Fig. 23.—Plan and Elevation Views of Piano Wire Bracing.
After fastening all of the wires their tension may be regulated by turning the nuts on the lower ends of the eye bolts. It is very necessary that the frame should be perfectly true and not warped or twisted. Otherwise the machine will be very hard to balance and manage when making a glide. Especially must the rudder be true with the rest of the machine.
Fig. 24.—Method of anchoring wires
Since there are no eyebolts about the rudder which could be used to tighten or loosen the truss wires, a turnbuckle must be included in each wire for that purpose.
Turnbuckles. The construction of these turnbuckles which are very simple and inexpensive is illustrated in Fig. 25. They are made of a bicycle spoke and nipple by cutting off one end of the spoke and using the part which is threaded. The end of this piece is bent back and twisted into an eye. A piece of 1/16 inch sheet brass 1/2 x 3/8 inch has a hole bored in its centre, the diameter of which is such that it will just admit the spoke nipple. The nipple is prevented from passing all the way through by the shoulder on one end. A piece of sheet iron 1/2 inch wide and 3 inches long has a similar hole bored in its centre. The ends of this strap are rounded and bored so that the piano wire may be passed through. The turnbuckle is then assembled and connected as shown in the illustration. The tension of the wire is regulated by turning the spoke nipple while the spoke itself is held rigid.
Fig. 25.—Bicycle spoke turnbuckle.
The second method of bracing illustrated in Fig. 22 requires that a turnbuckle be included in the diagonals of every rectangle, except those formed by the stanchions with the horizontal beams. This method is used on almost all aeroplanes and is considered the strongest but the first method is plenty strong enough for an ordinary glider. If after trussing, the machine is found to be warped or twisted, it must be trued up. By sighting along the horizontal beams and tightening or loosening the necessary wire any curvature may be easily corrected.