54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006
Edition: Model Aviation - 2008/07
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
Plane Talk: E-flite J-3 Cub 25 ARF on Floats
Optional fiberglass floats for the E-flite
J-3 25 are simple to install and include
all hardware and steering controls.
MICHAEL RAMSEY
This good-size scale model is versatile and practical for electric power
The J-3 25’s landing gear is slightly wider than scale to prevent ground looping. This Cub
is a joy to pilot on both land and sea.
+•
Outstanding construction and finish.
• Continental engine detail on cowling.
• Well designed to keep power-system
components cool.
• Easy five-minute conversion from land
to sea. -•
Factory motor location too low to
center in cowling.
• Some hardware and screws stripped
or were inadequate.
Pluses and Minuses
AFFORDABLE ELECTRIC-POWERED models are getting
bigger every season. We’re fortunate to be able to take advantage of
new technology while prices keep coming down.
These days the 25-size model (or helicopter) is practical to set up
for electric because it can typically be equipped with two identical
packs used to power the smaller 10- and 15-size aircraft. As we
would buy the same fuel to power more than one engine, we can
select batteries in the same practical manner.
E-flite is expanding its line of models—literally. The company
started with foamies and park flyers. Now its lineup of 25-size
airplanes is increasing, and it began with the release of the J-3 Cub
25.
An all-time favorite, many will recognize the Cub as a
remarkable model to fly regardless of what size it’s scaled to
represent. This version is no different; I found it to be beautifully
engineered and finished.
But having produced a fair number of Cublike products in their
time, E-flite’s designers kicked this Cub up a notch and released it at
the same time as a matching set of floats. Not only is this Cub a
classic, but it’s versatile.
Cub
Model type: Sport scale (1/7) ARF
Pilot skill level: Intermediate
Wingspan: 62 inches
Wing area: 552 square inches
Length: 35.5 inches
Weight (with battery): 4.0-4.25 pounds, 5.3 pounds with floats
Wing loading: 17.8 ounces/square foot
Power (recommended): 500-watt motor, 40-amp ESC, 12-
volt battery
Radio: Four channels (minimum), four miniservos
Construction: Balsa and light plywood with painted fiberglass
cowl, clear plastic windows
Covering/finish: UltraCote film, polyurethane paint
Price: $154.99
Floats
Type: 25-size set
Intended for: 4- to 5-pound models
Length: 28 inches
Weight: 1.3 pounds (complete)
Construction: Internal wood frame, fiberglass shell
Finish: Silver polyurethane paint
Included: Required hardware and linkages, subfin (for Cub),
water rudder, heavy-duty chrome-plated wire struts
Price: $49.99
The model cruises at a good clip under the burden of the floats.
The recommended Power 25 motor system is well matched.
Factory-included details such as scale wheels, graphics, and
painted trim greatly increase this ARF’s value.
The E-flite Cub float kit includes chrome-plated wire gear and a
subfin. All mounting points on the fuselage are laser-cut.
Motor: E-flite Power 25 outrunner
Battery: Thunder Power 3S 4200 mAh Li-Poly or E-flite 10-cell,
12-volt, 1800 mAh NiMH
Propeller: APC 12 x 6E
ESC: E-flite 40-amp brushless
Motor output: 550 watts maximum
Radio system: Spektrum DX7 transmitter; AR7000 receiver;
four JR Sport ST47 servos; Expert Electronics 4.8-volt, 720 mAh
receiver battery; standard switch; four servo extensions
Ready-to-fly weight: 3.94 pounds, 5.84 pounds with floats
Flight duration: 15 minutes, 10 minutes with floats
Specifications
Test-Model Details
July 2008 55
Construction: The J-3’s contents include a typical ARF list of
major assemblies and materials. Laser-cut parts are standard with
this model, which is a huge thing these days. And a good one.
The wings are provided in halves, with all the aileron hinge slots
made with the cyanoacrylate-type hinges dry-fitted in place. The
airfoil is similar to a Clark Y that’s flat aft of the main spar with
only a shallow curved entry at the LE. The full-scale Cub has a
similar airfoil that is accountable for its favorable high lift and slowspeed
handling characteristics.
