Plane Talk: Carl Goldberg Products Yak 54 ARF - 2007/11

BY ED ALT
Plane Talk: Carl Goldberg Products Yak 54 ARF
THE CARL GOLDBERG Yak 54 was delivered as a complete ARF,
with all the necessary hardware for control systems, engine mounting,
and fuel system. My first impressions were that the quality of
construction and finish were good overall. The model comprised balsa
and plywood formers, ribs, and sheeting.
This model was solidly constructed by today’s standards for ARFs,
especially with the integrated engine box and landing-gear design. A
great deal of attention was paid to detail, including a dowel-pinned
firewall. The control-surface/hinge-line beveling was quite good.
The covering job was above average. Relatively few spots required
tacking down and reshrinking, as is commonly necessary on an ARF.
That was especially surprising since the Yak had a good amount of
detail with many small pieces to complete its color scheme.
Some care was needed when removing the tape from the control
surfaces, to avoid lifting covering trim pieces, but nothing could not be
tacked back down effortlessly. The quality of the engine cowl’s and
wheel pants’ fiberglass was good, and those parts were reasonably
lightweight with a good paint finish.
Planning for Assembly: I weighed all the model’s parts and
hardware accessories in preparation for building. A big part of the
decision about engine choice, as well as the location of the rudder
servo, was made after I tallied the weight and did a trial balancepoint
estimate.
Given the large control surfaces on the Yak’s tail, as well as the
large fuselage volume aft of the balance point, this model could
easily have come out tail-heavy if this kind of preparation was not
done. Although an option was to mount the rudder servo in the tail,
it seemed that that installation would work only with a heavy
engine-and-muffler combination.
I ultimately selected a Brison 2.4 (39cc) gas engine, Bisson
muffler, and cabin-mounted rudder servo. With that combination, in
addition to a relatively heavy APC 20 x 8 propeller and placing the
ignition and flight-pack batteries as far forward as was practical, the
balance point came out right on the money.
Servo Selection: There were no recommendations in the kit for
minimum servo torque for any of the control surfaces, although a servo
rated at 57 ounce-inch of torque at 6.0 volts was shown for the
elevators. My experience with models this size told me that something
with substantially more torque would be needed.
Since Hitec HS-5625MG servos (130 ounce-inch at 6 volts) were
available to me, I used those on the elevators. I used Hitec HS-
5645HBs (164 ounce-inch at 6 volts) for the ailerons, even though their
combined torque was a bit of overkill for the application. I chose an
HS-5645MG for the rudder, which proved to be inadequate.
Since the Yak’s ailerons were designed to be driven by two servos
each, I considered programmable servos to be an advantage for ease of
This sport-scale model is
great for sport aerobatics
or 3-D fun
48 MODEL AVIATION
11sig2.QXD 9/21/07 9:20 AM Page 48
November 2007 49
Photos by the author
Wood-dowel spacers were used to offset
the engine from the firewall. Notice the
simple throttle-linkage arrangement.
The author removed the neatly packaged Yak’s parts from their plastic bagging and set
them aside to acclimate. He touched up the small wrinkles in the covering a few days later.
To correct for any wing-incidence
variations, remove the autorotation
doubler, resize the opening, and then
replace the doubler.
The Yak was constructed from accurate and well-engineered laser-cut parts. The
stressed skin sheeting made the structure extraordinarily stiff.
The rudder servo is a tight fit between the wing tube and the aft
former. Install a servo with no less than 200 inch-ounce of torque.
The fuel tank was mounted aft, closer to the CG, on a custom-built
plywood mount. The offset also helps balance the model laterally.
11sig2.QXD 9/21/07 9:21 AM Page 49
50 MODEL AVIATION
Test-Model Details
Pluses and Minuses
Specifications
The model features sharp hinge lines that
permit a 3-D control-throw setup.
Hardwood plates are located at the
control-horn locations.
There’s plenty of room up front to clear
the APC 20-inch propeller. A 1/4-scale pilot
would set off the model nicely.
The oversized control surfaces make this
Yak ideal for slow-speed aerobatics. The
recommended CG is accurate.
The large top hatch makes the Yak easy to maintain and quick to assemble.
Ground handling is solid with its wide landing gear.
The author performs a
ground check of all control
surfaces before taxiing the
model out.
