16
back, both go the same direction e.g. up or down,
then the rear difference is subtracted from the front
difference because it cancels out part of the angle.
If the differences are opposite, then the rear
difference is ADDED to the front difference and the
total for the two wings must be under 0.100”.
Whew!!
Drilling Wing Spar Holes
If you decide your wing spar holes are all
within tolerance and you want to drill the front to
size on the bench, do it in the following manner.
1. Make up a 90 degree drill guide, which
will be nothing more than a 1” x 3” piece of garden
variety iron plate no thinner than 5/8” (the thicker
the better) with a 3/8” hole drilled in it on a drill
press that has been checked for square. Sand the
back side smooth. You’re going to clamp this to the
spar face so it keeps your drill bit square to the face.
Remember to pad the clamp faces with masking
tape to prevent scratches. For flawless holes, rather
than using a 3/8” bit, drill the block for a 23/64th
bit and ream to 3/8”.
2. LOOSELY clamp the block in place with
the 3/16 hole in the spar as close to center as you
can make it.
3. Barely start the bit into the aluminum far
enough that it is centered on the hole. Let the block
move so it self-aligns.
4. Tighten the clamp firmly. this will align
the block with the hole. Tighten as much as neces-
sary to keep it from moving. Ream the hole after
drilling.
Position Wings on Fuselage
One of the easier ways to handle the wings
in this situation is to rent some sheet rock scaffold-
ing (some places call them “lifts”) and use that to
get the exact height needed. Don’t forget to pad the
scaffolding to prevent scratching. This is a good
application for the foam that the wings were packed
with. Or use cheap moving mats or last year’s car-
pet. If you can’t find the lifts, make up some 2 x 4
“T”s to hold the wing tips up
By now you’ve figured out that moving the
wings is a two-man job and sometimes three. This
will especially be the case, when you start having to
lift them over your head.
For the purpose of fitting the wings, it
sometimes helps to have a couple of extra 3/8 and
5/16” AN bolts. Grind the ends to a smooth taper to
make it easier to get them into the holes. Also, don’t
use hardware store bolts for this application
because many zinc-plated bolts are slightly over-
size and won’t want to go into the holes as they
should.
Before putting the wings on the scaffolds,
draw an accurate pencil line on the rear face of the
rear spar that runs vertically through the rear bolt
hole. This will help in keeping the rear bolt holes
lined up as you move the wing tip fore and aft after
the front bolt is in place.
The concept in the way we’re going to drill
the wing (details are in the following paragraphs)
is:
1. Push wing into approximate position so,
if it wasn’t drilled to size on the bench, the 3/16
holes in the wing are visible in the fuselage fitting
holes.
2. Slide a 3/16” piece of rod through the
holes or use long AN# bolts. This eliminates any
Although bench-drilling the holes in the wing spars can be
done free hand, a simple drill block, as described makes it
easier. Also, under-drilling and reaming gives a better hole.
Even when using sheetrock lifts to handle the wings, it is still
very much a two-man job.
Summary of Contents for Bearhawk N33RB
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