviator has become reasonably
expert in the management of his machine.

Putting the Machine Together.

Having obtained the necessary material, the first move is to have the
rib pieces steamed and curved. This curve may be slight, about 2 inches
for the 4 feet. While this is being done the other parts should be
carefully rounded so the square edges will be taken off. This may be
done with sand paper. Next apply a coat of shellac, and when dry rub
it down thoroughly with fine sand paper. When the ribs are curved treat
them in the same way.

Lay two of the long horizontal frame pieces on the floor 3 feet apart.
Between these place six of the strut pieces. Put one at each end, and
each 4 1/2 feet put another, leaving a 2-foot space in the center. This
will give you four struts 4 1/2 feet apart, and two in the center 2 feet
apart, as shown in the illustration