+
• Complete kit
• Good looks
• Easy assembly -• Heavier than advertised
• Antirotation pins required adjustment
Engine used: Brison 2.4
Propeller: APC 20 x 8
Fuel: 24-ounce tank, 93 octane fuel with
Amsoil 100:1 (after break-in)
Radio system: JR 10X transmitter with
frequency synthesis; JR R2000
synthesized receiver; six Hitec digital
servos; one Futaba 3004 servo; one JR
DS8611 servo; 2080 mAh, 7.4-volt Li-Ion
battery with dual ALR5 programmable 5-
amp regulators
Ready-to-fly weight: 16 pounds, 8
ounces
Wing loading: 32.4 ounces/square foot
Flight duration: 15 minutes
Type: RC aerobatic ARF
Pilot skill level: Intermediate to
advanced
Wingspan: 77 inches
Wing area: 1,139 square inches
Length: 72 inches
Weight: 13-14 pounds
Wing loading: 27 ounces/square
foot
Engine: 1.20-2.20 cu. in. (19.7-
36cc) two-stroke, 1.20-1.80 cu. in.
(19.7-29cc) four-stroke, or 2.4 cu.
in. (19.7-39cc) gasoline
Radio: Four channels (minimum),
eight servos
Construction: Balsa and plywood
Covering/finish: Polyester film,
painted fiberglass parts
Price: $389.99
11sig2.QXD 9/21/07 10:04 AM Page 50
Brison 2.4 Engine
IT WAS A pleasure to have a Brison 2.4
engine to review along with the Goldberg
Yak 54. Having owned other competition
gas engines in the 100- to 150cc range, this
was my first Brison and I was anxious to
see how it stacked up.
As delivered this engine was a beautiful
piece of work. It had a polished-aluminum
crankcase, with an aluminum bellcrank to
operate the Walbro carburetor. There was
an idle return spring that could be
disconnected but not removed since it
acted as a spacer for assembly, ensuring
that the butterfly valve did not come loose
and possibly be ingested by the engine.
I would have preferred to keep the
return spring engaged as a safety backup in
case the throttle linkage ever came apart in
flight, but I felt that the constant load on
the throttle servo would not be a good
thing.
I would like to see milder springs used
for these applications. I have not yet seen a
gas engine with which I felt comfortable
leaving the return spring engaged for this
reason.
The Brison 2.4 came supplied with a
RevMaster ignition module, which featured
continuous spark advance throughout the
usable rpm range. This eliminated the
original mechanical timing advance,
although the mechanical advance is still
available from Brison for those who prefer
it.
My experience with the Brison/
RevMaster combination was positive, and I
would not hesitate to run it again.
The Brison had a Nikasil-lined
cylinder/piston assembly that is made in the
USA by Dolmar. The Nikasil lining is
designed for low wear throughout the life
of the engine.
Propeller mounting was quick and easy
with a single propeller bolt hub. It was
advertised as being suitable for models
ranging in weight from 12 to 21 pounds,
depending on wing loading.
For this application, which required
wringing out the full performance of an
intermediate- to advanced-skill-level
aerobatic model, it was right at the upper
limit of its performance capability. The Yak
54 weighed 16.5 pounds with fuel.
My best estimate is that the Brison 2.4
would excel at powering aerobatic models
that are kept at less than 15 pounds ready
to fuel. The weight of the engine itself was
reasonable, at only 2.75 pounds.
The weight of the ignition module and
battery and the Brison’s all-up weight
without a muffler was a shade heavier than
3 pounds. That is extremely competitive
with the weight of some popular glow
engines in a similar displacement and power
range.
Brison recommends using high-octane
gasoline with a good-quality synthetic twocycle
oil such as Amsoil or Klotz.
Petroleum-based oils are also permissible,
at a 64:1 fuel-to-oil ratio. The
recommended ratios for synthetic oils are
64:1-100:1. My experience with Amsoil is
that you use it at 100:1. I used 93-octane
gasoline throughout.
There is no prescribed break-in
procedure per se since this engine is
considered ready to fly as delivered.
However, the instructions do point out (as
most would recommend) that you run the
engine to avoid surprises, ensuring that it
will operate reliably at all rpm ranges,
before taking off for that first flight.
Expect the engine to take 40-50 hours
of operation before it is fully run in, during
which time maximum rpm should increase
gradually. Other handling qualities can be
expected to improve during this time as
well, such as slower, steadier idling and
improved transition. Also, cylinder-head
temperatures tend to diminish as the engine
completes its run-in period.
During flight testing for this review, only
approximately one-tenth of the prescribed
run-in period was achieved. However, I
clearly observed that the engine had
improved in all respects during that time
(accompanied by some mixture
adjustments).