The model’s fuselage is constructed from light plywood with
balsa stringers and sheeting. I thought it was a nice touch that all the
56 MODEL AVIATION
The water rudder should work freely for
optimal effect. The brass rudder fits
loosely in the bracket so it can deflect
against obstacles.
The author finished the interior of his
model with black enamel paint for scale
effect.
Standard servos will fit in the laser-cut
mounting tray after a small modification of
the openings.
Static photos by the author Flight photos by Shawn Rubush
Cooling inlets for the E-flite 40 ESC and
Thunder Power 3S2P 4200 mAh Li-Poly
battery are extraordinarily effective.
The simulated Continental engine cylinders complete this Cub’s scale look. The author
hid the switches in the black stripe.
Get It Together
Horizon Hobby and E-flite pride themselves on producing an assembly manual that is just as good as the product. They consider
the beginner when writing and illustrating the instructions. No stone is left unturned, as they say. See how this model goes together
by downloading the instruction manuals.
• J-3 Cub 25 ARF: www.horizonhobby.com/ProdInfo/Files/EFL4000_J-3_Cub.pdf
• 25-Size Fiberglass ARF Floats: www.horizonhobby.com/ProdInfo/Files/EFLA500_Float_Set.pdf
Study these documents to aid in assembly speed or create a shopping list. What you don’t see in this review article will probably
be in these instruction manuals. MA
—Michael Ramsey
July 2008 57
Mounting slots for the vertical and horizontal fin were tight
enough that thin cyanoacrylate was sufficient to secure them.
The battery hatch is magnetically sealed. Formed clear plastic
windows are included.
The included metal pushrods offer authoritative control. The scale
wing struts are nonfunctional but look great!
Hard points for the molded-fiberglass floats are beefy. Holes for
the mounting screws are predrilled.
slots and openings were cleanly cut out and dressed at the factory;
even the pushrod exits were clean. This left me with time to finish
the J-3’s interior with semigloss black enamel.
The stick-built tail surfaces are prehinged, with crisp bevels that
are suitable for large control movements in case the pilot needs
them. The elevator halves are linked with a dual pushrod. I found
these easiest to align if the rudder were left to install later. That way
two sides of the elevator are easy to compare. The firewall is
doubled 3mm light plywood with large vent holes and motor-mount
blind nuts already pressed in place.
The primary adhesive used to construct the model appears to be
an aliphatic resin that isn’t waterproof. I coated the interior of the
motor compartment with clear epoxy paint as a sealer. Because the
Cub is electric, there are many vent holes and places for water to get
in.
The owner of such a model should do whatever is necessary to
protect it and its components from water damage. After many touchand-
gos, water from splashing will get into the Cub, but it seems to
run out all the same.
Assembling this Cub is a leisurely experience that left me with
time to consider adding special touches. It’s a beautiful model to
start with, but since E-flite did most of the work, I honored its effort
by painting the cockpit as mentioned.
I also dyed the fairing straps and nylon hardware yellow to match
the J-3’s finish. In addition I exchanged many of the screws, such as
those for the cowl and servo hatches, for nylon and dyed them to
match as well.
The landing gear is made light and strong, from music wire that
is spot-welded together and finished with matching paint.
Traditional Cub wheels are included and designed to conceal the
4mm wheel-collar locking mechanism. Nice.
The E-flite Power 25 motor fits precisely on the standard
mounting hardware and onto the premade holes on the firewall.
However, the cowling can’t fit flush with the top fuselage and align
with the center of the precut prop shaft opening.
Luckily the opening is oversized for motor cooling, so the
compromise is to offset the prop shaft at the top and fit the cowl
flush and parallel with the top of the fuselage. The result looks
pleasing from all angles.
Inside the magnetic closure-equipped hatch in the nose, I added a
small strip of 1/16 balsa to the left side of the battery compartment as
a mounting plate for the E-flite 40-amp ESC. Laser-cut slots in the
vented battery tray permit Velcro straps to wrap around without
slipping. I added rubber shelf liner to the tray floor to prevent the
battery from sliding.
Instead of the recommended miniservos, I equipped the Cub with
JR Sport ST47 units because I had them. They are a tight squeeze in
the wings, and inside the fuselage the servo-tray openings needed to
be slightly enlarged; no biggie. I located the AR7000 receiver on the
platform just behind the instrument-panel former.
