Plane Talk: Dymond Modelsport Bearcat ARF

44 MODEL AVIATION
A 40-size
sport-scale
version of the
US Navy’s
ultimate World
War II pursuit
fighter
MICHAEL RAMSEY
IT SEEMS THAT if a person wants a
realistic ARF warbird, he or she needs to look
at something that is roughly 60 size to find the
most options. Little is offered in 40 size
unless the modeler is looking for a Mustang
or a Texan. If an enthusiast wants to get into
heavy-metal warbirds, does that mean he or
she has to move up to a bigger model?
The Dymond Modelsport Bearcat ARF
took me by surprise when I first saw it
because it was rare and different. It was
compact and had features that were similar to
a 60-size model, such as a retract option, but
called for a more economical .40-size power
plant.
The fiberglass fuselage maintained the
Bearcat’s brute looks, and the kit’s low parts
count made the overall scale project seem less
daunting. In this article you’ll learn that this
Bearcat is a good selection for the modeler
who is looking for a 40-size warbird.
Dymond Modelsport offers the 57-inchwingspan
Bearcat in two colors: blue and
black. I chose blue because I wanted my
model to represent the famous warbird rather
than the famous racer the Bearcat became
after it was retired from the military.
The fiberglass fuselage includes the
cockpit detail and vertical fin. Plywood
formers and doublers are installed; they make
up the hard points, stabilizer saddle, and
firewall. They strengthen key areas of the
thin-skinned structure while adding minimal
weight.
The all-wood wing panels are fully
sheeted and use a strong wood joiner that
supports the structure after the assembly is
bound together with epoxy. The wing’s
semisymmetrical cross-section is relatively
thick, to promote lift and house the optional
retracts. The fair amount of dihedral in the
wing promotes stability.
The built-up ailerons appear to be the scale
shape. Hatch doors for the aileron servos are
located on the bottom of the wing, near the
tips. As are the ailerons, the rudder and
elevator are open-frame structures, identical to
the full-scale airplane, but the flat stabilizer
uses stick construction to keep the tail as light
as possible.
The clear canopy is painted and trimmed
to match the model. The accessory package
includes metric hardware, a fuel tank, fixed
landing gear, basic instructions, and a selfadhesive
decal sheet. The cowling and belly
pan are molded fiberglass, as is the fuselage,
and match the covering’s color wonderfully.
I like that this Bearcat maintains the fullscale
fighter’s short nose and scale outline,
but this typically means that balancing
requires extra ballast up front. From the start I
planned on going with glow power. Although
the specified .40- to .50-size engine could
power the model nicely, a larger engine would
satisfy the need for working nose weight; a
four-stroke would do the job even better.
The O.S. .70 Surpass that had been
dormant in my drawer seemed to be an ideal
choice for the round-nose beast. Only the
valve cover and muffler would stick out of the
cowling, and the engine could be mounted
inverted neatly since I had no trouble running
it that way before.
A clever modeler could convert this
Bearcat to electric power. However, it would
Top: The Bearcat can cruise smoothly with
mechanical retracts up. Above: The recommended
control throws are perfect for sport and scale flying.
The decals shown were included with the kit.
Plane Talk: Dymond Modelsport Bearcat ARF
01sig2.QXD 11/19/07 2:41 PM Page 44
Photos by the author and Mark Lanterman
The muffler is installed after the cowling. The fiberglass cowl is a
good fit around the nose.
The engine should be mounted offset to
the left and then shimmed 2°-3° to the
right. It has plenty of breathing room.
The Bearcat parts count is low. The fiberglass molded fuselage is stiff and straight. The
metric hardware is suitable. The wing is fully sheeted with balsa.
Each aileron has its own servo. The servo-arm hole was enlarged
to accept the nylon clevis.
The stabilizer is stick-built to save weight. The elevators are
tapered at the TE to provide crisp control response.
The landing-gear mount will accept almost any 6-pound-weightlimit
retract mechanism. Hobbico retracts are shown.
January 2008 45
01sig2.QXD 11/19/07 2:19 PM Page 45
46 MODEL AVIATION
The one-piece wing is secured with two 4mm machine screws. The Master Airscrew 12 x
6 three-blade propeller works well.