By the eighth flight the APC 20 x 8
propeller was being turned at 7,600-7,650
static rpm when fully warmed up, indicating
that the engine was ready for more
propeller load. Brison’s recommended
range for best output torque was 6,500-
7,500 rpm.
Although the operating instructions
were firm about the needle settings being
optimally adjusted at the factory, I found it
necessary to lean out both the low and high
end after a few flights to realize more of
the engine’s potential and get a smooth,
reliable midrange and throttle transition in
flight.
The final settings used were still on the
rich side since this engine’s running-in
period was incomplete. All the flying was
done at field elevations of 195-450 feet
ASL, so the mixture adjustment was not a
result of a high-altitude environment.
Although everything ended up working
out wonderfully with the Brison after
getting past a learning curve and later
carburetor mixture adjustments, my first
attempts at starting and running the engine
were a little frustrating. Following the
recommended starting procedures simply
didn’t work.
During the course of those 100-plus
flip-start attempts, I checked the ignition,
fuel connections, plug, etc. Not a pop, but
I sure got some good exercise. Note that
this was before making any carburetor
adjustments.
It may have been that this particular
Walbro carburetor was a bit weak at
drawing fuel at idle setting, but it was
impossible to draw enough fuel with the
choke closed and the throttle set below
full throttle.
The starting procedure that worked for
me was the following: fully choked,
throttle wide open, ignition on, and a few
flips until it fired. After the first pop I
closed the throttle to idle, opened the
choke, and continued flipping until it
started and ran at idle.
That is not my favorite procedure—I
am accustomed to doing the entire choke
procedure at idle—but it definitely worked
reliably by following the preceding
technique. Of course this entire procedure
was done with a helper holding the model.
As I noted, it was necessary to lean out
the low- and high-end mixture settings to
really let the Brison 2.4 perform. It had a
distinct tendency to load up in the
midrange and actually quit in flight once
because of this condition (at the factory
settings).
That was enough for me. I switched
into my normal mode of setting a gas
engine by ear and with a tachometer and
infrared temperature gauge to correlate
what I was hearing.
Once adjusted, which took only a
couple flights to tweak, the Brison became
one sweet-running engine. It is easily the
smoothest-running single-cylinder gas
engine I have flown and has a linear, rapid
throttle response. The idle is extremely
stable down to approximately 1,600 rpm
and is still exceedingly smooth at that
speed.
No doubt that others’ experiences
with the recommended starting
procedures will vary from my own, as will
what was found with the performance on
factory needle settings. But that goes to
show that I did the review with an off-theshelf
engine “by the book” and illustrates
what can happen with any manufacturer’s
product.
This is not a unique result; you have to
be ready to apply some of your own
experience to get things going just right
with any manufacturer’s power plant. The
Brison 2.4 is a great little gas engine and I
can recommend it without hesitation. MA
—Ed Alt
Manufacturer/Distributor:
Cimmaster Inc./Kangke Industrial USA
Inc.
49 E. Industry Ct. Unit N
Deer Park NY 11729
(631) 274-3058
www.kangkeusa.com
November 2007 51
11sig2.QXD 9/21/07 9:23 AM Page 51
installation and setup. Numerous single servos
could drive ailerons this size with no trouble,
but because of structural factors I advise you
to go with the manufacturer’s
recommendations of two each.
Ganging multiple servos on one control
surface requires careful attention to controllinkage
geometry to assure that for a fixed
amount of servo travel from either servo there
is a corresponding amount of control-surface
deflection. Otherwise the servos will fight
each other, wasting battery capacity, reducing
control effectiveness, and possibly
overheating and damaging the servos.
Matching servo centering and travel endpoints
is required for the same reason.
Although there are several means of doing
this, including using devices such as the JR
MatchBox or using transmitter multipoint
mixes, a simple method that works is to use
sets of programmable digital servos, such as
those Hitec offers. Simplicity was one of the
goals of this project, so I chose this path.
Assembly: Overall the instructions were fairly
clear and matched what was provided with the
kit. Among the minor discrepancies was that
the control-horn-hole locations were supposed
to be partially drilled, but none of the hard
points had any locations marked.
It was not difficult to find the hard points,
but it did require that I carefully measure and
drill to achieve the correct control-arm offsets
for each location so the control-linkage
geometry was consistent.
There were only two misses to the model’s
construction, although neither was serious,
one of which was that the hole in the fuselage
to accept the aft antirotation pin for the left
wing was misaligned. Out of the box it was
impossible to mate the left wing to the
fuselage.
The fix was to pop off the plywood
doughnut inside the fuselage that anchors the
pin, and then slightly open the hole in the
fuselage side and reglue the plywood
doughnut in the correct location.
