IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
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10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
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10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
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10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
Visit the MODEL AVIATION Digital Archives!
Featuring a searchable database of Model
Aviation issues and articles from 1975 to 2000.
This is by far one of the best
efforts AMA has made to
construct something that is for
every member.
—Marco Pinto
Peninsula Channel Commanders
San Francisco CA
“
”
Find it at www.modelaircraft.org. On the main page, click
on the “Members Only” section, and follow the directions
to access this great membership benefit!
10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
On August 13, 2001, on its second high altitude flight, the
Helios (built for NASA by AeroVironment) flew to 96,863
feet, shattering the world altitude record for both propeller
and jet-powered aircraft. PRO-SET ® epoxy was used to
fabricate carbon fiber and fiberglass parts for the Helios
project. PRO-SET is recommended for high performance
applications utilizing carbon fiber and aramid fabrics.
On August 11, 2003, Maynard Hill’s TAM-5 (Spirit of Butts
Farm) successfully crossed the Atlantic Ocean, flying a total
of 38 hours 23 minutes while covering 1,888.3 miles.
WEST SYSTEMS® epoxy was used in the construction of the
TAM-5 and is an excellent choice for construction with
wood, foam and fiberglass.
Product guides for WEST SYSTEM and PRO-SET epoxy systems are free with any purchase. Postage
will be charged if requested separate from an order. Dealer and manufacturer inquiries are welcome!
CST is an authorized distributor for PRO-SET and WEST SYSTEM epoxies which are registered trademarks of Gougeon Brothers, Inc.
CST
The Composites Store Inc.
www.cstsales.com
Order on-line or by phone
1-800-338-1278
Tech Support: 661-823-0108
Imagine how our EXTREME EPOXIES can help you!
Epoxy; The adhesive to use for Extreme Performance!
Here’s just a sample of what two of our customers
were able to do with our EXTREME EPOXIES.
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10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
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• Specially designed Rubber Seals for “Optimum” Performance
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all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
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Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
Visit the MODEL AVIATION Digital Archives!
Featuring a searchable database of Model
Aviation issues and articles from 1975 to 2000.
This is by far one of the best
efforts AMA has made to
construct something that is for
every member.
—Marco Pinto
Peninsula Channel Commanders
San Francisco CA
“
”
Find it at www.modelaircraft.org. On the main page, click
on the “Members Only” section, and follow the directions
to access this great membership benefit!
10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
On August 13, 2001, on its second high altitude flight, the
Helios (built for NASA by AeroVironment) flew to 96,863
feet, shattering the world altitude record for both propeller
and jet-powered aircraft. PRO-SET ® epoxy was used to
fabricate carbon fiber and fiberglass parts for the Helios
project. PRO-SET is recommended for high performance
applications utilizing carbon fiber and aramid fabrics.
On August 11, 2003, Maynard Hill’s TAM-5 (Spirit of Butts
Farm) successfully crossed the Atlantic Ocean, flying a total
of 38 hours 23 minutes while covering 1,888.3 miles.
WEST SYSTEMS® epoxy was used in the construction of the
TAM-5 and is an excellent choice for construction with
wood, foam and fiberglass.
Product guides for WEST SYSTEM and PRO-SET epoxy systems are free with any purchase. Postage
will be charged if requested separate from an order. Dealer and manufacturer inquiries are welcome!
CST is an authorized distributor for PRO-SET and WEST SYSTEM epoxies which are registered trademarks of Gougeon Brothers, Inc.
CST
The Composites Store Inc.
www.cstsales.com
Order on-line or by phone
1-800-338-1278
Tech Support: 661-823-0108
Imagine how our EXTREME EPOXIES can help you!
Epoxy; The adhesive to use for Extreme Performance!
Here’s just a sample of what two of our customers
were able to do with our EXTREME EPOXIES.
FIBERGLASS CLOTH
Premium Grade
3/4 oz 38”W 10 yrd. min. $2.50 yd.
