August 2007 73
BY JIM FELDMANN
Plane Talk: Seagull Models Dual Ace 46 Twin ARF
The Dual Ace closely resembles the full-scale Beechcraft Duke. A hefty aluminum
tube supports the model’s two-piece wing.
The painted cowl and nose cone match the UltraCote covering. Red spinners are included.
Evolution .46NT engines provided more than enough power and ran well
throughout the testing phase.
The Dual Ace flares for landing predictably, and its high-speed flight
traits are smooth and groovy.
This sleek-looking
twin flies smoothly
and reliably with
Evolution engines
A MYSTIQUE SURROUNDS twin-engine
RC models. They have a unique sound; they
often emulate full-scale, multiengine
aircraft; they can offer a performance
advantage compared with single-engine
models; and they draw a crowd.
On the other hand, twins have a
reputation for being dangerous and hard to
fly. Perhaps that is why double-engine
ARFs have been almost nonexistent until
recently.
Seagull Models’ Dual Ace is an
attractive, scalelike sport aircraft for two
40-size engines. Having had a number of
twins in my modeling past, I jumped at the
chance to try it.
The Dual Ace came in a big, colorful
08sig3.QXD 6/22/07 10:25 AM Page 73
74 MODEL AVIATION
Type: Sport aerobatic ARF
Pilot skill level: Intermediate/advanced
Wingspan: 70 inches
Wing area: 880 square inches (actual)
Length: 67 inches overall (actual)
Weight: 11 pounds
Wing loading: 29.3 ounces/square foot
Engine: Two .40-.46 two-strokes
Radio system: Four channels minimum,
seven servos
Construction: Built-up balsa and
plywood; fiberglass nose cone, tail cone,
nacelle covers; aluminum wing tube;
plastic canopy; wire landing gear
Covering/finish: UltraCote covering,
fuelproof paint on fiberglass parts
Street price: $189.99
+
• Easy to fly, hard to stall, great qualities
for a twin.
• Attracts attention on the ground and
in the air.
• Fast and reasonably aerobatic.
• Two-piece wing.
-
• Hard-mounted fuel tanks cause fuel to
foam.
• Fiberglass nacelle covers do not fit
well and are difficult to install.
• Rudder pushrod flexes when turning
right.
• Assembly manual contains numerous
minor errors and omissions
Pluses and Minuses
Engines used: Evolution .46NT
Propellers: APC 11 x 5
Fuel: Tank capacity, Morgan Fuels 15%
Cool Power
Radio system: Futaba 8UA transmitter;
FP129DP receiver; seven JR ST47 servos;
1200 mAh, 4.8-volt battery; four 12-inch
extensions; four 9-inch extensions
Ready-to-fly weight: 11 pounds, 3
ounces
Flight duration: 10-15 minutes plus
with normal throttle discipline
Test-Model Details
The stock side windows have a unique outline. The cloudy material
on the three rear windows is similar to packaging tape.
The author straightened the top and bottom lines of the windows to suit his
taste. The hatch structure remained solid.
The Windows
The Dual Ace’s side windows are covered with a self-stick film that is not
very clear and reminds me of packaging tape. The windows’ shape forms an
unusual descending curve that I didn’t like. And to pick a little more, the
bare-wood frame of the canopy/hatch shows through the windows. I decided
to do something about all that.
I pulled off the “packaging tape,” and then I used a hobby knife to
straighten the top and bottom lines of the side windows. I had to add a small
strip of wood at the front of the first side window to give the new covering
something to stick to, and I covered this piece of wood with a scrap of white
UltraCote.
I painted the edges of the window cutouts white, and then I painted the
wood framing and anything else inside the hatch that would show, flat black.
Using a cheap hobby paintbrush bent more than 90° approximately an inch
from the bristles makes reaching inside easier. You can look in through the
windows to see what you are doing.
After all the paint was dry I covered the side windows with clear
UltraCote. It is easy to iron on over the white, is heat-shrinkable for that tight
look, and is extremely clear.
Some will say this is more work than it is worth, and they may be right.
But I like the result, and that’s what a hobby is all about, isn’t it? MA
—Jim Feldmann
Specifications
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August 2007 75
The kit is complete and the components are of good quality. The
author used all supplied hardware and accessories.
With the canopy/hatch removed you can see the factory-installed
servo tray, receiver support tray, and cardboard wing socket.