The other issue was that the left stabilizer
had a twist to it. However, it required only a
minor degree of trimming the elevator halves
to offset this irregularity. The flying qualities
were fine with that small adjustment.
Engine Mounting: The Brison 2.4 fit within
the recommended engine requirements, but
since it had a rear-mounting flange it was
impossible to use the mounting hardware
supplied. I made a set of equal-length
hardwood dowels and drilled through the
center as mounting spacers to permit proper
alignment of the engine. The engine box was
already set with the firewall at the correct
engine-thrust offset angle built in, so this work
went quickly.
I selected a Bisson 2.4 inverted muffler,
which fit easily inside the large cowl.
Since the Brison engine mounting
locations caused the mounting bolts to
impinge on the area where the tank was
designed to be, I made a different
mounting system. I was also able to place
the tank closer to the balance point.
Brison’s Walbro carburetor’s strong
pumping action meant that moving it back
from the factory location wouldn’t pose a
fuel-delivery problem.
General Flying Qualities and Trimming:
Most of the flying was done with a 20 x 8
APC propeller, which allowed the Brison 2.4
to operate in a comfortable range up to 7,700
rpm. With this setup the Yak’s vertical
penetration was good for moderately difficult
aerobatics.
It was easily capable of flying through
Scale Aerobatics schedules up through
Sportsman. With good attention to energy
management it could also handle
Intermediate-level schedules.
Other schedules place more demand on
the power plant/airframe combination, and
the model would not perform the vertical
snaps and very tall complex geometric figures
well. Different propeller selections may yield
better performance, but not to the extent that
this airplane would excel in the higher-class
sequences.
However, it fits the bill for the intended
use of sport aerobatics or the first few classes
of Scale Aerobatics competition. The Yak is
also capable of many 3-D maneuvers, with
some limitations caused by wing loading.
This airplane follows some popular design
trends for models that are 3-D capable,
including large control-surface areas and
hinge-line beveling to allow for the extreme
control throws required for 3-D. It also has a
large aerodynamic counterbalance on the
rudder, which is intended to reduce the
demand on the rudder servo for extreme
control deflections.
As with everything in aircraft design,
there are trade-offs. What you gain in control
effectiveness at extreme throws can
sometimes result in other issues around
neutral positions.
That proved to be the case with the Yak. I
noticed its tendency to fishtail at higher
cruising speeds and wander in either direction
in the roll axis because of roll-coupling
effects as the model yawed.
At first, suspecting that this might be a
rear balance-point issue, I determined that a
stronger rudder servo was the answer to all
the tracking and rolling issues. Even with a
168 ounce-inch HS-5645MG Hitec servo it
was unable to keep the rudder completely
neutralized because the air tends to grab the
large counterbalance surface and cause an
unwanted deflection in the rudder.
Switching to an available JR DS8611
servo with 296 ounce-inch of torque at 6 volts
instantly solved the yawing and roll-coupling
problems. At the same time knife-edge
control effectiveness improved noticeably.
This also made a significant improvement to
the Yak’s snap-roll handling.
With the lower-torque rudder servo the
model would wallow and usually end up
doing a tight barrel roll instead of a snap roll.
Snap rolls are “stalled” maneuvers, in which
autorotation occurs by forcing one wing to
stall by quickly yawing the model with rudder
as it is on the verge of a stall caused by a
quick pitch change (lots of elevator rapidly
applied). The advancing wing continues to fly
as the retreating wing stalls, so the model
rolls in the direction of the rudder applied.
A weak rudder response will not always
hit the spot where autorotation can occur
promptly, hence the improved snap-roll
performance with the DS8611 servo. Snap
rolls stop much better with a good rudder
servo too.
With the fishtail and roll-coupling issues
resolved, it was time to see what the Yak
would really do. Starting with the basics I
completed the standard aerobatic trimming
procedures I use for RC Aerobatics (Pattern)-
and IMAC (International Miniature Aerobatic
Club)-type models.
A typical set of small trim changes was
needed; most of the adjustments were
corrected with the slight twist of a clevis. I
put in two clevis turns of offset to the left
elevator to compensate for the left stabilizer
twist and got good tracking through positive
and negative looping figures.
I ended up carrying a small amount of
right rudder trim, which gave a good balance
of up-line tracking without causing unwanted
skidding during level flight. Some use of the
rudder to offset propeller spiral slipstream
effects is necessary during vertical
maneuvers, especially during the transition
from level to vertical, but it was a normal
amount and felt comfortable.
