Control Line Aerobatics - 2008/03

Finishing the fuselage on the Hole Shot
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Control Line Aerobatics Bob Hunt
Also included in this column:
• Randy Smith landing gear
and Enya engines
• The importance of a drill
press
• Thoughts about rudder
offset
• Bob’s favorite fillet material
• Round homemade holes
• Bending a wire tail-wheel
strut
Left: Completed Hole Shot profile
fuselage with engine and landing gear testmounted.
The fuselage is carved and
sanded to a smooth contour. The 13/4-
inch-diameter spinner fits the front-end
shape perfectly.
The author selected the Enya SS25 to power the model. Aero
Products now handles the entire line of Enya engines.
Bob used SuperFil for the fillet between the fin and fuselage. It will
be used to fillet the wing to the fuselage later.
I LEFT THE Hole Shot project the last
time with the fuselage cut out, the engine
mounts installed, the plywood doublers
epoxied in place, and the entire fuselage
finish-sanded and almost ready for the wing
and tail components. Before leaving the
fuselage there are a few more things to do.
The plans show—I mentioned this in the
last column—bent-wire landing gear for the
model. Since the January column I found a
nice set of bent sheet-aluminum landing
gear that is much easier to install.
If you haven’t already made and installed
your landing gear, consider the aluminum
units. Randy Smith at Aero Products has this
gear set available. When you order, ask for
the small profile landing gear and mention
that you want it for the Hole Shot.
On the subject of Aero Products, the
company is now handling the entire line of
Enya engines. I bring this up not only
because Enya has a great line of finerunning
and durable model power plants,
but also because the company offers many
engines with CL venturis installed and ready
for use in our models.
That’s right; at least one more company
realizes the potential of the CL market and
is willing to produce products specifically
for our use!
Some years ago (roughly 1990) we
installed an Enya SS30 in my son, Robby’s,
RD-1. That engine ran extremely well for
many flights in that airplane and then in
other models as well. We gave the SS30 to
another modeler when we were finished
with it, and he is still running it. That power
plant is still producing strong runs and still
starts easily.
Enya engines have always been CL
fliers’ favorites because of their longevity.
The material used in the pistons and liners is
harder than normal, which means a bit
longer break-in time, but it also means
March 2008 153
03sig5.QXD 1/24/08 3:18 PM Page 153longer overall life. The SS30 also exhibited
a great 2/4-break CL Aerobatics (Stunt) run
with a 10 x 4 Rev-Up propeller, with no
additional rework required.
In speaking with Randy about the Enya
line, I learned that there is an SS25 Stunt
engine now available. I ordered one for use
in the project Hole Shot.
The SS25 Stunt weighs 7 ounces and is
priced near $79. A tube-type muffler is
included at that price (although I’ll probably
replace it with a lighter “tongue”-type
muffler).
Randy has informed me that there are
currently 16 Enya CL-ready engines in the
line, ranging in displacement from .09 to
.61. He also said that a new Enya CL fourstroke
is in the offing. For more information
about the SS25 Stunt, or any others in the
Enya line, contact Randy at Aero Products.
Now back to the project.
It is easier to install the engine and get the
bolt-hole placements accurate before
installing the wing. The same holds true for
the tank mount and the landing-gear mount
holes. Spot the holes for the items to be
mounted to the fuselage, and then drill the
holes using a quality drill press. This brings
me to the next piece of necessary modelbuilding
equipment.
If you are going to build models at
anything above the most rudimentary level,
a drill press is a critical item to have in your
shop. You can purchase a relatively good
one at a reasonable price from Lowe’s, The
Home Depot, Sears, or other retail homeimprovement
stores.
I suggest searching on the Internet and
comparing prices and features; you might
find that you can get a reasonably priced,
more robust machine that will serve not
only as an accurate drilling device, but as
one that can be fitted right away, or later,
with a milling machine X/Y-axis table,
which will allow you to make many special
parts for your models that may not be
readily obtainable.
A brand I keep hearing good things
about is Grizzly, which has an extensive line
of reasonably priced, wonderful-quality
machine tools. Go to the company’s Web
site and click on the machinery-selection tab
and then on the drill-press-selection tab.
There you will find several excellent drill
presses at affordable (not cheap) prices.
One interesting choice is the model
H0625 Oscillating Drill Press, which allows
you to hold spindle sanding drums in the
drill chuck. The oscillating motion yields a
great detail-sanding tool for which you will
find numerous uses in model building.
Be prepared to spend at least $100 when
shopping for a decent drill press. Think of it
as one more investment in model quality for
the long term.
All the required holes have been drilled in
the Hole Shot fuselage, and everything has
been test-mounted. You will probably have
to grind away some of the maple engine
mounts on either side of the engine to allow
it to sit flat on the plywood doubler. I prefer
to use a sanding drum and my rotary hand
tool for this chore.
The power tool you will use most often
in model building is the ubiquitous hand
tool; it is indispensable. Fortunately these
tools are easy to find at home-improvement
stores or online, and they are fairly
inexpensive.