The Bearcat has panel-line detail molded into the fuselage and cowling. Notice the semisymmetrical airfoil for good slow-speed handling.
be necessary to engineer a battery tray (likely
inside the cowl), and cooling ducts would be
needed.
Dymond Modelsport sells an electric
package that should fulfill the 500- to 600-
watt power requirement. Heavier batteries
such as the A123 Nanophosphate Li-Ion type
would offer loads of power and satisfy the
extra-nose-weight requirement.
Standard radio equipment is more than
adequate for this model. However, the small
ailerons require only approximately 30 inchounce
of torque for solid control. I used
miniservos instead to keep the wingtips light,
and they fit inside the hatch opening better.
Construction: My opinion about the
instructions led me to conclude that someone
with building experience, and practice at
installing retracts, would have no trouble
assembling this model. Because the instruction
text is minimal, vague, and out of order in
some areas, less-experienced builders might
do some head scratching.
The questions I had during the build were
quickly answered with a phone call to
Dymond Modelsport, and I found the data
provided in the manual, such as the CG, to be
correct. The value of this model is good
overall, even though the instructions aren’t the
super-detailed type such as those that
accompany some novice trainers.
The Bearcat’s landing-gear hard points
include solid-wood rails on plywood rib
doublers. To tie these parts together better I
poured a large amount of epoxy putty inside
the gear-mount area. With a brush and trowel I
saturated and filleted every joint with the glue
mixture. Whether I fly from grass or smooth
pavement, this extra step assures me that the
landing gear is less likely to be torn from the
model under normal conditions.
There’s no shame in installing the fixedgear
option as a start; it includes a hefty wood
filler block that is milled to accept the heavy
wire struts. The fixed-gear assembly is secured
with nylon straps and screws, which is simple
and easy to maintain. You can add retracts
later.
The mounting points in the wing can house
most of the popular 6-pound-rated retract
mechanisms. Matching wheel-well covers are
included to dress up the cutouts. They
interfere with the mechanics, but they dress up
the fixed-gear installation nicely.
You should mount the retract servo as far
into the wing as possible to avoid interference
with the fuel tank, which sits close to the wing
saddle. This means carving a little deeper into
the wing rib. The instructions contain good
advice for correctly sizing the builderprovided
retract pushrod linkages. Heavy-duty
EZ connectors on the servo make adjusting the
system painless.
The control linkage provided is strong and
well suited for this model. When setting up the
The rudder control
is pull-pull. Each
elevator half is
connected to a
split pushrod.
01sig2.QXD 11/19/07 2:24 PM Page 46
+
• Compact size to suit smaller glow
engines
• Fiberglass fuselage with handsome
scale detail
• Ready for retracts
• Fast, nimble performance
-• Generic instructions are not for
beginners
• Landing-gear mounts need
reinforcement
• Excessive ballast is required
• Elevator pushrod support is required
Pluses and Minuses
Model type: Sport-scale ARF
Pilot skill level:
Intermediate
Wingspan: 57 inches
Wing area: 500 square
inches
Length: 39 inches
Weight: 5.0-6.2 pounds
Wing loading: 25.6 ounces/
square foot
Engine: .40-.50 two-stroke
or .52-.63 four-stroke
Electric option: 500- to
600-watt power system
Radio: Four- to six-channel
radio, five or six servos
Construction: Fiberglass
fuselage and cowl, fully
sheeted balsa-and-plywood
wing, built-up balsa stabilizer,
elevator, rudder
Covering/finish:
Polyurethane paint, heatshrink
film covering
Price: $139
Specifications
Engine used: O.S. FS-70
Surpass
Propeller: Master Airscrew
12 x 6 three-blade
Fuel: 12.5-ounce tank,
Magnum #1 fuel
Radio system: Hitec Optic
6 transmitter; Hitec receiver;
three Hitec HS-325 servos;
two Hitec HS-81 servos; one
Futaba 136G retract servo;
600 mAh, 4.8-volt battery;
three 12-inch extensions;
one Y harness; one 9-inch
extension
Ready-to-fly weight: 6
pounds, 14 ounces
Ready-to-fly wing loading:
31.7 ounces/square foot
Flight duration: 10-15
minutes
aileron control, consider adjusting the linkage
to include mechanical differential: more up
than down movement. This setup will
promote axial rolls and lessen the possibility
of tip-stalling at low speeds when high
deflections of aileron input induce a rollreversal
effect. Computer-radio users can
program in this option and experiment to find
out how much this setup helps.