The author used a JR SPORT Universal AirPac and three ST47
servos. A stronger servo on the rudder would be beneficial.
To reduce fuel frothing, pad the fuel tanks to eliminate all tankto-
wood contact. Fuel-proof the interior too.
The author filled the forward half of the rudder pushrod exit in
the fuselage and soldered a length of 1/8-inch brass tubing over the
long, unsupported section of the pushrod to eliminate flex.
Balancing the model required an 8-ounce battery zip-tied inside,
11/4 ounces of lead on the front of the former, and 4 ounces of
lead in the front of the nose cone.
Static photos by the author; in-flight photos by Jim Pearson
08sig3.QXD 6/22/07 10:35 AM Page 75
box, and the packaging seemed adequate
to prevent shipping damage. The
individual parts appeared to be well built
and sturdy. The covering (UltraCote) on
my model was well done, with minimal
wrinkles, but seemed loose in some areas.
The fiberglass nose cone, tail cone, and
nacelle covers were thicker than most, and
the paint was generally smooth and a good
match to the covering. The engine nacelle
frames were factory assembled and needed
only to be glued into the wings.
The two-piece wing used an aluminum
tube joiner, and the fuselage had a large
hatch to provide access to the radio
equipment and wing-attachment bolts.
These advanced design features make
assembly, transportation, and maintenance
easier. The hardware and accessories
seemed adequate to the task, but I felt that
personal hardware changes were
necessary.
Getting It Together: The photoillustrated,
step-by-step assembly manual
is adequate for the experienced ARF
assembler. Some of the pictures don’t
match the text, and some of the text seems
to be borrowed from somewhere else.
Still, if you have assembled a few ARFs
you should have no trouble getting this
one together.
Assembly starts with the wings and
proceeds as with the typical ARF.
Cyanoacrylate hinges are installed, and
aileron servos are mounted inside the
servo bay covers. Extra-long servo arms
are needed for the aileron servos. The
control horns are different from what we
usually see, but they are heavy-duty and
easy to install.
The included metal clevises should be
more than adequate, but I recommend
adding a fuel-tubing “safety band” to help
keep them closed. I found one warped
aileron and one warped elevator, but
twisting them and then applying generous
amounts of heat from my covering iron
straightened them fairly well.
Installing the plywood nacelle frames,
throttle servos, tanks, and engines is no
more difficult than installing the engine in
a single-engine model; you just have to do
it twice. The second time is easier because
you have already done it once.
I started by epoxying the nacelle
frames into their “sockets” in the front of
the wings. But before I did that I thought
about keeping those engines running.
Twin engines make much more
vibration than a single power plant.
Vibration can cause the fuel in the tank to
froth, and when that happens the engine
will draw air bubbles instead of fuel,
causing it to lean out and probably stop
running.
The fuel tanks should be protected
from vibration. Unfortunately the Dual
Ace’s fuel tanks are hard mounted. To
make room for padding I removed the Ushaped
tank supports from inside the
nacelle frames.
The outside of the nacelle frames was
painted with a gray fuel-proofer, but since
the fiberglass nacelle covers don’t touch
the firewalls the entire nacelle and
everything in it will be exposed to fuel
residue.
After gluing the nacelle frames into the
wings I coated them, inside and out, with
finish-cure epoxy. This adds to the
structure’s strength and stiffness and
provides protection from fuel.
Installing and padding the tank will
have to wait until after the throttle pushrod
is in place. Skipping ahead in the manual,
I installed the engines.
The top edge of the engine-mount
beams should be within 1/16 inch of the top
of the firewall. Then I added the throttle
servos and hooked up the pushrods.
Creative bending is needed to keep the
pushrod up against the side of the nacelle,
but you can bend the second one to match
the first, and that makes it slightly easier.
I hooked up the servos with a “Y”
adapter and worked the throttle to make
sure both engines’ carburetor barrels
closed at the same time. This is critical if
you are planning to use a “Y” to drive the
servos, but it will give the best starting
point even if you plan on using separate
channels.
The included fuel tanks use plastic fuel
tubes instead of the usual brass or
aluminum. Bend these to shape using heat,
but be careful; I used too much heat on
one and melted it.
The included silicone fuel tubing is too
short and too stiff to allow the clunk to
reach the bottom of the tank. I had to
search for some softer fuel tubing for the
clunk line.
The choice of a two- or three-line setup
is yours. (The manual is no help here.) But
to add the third line you need to drill
through the molded nipple at the top of the
tank. Drill straight or you will break out
the side of the nipple and ruin the tank.
