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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
*The second method* of trussing is considerably harder to true up than
the first, since when one diagonal of a rectangle is tightened, the
other must be loosened. But since it makes an exceedingly firm and rigid
structure, it may be well recommended to those who care to undergo the
added expense and labor involved by the extra turnbuckles and wires.
*To take the glider apart*, first remove the bolts holding the rudder
beams in the sockets on the machine. Then unfasten the wires which brace
the rudder to the machine by loosening the turnbuckles until the spokes
and nipples unscrew and come apart. The rudder may now be removed from
the machine.
Next take off all the nuts on the eye bolts in the lower plane and pull
the eyebolts out of the sockets. The two planes will then come apart.
Remove the stanchions by pulling them out of the sockets. The two planes
are then laid one on top of the other and will occupy very little room.