All the slots are precut for the
cyanoacrylate-type hinges. The beveled
control surfaces have a nice, sharp point so the
hinge gap can be made as minimal as
possible.
There’s a slight mix-up in the directions.
They instruct the builder to install the rudder
before the tail-wheel assembly.
Install the tail wheel, and then bend the
wire at the proper location to make a tiller
arm. Transfer the tiller-arm location to the
rudder and trim the area as necessary for a
tight fit. Permanently glue the rudder in place
with a generous amount of epoxy on the tiller
arm so it can take the steering loads.
The slot in the tail for the horizontal
stabilizer is oversized so that final alignment
to the wing can be completed easily. The
instructions for how to align everything were
great. Be sure to shim the stabilizer evenly
with plywood so you don’t change its
incidence.
Sand the saddle to promote a good bond of
the epoxy/microballoon mix and balsa
stabilizer. You can hide the glue seam later
with a few light coats of Top Flite LustreKote
Sapphire Blue sprayed into a dish and then
applied with a fine-tip brush.
The rudder is controlled using a
lightweight pull-pull system. The only
challenge to the builder here is where to locate
the exit holes in the fuselage.
A yardstick is helpful in projecting where
the holes should be located on the fuselage
side. Mark on the outside where the servo
arms are located, and draw a line from that
point to the control horns. It’s important that
the pushrod exits straight to prevent binding.
The elevator pushrod and rudder-cable exit
holes should end up over the middle of the
stabilizer.
Elevator control is managed with the
factory-assembled split pushrod. To prevent
flutter and improve the accuracy of the
independent elevator halves’ movement, add a
balsa pushrod support at the former between
the stabilizer and the wing. I didn’t make this
modification until I had a few flights on the
airplane.
I used 1/4 x 1/2 stick balsa with a 3/8-inch
hole drilled on center to support the wood
pushrod. Do not skip this modification if you
choose to overpower your Bearcat, as I did.
Locate the engine by using the hole in the
center of the firewall as a guide. Offset the
engine to the left and shim it so right thrust
can be added. For a strong power plant such as
the O.S. .70, I found 3° of right thrust to be
helpful. If a .40 engine is used, approximately
2° of right offset will work fine.
Mount the engine on the nylon rails as far
forward as possible to effectively distribute
the weight. The cowl should be mounted so
that there’s a gap at the back of the right and
left sides. These bulges will promote air to
flow through the openings and keep the
engine cool.
Mount the battery and receiver as far
forward in the model as possible. I added a
pilot to the cockpit before securing the canopy
with RC/56 adhesive. Sandbags were helpful
to weight the canopy down around the lip
molded into the fuselage.
The belly pan was fitted to the wing as the
canopy was, using the sandbags to hold the
parts together while the glue dried. I added
strips of balsa to the inside of the belly pan to
increase the glue contact area. I covered the
gap between the two parts on the wing with
Sapphire Blue MonoKote.
With the Bearcat completely assembled
and pretty, I placed it inverted on a Great
Planes balancing stand. I had to add 5.8
ounces of ballast to the model’s nose to
achieve the recommended CG. I mixed lead
shot with a small amount of epoxy and
distributed it evenly around the front inside
lip of the cowling.
Once the cowl was ready I fitted it back
onto the model for the final CG check. Bits of
the lead shot could have been drilled out if
fine-tuning was required.
The airplane’s covering doesn’t like
extreme heat; it darkens the pigment. The
decals added the finishing touches to the
January 2008 47
Test-Model Details
01sig2.QXD 11/19/07 2:41 PM Page 47
model. Another final touch would have been
to seal the gear recesses with matching
fuelproof paint. The control surfaces were set
to have the recommended control movement
as low rates and maximum deflection at high
rates.
Flying: An overweight warbird model needs a
reliable engine, so I paid attention to the .70
Surpass. The inverted installation required a
leaner-than-normal low-end needle setting, but
the high-end needle could be set as required.
The Master Airscrew 12 x 6 three-blade
propeller absorbed the engine’s extra
horsepower and provided a unique sound.
There’s enough ground clearance to support a
13-inch propeller.
