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 1
1/4 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.
