P-40 Warhawk - 2012/02

48 MODEL AVIATION
The author named his Warhawk P-40 after his wife, Patrice.
P-40
Warhawk
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 48February 2012 49
Giant Scale foam fighter
by Keith Sparks
The most noticeable difference is that
foam is easier to cut and sand. The
airframe is less expensive to build using
foam, and its lighter weight allows for a
more affordable power system to be used.
It is hard to tell that this Warhawk P-40
is made with the material commonly
referred to as fan-fold foam, until you see
it fly.
Construction: The fuselage is the best
place to start, so I cut all the fuselage
formers then built the assembly fixture.
That turned out to be the best $10 I ever
spent. I placed the electrical conduit over
the plans, marked each former position,
then slid the formers into position on the
conduit and mounted the assembly on the
fixture. I used a piece of plywood as a tool
to slide the formers into position without
damaging them; the fit is tight.
I used the side view to lay out the cuts
needed for the fuselage sheeting and began
bonding them in place, starting at the
FROM THE START, the goal for this
project was to build a large, lightweight,
1/4-scale model with materials easily
obtained from home-improvement stores.
Material availability has proved to be one
of the major obstacles with most of my
foam-based designs. Although the P-40
Warhawk uses light plywood and balsa in
areas requiring extra strength, the majority
of the airframe was purchased at my local
home improvement store.
The construction method will be
familiar to most scratch builders by
substituting wood with lighter foam
materials and wood workers’ glue with
polyurethane glue. The finish applied to the
model uses the same fiberglass and epoxy
resin methods employed on conventionally
constructed models.
cockpit notch. Using masking tape for
clamp pressure, I alternated between the
top and bottom, working from the center
outward.
When the polyurethane adhesive had
dried, I rough-trimmed the sheeting and
used a bar sander to level the tops and
bottoms of the sheeting and formers to
prepare them for the cap strips. I cut the
foam strips to fit the fuselage then bonded
them in place using masking tape for
clamp pressure.
A bar sander with 90-grit sandpaper
attached makes short work of the general
shape of the foam blocks; I switched to
120-grit sandpaper for the final step of
blending it to the side sheeting. The aft
bottom cap strip was saved for last to
allow me to install the pushrod guide
tubing.
For additional strength in the
midsection, I added sheet foam in between
the formers in the wing saddle area, then
temporarily removed the fuselage from the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 4950 MODEL AVIATION
Photos by the author
tubing in position and installed the bottom
cap strip.
In order to return the fuselage to the
building fixture, I cut two 1-inch foam
blocks to fit snugly in the box beam and
drilled holes for only the upper conduit to
pass through. With the tubing level, the
fixture serves as the datum line and makes
the wing and stabilizer incidence easy to
set and check; it also gives you a
“floating” fuselage, making the application
of the 3/4-ounce fiberglass cloth easier.
I employed a water bottle as a round
sanding block to shape the window recess
and bonded the sheeting in place. After the
sheeting was sanded flush with the fuselage,
I applied the glass cloth.
Using a razor saw, I cut the equipment
hatch free from the fuselage and lined the
empty space with balsa sheeting to toughen
the lip of the hatch hole. I sanded the hatch
build fixture. I removed the conduit tubing
from the formers using a twisting motion.
The cowl was assembled with 3/4-inch
foam sheeting segments cut from the plans
patterns and assembled in a wedding-cake
fashion, paying attention to the alignment.
The assembly was tack-bonded onto the
fuselage and sanded to shape. The patterns
are close to net trim, so I advise that you cut
outside the line.
The fuselage was now fairly rigid, so I
removed the centers of the precut formers
before assembly started and installed the boxbeam
sides and bottom.
Several test fits, before applying the glue,
served as good assembly practice. Strips of
foam sheeting, cut 1/8 inch wider than the box
beam, were used for clamp pressure to hold
the box-beam walls against the formers while
the glue dried.
While that was drying, I put the pushrod
lid smaller to accommodate a balsa lining
for the same purpose.
With the hatch installed on the fuselage,
the balsa liners were sanded flush with the
fuselage surface. Rare earth magnets were
installed at the mating surface to hold it in
place. I repeated this “liner” treatment on
the cowl to fuselage seam.
Wing: I used the plans to cut the wing
sheeting panels and marked two of them
with the spar and rib positions by laying the
plans over the sheeting and piercing the
paper to give me accurate point-to-point
marks to work with.
Eight tapered spars were cut on a table
saw from a single piece of four-foot poplar
and lightly sanded. The forward spar is
bonded to the wing sheeting first.
After I used the ribs to locate the aft spar
position, the ribs and aft spar were bonded
Far left: This build fixture is invaluable for
complete access and keeping the formers
true during construction. It is used to
check angles as well as provide a hands-off
stand while applying the fiberglass cloth.
Left: The cowl was temporarily attached to the fuselage during the shaping step for a
perfect match. Keeping P-40 photos on hand helps to refine the shape.
Below left: The build fixture allowed the author to apply the fiberglass in one step. He
used two layers of masking tape on the hatch and cowl mating surfaces to prevent
them from bonding to the fuselage.
Below right: Weights and shims were used to bond the ribs to the bottom sheeting.
The polyurethane glue sets slowly, allowing plenty of time for adjustments.
