per cubic ft. Strength Strength
Wood in lbs. lbs. per sq. in. lbs. per sq in.
Hickory 53 12,000 8,500
Oak 50 12,000 9,000
Ash 38 12,000 6,000
Walnut 38 8,000 6,000
Spruce 25 8,000 5,000
Pine 25 5,000 4,500

Considering the marked saving in weight spruce has a greater percentage
of tensile strength than any of the other woods. It is also easier to
find in long, straight-grained pieces free from knots, and it is this
kind only that should be used in flying machine construction.

You will next need some spools or hanks of No. 6 linen shoe
thread, metal sockets, a supply of strong piano wire, a quantity of
closely-woven silk or cotton cloth, glue, turnbuckles, varnish, etc.

Names of the Various Parts.

The long strips, four in number, which form the front and rear edges of
the upper and lower frames, are called 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 twel