After I set up the tanks I glued 1/4-inch
foam rubber to the bottom and both sides
of the nacelles. I used two pieces of foam
on the right side—one above and one
below the throttle pushrod.
A couple layers of wing-saddle tape
stuck to the front and back of the tank
keeps it from touching wood there. A
padded sheet of light plywood glued
across the top of the tank between the
nacelle sides keeps everything in place. To
prevent frothing the tank must
The procedure outlined in the manual is
probably the best way to do it, but the first
step is fairly important and it seems to be
left out of the manual. It should instruct the
builder to make a mark on the top and
bottom of each wing, 8 inches from the
root end of the wing and 33/8 inches from
the aileron TE. Use those marks to align
the rear end of the nacelle covers.
Two of the covers are marked “1”
inside and two are marked “2.” It appears
that the 1s go together to make a set and
the 2s make the other set. There doesn’t
seem to be a difference between left and
right; it’s hard to tell. I used them
wherever they came closest to fitting.
Take your time and double check
everything before you drill the mounting
holes. Use the spinner backplate to guide
the way the top and bottom covers come
together at the front. The plywood “strap”
is not a good fit. Don’t try for perfection; it
just isn’t there.
A useful trick is to use your heat gun to
reshape the fiberglass parts. The heat will
soften the fiberglass without deforming it.
I bent the flanges down for a better fit to
the wings, and I lowered the entire front
end of one set of covers that came out 1/8
inch too high.
Once the nacelles are finished, the rest
of the assembly is straightforward and goes
quickly. Alignment of the tail surfaces with
the wing was nearly perfect and required
no sanding of the tail slots. The little block
that fills the gap in the fuselage behind the
stabilizer doesn’t fit properly, but if you
split it into left and right halves you can
make it look much better.
It would be wise to place a little threadlocking
compound on the canopy/hatch
retaining screws. Metal screws used with
blind nuts tend to loosen and fall out from
vibration.
The fiberglass nose and tail cones fit
well, although the painted trim lines did
not match the trim lines on the fuselage. I
see no reason to ever remove the tail cone,
so I glued it on rather than use the included
screws.
The kit includes four plywood washers
that are not mentioned in the manual. They
go under the wing retaining bolts inside the
fuselage.
There are no alignment pins, and the
laser-cut bolt holes in the fuselage sides
are large enough to allow some play in
each wing’s incidence. The washers are a
tighter fit on the wing bolts, so I assume
they are intended to do the fine-tuning on
the wing incidence.
I installed the wings loosely with the
washers on the bolts, checked and adjusted
the wing incidence, tightened the bolts, and
then wicked thin cyanoacrylate under the
washers to lock them in the correct
position.
On the subject of those wing bolts, it
was difficult to reach the rear set because
of the limited access space. The threads are
1/4-20, so I purchased Du-Bro socket-head
1/4-20 wing bolts, thinking they would be
easier to use, but the Seagull Models bolts
have a thicker section just under the head
that fits tightly in the wood washers to
align the wings.
The Du-Bro bolts were loose in the
washers and allowed the wing incidence to
vary from side to side by as much as 2°—
not good. I went back to the Seagull bolts
and worked out a way to tighten the rear
ones using my two forefingers, which
works reasonably well.
The rudder, elevator, and nose-wheel
pushrods are solid metal, running through
factory-installed plastic tubes in the
fuselage. The rudder and elevator use
metal clevises at the control horns and snap
keepers at the servo end. The nose wheel
uses EZ-style connectors at both ends.
The elevator servo arms should be
installed so they are 90° to the pushrods at
neutral. The manual shows them 90° to the
servo body, but this will cause up and
down travel to be different between the
two elevators.
These pushrods are simple and easy to
set up and work well, with one exception;
the rudder pushrod has a 9-inch
unsupported section between the fuselage
exit and the control horn. This section
flexes considerably when the rudder is
turned to the right and the slipstream puts
pressure on it.
To solve this problem I filled the
forward half of the exit slot in the fuselage
so the slot acts as a guide. Then I slipped a
1/8-inch brass tube over the exposed part of
the pushrod and soldered it on at both
ends. The rudder pushrod is now rigid
enough to do its job properly.