I added an 8% down-elevator mix at
throttle idle to prevent down-line shallowing
(pulling to the canopy). This percentage was
slightly higher than normal, most likely
because the Yak was a bit on the heavy side
at 16 pounds, which had it trimmed with
more pitch up force to hold upright, level
flight. This tends to contribute to down-line
shallowing.
The Yak also needed 8% rudder-to-aileron
mix to counteract a proverse roll in either
direction of rudder applied during knife edge.
However, pitch coupling was minimal; it was
so slight that I didn’t even bother to mix it
out.
Sport and Precision Aerobatics: I found that
tracking through inside and outside looping
figures was good as long as I started the
figures at a good cruising speed when entry
was from a horizontal attitude. Sharp-radius
figures were not as clean as larger figures
since the Yak tended to wallow a bit because
of its relatively high wing loading if the
radius was pulled fairly tight.
This model can present well with a
balance of speed and figure size that keeps
things moving at a moderate cruise and
doesn’t make maneuvers too tight or overly
large.
The Yak rolls nicely at moderate to high
cruising speeds with little work with the
rudder. I found that I didn’t need to adjust the
differential at all by using recommended
throws; i.e., the model rolled straight and true
with no tendency to wobble around its axis.
For finesse rolling maneuvers—that is,
with combinations of lower airspeeds and
extremely slow roll rates—the integrated
rudder and elevator workload is a bit high,
but good results are achievable.
The large rudder is extraordinarily
effective during Hammerheads, which can be
done easily within a half wingspan without
much tendency to tail wag after the yawing
over is finished. Carrying a bit of a fast idle
over the top was all that was needed.
With the correct rudder servo, knife-edge
flight at various speed ranges was good. The
Yak liked to be moving at a good cruising
speed to keep the fuselage angle reasonable
during knife edge, point rolls, or Slow Rolls
during sequence-type flying.
For show-off types of aerobatics you could
combine an extreme fuselage angle and
excessive rudder with plenty of throttle for an
impressive low-and-slow knife-edge pass. At
full power a series of knife-edge-to-knife-edge
snaps were fairly easy to catch accurately and
then continue along up to roughly 45° knifeedge
climbout.
Upright and inverted flat turns were
effective with the big rudder, and the Yak
could do some impressive tail-over-nose
tumbles integrated into those flat turns. This
required keeping a bit of power in, but they
were fun to do. Heligoin circles executed well
too, given at least a moderate airspeed.
The Yak snap-rolled well since everything
was set up right. I put it through many
combinations of Positive Snaps and Negative
Snaps in all attitudes, and it behaved nicely as
long as I had a decent amount of airspeed
going in and some power to pull through.
For vertical up-line snap rolls it worked
much better to keep the up-lines short before
and after the snap. They can use a great deal
of energy, but with proper technique the Yak
got through them fine with the Brison 2.4
pulling it along.
Unloading most of the elevator input after
the initial pitch break was the key. Otherwise
it would be difficult to get the model to come
out with a good line after the snap.
Upright Spins or Inverted Spins, such as
those performed during a precision aerobatic
sequence, need planning if you are thinking of
doing more than one or two rotations. With its
relatively high wing loading, the Yak tended
to come down fairly quickly after the pitch
break and autorotation start, although its rate
of spin rotation was comfortable and easy to
time right, so it came out on heading.
I found that it was helpful to be partially
on the power during spin recovery to get
enough speed to make the transition back to
level flight crisp. Flat spins, such as what you
might do as part of a Blender maneuver, work
well with approximately half or more throttle
rolled in to reduce the rate of descent and keep
the rotation rate high. It’s important to have a
little power in already to help with a positive
recovery.
3-D Aerobatics: The Yak handles 3-D rolling
maneuvers well, although it has a slightly
heavy feel and requires that you keep the
power slightly more than halfway. It won’t get
down to the speed range that makes it look
like it’s filled with helium, but it works and
still looks good doing it.
It wasn’t too hard to manage transitions
from straight-line rollers to circling in either
direction, as long as the speed was kept up a
bit. The Yak is perhaps not the best learning
platform for 3-D rolling maneuvers, but it was
quite capable of them.
I was also able to take the model from a 3-
D Rolling Circle into three-quarters of a 3-D
Rolling Loop. I think it would have made it
through the bottom quarter of the 3-D Rolling
Loop, but I wasn’t brave enough to continue
all the way around that day.
The Yak did Walls without snapping
away, but it did mush through them a bit (not
a sudden stop). Controlling the aftermath of
the Wall required getting on the power fairly
quickly.