Following the product alert posted on the Horizon Hobby Web
site, I disconnected the BEC wire from the ESC and used an Expert
Electronics 720 mAh, 4.8-volt NiMH battery to power the receiver
and servos. The switch and charge receptacles were located inside
the black UltraCote pinstripe near the rectangular window—
practically invisible on the outside. That battery just sits on a piece
of Velcro on the fuselage floor, exactly under the CG.
Assembling the wing and tail sections was close to effortless.
The built wing dropped into place and
aligned perfectly. The tail surfaces aligned
with no correction to the mounting slots.
The joints for the stabilizer and fin were so
tight and precise that I used only thin
cyanoacrylate instead of epoxy to lock them
into position.
The pushrods are my favorite: solid 2-56
metal wire. The two elevator rods join in the
cockpit with two 4mm wheel collars. The
setscrews in the collars were too short to
tightly bind the wires to my preference, so I
substituted longer screws. To be on the safe
side, I smeared J.B. Weld epoxy on the
collar and wire joints.
To make the recommended CG, the 3S
4200 mAh Thunder Power pack sits in the
front of the compartment. A 10-cell, 1800
NiMH pack has to sit back farther. I also
tested a 20C 3200 mAh 3S pack, which met
the power and aft CG limit with no problem.
I prefer the lighter pack for flying from
water.
Flying: This J-3 Cub on wheels jumps from
the runway like a leapfrog. Similar to all
Cubs, it wants to fly. The wheels are a little
small to cut through heavy grass, so I
recommend the soft-field takeoff technique.
The Power 25 motor and APC 12 x 6E
propeller blast tons of air over the control
surfaces, making them effective enough to
counter torque and crosswinds. The
recommended control throws are perfect for
scale handling, but I like more rudder
authority with a Cub, so I prefer the high
rate with approximately 30% exponential
mixed in.
The Cub stalls straight ahead with a
steady breeze but might drop a wingtip if the
winds are light; all stalls are predictable.
Turns require coordination of the aileron and
rudder. This can be done manually or mixed
with the radio. My DX7 uses a 60% aileronto-
rudder mix I can turn off with the gear
switch.
Rolling the Cub isn’t the easiest thing to
do with grace, nor is inverted flight. It will
do those maneuvers, but they look wobbly
and out of place. Have at it, though! I’d like
to see Farmer Brown do an outside loop in
his J-3 the way this model can do it. Just
kidding.
Landings on grass are best done in the
three-point style, to avoid nosing over or
ground loops. This airplane can touch down
on the mains on a smooth surface, just as the
full-scale J-3 can.
In a crosswind the Cub loves so crab and
slip into the current; approximately a 20°
angle is easy to hold until touchdown, where
the attitude can be changed to an upwind
wing-low position until the wheels are
down. In calm air this airplane can be
slipped all the way down to the numbers and
touch the ground one wheel at a time if the
pilot wants. This model is fun!
Time to Get Wet: The E-flite 25-size float
set emulates the look of Edo-style floats
used on the full-scale J-3. The float exterior
is fiberglass, watertight, and finished with
silver polyurethane paint to look like
aluminum. Internally there is a wooden
structure with a keel and formers (visible
through ripples in the fiberglass), which is
linked to hard points for the struts and water
rudder.
The float kit can be ordered to suit this
Cub or the Ultra Stick 25; different landing
gear and water-rudder locations set the two
apart. The struts for the Cub are made from
heavy-duty music wire and come prebent
and spot-welded together (in lieu of wire
wrap and silver solder). Chrome plating
protects the strut assembly from rust and
corrosion.
After two of the mounting screws
snapped off while securing them in the
predrilled holes, I decided to substitute my
own screws for both the gear legs and water
rudder. The hard-point material is suitable
for threading, so I ran a 4-40 tape in every
hole and attached everything with sockethead
screws.
With the exception of the water rudder,
which tended to bind easily, assembling the
float system on the J-3 Cub 25 was duck
soup. (Ducks float almost as well as this
airplane.) Once the rudder bracket was
carefully reamed, smooth operation of the
synchronous steering linkages ensued.
The brass water rudder naturally retracts
or bobs if it interacts with debris or an
obstacle in the water. It also lifts out of thewater on takeoff, which naturally reduces
its sensitivity—a good thing.