Although this Bearcat’s gear length is
shorter than scale, its low-rider form made
ground handling much easier. I did all testing
from a paved runway. The small wheels
included with the model were well suited to
this environment, but those who fly from grass
might nose-over more easily. Consider larger
wheels and opening the recesses in the wing.
Because of the higher-than-specified wing
loading, the first takeoff and subsequent
maneuvers were done in a scale and graceful
fashion. I didn’t want to do anything abrupt
that would cause the model to snap.
The Bearcat left the ground just after the
smooth throttle application passed the halfway
point. The .70’s power was overkill, but it was
very cool.
The low rates provided the smooth control
maneuverability I was hoping to have. The
Bearcat reached a high testing altitude before
the first circuit around the field could be
completed. Confidence in this airplane was
built quickly, and on the second pass the
retractable gear was brought up—although the
model was too high to appreciate the
sequence.
The Bearcat cruised smartly with the
throttle set at just less than half. In a cruise
only small trim adjustments were required,
mostly to the elevator.
The 3° of right thrust compensated for the
large engine’s torque; pulls to vertical and
loops could be flown straight with little or no
rudder correction. I had no complaints about
the aileron control, and rolling was axial and
smooth, as predicted. Crisp Point Rolls were
also possible.
Slow-speed testing had me giggling
because the heavy Bearcat showed no bad
habits. Stalls were soft and always broke to
the left, either up- or downwind. Testing the
model at high rates concluded that rolls could
be made as fast as with a 3-D sport model, but
the pitch stability was harder to manage.
I could see the higher control deflections
being helpful for Point Rolls, but the higher
elevator rate is probably best used only while
taxiing. Approximately 30% exponential
would be programmed into the high rates
later.
I used full throttle only for climbing.
During initial high-speed testing I found out
why the elevator pushrod support was needed.
Slow sport aircraft get away with a floating
pushrod, but fast, heavy models create enough
of a load on the tail to create flutter. Later
testing with the pushrod support installed
showed that the Bearcat could dive and run
flat out with no problems.
Earlier slow-speed testing also confirmed
that aileron control faded near the stall break,
so landings were best performed well above
stall speed. This airplane’s solid feel was a
comfort during the landing sequence.
Once it was lined up on the runway, it was
easy to settle down to the centerline. The lowrate
control input provided smooth pitch
corrections that allowed the model to maintain
steady airspeed until the flare. I wouldn’t
describe this short-coupled aircraft as touchy
at all.
The Bearcat slows quickly once the throttle
is reduced, so the high-throttle landing
approaches won’t stretch into long glides. This
model is easy to fly and land exactly where
you want it. It is possible to three-point the
landing since the wingtips stay level well after
the stall has occurred.
During later flights, tighter turns proved to
be comfortable to perform; again, no highwing-
loading issues surfaced. Inverted flight
requires just a touch of down, so the balance
point is precisely where I like it for this type of
model. Snaps can be flown, but they don’t
look like something a Bearcat should do.
I’ve been flying this model for almost a
full season and the Hobbico retracts are
wearing out. No structural issues have
surfaced, but some cracks in the paint are
appearing on the cowl.
Since I fly the model at half throttle most
of the time, I don’t see any reason why a .40-
class engine couldn’t work well in this
Bearcat. More ballast would be needed in
the nose area, which would put more stress
on the cowl mounting points. I like the extra
power the .70 provides, and who doesn’t like
a model that accelerates quickly?
The Dymond Modelsport Bearcat has been
a fun project. It turns heads at the field, and
because of its small size I can fit other
models in the car with it for a well-rounded
day of flying.
If you want one of these airplanes, keep
in mind that the quantity might be limited. If
Dymond Modelsport came out with another
warbird like the Bearcat, I’m sure it would
also be worthy of serious consideration. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
Dymond Modelsport Ltd.
