Fig. 83
Fig. 84
Fig. 85
Figs. 79 to 85.—General Arrangement and Details of Biplane
The elevator is constructed from one continuous length of No. 18 gauge piano wire. It is rectangular in plan, the joint being a soldered one at the centre of the trailing edge. The centre rib projects downwards for 1½ in., which projection fits into a hole bored in the nose of the machine with just sufficient friction to retain it in place. It should also be bent back at an angle to cause the trailing edge to bind on the spar sufficiently to allow it to swivel in the event of it striking any fixed object. From this centre rib the elevation of the complete machine is adjusted. The main planes are constructed from birch ¼ in. by ¹/₁₆ in. in cross-section, five ribs connecting the longer spars. No camber is given to the ribs; they should be cut off 1 in. or no longer than is necessary, pinned to the spars, so that the latter are 5 in. apart, and cut off flush after the glue is dry. The top plane, it will be noticed, has an overhang of 3 in. The planes are covered underneath to eliminate the undulations which would otherwise be caused by the ribs. Fabric should be sewn to the elevator frame.
The top plane is lashed to the struts in the manner shown in [Fig. 86], the centre rib resting on the small wooden blocks, while the bottom plane is sprung into the notches previously referred to. Four No. 20 s.w.g. wire stanchions, with eyes bent in them top and bottom, as shown in [Fig. 87], will next be required to form an anchorage for the wing bracing, and to maintain the “gap” at the tips of the wings. Brass wire will do for them, and when made their ends should be forced through the spars in the position shown in the end elevation, and then clinched over.
Bracing the wings should next be undertaken, and carpet thread should be requisitioned for this purpose. It is the easiest matter possible to warp the wings in this operation, so that too much care cannot be taken in this respect. It should be understood that the bracing is fixed to holes in the wooden stanchions, where it must be securely tied, and not continued to the opposite side without, or the wings will rock laterally, and so cause instability. Sufficient tension should be placed on the threads which pass to the wing tips of the bottom plane to impart a 1¼-in. dihedral angle.
