This is secured by using a
spirit-level. The set measurement will then be from the
top of the straight-edge to the centre of the bottom surface
of the main spar, or it may be from the top of the straight-
edge to the lowest part of the leading edge. Care should be
taken to measure from the centre of the spar and to see that
the bubble is exactly in the centre of the level. Remember
that all this will be useless if the aeroplane has not been placed
accurately in its flying position.
This method of finding the angle of incidence must be
used under every part of the lower surface where struts
occur. It should not be used between the struts, because,
in such places, the spars may have taken a slight permanent
set up or down; not, perhaps, sufficiently bad to make any
material difference to the flying of the machine, but quite bad
enough to throw out the angle of incidence, which cannot
be corrected at such a place.
If the angle is wrong, it should then be corrected as follows:
If it is too great, then the rear spar must be warped up
until it is right, and this is done by slackening ALL the wires
going to the top of the strut, and then tightening ALL the
wires going to the bottom of the strut.
If the angle is too small, then slacken ALL the wires going
to the bottom of the strut, and tighten ALL the wires going to
the top of the strut, until the correct adjustment is secured.
Never attempt to adjust the angle by warping the main spar.
Pages:
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132