The line along
which the measurement should be taken is laid down in the
aeroplane's specifications.
If a mistake is made and the measurement taken along
the wrong line, it may result in a difference of perhaps 1/4
will, in flight, be nose-heavy or tail-heavy.
After the adjustments of the angles of incidence, dihedral,
and stagger have been secured, it is as well to confirm all of
them, as, in making the last adjustment, the first one may
have been spoiled.
OVER-ALL ADJUSTMENTS.--The following over-all check
measurements should now be taken.
The straight lines AC and BC should be equal to within
1/8 inch. The point C is the centre of the propeller, or, in the
case of a ``pusher'' aeroplane, the centre of the nacelle.
The points A and B are marked on the main spar, and must
in each case be the same distance from the butt of the spar.
The rigger should not attempt to make A and B merely the
sockets of the outer struts, as they may not have been placed
quite accurately by the manufacturer. The lines AC and BC
must be taken from both top and bottom spars--two measurements
on each side of the aeroplane.
The two measurements FD and FE should be equal to
within 1/8 inch. F is the centre of the fuselage or rudder-
post. D and E are points marked on both top and bottom
rear spars, and each must be the same fixed distance from
the butt of the spar. Two measurements on each side of the
aeroplane.
If these over-all measurements are not correct, then it
is probably due to some of the drift or anti-drift wires being
too tight or too slack.
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