Left: Sanding strips, bought on a roll or
cut from sanding belts, helped shape the
large cap strips. The author used masking
tape to apply clamp pressure to the cap
strip.
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 50February 2012 51
to the bottom sheeting. The upper spars
were used in the rib slots to hold their angle
while the assembly dried. The steps were
repeated for the other wing panel and the
two panels were joined after I adjusted the
joint to give me the proper wing dihedral.
The support plates for the wing dowels,
bolts, servo mount, and guide tubes were
next. At this point, the panels are still fairly
flexible and susceptible to warping, so after
the ribs were lightly sanded, I shimmed the
TE and aft spar to prepare for the top
sheeting.
Prebending the foam sheet before
installation makes the sheeting job easy
and the only “clamp tape” needed is along
the LE; the rest of the sheeting clamp
pressure is done with small weights.
I bonded balsa strips to the TE for bump
protection and added the 1/2-inch foam LE
and wingtip. After sanding the additional
parts to shape, I applied 3/4-ounce fiberglass
cloth to the wing.
Wing Saddle: With the fuselage on the
build fixture, I removed side sheeting in
the wing saddle area in small amounts until
it rested in the saddle with the proper
incidence angle. I added the wing dowel
and checked the angle again before I
drilled the wing bolt holes.
Two plywood strips were bonded to the
fuselage wing saddle area and I bolted the
wing in place to apply the clamp pressure.
I cut foam blocks to fit the space between
the plywood strips and blended to the
fuselage with 120-grit sandpaper wrapped
around a plastic bottle to form the wing
fillet.
The stabilizer frames were assembled
upright on a flat board using tape and
spacers to hold them in place while they
Right: The wing panels were joined with a
pair of shear webbing-type plates that
doubled as the landing gear support. With
one panel flat on the work surface the
other was supported at the tip to achieve
the proper dihedral.
Right: Small portions of the fuselage were sanded away during the wing saddle step
with incidence checks along the way. The build fixture will hold the fuselage datum at
zero while you work, making the task easier.
Below: Building the wing fillets using small blocks rather than large ones will reduce
sanding and give you a more complete surface-to-surface bond joint.
Below right: After the stabilizer frame was complete, it was sandwiched between the
top and bottom sheeting. Bonding both sheets at the same time helps to prevent
surface warping.
Far right: Weights were used to clamp
the top sheeting in place. Scrap spar
sticks bridged the applied weight over the
ribs so the skin didn’t dip between them.
dried. One of the advantages of polyurethane
glue is that as it sets it thickens and foams,
allowing plenty adjustment time. I bonded
both sides of the sheeting to the stabilizer
frames at the same time to avoid building a
warped surface.
I used masking tape for clamp pressure
and applied it from the center of the edges
toward the corners. The LEs were added,
sanded to shape, and fiberglass applied.
I built the control surfaces with basic
balsa construction methods, which was
necessary to achieve the fabric-covered-rib
look needed on a P-40. I cut the panels to
profile, added the LEs, and installed the ribs.
Hinges were installed and the surfaces were
fitted to the wing and stabilizers. All that
remained was to sand them to shape and
cover with the iron-on covering.
Adding the horizontal stabilizer to the
fuselage was done by trim and fit with the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 5152 MODEL AVIATION
A hole was cut in the bottom wing
sheeting to install the gear support plate.
The lower spar extends beyond the plate
and masking tape caps the air lines to
avoid contamination.
The gear doors can be rigged to the
retract unit and operated automatically.
The wheel well has been lined with foam
sheeting.
With the model in the build fixture, the horizontal stabilizer was
fitted to the fuselage similar to the way the wing was attached.
The 1/16-plywood strip gives the hinge line a scale look.
After the fin was in place, foam blocks formed the fillet and fair
the fuselage into the tail group. A fuselage stand made from scrap
sheeting was constructed for storing and transport.
The motor and ESC mount in a good
position for cooling air and the box-type
motor mount allows for small thrustline
adjustments using shim washers.
Specifications
Type: RC Scale model
Skill level: Intermediate builder,
intermediate pilot
Wingspan: 95 inches
Wing area: 1,490 square inches
Length: 81 inches
Weight: 17 pounds
Power: E-flite Power 160 motor, Castle 85
amp ESC
Construction: Fan-fold foam, balsa, and
plywood
Covering/finish: Fiberglass cloth, automotive
primer, and acrylic enamel spray paint
Propeller: Zinger 20 x 6
fuselage in the build fixture. When the proper incidence angle was
found, I added sheeting doublers to the inside of the fuselage for a
wider joint and bonded the stabilizer in place.
The vertical fin has a thick base and shares its mount with a balsa
“spar” that extends to the fuselage tail. I needed to test-fit it several
times. Once it was in place, the LE block could be bonded in place
and blended with the fuselage.
For the Robart retracts to be in a scale position, the plywood
support ribs have to be installed after the wing is assembled. I
removed the sheeting between the ribs and cut the spar to
accommodate the stronger rib sections.
Enough of the spar was retained to make a good bond to the new
ribs; when the retract unit was fastened to the mount, the integrity of
the bottom spar was restored.