3904 Convoy St. #110
San Diego CA 92111
(858) 495-0092
www.rc-dymond.com
Products Used in Review:
FS-70 II Surpass:
O.S. Engines
(217) 398-8970
www.osengines.com
Radio system:
Hitec
(858) 748-6948
www.hitecrcd.com
Retract servo:
Futaba
(217) 398-8970
www.futaba-rc.com
Propeller:
Master Airscrew
(916) 631-8385
www.masterairscrew.com
Other Review Sources:
None
48 MODEL AVIATION
01sig2.QXD 11/19/07 2:24 PM Page 48

44 MODEL AVIATION
A 40-size
sport-scale
version of the
US Navy’s
ultimate World
War II pursuit
fighter
MICHAEL RAMSEY
IT SEEMS THAT if a person wants a
realistic ARF warbird, he or she needs to look
at something that is roughly 60 size to find the
most options. Little is offered in 40 size
unless the modeler is looking for a Mustang
or a Texan. If an enthusiast wants to get into
heavy-metal warbirds, does that mean he or
she has to move up to a bigger model?
The Dymond Modelsport Bearcat ARF
took me by surprise when I first saw it
because it was rare and different. It was
compact and had features that were similar to
a 60-size model, such as a retract option, but
called for a more economical .40-size power
plant.
The fiberglass fuselage maintained the
Bearcat’s brute looks, and the kit’s low parts
count made the overall scale project seem less
daunting. In this article you’ll learn that this
Bearcat is a good selection for the modeler
who is looking for a 40-size warbird.
Dymond Modelsport offers the 57-inchwingspan
Bearcat in two colors: blue and
black. I chose blue because I wanted my
model to represent the famous warbird rather
than the famous racer the Bearcat became
after it was retired from the military.
The fiberglass fuselage includes the
cockpit detail and vertical fin. Plywood
formers and doublers are installed; they make
up the hard points, stabilizer saddle, and
firewall. They strengthen key areas of the
thin-skinned structure while adding minimal
weight.
The all-wood wing panels are fully
sheeted and use a strong wood joiner that
supports the structure after the assembly is
bound together with epoxy. The wing’s
semisymmetrical cross-section is relatively
thick, to promote lift and house the optional
retracts. The fair amount of dihedral in the
wing promotes stability.
The built-up ailerons appear to be the scale
shape. Hatch doors for the aileron servos are
located on the bottom of the wing, near the
tips. As are the ailerons, the rudder and
elevator are open-frame structures, identical to
the full-scale airplane, but the flat stabilizer
uses stick construction to keep the tail as light
as possible.
The clear canopy is painted and trimmed
to match the model. The accessory package
includes metric hardware, a fuel tank, fixed
landing gear, basic instructions, and a selfadhesive
decal sheet. The cowling and belly
pan are molded fiberglass, as is the fuselage,
and match the covering’s color wonderfully.
I like that this Bearcat maintains the fullscale
fighter’s short nose and scale outline,
but this typically means that balancing
requires extra ballast up front. From the start I
planned on going with glow power. Although
the specified .40- to .50-size engine could
power the model nicely, a larger engine would
satisfy the need for working nose weight; a
four-stroke would do the job even better.
The O.S. .70 Surpass that had been
dormant in my drawer seemed to be an ideal
choice for the round-nose beast. Only the
valve cover and muffler would stick out of the
cowling, and the engine could be mounted
inverted neatly since I had no trouble running
it that way before.
A clever modeler could convert this
Bearcat to electric power. However, it would
Top: The Bearcat can cruise smoothly with
mechanical retracts up. Above: The recommended
control throws are perfect for sport and scale flying.
The decals shown were included with the kit.
Plane Talk: Dymond Modelsport Bearcat ARF
01sig2.QXD 11/19/07 2:41 PM Page 44
Photos by the author and Mark Lanterman
The muffler is installed after the cowling. The fiberglass cowl is a
good fit around the nose.
The engine should be mounted offset to
the left and then shimmed 2°-3° to the
right. It has plenty of breathing room.
The Bearcat parts count is low. The fiberglass molded fuselage is stiff and straight. The
metric hardware is suitable. The wing is fully sheeted with balsa.
Each aileron has its own servo. The servo-arm hole was enlarged
to accept the nylon clevis.
The stabilizer is stick-built to save weight. The elevators are
tapered at the TE to provide crisp control response.
The landing-gear mount will accept almost any 6-pound-weightlimit
retract mechanism. Hobbico retracts are shown.
January 2008 45
01sig2.QXD 11/19/07 2:19 PM Page 45
46 MODEL AVIATION
The one-piece wing is secured with two 4mm machine screws. The Master Airscrew 12 x
6 three-blade propeller works well.
