models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
Edition: Model Aviation - 2005/03
Page Numbers: 16,17,18,20,21,22
models, I decided to revisit this
design layout. This time I worked
around the popular (and
economical) Speed 400 motor
group with a seven-cell
battery pack. The resulting
model—Big Punkin—has
proven to be a joy to fly, with
an exceptionally broad flight
envelope.
If I am in the mood for
slow and lazy, I can take the Big
Punkin up to 300 feet or so and ride a
thermal, power off, for 30 minutes or more.
When the urge strikes for some action, this model
is capable of loops, rolls, spins, stall turns, and some tight,
low-level flying.
The takeoff roll in short grass is roughly 10 feet, and it’s even
shorter on pavement. A baseball-field-size open area is more than
enough room in which to enjoy the Big
Punkin.
In the interest of lightness, I used as little
sheet balsa as was practical in the
construction. Although light, the structure
has proven to be ample for any flight load
that the controls can produce, without strain.
I am certain that it would break in a crash,
but I design to fly and repair if that happens.
The result is a lighter model that flies much
better.
The fuselage on my Big Punkin is
covered with MonoKote for strength, while
the wings and stabilizer are covered with
Solite for lightness.
I installed one of the JR micro flight
packs for another small weight savings, and
it has worked fine. There is plenty of thrust
in those little servos for these controls.
Considering how far downfield I have
chased thermals with Big Punkin, I am
grateful for the plentiful range that the little
receiver provides.
THE BIG PUNKIN goes way back
in its ancestry. The first park flyer
on record was designed by Ken
Willard and published in Model
Airplane News under the name
Breezy. A biplane with a boxy
fuselage and unequal wings, it
caught my eye from the first.
No big deal? The year was 1955!
Ken became one of my
guiding lights through the years,
and the Breezy layout surfaced
several times in my building efforts.
Several years ago I took advantage of the
newly available micro equipment and built a 16-
inch-wingspan biplane with that basic layout with electric
power. By then the design had changed in many ways, so I
renamed this one Punkin. It was published in RC MicroFlight.
As I continued to fly and enjoy larger electric-powered
The author flies his design. The Big Punkin is a great slow flyer that will allow you to
make low, slow, and close passes with confidence and safety.
by Dave Robelen
16 MODEL AVIATION
RC electric-powered small-field
fun is only two wings away
Photos courtesy the author
March 2005 17
The drive is a Graupner Speed 400 6-volt motor coupled to a
Mini Olympus 2.33:1 gear drive, and that spins an APC Slowfly
10 x 4.7 propeller. The ESC is a Jeti 10A. I found all of these
drive components at Hobby Lobby International, and they have
been more than satisfactory.
Would you like to have a classy park flyer of your own with
roots that go way back? Read on.
CONSTRUCTION
Careful wood selection can make a substantial difference in
one of these models’ weight. My Big Punkin finished out at 17
ounces, and there is no heavy balsa in it. Most of the wood
averages 6-8 pounds per cubic foot in density.
Although I have to drive a considerable distance to a hobby
shop that stocks balsa, I enjoy going through the selection and
choosing the best pieces for the various jobs. I prefer the stiff Cgrain
wood for the wing ribs, and I watch for nice, stiff material
from which to cut the spars.
I purchase the wood in sheet form and slice off the strips as
needed. If you do not have access to a good local wood supply, I
have had success with Superior Balsa material, and Lone Star
Balsa has a great reputation.
I am going to assume that this is not your first scratch-building
project and that you will understand what tools to use and where.
Wing: Build the wings first; you will need them when you are
working on the fuselage.
My method for cutting ribs is to trim out a pair of 1⁄16 plywood
templates and make a “sandwich,” with the balsa rib blanks in the
The stabilizer is a sturdy built-up unit, and the elevators and the
rudder/fin assembly are made from balsa sheet.
The fuselage sides have been joined with the two main formers.
It’s important to achieve accuracy at this point.
The remainder of the fuselage formers have been added, and
the landing gear has been mounted to its floor.
