eat care should be taken to see that the wire
is perfectly clean and dry before being painted. A greasy finger-mark
is sufficient to stop the paint from sticking to the wire. In such
a case there will be a little space between the paint and the wire.
Air may enter there and cause the wire to rust.

4. _Tension of Wires._--The tension to which the wires are adjusted is
of the greatest importance. All the wires should be of the same tension
when the aeroplane is supported in such a way as to throw no stress upon
them. If some wires are in greater tension than others, the aeroplane
will quickly become distorted and lose its efficiency.

In order to secure the same tension of all wires, the aeroplane,
when being rigged, should be supported by packing underneath the lower
surfaces as well as by packing underneath the fuselage or nacelle. In
this way the anti-lift wires are relieved of the weight, and there is
no stress upon any of the wires.

As a general rule the wires of an aeroplane are tensioned too much.
The tension should be sufficient to keep the framework rigid. Anything
more than that lowers the factor of safety, throws various parts of the
framework into undue compression, pulls the fittings into the wood, and
will, in the end, distort the whole framework of the aeroplane.

Only experience will teach the rigger what tension to employ. Much may
be done by learning the construction of the various types of aeroplanes,
the work the various parts do, and in cultivating a touch for tensioning
wires by constantly handling them.

5. _Wires with no Opposition Wires._--In some few cases wires will be
found which have no opposition wires pulling in the opposite direction.
For instance, an auxiliary lift wire may run from the bottom of a strut
to a spar in the top plane at a point between struts. In such a case
great care should be taken not to tighten the wire beyond barely taking
up the slack.

[Illustration: Distortion of upper wing caused by auxiliary lift wire
being too tight.]

Such a wire must be a little slack, or, as illustrated above, it will
distort the framework. That, in the example given, will spoil the camber
(curvature) of the surface, and result in changing both the lift and
the drift at that part of the surface. Such a condition will cause the
aeroplane to lose its directional stability and also to fly one wing
down.

I cannot impress this matter of tension upon the reader too strongly.
It is of the