ds the air and
makes the machine buoyant. The kind of material employed is of small
account so long as it is light, strong, and wind-proof, or nearly so.
Some aviators use what is called rubberized silk, others prefer balloon
cloth. Ordinary muslin of good quality, treated with a coat of light
varnish after it is in place, will answer all the purposes of the
amateur.

Cut the cloth into strips a little over 4 feet in length. As you have
20 feet in width to cover, and the cloth is one yard wide, you will need
seven strips for each plane, so as to allow for laps, etc. This will
give you fourteen strips. Glue the end of each strip around the front
horizontal beams of the planes, and draw each strip back, over the ribs,
tacking the edges to the ribs as you go along, with small copper or
brass tacks. In doing this keep the cloth smooth and stretched tight.
Tacks should also be used in addition to the glue, to hold the cloth to
the horizontal beams.

Next, give the cloth a coat of varnish on the clear, or upper side, and
when this is dry your glider will be ready for use.

Reinforcing the Cloth.

While not absolutely necessary for amateur purposes, reinforcement
of the cloth, so as to avoid any tendency to split or tear out from
wind-pressure, is desirable. One way of doing this is to tack narrow
strips of some heavier material, like felt, over the cloth where it laps
on the ribs. Another is to sew slips or pockets in the cloth itself and
let the ribs run through them. Still another method is to sew 2-inch
strips (of the same material as the cover) on the cloth, placing them
about one yard apart, but having them come in the center of each piece
of covering, and not on the laps where the various pieces are joined.

Use of Armpieces.

Should armpieces be desired, aside from those afforded by the center
struts, take two pieces of spruce, 3 feet long, by 1 x 1 3/4 inches, and
bolt them to the front and rear beams of the lower plane about 14 inches
apart. These will be more comfortable than using the struts, as the
operator will not have to spread his arms so much. In using the struts
the operator, as a rule, takes hold of them with his hands, while with
the armpieces, as the name implies, he places his arms over them, one of
the strips coming under each armpit.

Frequently somebody asks why the ribs should be curved. The answer is
easy. The curvature tends to direct the air downward toward the rear
and, as the air is thu