There are many power hand-tool
manufacturers and dozens of different bits,
as well as several useful attachments that
expand the hand tool’s usage. Purchase one
for which you can easily obtain bits and
add-ons. Back to the Hole Shot.
It is important to remember to contour
the mounts to almost touch the lower
portion of the engine case, which is usually
curved. This way you will be removing no
more material than necessary, and more
strength and vibration resistance will be the
result.
The Enya SS25 is an exception to this
rule; the lower end is rather square.
However, not too much mount had to be
ground away, and it fit fine.
While the engine is test-fit to the
fuselage, the blind mounting nuts are not
permanently installed. But you should
counter-drill the blind-nut side of the bolt
holes to accept the blind-nut barrel.
After everything in the nose area has
been test-mounted on the profile fuselage,
make and install the vertical fin. Thiscomponent is made from 1/8 medium to
medium-soft sheet balsa. The grain in the fin
should run vertical and parallel to the fin LE.
This will give it an amazing amount of
strength and warp resistance when it is glued
to the fuselage.
No rudder offset is used on this design. I
have never liked inducing yaw with rudder
offset, and I find that my models fly much
cleaner through maneuvers without it. Speed
creates lift, and the speed will vary as the
model climbs and dives. The amount of yaw
induced by rudder offset will also vary
because of the speed variations.
As the model dives and picks up speed—
as in the diving portion of an Inside Loop—
the rudder offset will force the nose more
toward the outside of the circle. As the
model goes through the bottom of the loop
and begins to climb, the speed will diminish
and the nose of the model—which was
pushed outward in the dive—will start to
swing inward.
The result is less line tension in the
climbing portion of the maneuver and
generally varying line tension throughout all
maneuvers. It’s subtle, but it is a factor.
A thin fillet can be created, if desired, to
smoothly fair the fin into the top of the
profile fuselage. I prefer to use a product
called SuperFil: a two-part-mix epoxy filler
that works easily, has a fairly long pot life,
and sands extremely well when cured. I get
mine from F&M Enterprises.
The last item that is mounted to the fuselage
is the 1/16-inch-diameter-music-wire tailwheel
strut. It is bent so that it fits into a 1/4-
inch hardwood dowel that is sunk into the
bottom of the fuselage.
The dowel must, in turn, be drilled to
accept the wire. A small channel to allow
the wire to exit the side of the dowel will
have to be made. Use your new power
hand tool fitted with a grinding bit for this
chore.
The hole in the fuselage to accept the
dowel can be made by “skiving” the end of
a piece of 1/4-inch-outside-diameter brass
tubing. You can essentially sharpen the
tube’s end by running a #11 blade around
the inside perimeter of the tube at
approximately a 60° angle. The blade will
cut the brass to a fine edge. The result is a
neat cutting tool that will auger into balsa
when pushed and twisted, and it will leave
a clean hole.
It is a good idea to purchase several
different-diameter brass tubes from your
local hobby shop and skive the ends as I
described. This will be another set of
building tools for which you will find
many uses.
For blind holes, such as the one for the
tail-wheel mount dowel, you may have to
use the skived brass tubing to make the
hole and then slice through the side of the
fuselage at the proper point with a thin
#11-blade knife to get the plug of balsa to
release from the fuselage blank.
Sometimes the plug comes out with the
tube when you remove it, and sometimes it
does not.
You should bend the tail-wheel strut
with a pair of round-nose pliers, which
leads to the next piece of required
modeling equipment. All model builders
need a full range of pliers.
Needle-nose and square-nose pliers are
perhaps the most useful tools for mostmodel-building applications, but they
should not be used to bend wire. Bending
around a square edge will usually result in a
fracture of the wire. You need to bend wire
with a slight radius so it won’t crack at the
point of the bend.
I suggest that you buy at least two pairs of
round-nose pliers. One should have fairly
small-diameter jaws to bend wire as large as
1/32 inch in diameter, and one pair should
have somewhat larger-diameter jaws to bend
wire with a diameter as large as 3/32 inch.
I do not recommend using pliers to bend
wire that is larger than 3/32 inch in diameter.
At that point you will need a dedicated wire
bender, which I will discuss in a future
column.
After your model’s tail-wheel strut is
properly bent and the 1/4-inch dowel is
imbedded and glued in the fuselage, notch out
the bottom of the fuselage aft of the dowel to
allow the tail-wheel strut to sit flush. Glue the
strut in place using an epoxy-andmicroballoon
mix.
When the assembly has cured, lightly
sand the area smooth and then cover the
exposed strut and the adjacent area with a
piece of 3/4-ounce fiberglass or .02 carbon
mat. This piece can be glued in place using
thin cyanoacrylate.
That’s it. The fuselage is ready for the wing
and tail—or is it? Tune in next time for an
interesting twist in this project. MA
Sources:
Aero Products
(678) 407-9376
www.aeroproduct.net
Grizzly Industrial, Inc.
(800) 523-4777
www.grizzlyimports.com
F&M Enterprises
(817) 279-8045
www.fm-enterprises.com