An Electrified Stunter - 2011/05

me time to concentrate on my CL Precision
Aerobatics (Stunt) pattern and makes me a
better flier without worrying about whether or
not the engine is going to quit.
I started with an APC 12 x 6EP propeller
and was satisfied with my flights. Then I
switched to an APC 12 x 6 pusher, or
reversible-pitch propeller. There was no
comparison. The pusher setup keeps the model
out on the lines, and the line tension is
unbelievable when performing outside
maneuvers.
You can also see the effect it has when
taking off; the airplane pulls to the outside of
the circle. This is quite an advantage when
using a stooge.
The sidebar provides details about the
electric components I am using, which include
3000 mAh 20C four-cell Turnigy batteries. I
put back 72%-74% after each flight.
I have more than 30 flights on each
of my four batteries, which cost
approximately $30 each. When you
consider the cost of fuel, the batteries
have paid for themselves.
Next year I plan on using the new
Nano-Tech batteries, which claim to
have better longevity and faster
charging capabilities.
I have received many compliments
at the flying field about my power
system and was asked to write an
article for anyone who is interested in
electric flight. So I hope you find it
helpful.
When getting started in electric CL,
begin with a profile airplane; that way
all components are mounted on the
outside and easily accessible. I have
included a picture of my scratch-built
Apache and will provide some details
about how I constructed it.
Wing: The wing is constructed from
ribs from the Vector 40. Trace Rib 1
onto hard stock as a template for the
wing cutout in the fuselage and draw
a centerline.
60 MODEL AVIATION
Stunter
An
by Ron Heckler
A side view shows the shape
of the rudder and canopy
cutout with simulated pilot
and console.
A close-up of the electronics, including a Turnigy 4240-900 motor mounted on a 3/4-inch
aluminum angle iron, a Will Hubin FM7 timer, and a Phoenix-45 speed control mounted on the
landing gear to act as a heat sink. The propeller is a reverse-pitch APC 12 x 6.
I HAVE BEEN sport-flying CL models with
internal-combustion (IC) engines for more
than 35 years and have gone through all the
problems and frustrations other fliers have. In
fact, it was getting to the point where I was
ready to give up the hobby.
Then at the beginning of this year, Will,
my flying buddy, suggested that I fly his
electric-powered P-40. I cannot fully describe
how I felt about the ease of starting and flying
power; after the first flight I was convinced
that that was what I wanted, and I flew his
model three more times that day.
Before starting from scratch I decided to
convert one of my profile IC-powered aircraft
to electric. Will and I selected the components
that would work on my model. It turned out to
be a great success.
The best feature is that there is no drop in
power whatsoever throughout the flight! Once
you set the rpm, flight time, delay time, and
either rpm or governor mode on the timer,
everything remains the same flight after flight.
You can even set the timer for a 21/2-
minute flight to test all of the settings, make
adjustments if necessary, and then fly 21/2
minutes more on the same battery before
having to change it.
When everything is the way you want, it’s
a matter of pushing the button and flying your
aircraft. This is impossible with engine power.
The fact that all flights are consistent gives
Photos by the author
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May 2011 61
The battery is held on with Velcro between hooks with rubber bands.
Deans Ultra plugs are used to connect the battery and the ESC.
Could electric
power systems
change the
way you f ly?
The pusher propeller keeps this airplane
out on the lines, and line tension when
performing outside maneuvers is
unbelievable to the author.
The author with
his original-design:
the RH Stunter
Apache built for
electric power.
05sig2.QXD_00MSTRPG.QXD 3/23/11 12:28 PM Page 61
The ribs are spaced so that the complete
span, including wingtips, is 50 inches. I glued
16 pennies to the outboard tip, eight on the top
and eight on the bottom, for tip weight; that is
equal to 11/4 ounces. If desired, you can install
an adjustable tip-weight box instead.
Excess balsa is removed from the ribs, to
reduce weight. The leadout wires are
constructed from 7 inches of 1/32-inch-diameter
music wire connected to the bellcrank, and the
balance is flexible leadout cable. These are
connected by using a piece of 3/32-inch-diameter
copper tubing.
The 1/32 music wire and flexible cable are
pushed through the tubing in opposite directions
and then bent back over the tubing, wrapped,
and soldered or epoxied. Doing this keeps the
leadout wire from wearing through the
bellcrank and eliminates the chance of the solid
leadout wires being bent outside the wing.
Brodak Manufacturing sells laser-cut ribs
for the Vector wing. If you decide to use a
Vector foam wing, you can purchase one from
Randy Smith or Bob Hunt.
Fuselage: Required materials are one piece of
1/2 x 4 x 36-inch balsa, one piece of 1/2 x 3 x 36-
inch balsa, one piece of three-ply 3/32 x 12 x 12,
and 1/2 x 3/8 hard maple.
Sand the top and bottom of the 1/2 x 4 x 36
piece for a straight edge, and draw a centerline.
Draw an angle at the rear that is 31/4 inches
from the bottom, toward the front for the angled
rudder. (See diagram “A.”)
Measure 9 inches from the front, on the
centerline, and trace the wing cutout. Measure
14 inches from the end of the cutout, and use a
T-square to mark this spot at the top of the
fuselage.
Draw a line 3/8 inch down and back toward
the front of the fuselage. Make sure that this
line is parallel to the centerline, because it is the
cutout for the stabilizer and must be straight.
(See diagram “B.”)
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These drawings should aid you in constructing your
own Apache. They are referenced in the text.
The Apache is happy with either side up during flight. The author finished it with
Black Baron covering and MonoKote Trim Sheets.
