The report in question refers to the experiments conducted with Professor Langely’s model aerodrome.
Some experimenters claim that the parabolic curve gives the greatest lift with the least power required for propulsion but it can be safely doubted. The Wright machine is probably the most efficient in existence. Their curve is very nearly the arc of a circle and is not of the parabolic form.
Four per cent is about the proper curve to give the planes of a glider. This is about two inches for ribs four feet long. After fastening the front end of the ribs, curve them up in the centre by pressing down on the loose and at the rear. Then nail the rib to the rear beam with a small wire brad and screw on the clamp. The nails prevent the ribs from slipping longitudinally while the clamps serve to prevent them from moving sideways or pulling off when the fabric is under the pressure of the air.
Fig. 11 is a plan view of the top and bottom planes. Twenty one ribs, each one foot apart are used on the upper plane. Only twenty ribs are required on the bottom surface because an opening two feet wide must be left in the centre for the body of the operator.
Arm pieces. The operator is supported in the machine by two strips of wood passing under his armpits. These armpieces are 3 feet long, 1 inch wide and 1 3/4 inches deep.
Fig. 11.—Plan View of Planes showing Ribs.
They are fastened to the horizontal beams by means of a 3/16 inch round headed stove bolt. The distance between should be just wide enough to be comfortable and is variable with the breadth of the operator between his shoulders. Thirteen inches is about the proper distance for the average person. The upper side of the arm pieces is rounded so that they will not be quite so uncomfortable as they would be if left square. It is not a good plan to pad these pieces by wrapping them with cloth for it will impede the movements of the body in balancing.
Fig. 12.—Arm piece.