With the retract units in place, I started removing wing
sheeting and rib material until the wheels were inside the wing
with a 3/8-inch gap between the wheel and the wing sheeting. A
foam strip was cut to fit the wheel well and bonded in place. The
formed plastic gear fairings and gear doors were bonded to the
wing and rigged to the retract unit.
The motor mount was assembled on a flat surface to help get the
angles correct from the start. Its pyramid shape distributes the
motor’s load over a wider space and eases the cowl installation.
I bolted the motor to the mount and placed the assembly on the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 52February 2012 53 P-40
Warhawk Full-Size Plans Available—See Page 175
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:27 PM Page 5354 MODEL AVIATION
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:28 PM Page 54firewall with the fuselage held vertical. I
put the cowl in place and centered the shaft
to the cowl using the spinner backplate.
I removed the cowl carefully and
marked the motor mount position and
bonded it in place. I made small
adjustments to the thrustline using shim
washers.
Formed Plastic and Finish: A plastic set
for this model is available from Parkflyer
Plastics. This includes a 6-inch spinner and
backplate, gear fairings and doors, cockpit
detail, a pilot figure, canopy, cowl flaps,
exhaust stacks, and gun blisters.
The plans include a shopping list for the
materials from Lowe’s; however, you will
need to visit a hobby shop for the 3/4-ounce
fiberglass cloth and Zap finishing resin as
well as the basic RC hardware. I used
automotive primer to bring the surface to a
smooth finish and acrylic enamel spray
paint to apply the colors and markings.
Equipment: The E-flite 160 motor
provides enough power to fly this model
with a 20 x 6 propeller; however, you will
be pulling the maximum recommended 60
amps.
I chose the Castle 85 amp ESC for its
easy programming ability. There is plenty
of room for any servo you would likely use;
running dual servos for redundancy is the
safest route to take.
I’m using servos with 77 ounces of
torque for positive control. The battery
compartment is large enough to
accommodate any battery size you may
want to use. I’m running 10s, 5,000 mAh
lithium cells for longer flight times and
better wind penetration.
The Robart rotating retracts used on this
design will require removing the strut spring
and replacing it with one at half the wire
diameter for the strut to function properly.
This is an intimidating task and I assume it
voids the warranty, so the plans also include
patterns to build the model with fixed gear.
This option will save you nearly 2 pounds.
Flying: The Warhawk P-40 performs as you
would expect, given its light wing loading,
with shorter takeoff rolls, slower approach
speeds, and fly-bys that don’t look like you
are being chased. The model pulls to the left
on takeoff, but after the tail is off the ground
the rudder has positive control. Easing into
the throttle makes it predictable and looks
true to scale.
Adding flaps to this design would be a
waste; at half-power the P-40 will give you
the control you need and it will set up with a
good descent rate. A slight flair at touchdown
and cutting the power will give you a roll out
of roughly 25 feet.
At 2,100 watts of power, the E-flite 160
will provide enough power for basic flight in
5 to 10 mph winds. A roll required strict
attention to the controls and a loop needed a
dive to complete with a sluggish feel at the
top.
With my flight program complete, I have
found the minimum power requirement for
this design. Since the batteries barely get
warm after a flight, there is room for more
power so I will be installing a larger motor
soon to turn this design into a true warbird.
To my wife, Patrice—you have
supported me and my hobby for 22 years.
This one is for you. MA
Keith Sparks
[email protected]
Sources:
Robart
(630) 584-7616
www.robart.com
Park Flyer Plastics
(817) 233-1215
www.parkflyerplastics.com
E-flite
(877) 504-0233
www.e-fliterc.com
Castle Creations
(913) 390-6939
www.castlecreations.com

48 MODEL AVIATION
The author named his Warhawk P-40 after his wife, Patrice.
P-40
Warhawk
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 48February 2012 49
Giant Scale foam fighter
by Keith Sparks
The most noticeable difference is that
foam is easier to cut and sand. The
airframe is less expensive to build using
foam, and its lighter weight allows for a
more affordable power system to be used.
It is hard to tell that this Warhawk P-40
is made with the material commonly
referred to as fan-fold foam, until you see
it fly.
Construction: The fuselage is the best
place to start, so I cut all the fuselage
formers then built the assembly fixture.
That turned out to be the best $10 I ever
spent. I placed the electrical conduit over
the plans, marked each former position,
then slid the formers into position on the
conduit and mounted the assembly on the
fixture. I used a piece of plywood as a tool
to slide the formers into position without
damaging them; the fit is tight.
I used the side view to lay out the cuts
needed for the fuselage sheeting and began
bonding them in place, starting at the
FROM THE START, the goal for this
project was to build a large, lightweight,
1/4-scale model with materials easily
obtained from home-improvement stores.
Material availability has proved to be one
of the major obstacles with most of my
foam-based designs. Although the P-40
Warhawk uses light plywood and balsa in
areas requiring extra strength, the majority
of the airframe was purchased at my local
home improvement store.
The construction method will be
familiar to most scratch builders by
substituting wood with lighter foam
materials and wood workers’ glue with
polyurethane glue. The finish applied to the
model uses the same fiberglass and epoxy
resin methods employed on conventionally
constructed models.
cockpit notch. Using masking tape for
clamp pressure, I alternated between the
top and bottom, working from the center
outward.