Parachutes also worked, although this
airplane didn’t exactly “stop and suspend.”
Instead it mushed through somewhat and
needed power applied fairly promptly to then
sustain an Elevator, 3-D roller, or some 3-D
maneuver transition.
Elevators had some wing rock and would
probably stabilize better with some crow mix
in the ailerons, even though I didn’t try that.
The wing rocking wasn’t so severe that it
couldn’t be dealt with with normal technique.
The Blenders the Yak could do were fairly
exciting. Starting with roughly 400 feet of
altitude, it wound up nicely as I banged it
from the aileron roll to negative snap
transition into the flat spin.
Hovering and torque rolls needed a fair bit
of power at this Yak’s weight. The setup was
capable, but I wouldn’t classify it as a good
learning setup. You need to get airspeed back
quickly at full throttle if a hovering maneuver
is aborted at low altitude, so being on your
toes is important.
I was unable to get the Yak to do more
than one consecutive Waterfall. Power to
weight was the issue in this case.
The Goldberg Yak 54 will give you the
capability to cross over between a good range
of 3-D maneuvers to medium-difficulty
precision sequence flying with the flip of a
few rate switches, without investing
megabucks to do it. MA
Ed Alt
[email protected]
Manufacturer/Distributor:
Carl Goldberg Models
Box 88
Oakwood GA 30566
(678) 450-0085
www.carlgoldbergproducts.com
Products Used In Review:
Radio:
JR
(217) 352-1913
www.horizonhobby.com
Servos:
Hitec
(858) 748-6948
www.hitecrcd.com
Other Printed Review Sources:
Non

BY ED ALT
Plane Talk: Carl Goldberg Products Yak 54 ARF
THE CARL GOLDBERG Yak 54 was delivered as a complete ARF,
with all the necessary hardware for control systems, engine mounting,
and fuel system. My first impressions were that the quality of
construction and finish were good overall. The model comprised balsa
and plywood formers, ribs, and sheeting.
This model was solidly constructed by today’s standards for ARFs,
especially with the integrated engine box and landing-gear design. A
great deal of attention was paid to detail, including a dowel-pinned
firewall. The control-surface/hinge-line beveling was quite good.
The covering job was above average. Relatively few spots required
tacking down and reshrinking, as is commonly necessary on an ARF.
That was especially surprising since the Yak had a good amount of
detail with many small pieces to complete its color scheme.
Some care was needed when removing the tape from the control
surfaces, to avoid lifting covering trim pieces, but nothing could not be
tacked back down effortlessly. The quality of the engine cowl’s and
wheel pants’ fiberglass was good, and those parts were reasonably
lightweight with a good paint finish.
Planning for Assembly: I weighed all the model’s parts and
hardware accessories in preparation for building. A big part of the
decision about engine choice, as well as the location of the rudder
servo, was made after I tallied the weight and did a trial balancepoint
estimate.
Given the large control surfaces on the Yak’s tail, as well as the
large fuselage volume aft of the balance point, this model could
easily have come out tail-heavy if this kind of preparation was not
done. Although an option was to mount the rudder servo in the tail,
it seemed that that installation would work only with a heavy
engine-and-muffler combination.
I ultimately selected a Brison 2.4 (39cc) gas engine, Bisson
muffler, and cabin-mounted rudder servo. With that combination, in
addition to a relatively heavy APC 20 x 8 propeller and placing the
ignition and flight-pack batteries as far forward as was practical, the
balance point came out right on the money.
Servo Selection: There were no recommendations in the kit for
minimum servo torque for any of the control surfaces, although a servo
rated at 57 ounce-inch of torque at 6.0 volts was shown for the
elevators. My experience with models this size told me that something
with substantially more torque would be needed.
Since Hitec HS-5625MG servos (130 ounce-inch at 6 volts) were
available to me, I used those on the elevators. I used Hitec HS-
5645HBs (164 ounce-inch at 6 volts) for the ailerons, even though their
combined torque was a bit of overkill for the application. I chose an
HS-5645MG for the rudder, which proved to be inadequate.
Since the Yak’s ailerons were designed to be driven by two servos
each, I considered programmable servos to be an advantage for ease of
This sport-scale model is
great for sport aerobatics
or 3-D fun
48 MODEL AVIATION
11sig2.QXD 9/21/07 9:20 AM Page 48
November 2007 49
Photos by the author
Wood-dowel spacers were used to offset
the engine from the firewall. Notice the
simple throttle-linkage arrangement.
