the horizontal beams. These are each 20 feet in length.
These horizontal beams are connected by upright strips,
4 feet long, called stanchions. There are usually 12 of
these, six on the front edge, and six on the rear. They
serve to hold the upper plane away from the lower one.
Next comes the ribs. These are 4 feet in length (projecting
for a foot over the rear beam), and while intended
principally as a support to the cloth covering of
the planes, also tend to hold the frame together in a
horizontal position just as the stanchions do in the vertical.
There are forty-one of these ribs, twenty-one on
the upper and twenty on the lower plane. Then come
the struts, the main pieces which join the horizontal
beams. All of these parts are shown in the illustrations,
reference to which will make the meaning of the
various names clear.

Quantity and Cost of Material.

For the horizontal beams four pieces of spruce, 20 feet
long, 1 1/2 inches wide and 3/4 inch thick are necessary.
These pieces must be straight-grain, and absolutely free
from knots. If it is impossible to obtain clear pieces
of this length, shorter ones may be spliced, but this is
not advised as it adds materially to the weight. The
twelve stanchions should be 4 feet long and 7/8 inch in
diameter and rounded in form so as to offer as little
resistance as possible to the wind. The struts, there
are twelve 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