My Cub balanced perfectly with the
floats mounted. I’ve seen some that needed
roughly an ounce of lead on the front of the
floats. The model sits correctly, with the
bow of the floats raised out of the water
slightly. Approximately 60% of the floats
is visible above the water line, which is
what I live to see; otherwise, they look like
they’re sinking. The floats’ wide spread
makes the water rudder essential, but a
crosswind will have a hard time flipping
this model over.
When flying from the water, I try to
remember that the pilot isn’t finished flying
until the motor is off and the airplane is
beached. The model is as susceptible to the
wind in the water as in the air, plus it has
waves and water current to manage. This J-
3 on floats can handle those elements.
The water rudder makes steering a joy,
even in the wind, but be sure to mix the
elevator and aileron controls to keep any
wind from digging the floats into the water.
Once into the wind, the Cub can be
managed similar to as if it were on wheels,
but a smooth acceleration procedure is
essential. Once the model is on the step, it
quickly gains airspeed and can be rotated
smoothly from the water.
It’s best to keep the climb rate fairly
shallow until the feel of the float-laden Cub
is appreciated. Use smooth control inputs
and keep the flying scalelike. With 1.3 extra
pounds, and a ton of drag added, this J-3
isn’t as sprightly as it was before with just
wheels.
Now more than before, a pilot will
appreciate the DX7 aileron/rudder mixing.
Only a small amount of up-trim was
required, and a more gingerly touch to the
controls was a talent the model appreciated.
With the floats the Cub will loop and
roll, but inverted flight is naturally a
struggle. Rolls are much quicker with the
aileron/rudder mix turned on. Okay, they
look like snaps. (Farmer Brown says
“Ouch!”)
Stall turns are a thing of beauty. Where
on wheels the Cub could cruise at half
power, with the floats roughly two-thirds
throttle is needed unless there’s a strong
head wind; then full power will be used
often.
Landing approaches appreciate the
pendulum effect the floats add to the model.
Even with the higher wing loading, the Cub
has a comfortable glide and naturally finds
its approach glide slope to landing. As with
the grass landing on wheels, go for the
three-point landing, keeping the floats’ tips
as far from the water as possible.
As the pilot’s comfort level increases, this
J-3 can grow. I found the aft CG point to be
stable, which made the flare for landing
much more stable. The limit was found
during spin testing, where the Cub would
depart and stick in a spin, especially when
burdened with the floats.
Mindful of this condition, the Cub is still
a joy to fly. But that is a reminder that
experimentation with the flight envelope
should be done with a great deal of air
between the wings and ground/water.
I like this Cub very much. I catch myself
peeking at it in the shop, admiring the tight
covering and close-fitting joinery that is
faintly visible. Thank goodness E-flite
didn’t skimp on the cowling detail; a Cub
without Continental valve covers protruding
proudly just isn’t finished.
On wheels, this Cub is so light that it
could be flown from small fields. From
water I like having a wide-open space;
avoid the local pond that is surrounded by
trees.
For power I favored the lighter 3200
mAh 3S pack, but the Thunder Power 4200
mAh 3S Li-Poly battery provided the
longest flight time and could easily be
shifted to achieve the CG I liked.
I wasn’t at all happy with the 12-volt
NiMH performance. For a short flight from
land it’s an economical option, but it added
a sense of struggle that this fine model
didn’t deserve.
A practical alternative to economy
would be to use two 2100 mAh 3S Li-Poly
batteries in series. The power and weight
would be identical to that of the 3S 4200
mAh battery, and the two 2100 packs are
great to use with smaller park flyer models
as well. MA
Michael Ramsey
[email protected]
Manufacturer/Distributor:
E-flite/Horizon Hobby Distributors
4105 Fieldstone Rd.
Champaign IL 61822
(800) 338-4639
www.horizonhobby.com
Products Used in Review:
DX7, AR7000:
Spektrum
(800) 338-4639
www.spektrumrc.com
Batteries:
Thunder Power RC
(702) 228-8883
www.thunderpowerrc.com
Receiver, servo batteries:
Expert Electronics
(800) 338-4639
www.horizonhobby.com
APC Propeller:
Landing Products
(530) 661-0399
www.apcprop.com
Other Review Articles:
Quiet Flyer: July 2006