When the polyurethane adhesive had
dried, I rough-trimmed the sheeting and
used a bar sander to level the tops and
bottoms of the sheeting and formers to
prepare them for the cap strips. I cut the
foam strips to fit the fuselage then bonded
them in place using masking tape for
clamp pressure.
A bar sander with 90-grit sandpaper
attached makes short work of the general
shape of the foam blocks; I switched to
120-grit sandpaper for the final step of
blending it to the side sheeting. The aft
bottom cap strip was saved for last to
allow me to install the pushrod guide
tubing.
For additional strength in the
midsection, I added sheet foam in between
the formers in the wing saddle area, then
temporarily removed the fuselage from the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 4950 MODEL AVIATION
Photos by the author
tubing in position and installed the bottom
cap strip.
In order to return the fuselage to the
building fixture, I cut two 1-inch foam
blocks to fit snugly in the box beam and
drilled holes for only the upper conduit to
pass through. With the tubing level, the
fixture serves as the datum line and makes
the wing and stabilizer incidence easy to
set and check; it also gives you a
“floating” fuselage, making the application
of the 3/4-ounce fiberglass cloth easier.
I employed a water bottle as a round
sanding block to shape the window recess
and bonded the sheeting in place. After the
sheeting was sanded flush with the fuselage,
I applied the glass cloth.
Using a razor saw, I cut the equipment
hatch free from the fuselage and lined the
empty space with balsa sheeting to toughen
the lip of the hatch hole. I sanded the hatch
build fixture. I removed the conduit tubing
from the formers using a twisting motion.
The cowl was assembled with 3/4-inch
foam sheeting segments cut from the plans
patterns and assembled in a wedding-cake
fashion, paying attention to the alignment.
The assembly was tack-bonded onto the
fuselage and sanded to shape. The patterns
are close to net trim, so I advise that you cut
outside the line.
The fuselage was now fairly rigid, so I
removed the centers of the precut formers
before assembly started and installed the boxbeam
sides and bottom.
Several test fits, before applying the glue,
served as good assembly practice. Strips of
foam sheeting, cut 1/8 inch wider than the box
beam, were used for clamp pressure to hold
the box-beam walls against the formers while
the glue dried.
While that was drying, I put the pushrod
lid smaller to accommodate a balsa lining
for the same purpose.
With the hatch installed on the fuselage,
the balsa liners were sanded flush with the
fuselage surface. Rare earth magnets were
installed at the mating surface to hold it in
place. I repeated this “liner” treatment on
the cowl to fuselage seam.
Wing: I used the plans to cut the wing
sheeting panels and marked two of them
with the spar and rib positions by laying the
plans over the sheeting and piercing the
paper to give me accurate point-to-point
marks to work with.
Eight tapered spars were cut on a table
saw from a single piece of four-foot poplar
and lightly sanded. The forward spar is
bonded to the wing sheeting first.
After I used the ribs to locate the aft spar
position, the ribs and aft spar were bonded
Far left: This build fixture is invaluable for
complete access and keeping the formers
true during construction. It is used to
check angles as well as provide a hands-off
stand while applying the fiberglass cloth.
Left: The cowl was temporarily attached to the fuselage during the shaping step for a
perfect match. Keeping P-40 photos on hand helps to refine the shape.
Below left: The build fixture allowed the author to apply the fiberglass in one step. He
used two layers of masking tape on the hatch and cowl mating surfaces to prevent
them from bonding to the fuselage.
Below right: Weights and shims were used to bond the ribs to the bottom sheeting.
The polyurethane glue sets slowly, allowing plenty of time for adjustments.
Left: Sanding strips, bought on a roll or
cut from sanding belts, helped shape the
large cap strips. The author used masking
tape to apply clamp pressure to the cap
strip.
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 50February 2012 51
to the bottom sheeting. The upper spars
were used in the rib slots to hold their angle
while the assembly dried. The steps were
repeated for the other wing panel and the
two panels were joined after I adjusted the
joint to give me the proper wing dihedral.
The support plates for the wing dowels,
bolts, servo mount, and guide tubes were
next. At this point, the panels are still fairly
flexible and susceptible to warping, so after
the ribs were lightly sanded, I shimmed the
TE and aft spar to prepare for the top
sheeting.
Prebending the foam sheet before
installation makes the sheeting job easy
and the only “clamp tape” needed is along
the LE; the rest of the sheeting clamp
pressure is done with small weights.
I bonded balsa strips to the TE for bump
protection and added the 1/2-inch foam LE
and wingtip. After sanding the additional
parts to shape, I applied 3/4-ounce fiberglass
cloth to the wing.
Wing Saddle: With the fuselage on the
build fixture, I removed side sheeting in
the wing saddle area in small amounts until
it rested in the saddle with the proper
incidence angle. I added the wing dowel
and checked the angle again before I
drilled the wing bolt holes.
Two plywood strips were bonded to the
fuselage wing saddle area and I bolted the
wing in place to apply the clamp pressure.
I cut foam blocks to fit the space between
the plywood strips and blended to the
fuselage with 120-grit sandpaper wrapped
around a plastic bottle to form the wing
fillet.
The stabilizer frames were assembled
upright on a flat board using tape and
spacers to hold them in place while they
Right: The wing panels were joined with a
pair of shear webbing-type plates that
doubled as the landing gear support. With
one panel flat on the work surface the
other was supported at the tip to achieve
the proper dihedral.
