15
highly unlikely because the fittings are generally
well within tolerances.
If, after drilling the holes to size, some
angular difference still exists, it can be corrected
when drilling the wing spar holes to size in the next
steps.
NOTE: In all probability, you won’t have to
do any of the foregoing. So far, virtually every
fuselage that has been measured has needed very
little, or no, adjustment.
After doing all the foregoing, the holes in
both sides of your fuselage will be final sized and
at the same angle.
Measuring Differences in the Wings
Here too, in all likelihood, your wings are
going to be close to being identical, but to be on the
safe side, we’re going to measure them and make
sure because, with the fuselage fittings correct and
nearly perfect, when mounting the wings, we can
make changes in wing position to correct for any
wing differences.
The closer both wings come to being
mounted at exactly the same angle, the easier rig-
ging will be when you get it flying.
It should be mentioned that even wings on
certified airplanes have a surprising amount of
deviation, one to the other. Our goal here is to make
them as identical as we can make them.
To make accurate measurements on the
wings, we need to create a stable surface from
which measurements can be taken. The first step in
that direction is to cut a piece of 5/8 or 3/4” ply-
wood 31” long (the distance between the spars).
Make it wide enough that it goes from the second
rib on the wing to just beyond the wing fitting
holes.
Clamp this wood to the bottom of the wing,
centered between the spars and protruding out from
under the wing and under the spar bolt holes. This
will become the datum you measure your holes
from.
Measure exactly vertically from the surface
of the wood to the bottom edge of the front spar
hole ON THE BACK FACE OF THE SPAR (we’re
using the edge of the hole because it’s more exact
than estimating the center). This is most easily done
by using a square block of wood and marking the
dimension on that, then measuring the marks.
Do the same thing for the rear spar BUT
MEASURE THE HOLE ON THE FRONT FACE
OF THE SPAR.
Now, repeat exactly the same process on the
other wing and compare the two.
If you zeroed out the differences in the fuse-
lage fittings and the accumulated diff e r e n c e
between the left and right wing spar bolt holes is
less than .100”, you can drill both front and rear
spar holes on the bench (3/8” front, 5/16 rear).
If you want the angle of incidence to be
“exactly” the same left to right, OR the differences
exceed .100”, then the holes have to be drilled on
assembly. We’ll clamp the wings into position and
use the fuselage fittings to locate the drill bit.
Understanding the dimensions
It’s easy to get confused on how to apply
the differences between the two wings, as indicated
by the dimensions, so use the following procedure.
1. Pick one wing as the master wing, i.e.
that right wing. We’ll compare everything to that
wing.
2. After measuring both wings, clearly mark
how far above, or below, the right wing the left
wing is. Meaning, is the front spar on the left above
or below the front spar on the right? Same thing for
the rear spar. Establish a numerical difference.
3. Try to picture what the numbers are
telling you. Are they saying the left wing is nose up
or nose down compared to the right wing or do they
indicate only that one wing is higher than the other
because the differences on the rear spar cancel out
the differences on the front spar. Example: If the
spar on the left is .050” BELOW the spar on the
right (nose down) but the rear spar is .025 below
the right rear spar (nose up) they partially cancel
each other out and the cumulative difference will
be .025 or half of one/tenth degree (0.05 degree).
0.100” is 0.20 degree, remember? .
If the left is .050” ABOVE the right spar but
the rear is .025” BELOW the right spar, then the
differences add up to .075, making the angle much
higher and putting the left wing at one and a half
tenths of a degree (0.15 degree) of a degree higher
angle of incidence than the right, which is still
below the maximum allowable difference of 0.20
degree.
In summary, if the differences, front and
Содержание Bearhawk N33RB
Страница 1: ......