The 1⁄16 sheet-balsa fuselage sides are ready to be joined. Notice
the reinforcements that have been glued to the sides.
Type: RC sport
Wingspan: 37 inches
Power: Graupner Speed 400 6-volt motor
coupled to Mini Olympus 2.33:1 gear drive
Flying weight: 18 ounces
Construction: Balsa and plywood
Covering/finish: Solite and MonoKote
The Speed 400 motor is mounted to a 1⁄16 plywood plate.
The battery resides in the top of the fuselage cabin section. A balsa floor separates the
two sections.
In this close-up photo you can see the spars and the shear webs
in great detail. The construction is strong and light.
There is abundant room in the bottom section of the fuselage for
the receiver and two JR microservos.
Two 1⁄8-inch-diameter aluminum tubes are
used at the front of the wing as forward
hold-down pegs. The rear bolts in place.
After the wing is assembled and the spars have been added, the
dihedral joint cuts are made and the wing is fixtured while glue dries.
middle and the plywood templates on
either side. I have a couple of small Cclamps
that are handy for holding all of
this together.
While clamped, sand the balsa ribs to
the finished shape and cut the notches.
Strip out the spars and TEs, and trim the
angle into the TEs.
Pin the TE strip to the board (notice
the shims to tilt it), and then use the ribs
as spacers to locate and pin the LE. Glue
the ribs in place. When they’re dry, cut
through the LE and TE where shown, and
trim the ends to match the dihedral. Using
props to hold the panels at the correct
angle for the dihedral, glue the outer
panels to the center. Add the top spars.
When all of that is dry, lift it off the
board and glue in the filler strips between
the spars where shown. Now you can glue
the bottom spar in place.
At this time, trim the LE to the proper
cross-section and sand away any glue
bumps, etc. You can add the tips now,
along with the little plywood
reinforcements for the hold-down screws.
Do all of this again, and you have a nice
pair of wings!
Fuselage: Begin the fuselage by splicing
two sheets of 1⁄16 balsa to the width
necessary for the fuselage sides. Cut the
pieces to the outline shown on the plans,
leaving the various openings solid for
now.
Pinning the sides to a flat surface, glue
all of the 1⁄8 balsa bracing in place where
shown. Instead of bulkheads in the cabin,
use strips of 1⁄8 x 3⁄8-inch balsa glued on
edge in the front and back of the wings.
With all of the bracing in place, cut the
various openings in the sheet sides.
Join the sides at the cabin, using strips
of 1⁄8 x 1⁄2-inch balsa as crosspieces. The
tail may be pulled together now and
glued; watch that you avoid building a
banana! I had to cut partway through the
bracing on the sides to pull the nose
together and keep the sides straight. Add
the rear cross bracing and the plywood
parts for mounting the wings.
This is where those wings come in
handy. Holding a wing in place, drill
through the fuselage and wing for the
front tubes and then the rear screws. Be
sure to use the tap-size drill for the rear
screws to avoid a mess later.
Open up the holes in the wings for
clearance at the screw locations, and tap
the plates in the fuselage 6-32 for the
hold-down screws. I found my plastic
screws in an assortment sold at
RadioShack.
Landing Gear: I use soft copper wire to
lace the 1⁄16-inch-diameter-wire landing
gear to the plywood plate, and then I flow
a bit of cyanoacrylate glue over the lacing.
Mine holds fine.
Glue the assembly in the location
shown, placing it high enough to clear the
bottom planking. Cover the front bottom
with 1⁄16 balsa with the grain running
across the fuselage. The top bulkheads
and sheeting can go in next.
Cowl Block: I made the top cowl from a
block of balsa and hollowed it, but
bulkheads and sheet will work too. Fit the
front block and sand the nose smooth.
I fashioned the motor mount from a
plate of 1⁄16 plywood supported with a
piece of 1⁄4 balsa on each side. This is a
good time to fit the motor assembly and
trim the necessary clearances in the front
block. Set the motor aside for now, along
with the fuselage.