Right: Small portions of the fuselage were sanded away during the wing saddle step
with incidence checks along the way. The build fixture will hold the fuselage datum at
zero while you work, making the task easier.
Below: Building the wing fillets using small blocks rather than large ones will reduce
sanding and give you a more complete surface-to-surface bond joint.
Below right: After the stabilizer frame was complete, it was sandwiched between the
top and bottom sheeting. Bonding both sheets at the same time helps to prevent
surface warping.
Far right: Weights were used to clamp
the top sheeting in place. Scrap spar
sticks bridged the applied weight over the
ribs so the skin didn’t dip between them.
dried. One of the advantages of polyurethane
glue is that as it sets it thickens and foams,
allowing plenty adjustment time. I bonded
both sides of the sheeting to the stabilizer
frames at the same time to avoid building a
warped surface.
I used masking tape for clamp pressure
and applied it from the center of the edges
toward the corners. The LEs were added,
sanded to shape, and fiberglass applied.
I built the control surfaces with basic
balsa construction methods, which was
necessary to achieve the fabric-covered-rib
look needed on a P-40. I cut the panels to
profile, added the LEs, and installed the ribs.
Hinges were installed and the surfaces were
fitted to the wing and stabilizers. All that
remained was to sand them to shape and
cover with the iron-on covering.
Adding the horizontal stabilizer to the
fuselage was done by trim and fit with the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 5152 MODEL AVIATION
A hole was cut in the bottom wing
sheeting to install the gear support plate.
The lower spar extends beyond the plate
and masking tape caps the air lines to
avoid contamination.
The gear doors can be rigged to the
retract unit and operated automatically.
The wheel well has been lined with foam
sheeting.
With the model in the build fixture, the horizontal stabilizer was
fitted to the fuselage similar to the way the wing was attached.
The 1/16-plywood strip gives the hinge line a scale look.
After the fin was in place, foam blocks formed the fillet and fair
the fuselage into the tail group. A fuselage stand made from scrap
sheeting was constructed for storing and transport.
The motor and ESC mount in a good
position for cooling air and the box-type
motor mount allows for small thrustline
adjustments using shim washers.
Specifications
Type: RC Scale model
Skill level: Intermediate builder,
intermediate pilot
Wingspan: 95 inches
Wing area: 1,490 square inches
Length: 81 inches
Weight: 17 pounds
Power: E-flite Power 160 motor, Castle 85
amp ESC
Construction: Fan-fold foam, balsa, and
plywood
Covering/finish: Fiberglass cloth, automotive
primer, and acrylic enamel spray paint
Propeller: Zinger 20 x 6
fuselage in the build fixture. When the proper incidence angle was
found, I added sheeting doublers to the inside of the fuselage for a
wider joint and bonded the stabilizer in place.
The vertical fin has a thick base and shares its mount with a balsa
“spar” that extends to the fuselage tail. I needed to test-fit it several
times. Once it was in place, the LE block could be bonded in place
and blended with the fuselage.
For the Robart retracts to be in a scale position, the plywood
support ribs have to be installed after the wing is assembled. I
removed the sheeting between the ribs and cut the spar to
accommodate the stronger rib sections.
Enough of the spar was retained to make a good bond to the new
ribs; when the retract unit was fastened to the mount, the integrity of
the bottom spar was restored.
With the retract units in place, I started removing wing
sheeting and rib material until the wheels were inside the wing
with a 3/8-inch gap between the wheel and the wing sheeting. A
foam strip was cut to fit the wheel well and bonded in place. The
formed plastic gear fairings and gear doors were bonded to the
wing and rigged to the retract unit.
The motor mount was assembled on a flat surface to help get the
angles correct from the start. Its pyramid shape distributes the
motor’s load over a wider space and eases the cowl installation.
I bolted the motor to the mount and placed the assembly on the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 52February 2012 53 P-40
Warhawk Full-Size Plans Available—See Page 175
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:27 PM Page 5354 MODEL AVIATION
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:28 PM Page 54firewall with the fuselage held vertical. I
put the cowl in place and centered the shaft
to the cowl using the spinner backplate.
I removed the cowl carefully and
marked the motor mount position and
bonded it in place. I made small
adjustments to the thrustline using shim
washers.
Formed Plastic and Finish: A plastic set
for this model is available from Parkflyer
Plastics. This includes a 6-inch spinner and
backplate, gear fairings and doors, cockpit
detail, a pilot figure, canopy, cowl flaps,
exhaust stacks, and gun blisters.
The plans include a shopping list for the
materials from Lowe’s; however, you will
need to visit a hobby shop for the 3/4-ounce
fiberglass cloth and Zap finishing resin as
well as the basic RC hardware. I used
automotive primer to bring the surface to a
smooth finish and acrylic enamel spray
paint to apply the colors and markings.
Equipment: The E-flite 160 motor
provides enough power to fly this model
with a 20 x 6 propeller; however, you will
be pulling the maximum recommended 60
amps.
I chose the Castle 85 amp ESC for its
easy programming ability. There is plenty
of room for any servo you would likely use;
running dual servos for redundancy is the
safest route to take.
I’m using servos with 77 ounces of
torque for positive control. The battery
compartment is large enough to
accommodate any battery size you may
want to use. I’m running 10s, 5,000 mAh
lithium cells for longer flight times and
better wind penetration.
