CL AEROBATICS 2013/07 The Vulcan’s battery mount

Above: Here are the parts required
for the rib-type battery mount that
Bob is using in the Vulcan.
Below: This
battery mount
bridge is made
from 3/8 x 1/2-
inch hard maple.
It mounts to
the 1/8-inch
birch plywood
former at the
rear of the motor
compartment,
providing a
mounting surface
and hold-down
for the battery
mount plate.
The bridge piece is
secured to the plywood
former with two 4-40
machine screws.
The Vulcan’s battery mount
by Bob Hunt
[email protected]
As promised, this time I’ll discuss
a battery mount for my project
Vulcan. I have a specifi c way to
mount batteries in my CL models that
makes sense to me.
There are probably as many different
ways to safely mount a battery in a CL
model as there are people who want to
mount batteries in a CL model! What
I’m going to show you is one method.
Feel free to modify, rework, redesign, or
totally discard my mounting system for
one that makes sense to you.
As do most, I started out mounting
my batteries using hook-and-loop
(Velcro) fasteners. I quickly stopped
doing that when I saw a battery that
was held in with that type of fastener
eject from a CL model.
Some still use that method and don’t
seem to have any problems, but my
image of a perfectly good battery fl ying
through the air and then impacting
the tarmac is still vivid; I wanted
something more secure. I’m basically
a “belt-and-suspenders” person, so I
opted to use a system that holds the
battery in with bolts.
When I started searching for a better
way to mount my battery packs, I
called my brainstorming buddy, Dean
Pappas, and asked him for his thoughts.
We studied the forces involved and
concluded that
there was no
signifi cant force
exerted on
the pack that
would make it
move inward
toward the pilot;
centrifugal force
takes care of that.
All we needed
to come up with
was something
that kept the
battery from
moving up or
down under fl ight
loads.
We also
concluded that we needed to install a
soft “bumper” on the inner face of the
outside fuselage side for the battery to
rest against in fl ight. Dean and I said
nearly simultaneously, “We need a rib!”
A simple, light, plywood plate,
oriented vertically, captured the battery
pack from front to back. At the time,
I was retrofi tting my Genesis Extreme
with an electric system, and decided to
try the “rib” battery mount. The model
has fl own hundreds of fl ights with that
battery mount system and has proven
to be strong and reliable.
As you may recall, I installed a birch
plywood former slightly aft of the
motor bay in the Vulcan’s fuselage. This
former had a large “U” shape cut from
its center to allow air to fl ow out of the
motor bay.
I used the narrow, vertical legs on
this former as a mount for the front
battery hold-down bridge. Before
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The battery pack is
positioned in the
plywood rib and
is secured by the
horizontal mount
support plate. Secure
the support plate
on top of the bridge
piece with two 4-40
screws.
installing the plywood former, I drilled
and installed two 4-40 blind nuts on its
front face. These nuts allow a custommade
bridge that has two 4-40 blind
nuts to be installed on its bottom face
to accept the bolts that secure the
battery holder.
The result is a removable front
battery hold-down. The accompanying
photos should answer questions about
this part.
The rib that
holds the battery
pack can be
custom designed
to suspend it in
the electronics
bay (what used to be called the tank
compartment) wherever you desire.
This system allows you to make
several ribs and experiment with
battery placement vertically and
horizontally within the electronics bay
so that you can affect vertical (roll) and
horizontal (pitch) CG changes at will.
The battery rib is designed with a tab
at the rear that fits snugly into a slot in
the light plywood former at the rear
of the electronics bay. The rib should
be custom fitted to the specific battery
pack you are using.
Packs of a certain mAh capacity
from each of the manufacturers tend
to be the same size, so one rib should
accommodate all of your packs. You
can also experiment with ribs that
place the battery in different positions
within the electronics bay and then
make several ribs—one to fit each of
your battery packs—after you find the
optimum placement.
The actual fit of the battery inside
the rib should be such that the rib is
not exerting too much pressure on the
outside of the pack, but snugly enough
so that the pack will not easily move
within the rib.
A light friction fit is desired. You
can use some clear acrylic adhesive to
secure the battery within the rib or
secure it to the rib with a short piece of
1/2-inch-wide reinforced packing tape.
I make a hold-down plate that
interlocks with—and is securely
glued to—the battery rib. This hold-
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The rear of the battery rib has
a tab that slips into a slot in
the former at the rear of the
electronics bay. The front
support plate is bolted
to the bridge piece.
down plate prevents the battery from
“rocking” within the rib. The front of
this hold-down plate extends forward
and rests on top of the front hold-down
bridge mentioned earlier.
There are two slots in the front of
the hold-down plate that correspond
to the holes in the bridge piece that is
fitted with the blind nuts. This is what
secures the battery within the model.
I mentioned a “bumper.” I like to
use a small piece of adhesive-backed
weather strip attached to the outside
wall of the electronics bay as a bumper
to cushion the battery as it presses
against the inside wall of the fuselage
side under centrifugal force.
The pieces I use are nominally
1-inch long and 1/2-inch high. I use one
positioned near the front of the pack
and one near the rear of the pack.
Depending on how wide the fuselage
is, you may have to
make small balsa pillars
on which to mount the
bumpers to center the
battery in the fuselage.
Study the
accompanying photos
for details of the battery
mount fabrication and
installation.
SOURCES:
Precision Aerobatics Model Pilot’s
Association
www.control-line.org
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