The Bearcat has panel-line detail molded into the fuselage and cowling. Notice the semisymmetrical airfoil for good slow-speed handling.
be necessary to engineer a battery tray (likely
inside the cowl), and cooling ducts would be
needed.
Dymond Modelsport sells an electric
package that should fulfill the 500- to 600-
watt power requirement. Heavier batteries
such as the A123 Nanophosphate Li-Ion type
would offer loads of power and satisfy the
extra-nose-weight requirement.
Standard radio equipment is more than
adequate for this model. However, the small
ailerons require only approximately 30 inchounce
of torque for solid control. I used
miniservos instead to keep the wingtips light,
and they fit inside the hatch opening better.
Construction: My opinion about the
instructions led me to conclude that someone
with building experience, and practice at
installing retracts, would have no trouble
assembling this model. Because the instruction
text is minimal, vague, and out of order in
some areas, less-experienced builders might
do some head scratching.
The questions I had during the build were
quickly answered with a phone call to
Dymond Modelsport, and I found the data
provided in the manual, such as the CG, to be
correct. The value of this model is good
overall, even though the instructions aren’t the
super-detailed type such as those that
accompany some novice trainers.
The Bearcat’s landing-gear hard points
include solid-wood rails on plywood rib
doublers. To tie these parts together better I
poured a large amount of epoxy putty inside
the gear-mount area. With a brush and trowel I
saturated and filleted every joint with the glue
mixture. Whether I fly from grass or smooth
pavement, this extra step assures me that the
landing gear is less likely to be torn from the
model under normal conditions.
There’s no shame in installing the fixedgear
option as a start; it includes a hefty wood
filler block that is milled to accept the heavy
wire struts. The fixed-gear assembly is secured
with nylon straps and screws, which is simple
and easy to maintain. You can add retracts
later.
The mounting points in the wing can house
most of the popular 6-pound-rated retract
mechanisms. Matching wheel-well covers are
included to dress up the cutouts. They
interfere with the mechanics, but they dress up
the fixed-gear installation nicely.
You should mount the retract servo as far
into the wing as possible to avoid interference
with the fuel tank, which sits close to the wing
saddle. This means carving a little deeper into
the wing rib. The instructions contain good
advice for correctly sizing the builderprovided
retract pushrod linkages. Heavy-duty
EZ connectors on the servo make adjusting the
system painless.
The control linkage provided is strong and
well suited for this model. When setting up the
The rudder control
is pull-pull. Each
elevator half is
connected to a
split pushrod.
01sig2.QXD 11/19/07 2:24 PM Page 46
+
• Compact size to suit smaller glow
engines
• Fiberglass fuselage with handsome
scale detail
• Ready for retracts
• Fast, nimble performance
-• Generic instructions are not for
beginners
• Landing-gear mounts need
reinforcement
• Excessive ballast is required
• Elevator pushrod support is required
Pluses and Minuses
Model type: Sport-scale ARF
Pilot skill level:
Intermediate
Wingspan: 57 inches
Wing area: 500 square
inches
Length: 39 inches
Weight: 5.0-6.2 pounds
Wing loading: 25.6 ounces/
square foot
Engine: .40-.50 two-stroke
or .52-.63 four-stroke
Electric option: 500- to
600-watt power system
Radio: Four- to six-channel
radio, five or six servos
Construction: Fiberglass
fuselage and cowl, fully
sheeted balsa-and-plywood
wing, built-up balsa stabilizer,
elevator, rudder
Covering/finish:
Polyurethane paint, heatshrink
film covering
Price: $139
Specifications
Engine used: O.S. FS-70
Surpass
Propeller: Master Airscrew
12 x 6 three-blade
Fuel: 12.5-ounce tank,
Magnum #1 fuel
Radio system: Hitec Optic
6 transmitter; Hitec receiver;
three Hitec HS-325 servos;
two Hitec HS-81 servos; one
Futaba 136G retract servo;
600 mAh, 4.8-volt battery;
three 12-inch extensions;
one Y harness; one 9-inch
extension
Ready-to-fly weight: 6
pounds, 14 ounces
Ready-to-fly wing loading:
31.7 ounces/square foot
Flight duration: 10-15
minutes
aileron control, consider adjusting the linkage
to include mechanical differential: more up
than down movement. This setup will
promote axial rolls and lessen the possibility
of tip-stalling at low speeds when high
deflections of aileron input induce a rollreversal
effect. Computer-radio users can
program in this option and experiment to find
out how much this setup helps.
