The set measurement, which is of course stated in the
aeroplane's specifications, should be accurate to 1/16 inch.
LATERAL DIHEDRAL ANGLE.--One method of securing
this is as follows, and this method will, at the same time,
secure the correct angle of incidence:
The strings, drawn very tight, must be taken over both
the main and rear spars of the top surface. They must run
between points on the spars just inside the outer struts.
The set measurement (which should be accurate to 1/16 inch
or less) is then from the strings down to four points on the
main and rear spars of the centre-section surface. These
points should be just inside the four centre-section struts;
that is to say, as far as possible away from the centre of the
centre-section. Do not attempt to take the set measurement
near the centre of the centre-section.
The strings should be as tight as possible, and, if it can
be arranged, the best way to accomplish that is as shown in
the above illustration, i.e., by weighting the strings down to
the spars by means of weights and tying each end of the strings
to a strut. This will give a tight and motionless string.
However carefully the above adjustment is made, there is
sure to be some slight error. This is of no great importance,
provided it is divided equally between the left- and right-
hand wings. In order to make sure of this, certain check
measurements should be taken as follows:
Each bay must be diagonally measured, and such measurements
must be the same to within 1/16 inch on each side of
the aeroplane.
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