Lower Prices 30 yds. & up
Other Weights Available
TinLin’s
17 Andrews Drive • Daleville, AL 36322
(334) 598-2287 • 4:00 - 10:00 CST
10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
• NEW! High Performance Engine Kits
• Designed to Resolve Your “Leakage” problems
• Specially designed Rubber Seals for “Optimum” Performance
• Also Available as a Ceramic Hybrid Bearing
• High Performance Polymite Retainers
• Additionally we offer a full range of wheel bearings, and full replacement kits, for
all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
1500 SW 30th Ave., Suite #3 • Boynton Beach, FL 33426
Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
Visit the MODEL AVIATION Digital Archives!
Featuring a searchable database of Model
Aviation issues and articles from 1975 to 2000.
This is by far one of the best
efforts AMA has made to
construct something that is for
every member.
—Marco Pinto
Peninsula Channel Commanders
San Francisco CA
“
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on the “Members Only” section, and follow the directions
to access this great membership benefit!
10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
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TinLin’s
17 Andrews Drive • Daleville, AL 36322
(334) 598-2287 • 4:00 - 10:00 CST
10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
• NEW! High Performance Engine Kits
• Designed to Resolve Your “Leakage” problems
• Specially designed Rubber Seals for “Optimum” Performance
• Also Available as a Ceramic Hybrid Bearing
• High Performance Polymite Retainers
• Additionally we offer a full range of wheel bearings, and full replacement kits, for
all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
1500 SW 30th Ave., Suite #3 • Boynton Beach, FL 33426
Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
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Featuring a searchable database of Model
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This is by far one of the best
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construct something that is for
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on the “Members Only” section, and follow the directions
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10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
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10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
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10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
Visit the MODEL AVIATION Digital Archives!
Featuring a searchable database of Model
Aviation issues and articles from 1975 to 2000.
This is by far one of the best
efforts AMA has made to
construct something that is for
every member.
—Marco Pinto
Peninsula Channel Commanders
San Francisco CA
“
”
Find it at www.modelaircraft.org. On the main page, click
on the “Members Only” section, and follow the directions
to access this great membership benefit!
10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
On August 13, 2001, on its second high altitude flight, the
Helios (built for NASA by AeroVironment) flew to 96,863
feet, shattering the world altitude record for both propeller
and jet-powered aircraft. PRO-SET ® epoxy was used to
fabricate carbon fiber and fiberglass parts for the Helios
project. PRO-SET is recommended for high performance
applications utilizing carbon fiber and aramid fabrics.
On August 11, 2003, Maynard Hill’s TAM-5 (Spirit of Butts
Farm) successfully crossed the Atlantic Ocean, flying a total
of 38 hours 23 minutes while covering 1,888.3 miles.
WEST SYSTEMS® epoxy was used in the construction of the
TAM-5 and is an excellent choice for construction with
wood, foam and fiberglass.
Product guides for WEST SYSTEM and PRO-SET epoxy systems are free with any purchase. Postage
will be charged if requested separate from an order. Dealer and manufacturer inquiries are welcome!
CST is an authorized distributor for PRO-SET and WEST SYSTEM epoxies which are registered trademarks of Gougeon Brothers, Inc.
CST
The Composites Store Inc.
www.cstsales.com
Order on-line or by phone
1-800-338-1278
Tech Support: 661-823-0108
Imagine how our EXTREME EPOXIES can help you!
Epoxy; The adhesive to use for Extreme Performance!
Here’s just a sample of what two of our customers
were able to do with our EXTREME EPOXIES.
FIBERGLASS CLOTH
Premium Grade
3/4 oz 38”W 10 yrd. min. $2.50 yd.
Lower Prices 30 yds. & up
Other Weights Available
TinLin’s
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(334) 598-2287 • 4:00 - 10:00 CST
10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
• NEW! High Performance Engine Kits
• Designed to Resolve Your “Leakage” problems
• Specially designed Rubber Seals for “Optimum” Performance
• Also Available as a Ceramic Hybrid Bearing
• High Performance Polymite Retainers
• Additionally we offer a full range of wheel bearings, and full replacement kits, for
all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
1500 SW 30th Ave., Suite #3 • Boynton Beach, FL 33426
Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
Visit the MODEL AVIATION Digital Archives!