Electric Apache Specifications
Wingspan: 50 inches
Length: 39 inches
Weight: 3 pounds, 2 ounces
Motor: Turnigy 4240-900 brushless outrunner with Castle Creations Phoenix-45 ESC
Battery: Four-cell, 3000 mAh Turnigy Li-Poly
Propeller: APC 12 x 6 pusher
05sig2.QXD_00MSTRPG.QXD 3/22/11 2:16 PM Page 62
Make a U-shaped motor cutout to allow
clearance for the power plant you are using. I
am using a Turnigy 4240-900 with a 21/4-inch
spinner. I started 1/2 inch from the top, and the
shape for this motor is 21/8 inches long and 2
inches wide. I made two 11/2-inch-long slots
for the motor mounts at the top and bottom of
the cutout.
Drill a hole in the center of the cutout to
allow the shaft of the motor to turn freely.
(See diagram “C” for correct locations.)
The piece of balsa between these two slots
is left solid for the doublers. Glue the motor
mounts in place and let dry. Draw an angle
from the bottom of the spinner to the fuselage,
to simulate air intake.
Trace the front of the fuselage on plywood
doublers. Cut and sand the edges at an angle,
to blend with the fuselage around the wing
area, and then glue in place.
Turtledeck: A 1/2 x 3 x 36-inch piece of balsa
is required. Sand for a straight edge, and line it
up with the top of the fuselage. Place it on top
of the fuselage 8 inches from the front.
Tape those pieces together and draw the
shape of the canopy 21/2 inches high
maximum and down to 1/4 inch at the end of
the fuselage. Cut at an angle to match the end
of the fuselage.
Draw the inside dimensions of the canopy,
which will be 63/4 inches long and 23/8 inches
high, maximum. When this is cut out, it will
lighten the weight of the turtledeck. (See
diagram “D.”)
I decided to cover that area with clear
MonoKote. A pilot could also be added.
Plane the rear of the fuselage and
turtledeck to 1/4 inch, to blend with the rudder.
Cut lightening holes in the fuselage. (Shown
in diagram “E.”) Diagonals are left to support
the covering. You can also cut a few holes in
the turtledeck, to lighten it.
Rudder and Fin: A piece of 1/4 x 3 x 36-inch
balsa is required.
Lay the fuselage on its side. Place the
balsa sheet at the rear, against the angle of the
fuselage. (See diagram “F.”) Leave a bit of
extra at the bottom (approximately 1/2 inch)
for final shaping and blending with the rear of
the fuselage.
Tape the balsa piece to the fuselage and
measure 8 inches up from the bottom. Using a
straightedge, draw a line parallel to the top of
the fuselage. Cut the 1/4 balsa at this line, and
you have the rudder 3 x 81/2 inches.
Make the fin from the remaining sheet of
1/4 balsa. Place fuselage on its side. Tape the
turtledeck in place at the top, flush with the
rear, and tape the rudder to the rear of the
fuselage extending 1/2 inch, as before.
Make a light mark on the turtledeck 10
inches from the rear. This is where the fin will
end and blend into the turtledeck.
Place the piece of 1/4 balsa lengthwise
under the fuselage and rudder past the 10-inch
mark. Draw a line from that mark tracing the
turtledeck to the rudder to get the proper angle
and contour.
Sketch a line straight down from the top of
the rudder to the turtledeck and then from the
top of the rudder to the 10-inch mark on the
turtledeck. This makes the fin.
When you cut out the fin, make the angle
from the 10-inch mark to the rudder by hand
to match the contour of the turtledeck. You
can cut the other lines with a straightedge.
Trial-fit and glue the pieces together with
no offset. (See diagram “G.”) When dry,
draw a section for lightening holes. (Shown
in diagram “H.”) Cut out the areas at the top
left and bottom right, leaving diagonals to
support the covering.
Stabilizer and Elevators: A 3/8 x 3 x 36-inch
and a 1/4 x 3 x 36-inch piece of balsa are
needed for this section.
Draw the stabilizer as shown (see diagram
“J”) on the 3/8 balsa. It should be 22 inches
long and 3 inches wide at the center,
decreasing to 2 inches wide at each end. (See
diagram “J.”)
Measure 1/4 inch on each side of the center
and draw straight lines. This creates gluing
area for the fuselage and centering.
Draw the elevators on the 1/4 balsa. They
should be 22 inches long and 3 inches wide at
the center, dropping to 2 inches wide at each
end from the stabilizer. (See diagram “K.”)
Measure 3/8 inch on both sides of center,
for fuselage clearance, and draw straight lines
(cutting lines). Mark and drill joiner wire
holes before cutting.
Tape to the stabilizer and shape the
ends as desired. Then cut apart and add
joiner wire.
Flaps: Two 1/4 x 3 x 36-inch pieces of balsa
are required. Make full flaps 3 inches wide at
the fuselage to 1 inch wide at the wingtips.
Landing Gear: This component is made
from 1/8 x 3/4-inch aluminum stock, bent in a
vise and drilled for lightness.
The preformed Sig Fazer landing gear or
any profile landing gear that Brodak sells,
such as that for the Cardinal, will work just
as well, because it is bolted to the sides of the
fuselage.
Finishing: The Apache’s total flying weight
(including an 11-ounce battery) is 50 ounces.
When finishing your model, make it as light
as possible. I like to use iron-on covering.
I covered the Apache with Black Baron
material and MonoKote Trim Sheets (using
the soapy-water method). Since no liquid fuel
will be used, you can paint your model
without using fuelproof paints. But be careful
at the flying field to keep your airplane away
from IC engine exhaust.
I am sure you will enjoy electric CL flying
once you try it and see all of the advantages
for yourself. MA
Ron Heckler
[email protected]
Sources:
Brodak Manufacturing
(724) 966-2726
www.brodak.com
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