ALL OF THE Project Hole Shot model’s subassemblies are
finally finished and ready to join. However, there is one more
small—but important—job to do on the wing and the fuselage.
The last woodworking task before assembly is to install bellcrank
mount pieces over the bellcrank post, which extends out from the
top and the bottom of the wing.
The bellcrank mounts are made from 1/8 plywood, are 1 inch
long, and should be cut to be as wide as the fuselage in the area
where they will be installed. Drill a 1/8-inch-diameter hole in the
center of each of these mount pieces so that they can slide over
the bellcrank post and sit flush against the wing’s surface.
Epoxy the bellcrank mount pieces in place. When the glue has
cured, use a hand grinder fitted with a carbide cutting disk to trim
the bellcrank post flush with surface of each of the plywood
mounts.
Even though we installed the bellcrank post in half-round
grooves that were filed into each of the vertical 1/8 light-plywood
spars before we joined the wing, it is very important to also install
the external mounts for extra security. Please do not omit this
step.
Wing Installation: Slide the fuselage onto the wing, and position
it against the plywood mount pieces. Mark the areas in the top and
bottom of the wing opening where clearance slots will be required
to let the fuselage slide over the mount pieces.
Remove the wing, and use a sharp #11 blade in an X-Acto
knife handle to cut the notches to clear the bellcrank mount
pieces. Finish these notches with a sanding stick.
Measure the fuselage width at the front and rear of the wing
opening, and use a pencil to transfer these marks to the
corresponding places on the upper surface of the wing. Make a
mark that is half the fuselage width on either side of the wing
centerline. Do this at the front and the rear of the wing.
Slide the wing into place, and align it with the pencil marks.
Use a square to do the final alignment. The angle where the
fuselage doubler and the LE meet should be 90°.
Check this angle on both sides, to make sure you have the wing
in square. Check the angle from the front in the same manner,
using the square against the side of the fuselage doublers and the
top of the wing surface for reference.
When you are certain that the wing is square to the fuselage in
every respect, tack-glue it to the fuselage
in two or three places using mediumviscosity
cyanoacrylate. (I have switched
to Zap CA glue and have found it to be
excellent!)
Mix a half ounce of 45-minute epoxy
and add a generous amount of white
microballoons. Using a small balsa
applicator, force the epoxy into any gaps
between the wing and fuselage, and make a
small fillet around the entire wing/fuselage
joint. Wipe off any excess epoxy and let
this assembly cure thoroughly.
Wing and Tail Alignment: Most
experienced CL Precision Aerobatics
(Stunt) fliers would, I’m sure, agree that
installing the stabilizer accurately and with
no negative incidence in relation to the
wing is the most important step in building
a Stunt model. If the stabilizer is
improperly lined up, the result will be an
airplane that will never perform up to the
design’s potential.
If the stabilizer/wing incidence is off by
even a bit, the model will never groove
properly and will never “lock” after a turn
during a square maneuver. I cannot stress
this enough; the stabilizer must be
installed perfectly.
Some believe in adding a tiny amount
of positive incidence (stabilizer LE slightly
elevated). I’ve never found this necessary,
and I try to make my installations zerozero.
I will concede this point. If the
stabilizer is installed with any incidence, it
should be slightly to the positive side. A
tenth of a degree of positive incidence
would be a good compromise.
There are probably as many alignment
ideas and procedures as there are model
builders. Most builders are also good
“backyard” engineers, and many of them
come up with fixtures that do the job of
alignment well. I have come up with a
simple fixture that does the job for me.
I use the side view of the plans of the
model I’m building to make my alignment
fixture. I start by ensuring that the
dimensions and placements of the surfaces
on the drawing are accurate.
Then I find two pieces of 1/8 balsa that
are long enough and wide enough to make
alignment plates that will sit on a flat table
and have the wing opening and stabilizer
openings cut into them. I tape the 1/8 balsa
portions together and position this
assembly under the plans.
I use a pin to punch holes around the
wing opening and tail opening. Before I
remove the plans from the balsa, I make
holes to allow me to draw a baseline that
is parallel to the wing and stabilizer
centerline. Then I remove the plans and
carefully connect the dots with a finepoint
pen.
The next step is to accurately cut out
the fixture plates. I use a Dremel scroll
saw to do this. I cut just inside the lines
and test and then fit the wing snugly into
its opening, using a sanding stick to
achieve a perfect fit.
I remove the tape that is holding the
two plates together. One fixture plate will
slip over the right wing half and the other
will slip over the left wing half. They
should be positioned far enough onto the
wing halves to allow the stabilizer to be
captured in its fixture slot on either side of
the fuselage.
Position the fixture on a flat table and
install the stabilizer into its slot in the
fuselage and into the slots in the alignment
fixture. The fit at the fuselage should not
be so snug that it forces the stabilizer into
a tilt either way. There should be no
“slop” in the slot, but it should not be too
tight. Think Goldilocks and the porridge:
just right.
Check the measurement from the rear
edge of the wing TE to the stabilizer TE
on each side of the fuselage. Make this
measurement as far out on the stabilizer
on each side as possible. The
measurements should match.
When you are certain that the
stabilizer is square in all axes, carefully
tack-glue it to the fuselage using thin
cyanoacrylate. Check the alignment one
more time, and then permanently glue
the stabilizer to the fuselage using an
epoxy-and-microballoon mix.
Use only enough epoxy to ensure a
good bond. Epoxy is heavy, and you don’t
want to add unnecessary weight to the
back of the Hole Shot.
That’s it for this month. Next time I’ll
cover the final details of assembly and
finish.