The Robart rotating retracts used on this
design will require removing the strut spring
and replacing it with one at half the wire
diameter for the strut to function properly.
This is an intimidating task and I assume it
voids the warranty, so the plans also include
patterns to build the model with fixed gear.
This option will save you nearly 2 pounds.
Flying: The Warhawk P-40 performs as you
would expect, given its light wing loading,
with shorter takeoff rolls, slower approach
speeds, and fly-bys that don’t look like you
are being chased. The model pulls to the left
on takeoff, but after the tail is off the ground
the rudder has positive control. Easing into
the throttle makes it predictable and looks
true to scale.
Adding flaps to this design would be a
waste; at half-power the P-40 will give you
the control you need and it will set up with a
good descent rate. A slight flair at touchdown
and cutting the power will give you a roll out
of roughly 25 feet.
At 2,100 watts of power, the E-flite 160
will provide enough power for basic flight in
5 to 10 mph winds. A roll required strict
attention to the controls and a loop needed a
dive to complete with a sluggish feel at the
top.
With my flight program complete, I have
found the minimum power requirement for
this design. Since the batteries barely get
warm after a flight, there is room for more
power so I will be installing a larger motor
soon to turn this design into a true warbird.
To my wife, Patrice—you have
supported me and my hobby for 22 years.
This one is for you. MA
Keith Sparks
[email protected]
Sources:
Robart
(630) 584-7616
www.robart.com
Park Flyer Plastics
(817) 233-1215
www.parkflyerplastics.com
E-flite
(877) 504-0233
www.e-fliterc.com
Castle Creations
(913) 390-6939
www.castlecreations.com

48 MODEL AVIATION
The author named his Warhawk P-40 after his wife, Patrice.
P-40
Warhawk
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 48February 2012 49
Giant Scale foam fighter
by Keith Sparks
The most noticeable difference is that
foam is easier to cut and sand. The
airframe is less expensive to build using
foam, and its lighter weight allows for a
more affordable power system to be used.
It is hard to tell that this Warhawk P-40
is made with the material commonly
referred to as fan-fold foam, until you see
it fly.
Construction: The fuselage is the best
place to start, so I cut all the fuselage
formers then built the assembly fixture.
That turned out to be the best $10 I ever
spent. I placed the electrical conduit over
the plans, marked each former position,
then slid the formers into position on the
conduit and mounted the assembly on the
fixture. I used a piece of plywood as a tool
to slide the formers into position without
damaging them; the fit is tight.
I used the side view to lay out the cuts
needed for the fuselage sheeting and began
bonding them in place, starting at the
FROM THE START, the goal for this
project was to build a large, lightweight,
1/4-scale model with materials easily
obtained from home-improvement stores.
Material availability has proved to be one
of the major obstacles with most of my
foam-based designs. Although the P-40
Warhawk uses light plywood and balsa in
areas requiring extra strength, the majority
of the airframe was purchased at my local
home improvement store.
The construction method will be
familiar to most scratch builders by
substituting wood with lighter foam
materials and wood workers’ glue with
polyurethane glue. The finish applied to the
model uses the same fiberglass and epoxy
resin methods employed on conventionally
constructed models.
cockpit notch. Using masking tape for
clamp pressure, I alternated between the
top and bottom, working from the center
outward.
When the polyurethane adhesive had
dried, I rough-trimmed the sheeting and
used a bar sander to level the tops and
bottoms of the sheeting and formers to
prepare them for the cap strips. I cut the
foam strips to fit the fuselage then bonded
them in place using masking tape for
clamp pressure.
A bar sander with 90-grit sandpaper
attached makes short work of the general
shape of the foam blocks; I switched to
120-grit sandpaper for the final step of
blending it to the side sheeting. The aft
bottom cap strip was saved for last to
allow me to install the pushrod guide
tubing.
For additional strength in the
midsection, I added sheet foam in between
the formers in the wing saddle area, then
temporarily removed the fuselage from the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:25 PM Page 4950 MODEL AVIATION
Photos by the author
tubing in position and installed the bottom
cap strip.
In order to return the fuselage to the
building fixture, I cut two 1-inch foam
blocks to fit snugly in the box beam and
drilled holes for only the upper conduit to
pass through. With the tubing level, the
fixture serves as the datum line and makes
the wing and stabilizer incidence easy to
set and check; it also gives you a
“floating” fuselage, making the application
of the 3/4-ounce fiberglass cloth easier.
I employed a water bottle as a round
sanding block to shape the window recess
and bonded the sheeting in place. After the
sheeting was sanded flush with the fuselage,
I applied the glass cloth.
Using a razor saw, I cut the equipment
hatch free from the fuselage and lined the
empty space with balsa sheeting to toughen
the lip of the hatch hole. I sanded the hatch
build fixture. I removed the conduit tubing
from the formers using a twisting motion.
The cowl was assembled with 3/4-inch
foam sheeting segments cut from the plans
patterns and assembled in a wedding-cake
fashion, paying attention to the alignment.
The assembly was tack-bonded onto the
fuselage and sanded to shape. The patterns
are close to net trim, so I advise that you cut
outside the line.