All the slots are precut for the
cyanoacrylate-type hinges. The beveled
control surfaces have a nice, sharp point so the
hinge gap can be made as minimal as
possible.
There’s a slight mix-up in the directions.
They instruct the builder to install the rudder
before the tail-wheel assembly.
Install the tail wheel, and then bend the
wire at the proper location to make a tiller
arm. Transfer the tiller-arm location to the
rudder and trim the area as necessary for a
tight fit. Permanently glue the rudder in place
with a generous amount of epoxy on the tiller
arm so it can take the steering loads.
The slot in the tail for the horizontal
stabilizer is oversized so that final alignment
to the wing can be completed easily. The
instructions for how to align everything were
great. Be sure to shim the stabilizer evenly
with plywood so you don’t change its
incidence.
Sand the saddle to promote a good bond of
the epoxy/microballoon mix and balsa
stabilizer. You can hide the glue seam later
with a few light coats of Top Flite LustreKote
Sapphire Blue sprayed into a dish and then
applied with a fine-tip brush.
The rudder is controlled using a
lightweight pull-pull system. The only
challenge to the builder here is where to locate
the exit holes in the fuselage.
A yardstick is helpful in projecting where
the holes should be located on the fuselage
side. Mark on the outside where the servo
arms are located, and draw a line from that
point to the control horns. It’s important that
the pushrod exits straight to prevent binding.
The elevator pushrod and rudder-cable exit
holes should end up over the middle of the
stabilizer.
Elevator control is managed with the
factory-assembled split pushrod. To prevent
flutter and improve the accuracy of the
independent elevator halves’ movement, add a
balsa pushrod support at the former between
the stabilizer and the wing. I didn’t make this
modification until I had a few flights on the
airplane.
I used 1/4 x 1/2 stick balsa with a 3/8-inch
hole drilled on center to support the wood
pushrod. Do not skip this modification if you
choose to overpower your Bearcat, as I did.
Locate the engine by using the hole in the
center of the firewall as a guide. Offset the
engine to the left and shim it so right thrust
can be added. For a strong power plant such as
the O.S. .70, I found 3° of right thrust to be
helpful. If a .40 engine is used, approximately
2° of right offset will work fine.
Mount the engine on the nylon rails as far
forward as possible to effectively distribute
the weight. The cowl should be mounted so
that there’s a gap at the back of the right and
left sides. These bulges will promote air to
flow through the openings and keep the
engine cool.
Mount the battery and receiver as far
forward in the model as possible. I added a
pilot to the cockpit before securing the canopy
with RC/56 adhesive. Sandbags were helpful
to weight the canopy down around the lip
molded into the fuselage.
The belly pan was fitted to the wing as the
canopy was, using the sandbags to hold the
parts together while the glue dried. I added
strips of balsa to the inside of the belly pan to
increase the glue contact area. I covered the
gap between the two parts on the wing with
Sapphire Blue MonoKote.
With the Bearcat completely assembled
and pretty, I placed it inverted on a Great
Planes balancing stand. I had to add 5.8
ounces of ballast to the model’s nose to
achieve the recommended CG. I mixed lead
shot with a small amount of epoxy and
distributed it evenly around the front inside
lip of the cowling.
Once the cowl was ready I fitted it back
onto the model for the final CG check. Bits of
the lead shot could have been drilled out if
fine-tuning was required.
The airplane’s covering doesn’t like
extreme heat; it darkens the pigment. The
decals added the finishing touches to the
January 2008 47
Test-Model Details
01sig2.QXD 11/19/07 2:41 PM Page 47
model. Another final touch would have been
to seal the gear recesses with matching
fuelproof paint. The control surfaces were set
to have the recommended control movement
as low rates and maximum deflection at high
rates.
Flying: An overweight warbird model needs a
reliable engine, so I paid attention to the .70
Surpass. The inverted installation required a
leaner-than-normal low-end needle setting, but
the high-end needle could be set as required.
The Master Airscrew 12 x 6 three-blade
propeller absorbed the engine’s extra
horsepower and provided a unique sound.
There’s enough ground clearance to support a
13-inch propeller.