I used two Evolution .46NT two-stroke
engines, as shown in the manual, turning
APC 11 x 5 propellers and running 15%
Cool Power fuel. I was surprised by easily
the .46NTs broke in and how reliably they
ran throughout testing. They seem to be at
least as powerful as their competitors, and
I experienced no unplanned engine
shutdowns on the ground or in the air.
My model uses a complete JR SPORT
standard AirPac. This inexpensive
of weight (including battery) in the nose to
balance at the 95mm recommendation.
I attached my 8-ounce sub-C battery to
the back of the front former, added 1.5
ounces of stick-on lead to the front of the
former, and added 4 ounces of lead shot/
epoxy in the tip of the nose cone. I added a
fifth mounting block at the top of the
former to help support the added weight in
the nose cone.
I set the flight controls to the low- and
high-rate control throws cited in the
manual for the first flight.
Flying: When both engines run at
approximately the same speed, a twin flies
the same as a single-engine model. When
both engines are at idle or shutdown, it
flies like a single. Only when one engine is
running at high speed and the other isn’t
can a twin become unstable.
Keeping both power plants running
together is critical. A couple things I did to
the TwinStar II were aimed specifically at
that goal. And learning to tune an engine
for reliability is a prerequisite for success
with any twin.
On the first trip to the field I spent the
day running in the .46NTs and fine-tuning
them to avoid surprises. I adjusted each
separately to run smoothly and reliably at
idle, through the midrange, and at a nice,
rich top end.
Both engines were started and the idle
speeds were synchronized at roughly 2,850
rpm. This is easy to do when using
separate throttle channels by simply
adjusting the low-throttle adjustable travel
volume (ATV) on one of the engines. If
you are using a Y adapter on the throttles,
adjust the length of one of the pushrods to
get the idle speeds in sync.
It is unnecessary to synchronize the
engines at full throttle. If you must, do it
with separate channels, using the highthrottle
ATV function.
Never try to synchronize the power
plants using the needle valves. Whether
you lean out the slower engine or richen
the faster one, you have detuned that
engine and made it more likely to sag or
shut down at the wrong time. Adjust the
engines separately to run their best and
then leave them alone.
The next day I was back at the field
with my photographer for the test flights.
After a couple aborted takeoffs, just to
make sure the engines would pull together,
the time had come. The Dual Ace uses a
fair amount of runway, but the .46NTs give
it plenty of acceleration, and it lifts off
smoothly and climbs out with authority.
It took several “beeps” of left aileron
trim to compensate for the still slightly
warped aileron, but otherwise the model
flew straight and level—and fast. Even
with 5-inch-pitch propellers I felt the need
to fly most of the flight at reduced throttle.
Stall tests showed that the wing is
extremely forgiving. I could not get the
Dual Ace to tip-stall in normal flight.
Stalled from level flight at idle power,
holding full up-elevator (low rate), the
nose barely drops below the horizon before
the airplane starts flying again. The CG
seemed just right at 95mm.
For my flying style I preferred the highrate
setting on the ailerons and the low-rate
setting on the elevator. The rudder is not
too effective, even on high rates, but the
nose wheel is sensitive. I moved the nosewheel
pushrod closer to the center of the
servo arm after the first couple taxi tests.
The Dual Ace tracks well once in the
air. Loops can be big or tight, with no
rollout or wandering off track. Rolls have
an odd little bounce while passing through
inverted, but practice eliminates it.
Inverted flight requires 10%-15% of downelevator
with the CG set at 95mm, but the
tracking and stability are just as good as
normal flight.
Twins with only one vertical fin have
no propeller blast over the rudder. You do
notice the difference. Steering on takeoff
relies heavily on the nose-wheel, knifeedge
flight, flat turns are difficult, and stall
turns are impossible. If you decide to put
on floats, you will need water rudders
because you can’t steer on the water with
the air rudder.
Because of its fairly high wing loading,
the Dual Ace has a higher approach speed
than many sport airplanes, but that nice,
forgiving wing lets you get the nose up and
land on the mains at a speed that is not
much higher than that of a lighter singleengine
model.
The Seagull Models Dual Ace is
attractive, sturdy, a good flier, and gets
attention at the flying field. It is a great
sport aircraft for the modeler who wants to
try something different, and it would make
an excellent twin trainer for someone who
is interested in moving into more
sophisticated multiengine models such as a
P-38 or a DC-3.
The kit has minor issues, but if you
have assembled a few ARFs, are careful,
and take your time, you should have no
difficulty getting it together properly. The
pilot should be comfortable