The fuselage was now fairly rigid, so I
removed the centers of the precut formers
before assembly started and installed the boxbeam
sides and bottom.
Several test fits, before applying the glue,
served as good assembly practice. Strips of
foam sheeting, cut 1/8 inch wider than the box
beam, were used for clamp pressure to hold
the box-beam walls against the formers while
the glue dried.
While that was drying, I put the pushrod
lid smaller to accommodate a balsa lining
for the same purpose.
With the hatch installed on the fuselage,
the balsa liners were sanded flush with the
fuselage surface. Rare earth magnets were
installed at the mating surface to hold it in
place. I repeated this “liner” treatment on
the cowl to fuselage seam.
Wing: I used the plans to cut the wing
sheeting panels and marked two of them
with the spar and rib positions by laying the
plans over the sheeting and piercing the
paper to give me accurate point-to-point
marks to work with.
Eight tapered spars were cut on a table
saw from a single piece of four-foot poplar
and lightly sanded. The forward spar is
bonded to the wing sheeting first.
After I used the ribs to locate the aft spar
position, the ribs and aft spar were bonded
Far left: This build fixture is invaluable for
complete access and keeping the formers
true during construction. It is used to
check angles as well as provide a hands-off
stand while applying the fiberglass cloth.
Left: The cowl was temporarily attached to the fuselage during the shaping step for a
perfect match. Keeping P-40 photos on hand helps to refine the shape.
Below left: The build fixture allowed the author to apply the fiberglass in one step. He
used two layers of masking tape on the hatch and cowl mating surfaces to prevent
them from bonding to the fuselage.
Below right: Weights and shims were used to bond the ribs to the bottom sheeting.
The polyurethane glue sets slowly, allowing plenty of time for adjustments.
Left: Sanding strips, bought on a roll or
cut from sanding belts, helped shape the
large cap strips. The author used masking
tape to apply clamp pressure to the cap
strip.
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 50February 2012 51
to the bottom sheeting. The upper spars
were used in the rib slots to hold their angle
while the assembly dried. The steps were
repeated for the other wing panel and the
two panels were joined after I adjusted the
joint to give me the proper wing dihedral.
The support plates for the wing dowels,
bolts, servo mount, and guide tubes were
next. At this point, the panels are still fairly
flexible and susceptible to warping, so after
the ribs were lightly sanded, I shimmed the
TE and aft spar to prepare for the top
sheeting.
Prebending the foam sheet before
installation makes the sheeting job easy
and the only “clamp tape” needed is along
the LE; the rest of the sheeting clamp
pressure is done with small weights.
I bonded balsa strips to the TE for bump
protection and added the 1/2-inch foam LE
and wingtip. After sanding the additional
parts to shape, I applied 3/4-ounce fiberglass
cloth to the wing.
Wing Saddle: With the fuselage on the
build fixture, I removed side sheeting in
the wing saddle area in small amounts until
it rested in the saddle with the proper
incidence angle. I added the wing dowel
and checked the angle again before I
drilled the wing bolt holes.
Two plywood strips were bonded to the
fuselage wing saddle area and I bolted the
wing in place to apply the clamp pressure.
I cut foam blocks to fit the space between
the plywood strips and blended to the
fuselage with 120-grit sandpaper wrapped
around a plastic bottle to form the wing
fillet.
The stabilizer frames were assembled
upright on a flat board using tape and
spacers to hold them in place while they
Right: The wing panels were joined with a
pair of shear webbing-type plates that
doubled as the landing gear support. With
one panel flat on the work surface the
other was supported at the tip to achieve
the proper dihedral.
Right: Small portions of the fuselage were sanded away during the wing saddle step
with incidence checks along the way. The build fixture will hold the fuselage datum at
zero while you work, making the task easier.
Below: Building the wing fillets using small blocks rather than large ones will reduce
sanding and give you a more complete surface-to-surface bond joint.
Below right: After the stabilizer frame was complete, it was sandwiched between the
top and bottom sheeting. Bonding both sheets at the same time helps to prevent
surface warping.
Far right: Weights were used to clamp
the top sheeting in place. Scrap spar
sticks bridged the applied weight over the
ribs so the skin didn’t dip between them.
dried. One of the advantages of polyurethane
glue is that as it sets it thickens and foams,
allowing plenty adjustment time. I bonded
both sides of the sheeting to the stabilizer
frames at the same time to avoid building a
warped surface.
I used masking tape for clamp pressure
and applied it from the center of the edges
toward the corners. The LEs were added,
sanded to shape, and fiberglass applied.
I built the control surfaces with basic
balsa construction methods, which was
necessary to achieve the fabric-covered-rib
look needed on a P-40. I cut the panels to
profile, added the LEs, and installed the ribs.
Hinges were installed and the surfaces were
fitted to the wing and stabilizers. All that
remained was to sand them to shape and
cover with the iron-on covering.
Adding the horizontal stabilizer to the
fuselage was done by trim and fit with the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 5152 MODEL AVIATION
A hole was cut in the bottom wing
sheeting to install the gear support plate.
The lower spar extends beyond the plate
and masking tape caps the air lines to
avoid contamination.
The gear doors can be rigged to the
retract unit and operated automatically.
The wheel well has been lined with foam
sheeting.
With the model in the build fixture, the horizontal stabilizer was
fitted to the fuselage similar to the way the wing was attached.