Featuring a searchable database of Model
Aviation issues and articles from 1975 to 2000.
This is by far one of the best
efforts AMA has made to
construct something that is for
every member.
—Marco Pinto
Peninsula Channel Commanders
San Francisco CA
“
”
Find it at www.modelaircraft.org. On the main page, click
on the “Members Only” section, and follow the directions
to access this great membership benefit!
10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
On August 13, 2001, on its second high altitude flight, the
Helios (built for NASA by AeroVironment) flew to 96,863
feet, shattering the world altitude record for both propeller
and jet-powered aircraft. PRO-SET ® epoxy was used to
fabricate carbon fiber and fiberglass parts for the Helios
project. PRO-SET is recommended for high performance
applications utilizing carbon fiber and aramid fabrics.
On August 11, 2003, Maynard Hill’s TAM-5 (Spirit of Butts
Farm) successfully crossed the Atlantic Ocean, flying a total
of 38 hours 23 minutes while covering 1,888.3 miles.
WEST SYSTEMS® epoxy was used in the construction of the
TAM-5 and is an excellent choice for construction with
wood, foam and fiberglass.
Product guides for WEST SYSTEM and PRO-SET epoxy systems are free with any purchase. Postage
will be charged if requested separate from an order. Dealer and manufacturer inquiries are welcome!
CST is an authorized distributor for PRO-SET and WEST SYSTEM epoxies which are registered trademarks of Gougeon Brothers, Inc.
CST
The Composites Store Inc.
www.cstsales.com
Order on-line or by phone
1-800-338-1278
Tech Support: 661-823-0108
Imagine how our EXTREME EPOXIES can help you!
Epoxy; The adhesive to use for Extreme Performance!
Here’s just a sample of what two of our customers
were able to do with our EXTREME EPOXIES.
FIBERGLASS CLOTH
Premium Grade
3/4 oz 38”W 10 yrd. min. $2.50 yd.
Lower Prices 30 yds. & up
Other Weights Available
TinLin’s
17 Andrews Drive • Daleville, AL 36322
(334) 598-2287 • 4:00 - 10:00 CST
10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
• NEW! High Performance Engine Kits
• Designed to Resolve Your “Leakage” problems
• Specially designed Rubber Seals for “Optimum” Performance
• Also Available as a Ceramic Hybrid Bearing
• High Performance Polymite Retainers
• Additionally we offer a full range of wheel bearings, and full replacement kits, for
all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
1500 SW 30th Ave., Suite #3 • Boynton Beach, FL 33426
Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52
Edition: Model Aviation - 2004/10
Page Numbers: 44,45,46,47,48,50,51,52
IN 1976, THE smallest practical RC models used Cannon
Electronics “micro” RC equipment. AMA Hall of Famer Bill
Cannon was a pioneer in small RC models well more than a
quarter century ago.
At roughly that time I came up with a little 125-square-inch
model powered by a Cox Tee Dee .020 engine that weighed a total
of 11 ounces, using a two-channel Cannon RC system. A Ken
Willard design of the same period was called the “Cannonshot,”
so the Flying Models (FM) editor at the time—Don McGovern—
christened my new design the “Cannonball.”
It flew well and was highly maneuverable on just ailerons and
elevator control. To add a little distinction to the aircraft, and
because I was a Grumman engineer, I employed twin vertical
tails, similar to the F-14 Tomcat’s. This design was published as a
construction article in the July 1976 FM.
In 1983, FM’s “new” editor Bob Hunt (MA’s aeromodeling
editor) invited me to do a scaled-up version of the Cannonball for
Cox Tee Dee .049 power. It was a 20-ounce, 210-square-inch
version that Bob named the “Fastball.” It was published in the
October 1983 issue.
That model’s wing was a balsa-sheeted foam-core type that
Bob constructed. He internally cored the wing in the interest of
saving weight. The Fastball proved to be another excellent flier,
and, as you will see in the accompanying photos, it still exists
some 20 years later.