Although this Bearcat’s gear length is
shorter than scale, its low-rider form made
ground handling much easier. I did all testing
from a paved runway. The small wheels
included with the model were well suited to
this environment, but those who fly from grass
might nose-over more easily. Consider larger
wheels and opening the recesses in the wing.
Because of the higher-than-specified wing
loading, the first takeoff and subsequent
maneuvers were done in a scale and graceful
fashion. I didn’t want to do anything abrupt
that would cause the model to snap.
The Bearcat left the ground just after the
smooth throttle application passed the halfway
point. The .70’s power was overkill, but it was
very cool.
The low rates provided the smooth control
maneuverability I was hoping to have. The
Bearcat reached a high testing altitude before
the first circuit around the field could be
completed. Confidence in this airplane was
built quickly, and on the second pass the
retractable gear was brought up—although the
model was too high to appreciate the
sequence.
The Bearcat cruised smartly with the
throttle set at just less than half. In a cruise
only small trim adjustments were required,
mostly to the elevator.
The 3° of right thrust compensated for the
large engine’s torque; pulls to vertical and
loops could be flown straight with little or no
rudder correction. I had no complaints about
the aileron control, and rolling was axial and
smooth, as predicted. Crisp Point Rolls were
also possible.
Slow-speed testing had me giggling
because the heavy Bearcat showed no bad
habits. Stalls were soft and always broke to
the left, either up- or downwind. Testing the
model at high rates concluded that rolls could
be made as fast as with a 3-D sport model, but
the pitch stability was harder to manage.
I could see the higher control deflections
being helpful for Point Rolls, but the higher
elevator rate is probably best used only while
taxiing. Approximately 30% exponential
would be programmed into the high rates
later.
I used full throttle only for climbing.
During initial high-speed testing I found out
why the elevator pushrod support was needed.
Slow sport aircraft get away with a floating
pushrod, but fast, heavy models create enough
of a load on the tail to create flutter. Later
testing with the pushrod support installed
showed that the Bearcat could dive and run
flat out with no problems.
Earlier slow-speed testing also confirmed
that aileron control faded near the stall break,
so landings were best performed well above
stall speed. This airplane’s solid feel was a
comfort during the landing sequence.
Once it was lined up on the runway, it was
easy to settle down to the centerline. The lowrate
control input provided smooth pitch
corrections that allowed the model to maintain
steady airspeed until the flare. I wouldn’t
describe this short-coupled aircraft as touchy
at all.
The Bearcat slows quickly once the throttle
is reduced, so the high-throttle landing
approaches won’t stretch into long glides. This
model is easy to fly and land exactly where
you want it. It is possible to three-point the
landing since the wingtips stay level well after
the stall has occurred.
During later flights, tighter turns proved to
be comfortable to perform; again, no highwing-
loading issues surfaced. Inverted flight
requires just a touch of down, so the balance
point is precisely where I like it for this type of
model. Snaps can be flown, but they don’t
look like something a Bearcat should do.
I’ve been flying this model for almost a
full season and the Hobbico retracts are
wearing out. No structural issues have
surfaced, but some cracks in the paint are
appearing on the cowl.
Since I fly the model at half throttle most
of the time, I don’t see any reason why a .40-
class engine couldn’t work well in this
Bearcat. More ballast would be needed in
the nose area, which would put more stress
on the cowl mounting points. I like the extra
power the .70 provides, and who doesn’t like
a model that accelerates quickly?
The Dymond Modelsport Bearcat has been
a fun project. It turns heads at the field, and
because of its small size I can fit other
models in the car with it for a well-rounded
day of flying.
If you want one of these airplanes, keep
in mind that the quantity might be limited. If
Dymond Modelsport came out with another
warbird like the Bearcat, I’m sure it would
also be worthy of serious consideration. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
Dymond Modelsport Ltd.
3904 Convoy St. #110
San Diego CA 92111
(858) 495-0092
www.rc-dymond.com
Products Used in Review:
FS-70 II Surpass:
O.S. Engines
(217) 398-8970
www.osengines.com
Radio system:
Hitec
(858) 748-6948
www.hitecrcd.com
Retract servo:
Futaba
(217) 398-8970
www.futaba-rc.com
Propeller:
Master Airscrew
(916) 631-8385
www.masterairscrew.com
Other Review Sources:
None
48 MODEL AVIATION
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