The 1/16-plywood strip gives the hinge line a scale look.
After the fin was in place, foam blocks formed the fillet and fair
the fuselage into the tail group. A fuselage stand made from scrap
sheeting was constructed for storing and transport.
The motor and ESC mount in a good
position for cooling air and the box-type
motor mount allows for small thrustline
adjustments using shim washers.
Specifications
Type: RC Scale model
Skill level: Intermediate builder,
intermediate pilot
Wingspan: 95 inches
Wing area: 1,490 square inches
Length: 81 inches
Weight: 17 pounds
Power: E-flite Power 160 motor, Castle 85
amp ESC
Construction: Fan-fold foam, balsa, and
plywood
Covering/finish: Fiberglass cloth, automotive
primer, and acrylic enamel spray paint
Propeller: Zinger 20 x 6
fuselage in the build fixture. When the proper incidence angle was
found, I added sheeting doublers to the inside of the fuselage for a
wider joint and bonded the stabilizer in place.
The vertical fin has a thick base and shares its mount with a balsa
“spar” that extends to the fuselage tail. I needed to test-fit it several
times. Once it was in place, the LE block could be bonded in place
and blended with the fuselage.
For the Robart retracts to be in a scale position, the plywood
support ribs have to be installed after the wing is assembled. I
removed the sheeting between the ribs and cut the spar to
accommodate the stronger rib sections.
Enough of the spar was retained to make a good bond to the new
ribs; when the retract unit was fastened to the mount, the integrity of
the bottom spar was restored.
With the retract units in place, I started removing wing
sheeting and rib material until the wheels were inside the wing
with a 3/8-inch gap between the wheel and the wing sheeting. A
foam strip was cut to fit the wheel well and bonded in place. The
formed plastic gear fairings and gear doors were bonded to the
wing and rigged to the retract unit.
The motor mount was assembled on a flat surface to help get the
angles correct from the start. Its pyramid shape distributes the
motor’s load over a wider space and eases the cowl installation.
I bolted the motor to the mount and placed the assembly on the
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:26 PM Page 52February 2012 53 P-40
Warhawk Full-Size Plans Available—See Page 175
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:27 PM Page 5354 MODEL AVIATION
02sig2.QXD_00MSTRPG.QXD 12/16/11 12:28 PM Page 54firewall with the fuselage held vertical. I
put the cowl in place and centered the shaft
to the cowl using the spinner backplate.
I removed the cowl carefully and
marked the motor mount position and
bonded it in place. I made small
adjustments to the thrustline using shim
washers.
Formed Plastic and Finish: A plastic set
for this model is available from Parkflyer
Plastics. This includes a 6-inch spinner and
backplate, gear fairings and doors, cockpit
detail, a pilot figure, canopy, cowl flaps,
exhaust stacks, and gun blisters.
The plans include a shopping list for the
materials from Lowe’s; however, you will
need to visit a hobby shop for the 3/4-ounce
fiberglass cloth and Zap finishing resin as
well as the basic RC hardware. I used
automotive primer to bring the surface to a
smooth finish and acrylic enamel spray
paint to apply the colors and markings.
Equipment: The E-flite 160 motor
provides enough power to fly this model
with a 20 x 6 propeller; however, you will
be pulling the maximum recommended 60
amps.
I chose the Castle 85 amp ESC for its
easy programming ability. There is plenty
of room for any servo you would likely use;
running dual servos for redundancy is the
safest route to take.
I’m using servos with 77 ounces of
torque for positive control. The battery
compartment is large enough to
accommodate any battery size you may
want to use. I’m running 10s, 5,000 mAh
lithium cells for longer flight times and
better wind penetration.
The Robart rotating retracts used on this
design will require removing the strut spring
and replacing it with one at half the wire
diameter for the strut to function properly.
This is an intimidating task and I assume it
voids the warranty, so the plans also include
patterns to build the model with fixed gear.
This option will save you nearly 2 pounds.
Flying: The Warhawk P-40 performs as you
would expect, given its light wing loading,
with shorter takeoff rolls, slower approach
speeds, and fly-bys that don’t look like you
are being chased. The model pulls to the left
on takeoff, but after the tail is off the ground
the rudder has positive control. Easing into
the throttle makes it predictable and looks
true to scale.
Adding flaps to this design would be a
waste; at half-power the P-40 will give you
the control you need and it will set up with a
good descent rate. A slight flair at touchdown
and cutting the power will give you a roll out
of roughly 25 feet.
At 2,100 watts of power, the E-flite 160
will provide enough power for basic flight in
5 to 10 mph winds. A roll required strict
attention to the controls and a loop needed a
dive to complete with a sluggish feel at the
top.
With my flight program complete, I have
found the minimum power requirement for
this design. Since the batteries barely get
warm after a flight, there is room for more
power so I will be installing a larger motor
soon to turn this design into a true warbird.
To my wife, Patrice—you have
supported me and my hobby for 22 years.
This one is for you. MA
Keith Sparks
[email protected]
Sources:
Robart
(630) 584-7616
www.robart.com
Park Flyer Plastics
(817) 233-1215
www.parkflyerplastics.com
E-flite
(877) 504-0233
www.e-fliterc.com
Castle Creations
(913) 390-6939
www.castlecreations.com