Enter the “Microball”: With the current popularity of backyard
and parking lot flyers, it seemed a good idea to pursue the little
twin-tail design again, but this time with electric power and
throttle control.
I’ll tell you in advance that this new version flies as well as its
predecessors. In all honesty, it isn’t as hot as it was with a highrevving
Cox glow engine; however, it proved highly
maneuverable and is a pleasure to fly.
44 MODEL AVIATION
MICROBALLby Bob Aberle
With design elements that go back 28 years, this electric park
flyer is surprisingly modern
Test pilot Tom Hunt makes a flyby. This model is “comfortably
fast” and maneuverable. Roll rate was set to be quite fast.
10sig2.QXD 7/23/04 11:32 am Page 44
I settled on 100 square inches of wing area, which is slightly
smaller than the Cannonball’s. The target weight was set at
approximately 7 ounces complete. I wanted that weight because I
had every intention of using an inexpensive GWS geared IPS
motor, similar to the type supplied with GWS’s popular Lite Stik
ARF design.
To provide better performance at somewhat slower flight
speeds, I increased the wing aspect ratio from 3.9 to 5.6:1. That
means I made the wing planform longer in span and narrower in
width (chord).
The original wing had a semisymmetrical NACA 2412 airfoil
section. I wanted some extra lift and chose a simple, slightly
modified Clark Y flat-bottom airfoil as an alternative. To
maintain the same appearance, I kept the twin vertical (F-14) fins.
As on the Cannonball and Fastball designs, the wing is
permanently affixed to the fuselage, with a removable bottom
hatch that allows you access to the RC equipment and the battery
for charging purposes.
In an attempt to keep it really simple, I installed the aileron
servo on top of the wing, out in the open. A balsa-block simulated
canopy provides some streamlining of the airflow directly in front
of that externally mounted servo.
Motor System/Battery: The motor I chose was the GWS IPS S-1
model, which has a lower-than-average gear-reduction ratio at
October 2004 45
The Fastball (left), published 20 years ago, was the design
inspiration for the smaller electric Microball (right).
Spars have been added along with top wing-rib sticks. The bent
sticks provide airfoil shape without need for wing ribs.
Plywood fuselage formers—F1 and F2—have square center holes
to accept motor-mount stick. That stick (L) is made from the two
pieces of spruce.
Initial wing construction begins by pinning down LE and TE
stock, and then add bottom 1⁄32 x 3⁄16 wing-rib sticks.
MICROBALL
Type: RC electric park flyer
Wingspan: 24 inches
Power: GWS IPS S-1 motor
Flying weight: 6-7 ounces
Construction: Balsa and plywood
Covering/finish: Shrink film
Photos by the author
erle
10sig2.QXD 7/23/04 11:33 am Page 45
46 MODEL AVIATION
At top is template cut from manila-folder stock. It is used to cut
two identical 1⁄16 balsa fuselage sides.
Motor-mount stick has been inserted into motor. End of same
stick passes through hole in each of two formers.
Motor, mounting stick, formers assembled in fuselage. Note how
motor cable is routed back through holes cut in both formers.
Lower hatch cover is made from part balsa and part thin
plywood. Note tongue at front. Rear portion is held down by
swiveling piece of plastic.
The bottom of the fuselage showing the landing skid that was
made from double-stick tape and SR Gapless Hinge Tape.
After covering all tail surfaces, cement fins in place with slow
cyanoacrylate. Template is used to establish correct 75° angle.
10sig2.QXD 7/23/04 11:37 am Page 46
October 2004 47
Top-mounted HS-50 aileron servo is attached to hardwood
pieces with two tiny sheet-metal screws. Wire rods are attached
to servo output arm using Z bends.
A soft-balsa simulated canopy adds to jetlike appearance and
acts to smooth airflow over exposed aileron servo.
With hatch cover open and moved to side, part of seven-cell 280
mAh NiMH pack is visible. Keep battery this far forward to
properly balance model.
With battery removed, you can see FMA Direct Extreme receiver
double-stick-taped to wing bottom and bottom of aileron servo
and elevator servo that is taped to fuselage side.