The author removed the neatly packaged Yak’s parts from their plastic bagging and set
them aside to acclimate. He touched up the small wrinkles in the covering a few days later.
To correct for any wing-incidence
variations, remove the autorotation
doubler, resize the opening, and then
replace the doubler.
The Yak was constructed from accurate and well-engineered laser-cut parts. The
stressed skin sheeting made the structure extraordinarily stiff.
The rudder servo is a tight fit between the wing tube and the aft
former. Install a servo with no less than 200 inch-ounce of torque.
The fuel tank was mounted aft, closer to the CG, on a custom-built
plywood mount. The offset also helps balance the model laterally.
11sig2.QXD 9/21/07 9:21 AM Page 49
50 MODEL AVIATION
Test-Model Details
Pluses and Minuses
Specifications
The model features sharp hinge lines that
permit a 3-D control-throw setup.
Hardwood plates are located at the
control-horn locations.
There’s plenty of room up front to clear
the APC 20-inch propeller. A 1/4-scale pilot
would set off the model nicely.
The oversized control surfaces make this
Yak ideal for slow-speed aerobatics. The
recommended CG is accurate.
The large top hatch makes the Yak easy to maintain and quick to assemble.
Ground handling is solid with its wide landing gear.
The author performs a
ground check of all control
surfaces before taxiing the
model out.
+
• Complete kit
• Good looks
• Easy assembly -• Heavier than advertised
• Antirotation pins required adjustment
Engine used: Brison 2.4
Propeller: APC 20 x 8
Fuel: 24-ounce tank, 93 octane fuel with
Amsoil 100:1 (after break-in)
Radio system: JR 10X transmitter with
frequency synthesis; JR R2000
synthesized receiver; six Hitec digital
servos; one Futaba 3004 servo; one JR
DS8611 servo; 2080 mAh, 7.4-volt Li-Ion
battery with dual ALR5 programmable 5-
amp regulators
Ready-to-fly weight: 16 pounds, 8
ounces
Wing loading: 32.4 ounces/square foot
Flight duration: 15 minutes
Type: RC aerobatic ARF
Pilot skill level: Intermediate to
advanced
Wingspan: 77 inches
Wing area: 1,139 square inches
Length: 72 inches
Weight: 13-14 pounds
Wing loading: 27 ounces/square
foot
Engine: 1.20-2.20 cu. in. (19.7-
36cc) two-stroke, 1.20-1.80 cu. in.
(19.7-29cc) four-stroke, or 2.4 cu.
in. (19.7-39cc) gasoline
Radio: Four channels (minimum),
eight servos
Construction: Balsa and plywood
Covering/finish: Polyester film,
painted fiberglass parts
Price: $389.99
11sig2.QXD 9/21/07 10:04 AM Page 50
Brison 2.4 Engine
IT WAS A pleasure to have a Brison 2.4
engine to review along with the Goldberg
Yak 54. Having owned other competition
gas engines in the 100- to 150cc range, this
was my first Brison and I was anxious to
see how it stacked up.
As delivered this engine was a beautiful
piece of work. It had a polished-aluminum
crankcase, with an aluminum bellcrank to
operate the Walbro carburetor. There was
an idle return spring that could be
disconnected but not removed since it
acted as a spacer for assembly, ensuring
that the butterfly valve did not come loose
and possibly be ingested by the engine.
I would have preferred to keep the
return spring engaged as a safety backup in
case the throttle linkage ever came apart in
flight, but I felt that the constant load on
the throttle servo would not be a good
thing.
I would like to see milder springs used
for these applications. I have not yet seen a
gas engine with which I felt comfortable
leaving the return spring engaged for this
reason.
The Brison 2.4 came supplied with a
RevMaster ignition module, which featured
continuous spark advance throughout the
usable rpm range. This eliminated the
original mechanical timing advance,
although the mechanical advance is still
available from Brison for those who prefer
it.
My experience with the Brison/
RevMaster combination was positive, and I
would not hesitate to run it again.
The Brison had a Nikasil-lined
cylinder/piston assembly that is made in the
USA by Dolmar. The Nikasil lining is
designed for low wear throughout the life
of the engine.
Propeller mounting was quick and easy
with a single propeller bolt hub. It was
advertised as being suitable for models
ranging in weight from 12 to 21 pounds,
depending on wing loading.
For this application, which required
wringing out the full performance of an
intermediate- to advanced-skill-level
aerobatic model, it was right at the upper
limit of its performance capability. The Yak
54 weighed 16.5 pounds with fuel.
