How To Build A 20-Foot Bi-Plane Glider

by Alfred Powell Morgan

The strength of the glider lies in its proper trussing with piano wires which when tightened up should so brace the framework that it will support without appreciable sag or strain, a heavy man hanging from the arm pieces and the ends of the planes resting on a pair of carpenters’ horses.

Two methods of trussing the planes are illustrated in Fig. 22. The machine is divided into five cells the vertical boundaries of which are formed by the stanchions. .

The first method illustrated is the one used in this case for the glider. It is somewhat simpler than the second and does not require the use of any turnbuckles.

Each wire is fastened to one of the eyebolts on the horizontal beams and then run diagonally across to the socket on the opposite beam in the other plane, considering front and rear to be opposed.

Four of these diagonal wires, represented by J in Fig. 23 brace each of the four large cells. The middle cell cannot be trussed up in this manner because the wires would interfere with the body of the operator. So the rectangles formed by the two centre struts with the upper horizontal beams and the two centre rear stanchions with the rear horizontal beams of the upper and lower planes, are braced by means of wires running across their diagonals.

Fig. 22.—Trussing Of Cells.

The rudder is stiffened and trussed to the planes by sixteen wires. Two of these F and H run from the top of the vertical rudder plane to the lower sockets in the rear, 4 1/2 feet from the ends of the planes. The corresponding pair E and G run from the bottom of the rudder to the top sockets of the same stanchions. Four wires A, B, C, D steady the horizontal plane and run from its corners to the sockets in which the rudder beams are stepped on the frame of the glider itself. The remaining eight, indicated by I in the illustration brace the horizontal and vertical planes of the rudder to each other.

Fig. 24 illustrates the method of anchoring piano wires.

The wire is first passed through a short piece of 1/8 inch copper tubing about 3/8 of an inch long, then through the eyebolt. The end is doubled back passed through the tube again but now in a reverse direction. By bending the extreme end of the wire over in the form of a hook and shoving the tube down close to the eye bolt, the wire is secured and cannot pull out. The other end of the wire is fastened in the same manner but before the end is bent over into a hook, the wire must be first pulled tight.