f 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.

1. The aeroplane must be placed in its flying position and sufficiently
high to ensure the wheels being off the ground when rigged. When in this
position the axle must be horizontal and the bracing wires adjusted to
secure the various set measurements stated in the specifications.

2. Make sure that the struts bed well down into their sockets.

3. Make sure that the shock absorbers are of equal tension. In the case
of rubber shock absorbers, both the number of turns and the lengths must
be equal.

HOW TO DIAGNOSE FAULTS IN FLIGHT, STABILITY, AND CONTROL.

DIRECTIONAL STABILITY will be badly affected if there is more drift
(_i.e._, resistance) on one side of the aeroplane than there is on the
other side. The aeroplane will tend to turn towards the side having the
most drift. This may be caused as follows:

1. The angle of incidence of the main surface or the tail surface may be
wrong. The greater the angle of incidence, the greater the drift. The
less the angle, the less the drift.

2. If