Hitec HS-50 microservo used for elevator control. Control rod is
small-diameter wire that passes through inside of Sullivan
Products No. 508 yellow plastic tube.
Extreme micro dual-conversion receiver—weighing 0.4 ounce—
with E-Cubed RC short antenna rod, which takes place of 39-inch
antenna wire.
10sig2.QXD 7/23/04 11:41 am Page 47
50 MODEL AVIATION
4.14:1. The lower ratio allows the use of a
smaller-diameter propeller: an APC Slow
Flyer 7 x 5 for this model.
The rule of thumb when operating this
particular GWS motor series is to keep the
motor current at less than 2.0 amps and
approximately 15 watts power. A six-cell
battery would normally be recommended; I
found it possible to go to a seven-cell
NiMH pack of 280 mAh capacity. By
doing that, my start-up current was
measured at 2.1 amps at 16.9 watts. This
quickly diminishes to less than the
recommended limits as the charge wears
off.
But to be on the safe side, I added a
GWS motor heat sink, which helps
dissipate some of the extra heat that is
generated. With this arrangement, the
propeller speed is roughly 5,100 rpm, and
motor runs of 8-10 minutes are possible—
more if you throttle back sometimes during
a flight.
RC System: I like to fly with my regular
SEFLI (Silent Electric Flyers of Long
Island) club members at the east end of the
island. We draw a big crowd on the
weekends, so selective, dual-conversion
RC receivers are the better way to go. For
the Microball I chose the .4-ounce FMA
Direct Extreme dual-conversion receiver.
(Editor’s note: Since this article was
written, FMA Direct discontinued its
Extreme receiver and replaced it with the
new M5 micro-size dual-conversion
receiver which weighs slightly more than
.3 ounce. Bob has substituted this new
receiver and reports complete success!)
The two servos were the popular Hitec
RCD HS-50 submicro variety. My choice
of ESC, as usual, was Pat DelCastillo’s
Castle Creations Pixie-7P, in which you
can program the cutoff voltage.
Not wanting a trailing 39-inch-long
antenna wire on such a small model, I
substituted it with Azarr’s E-Cubed R/C
short antenna stick (model M-72-U). The
entire antenna is literally wrapped around
a 11⁄2-inch-long rod. You cut off the
existing antenna approximately an inch
from the case and solder the E-Cubed R/C
antenna lead wire to it.
In the photos you will notice that I
located the antenna stub right inside the
RC compartment. During my initial range
checks I noted some interference
problems. To correct that, I moved the
antenna stub to a point several inches
behind the wing TE, inside the fuselage. I
used double-stick tape to hold it in place.
In this new location I experienced no
radio-range problems, but do range check
before that first flight.
Also of interest is my choice of
connectors. Many of the smaller parking
lot models employ the JST connectors
(with the red plastic housing), which can
be purchased from Balsa Products and
Radical R/C. The wires come already
crimped to the connector pins.
I used a pair of these connectors
between the motor and ESC and another
pair from the battery to the ESC. They are
polarized and use the basic red/black wire
colors for positive and negative polarity
identification.
Construction Hints: The Microball’s
basic construction is all balsa. It uses little
material, and you can build it in a matter
of days. Those are some basic advantages
of parking lot and backyard flyers.
Most modelers don’t like cutting wing
ribs. As such, I used Tom Hunt’s
Modelair-Tech “Stik”-type wing
construction. Instead of actual wing ribs,
you substitute strips of balsa measuring 1⁄32
(thick) x 3⁄16 inch (wide). One set of these
sticks lays flat on your building board with
the LEs and TEs pinned in place, and then
two wing spars (cut from 1⁄16 balsa) are
added. Note that the height of these spars
taper as you approach the wingtips.
The last step is to bend a second set of
the 1⁄32 balsa strips over both spars,
running from the LE to the TE. The result
is a neat airfoil effect without the need for
the more traditional wing ribs.
The ailerons are simply cut from sheet
balsa, as are all the tail pieces (stabilizer,
elevator, and twin vertical fins). The
fuselage sides are made from 1⁄16 balsa.
