It may possibly be due to the fuselage
being out of truth, but of course the rigger should have made
quite sure that the fuselage was true before rigging the rest
of the machine. Again, it may be due to the internal bracing
wires within the lifting surfaces not being accurately adjusted,
but of course this should have been seen to before covering the
surfaces with fabric.
FUSELAGE.--The method of truing the fuselage is laid
down in the aeroplane's specifications. After it has been
adjusted according to the specified directions, it should then
be arranged on trestles in such a way as to make about three-
quarters of it towards the tail stick out unsupported. In
this way it will assume a condition as near as possible to
flying conditions, and when it is in this position the set
measurements should be confirmed. If this is not done it
may be out of truth, but perhaps appear all right when
supported by trestles at both ends, as, in such case, its
weight may keep it true as long as it is resting upon the
trestles.
THE TAIL-PLANE (EMPENNAGE).--The exact angle of
incidence of the tail-plane is laid down in the aeroplane's
specifications. It is necessary to make sure that the spars
are horizontal when the aeroplane is in flying position and
the tail unsupported as explained above under the heading
of Fuselage. If the spars are tapered, then make sure that
their centre lines are horizontal.
UNDERCARRIAGE.--The undercarriage must be very carefully
aligned as laid down in the specifications.
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