Empennage: To get a stiff, light
stabilizer, I assembled it from a 1⁄8 balsa
core and added 1⁄16 sheet on the top and
bottom as shown. When it was dry, I
sanded the center sheeting to the wedge
shape shown and rounded the front and tip
edges. I left the TE square.
I cut the elevators from a sheet of 1⁄8
balsa. I installed the wire joiner before I
cut the two apart. I also sanded the taper
into the elevators while they were joined.
I cut the center apart, sanded a sharp edge
bevel on the front edge, and then set it
aside. Cut the fin and rudder from 3⁄32
balsa sheet. You may have to do some
splicing to get the width shown.
Covering: Chances are that you can do a
neater job than I did, so my main
suggestion is to carefully read and follow
the instructions that come with the
material of your choice. Avoid using
MonoKote or other thick material on the
wings and stabilizer that would add
unnecessary weight and risk warps.
Make sure the covering is firmly
attached to the rib bottoms to follow the
undercamber. I found one of the little trim
sealing irons handy for this. It let me bond
the ribs without shrinking the covering
away from them.
The windows on the fuselage sides are
scraps of clear MonoKote ironed in place.
The windshield came from one of those
clear document protectors.
Final Assembly: I used full-span strips of
clear packing tape (Scotch brand) to hinge
the elevators and rudder. I left a gap of
approximately 1⁄16 inch in the hinge line.
This worked out extremely well. The
hinges are free and smooth, and there is
no leakage along the hinge line.
I mounted the wings to serve as a
reference while I installed the tail. My
system is to set the model flat on a
countertop or other large, flat surface and
level the wings. Then I trim the stabilizer
cutout until it is level and glue it on with
the hinge line squared to the fuselage.
Glue on the vertical tail next. Sight it
carefully to avoid any tilting. I put a short
piece of packing tape between the
fuselage end and the rudder as a bottom
hinge. Glue on the control horns.
I installed the motor unit next, and I
used strips of the clear tape to attach the
front nosepiece. The cowl block has a strip
of tape on each side, with one side folded
under to form a tab. This gave me a handy
location for my battery connector, for
charging, etc. I used hook-and-loop
material to install the battery, with the
grabby loops in the airplane.
Install the receiver and servos on the
bottom of the equipment plate. Servo
mounting tape worked fine for me. I made
my pushrods from 3⁄16-inch square balsa
sticks, with 1⁄32-inch-diameter-wire ends.
Rather than have adjusters, I made the last
wire/stick joint with the servo in neutral
and the control aligned.
The wheels are the light foam type,
held on with plastic push-on keepers. I cut
the tail skid from 3⁄32 plywood and painted
it to match the fuselage. Being the
independent type, I made my spinner from
balsa and covered it with fiberglass cloth
and cyanoacrylate glue.
A commercial 1.5-inch-diameter
spinner would do fine. I ended up settling
on an APC 10 x 4.7 propeller for my Big
Punkin, but you might want to try a few
sizes to get the best match.
With all but the top wing assembled,
put the battery in place and then mount the
wing. Check the balance, and move the
battery as necessary to get the correct
balance. Perform a good range check on
the radio, and run up the motor to ensure
that it does not interfere with the controls
when the signal is weak.
Flying: Flying the Big Punkin is simple. I
have never hand launched mine, but there
is plenty of power if that is necessary. The
ground handling on takeoffs is normal.
On grass, hold full up until the speed
builds a bit, and then go to neutral. A
small tug of up will lift it right off. On
pavement, it is only necessary to steer with
the rudder for a few feet until there is
adequate airflow over the fin.
Climb up to 100 feet or so and feel out
the low-speed handling. Mine will reach
full up-elevator without dropping a wing if
I leave the power low and do not make
large movements with the rudder. Holding
full up and pushing the rudder full over
should result in a spin entry. The spins are
pretty, and the recovery is immediate when
you neutralize the controls.
From this point on, see how much fun
you can have with your Big Punkin. Let
me know how you make out, and I always
enjoy pictures. Happy landings. MA
Dave Robelen
Route 4 Box 369
Farmville VA 23901
[email protected]