Several stiffeners and a doubler are added
to the inside of each side. (Make sure you
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Featuring a searchable database of Model
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This is by far one of the best
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construct something that is for
every member.
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Peninsula Channel Commanders
San Francisco CA
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on the “Members Only” section, and follow the directions
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10sig2.QXD 7/23/04 11:42 am Page 50
October 2004 51
make one right and one left side!)
The motor-mount scheme was adapted
from Larry Sribnick’s SR Bantam kit. Two
plywood formers are prepared, each with a
square hole cut in it to accept the motormount
stick. This stick is actually made
from two pieces of spruce or basswood so
that it can be press-fit into the square hole
molded into the GWS/IPS motor casing.
Place the motor on the stick, and pin it
in place with a small sheet-metal screw.
Leave enough stick projecting from the
motor to pass through the holes cut in both
plywood formers. A small dowel inserted
in front of the first former and a small
sheet-metal screw added behind the second
former will help lock the motor in place.
In the event of a hard landing or a
crash, this stick will break long before
your motor shaft bends. Using a connector
set as described earlier, you can easily
change motors at the flying field.
Fashion a lower hatch cover from part
balsa and part 1⁄32 plywood. Form a tongue
at the front end, and a swiveling plastic
retainer holds the rear of the hatch in
position. Keep this simple since you need
access to the battery for charging purposes
after every flight.
Adhere the wing to the fuselage with
five-minute epoxy. Doing this eliminates
the need for wing dowels or rubber bands.
I found it easier to precover the stabilizer,
elevator, and fins before final assembly. I
cemented the fins in place with slow
(thick) cyanoacrylate and attached the
entire stabilizer to the fuselage with fiveminute
epoxy. I left the top fuselage
sheeting off until after I hooked up the
control rod to the elevator.
Covering and Final Assembly: My
favorite covering for this size model is the
Hangar 9 UltraCote Lite Transparent ironon
material. I covered the entire Microball
with it. I use two irons: one set at a low
temperature to tack the covering material
in place and one set at a moderately high
temperature to do the final shrinking.
Believe it or not, the thin balsa tail
surfaces can be covered easily, and it does
not cause any undo warping.
Once completely covered, you can
install the ailerons and elevator hinges. I
resorted to Larry Sribnick’s SR Bantamseries
kit and used his SR Gapless Hinge
Tape. Instructions are supplied with this
material, and it works great.
I used Du-Bro’s new micro-size control
horns and EZ connectors exclusively on
the ailerons and elevator. These items were
specifically designed for the micro-flyer.
The single elevator control rod is made
from Sullivan Products No. 508 yellow
plastic tubing, with a length of .020-inchdiameter
wire running inside the tube.
Once the tube is in place and you are
satisfied with the elevator control action,
you can finish the top fuselage sheeting
and covering.
Final control-surface movement
amounted to 1⁄4 inch on either extreme of
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10sig2.QXD 7/23/04 11:42 am Page 51
52 MODEL AVIATION
neutral on the ailerons and 1⁄4 inch on
either side of neutral elevator. The final
balance point was approximately by the
front wing spar. This was only achieved by
placing the seven-cell 280 mAh NiMH
battery pack (in-line configuration) as far
up against the front fuselage former (F-1)
as possible. Anything less than this would
have made the model tail-heavy and
unmanageable in flight.
Flying: The 6.7-ounce final weight was
slightly lighter than my target, which
resulted in a wing loading of 9.6 ounces
per square foot. With the power system
and seven-cell 280 mAh NiMH battery, the
watts-per-ounce figure worked out to 2.52;
a six-cell NiMH battery pack will yield
closer to 2.00 watts per ounce. Anything
heavier than 2.00 will generally yield
medium through aggressive aerobatic
performance. That’s just about what I
observed.
All flights must be hand launched
because of the lack of a landing gear. I did
add a piece of double-stick tape, followed
by a piece of SR Gapless Hinge Tape, to
act as a lower landing skid. That way, the
underside of the fuselage doesn’t take a
beating on every landing.