Till then, fly Stunt! MA
Sources:
Precision Aerobatics Model Pilots
Association
www.control-line.org
Edition: Model Aviation - 2009/07
Page Numbers: 126,127
Edition: Model Aviation - 2009/07
Page Numbers: 126,127
ALL OF THE Project Hole Shot model’s subassemblies are
finally finished and ready to join. However, there is one more
small—but important—job to do on the wing and the fuselage.
The last woodworking task before assembly is to install bellcrank
mount pieces over the bellcrank post, which extends out from the
top and the bottom of the wing.
The bellcrank mounts are made from 1/8 plywood, are 1 inch
long, and should be cut to be as wide as the fuselage in the area
where they will be installed. Drill a 1/8-inch-diameter hole in the
center of each of these mount pieces so that they can slide over
the bellcrank post and sit flush against the wing’s surface.
Epoxy the bellcrank mount pieces in place. When the glue has
cured, use a hand grinder fitted with a carbide cutting disk to trim
the bellcrank post flush with surface of each of the plywood
mounts.
Even though we installed the bellcrank post in half-round
grooves that were filed into each of the vertical 1/8 light-plywood
spars before we joined the wing, it is very important to also install
the external mounts for extra security. Please do not omit this
step.
Wing Installation: Slide the fuselage onto the wing, and position
it against the plywood mount pieces. Mark the areas in the top and
bottom of the wing opening where clearance slots will be required
to let the fuselage slide over the mount pieces.
Remove the wing, and use a sharp #11 blade in an X-Acto
knife handle to cut the notches to clear the bellcrank mount
pieces. Finish these notches with a sanding stick.
Measure the fuselage width at the front and rear of the wing
opening, and use a pencil to transfer these marks to the
corresponding places on the upper surface of the wing. Make a
mark that is half the fuselage width on either side of the wing
centerline. Do this at the front and the rear of the wing.
Slide the wing into place, and align it with the pencil marks.
Use a square to do the final alignment. The angle where the
fuselage doubler and the LE meet should be 90°.
Check this angle on both sides, to make sure you have the wing
in square. Check the angle from the front in the same manner,
using the square against the side of the fuselage doublers and the
top of the wing surface for reference.
When you are certain that the wing is square to the fuselage in
every respect, tack-glue it to the fuselage
in two or three places using mediumviscosity
cyanoacrylate. (I have switched
to Zap CA glue and have found it to be
excellent!)
Mix a half ounce of 45-minute epoxy
and add a generous amount of white
microballoons. Using a small balsa
applicator, force the epoxy into any gaps
between the wing and fuselage, and make a
small fillet around the entire wing/fuselage
joint. Wipe off any excess epoxy and let
this assembly cure thoroughly.
Wing and Tail Alignment: Most
experienced CL Precision Aerobatics
(Stunt) fliers would, I’m sure, agree that
installing the stabilizer accurately and with
no negative incidence in relation to the
wing is the most important step in building
a Stunt model. If the stabilizer is
improperly lined up, the result will be an
airplane that will never perform up to the
design’s potential.
If the stabilizer/wing incidence is off by
even a bit, the model will never groove
properly and will never “lock” after a turn
during a square maneuver. I cannot stress
this enough; the stabilizer must be
installed perfectly.
Some believe in adding a tiny amount
of positive incidence (stabilizer LE slightly
elevated). I’ve never found this necessary,
and I try to make my installations zerozero.
I will concede this point. If the
stabilizer is installed with any incidence, it
should be slightly to the positive side. A
tenth of a degree of positive incidence
would be a good compromise.
There are probably as many alignment
ideas and procedures as there are model
builders. Most builders are also good
“backyard” engineers, and many of them
come up with fixtures that do the job of
alignment well. I have come up with a
simple fixture that does the job for me.
I use the side view of the plans of the
model I’m building to make my alignment
fixture. I start by ensuring that the
dimensions and placements of the surfaces
on the drawing are accurate.
Then I find two pieces of 1/8 balsa that
are long enough and wide enough to make
alignment plates that will sit on a flat table
and have the wing opening and stabilizer
openings cut into them. I tape the 1/8 balsa
portions together and position this
assembly under the plans.
I use a pin to punch holes around the
wing opening and tail opening. Before I
remove the plans from the balsa, I make
holes to allow me to draw a baseline that
is parallel to the wing and stabilizer
centerline. Then I remove the plans and
carefully connect the dots with a finepoint
pen.
The next step is to accurately cut out
the fixture plates. I use a Dremel scroll
saw to do this. I cut just inside the lines
and test and then fit the wing snugly into
its opening, using a sanding stick to
achieve a perfect fit.
I remove the tape that is holding the
two plates together. One fixture plate will
slip over the right wing half and the other
will slip over the left wing half. They
should be positioned far enough onto the
wing halves to allow the stabilizer to be
captured in its fixture slot on either side of
the fuselage.
Position the fixture on a flat table and
install the stabilizer into its slot in the
fuselage and into the slots in the alignment
fixture. The fit at the fuselage should not
be so snug that it forces the stabilizer into
a tilt either way. There should be no
“slop” in the slot, but it should not be too
tight. Think Goldilocks and the porridge:
just right.
Check the measurement from the rear
edge of the wing TE to the stabilizer TE
on each side of the fuselage. Make this
measurement as far out on the stabilizer
on each side as possible. The
measurements should match.
When you are certain that the
stabilizer is square in all axes, carefully
tack-glue it to the fuselage using thin
cyanoacrylate. Check the alignment one
more time, and then permanently glue
the stabilizer to the fuselage using an
epoxy-and-microballoon mix.
Use only enough epoxy to ensure a
good bond. Epoxy is heavy, and you don’t
want to add unnecessary weight to the
back of the Hole Shot.
That’s it for this month. Next time I’ll
cover the final details of assembly and
finish.
Till then, fly Stunt! MA
Sources:
Precision Aerobatics Model Pilots
Association
www.control-line.org