The Microball’s flight performance was
much like that of its predecessors, but not
quite as fast. The roll rate is quite fast, so
you might want to use some dual-rate cutback
initially, until you get familiar with
the model. Aileron control on a parking lot
flyer can open many doors to more
advanced maneuvering. I think you will
enjoy this aircraft’s performance. Landings
can be made at slow speeds, with the nose
high and without a tendency to stall or fall
off.
The Microball might benefit from the
new Li-Poly batteries. I didn’t try them
because the lighter weight would have
made it impossible to balance the model at
the prescribed CG. If you intend to use Li-
Poly cells, add approximately 11⁄2 inches
to the nose length; move the motor
forward.
I did try two FMA Direct/Kokam 540
mAh Li-Poly cells hooked up in series.
The motor current, voltage, wattage, and
propeller rpm came out almost identical to
that obtained with the six-cell 280 mAh
NiMH battery, but the Li-Poly cells
weighed exactly half of the NiMH pack.
The resulting .9-ounce reduction in the
Microball’s weight produced a 2.34-wattsper-
ounce parameter. That indicates that
the Microball should fly better than it does
with the six-cell pack and almost as well
as it does with a seven-cell pack. But the
real advantage is that the motor run time
will likely be extended from eight to 10
minutes, upward to 18 minutes! That is a
great improvement! If you try these new
batteries, please write in and share your
experiences. MA
Bob Aberle
[email protected]
Specifications:
Wing area: 100 square inches
Wing loading: 9.6 ounces per square foot
Length: 18 inches
Propeller: APC 7 x 5 Slow Flyer
Motor current: 2.1 amps at the start on a
full charge (1.78 amps on six cells)
Motor power: 16.9 watts (13.1 watts on six
cells)
rpm: 5,100 (4,700 on six cells)
Watts per ounce: 2.52 (2.04 on six cells)
Battery: Seven-cell 280 mAh NiMH pack
(six-cell pack: one less cell but same inline
configuration)
Radio used: FMA Direct Extreme micro
dual-conversion receiver, two Hitec HS-50
microservos, Castle Creations Pixie-7P
ESC with BEC, E-Cubed R/C short (11⁄2-
inch) antenna, Hitec Eclipse transmitter
with Spectra module
Flight duration: Eight to 10 minutes with
seven-cell 280 mAh NiMH battery and
some throttling back during flight
Manufacturers:
Motor and NiMH batteries:
Balsa Products
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Pixie-7P ESC:
Castle Creations
18773 W. 117th St.
Olathe KS 66061
(913) 438-6325
Fax: (913) 438-1394
www.castlecreations.com
Micro control horns and EZ connectors:
Du-Bro RC
Box 815
Wauconda IL 60084
(800) 848-9411
Fax: (847) 526-1604
[email protected].
www.dubro.com
Short antenna rod:
E-Cubed R/C
1750 Lundgren Rd.
New Carlisle OH 45344
(937) 849-0418
Fax: (937) 849-0341
[email protected]
www.ecubedrc.com
Receiver and Lithium batteries:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Transmitter and servos:
Hitec RCD
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
JST connectors and NiMH batteries:
Radical R/C
7046 Harshmanville Rd.
Huber Heights OH 45424
(937) 237-7889
[email protected]
www.radicalrc.com
• NEW! High Performance Engine Kits
• Designed to Resolve Your “Leakage” problems
• Specially designed Rubber Seals for “Optimum” Performance
• Also Available as a Ceramic Hybrid Bearing
• High Performance Polymite Retainers
• Additionally we offer a full range of wheel bearings, and full replacement kits, for
all makes of R/C cars & trucks in: Econo (standard), Green Seals and Ceramics
• Information available on our website: www.bocabearings.com
1500 SW 30th Ave., Suite #3 • Boynton Beach, FL 33426
Toll Free Phone: 800-332-3256 • Toll Free Fax: 800-409-9191
Email: [email protected]
STOP
Leaks!
10sig2.QXD 7/23/04 11:42 am Page 52