My best estimate is that the Brison 2.4
would excel at powering aerobatic models
that are kept at less than 15 pounds ready
to fuel. The weight of the engine itself was
reasonable, at only 2.75 pounds.
The weight of the ignition module and
battery and the Brison’s all-up weight
without a muffler was a shade heavier than
3 pounds. That is extremely competitive
with the weight of some popular glow
engines in a similar displacement and power
range.
Brison recommends using high-octane
gasoline with a good-quality synthetic twocycle
oil such as Amsoil or Klotz.
Petroleum-based oils are also permissible,
at a 64:1 fuel-to-oil ratio. The
recommended ratios for synthetic oils are
64:1-100:1. My experience with Amsoil is
that you use it at 100:1. I used 93-octane
gasoline throughout.
There is no prescribed break-in
procedure per se since this engine is
considered ready to fly as delivered.
However, the instructions do point out (as
most would recommend) that you run the
engine to avoid surprises, ensuring that it
will operate reliably at all rpm ranges,
before taking off for that first flight.
Expect the engine to take 40-50 hours
of operation before it is fully run in, during
which time maximum rpm should increase
gradually. Other handling qualities can be
expected to improve during this time as
well, such as slower, steadier idling and
improved transition. Also, cylinder-head
temperatures tend to diminish as the engine
completes its run-in period.
During flight testing for this review, only
approximately one-tenth of the prescribed
run-in period was achieved. However, I
clearly observed that the engine had
improved in all respects during that time
(accompanied by some mixture
adjustments).
By the eighth flight the APC 20 x 8
propeller was being turned at 7,600-7,650
static rpm when fully warmed up, indicating
that the engine was ready for more
propeller load. Brison’s recommended
range for best output torque was 6,500-
7,500 rpm.
Although the operating instructions
were firm about the needle settings being
optimally adjusted at the factory, I found it
necessary to lean out both the low and high
end after a few flights to realize more of
the engine’s potential and get a smooth,
reliable midrange and throttle transition in
flight.
The final settings used were still on the
rich side since this engine’s running-in
period was incomplete. All the flying was
done at field elevations of 195-450 feet
ASL, so the mixture adjustment was not a
result of a high-altitude environment.
Although everything ended up working
out wonderfully with the Brison after
getting past a learning curve and later
carburetor mixture adjustments, my first
attempts at starting and running the engine
were a little frustrating. Following the
recommended starting procedures simply
didn’t work.
During the course of those 100-plus
flip-start attempts, I checked the ignition,
fuel connections, plug, etc. Not a pop, but
I sure got some good exercise. Note that
this was before making any carburetor
adjustments.
It may have been that this particular
Walbro carburetor was a bit weak at
drawing fuel at idle setting, but it was
impossible to draw enough fuel with the
choke closed and the throttle set below
full throttle.
The starting procedure that worked for
me was the following: fully choked,
throttle wide open, ignition on, and a few
flips until it fired. After the first pop I
closed the throttle to idle, opened the
choke, and continued flipping until it
started and ran at idle.
That is not my favorite procedure—I
am accustomed to doing the entire choke
procedure at idle—but it definitely worked
reliably by following the preceding
technique. Of course this entire procedure
was done with a helper holding the model.
As I noted, it was necessary to lean out
the low- and high-end mixture settings to
really let the Brison 2.4 perform. It had a
distinct tendency to load up in the
midrange and actually quit in flight once
because of this condition (at the factory
settings).
That was enough for me. I switched
into my normal mode of setting a gas
engine by ear and with a tachometer and
infrared temperature gauge to correlate
what I was hearing.
Once adjusted, which took only a
couple flights to tweak, the Brison became
one sweet-running engine. It is easily the
smoothest-running single-cylinder gas
engine I have flown and has a linear, rapid
throttle response. The idle is extremely
stable down to approximately 1,600 rpm
and is still exceedingly smooth at that
speed.
No doubt that others’ experiences
with the recommended starting
procedures will vary from my own, as will
what was found with the performance on
factory needle settings. But that goes to
show that I did the review with an off-theshelf
engine “by the book” and illustrates
what can happen with any manufacturer’s
product.
This is not a unique result; you have to
be ready to apply some of your own
experience to get things going just right
with any manufacturer’s power plant. The
Brison 2.4 is a great little gas engine and I
can recommend it without hesitation. MA
—Ed Alt
Manufacturer/Distributor:
Cimmaster Inc./Kangke Industrial USA
Inc.
49 E. Industry Ct. Unit N
Deer Park NY 11729
(631) 274-3058
www.kangkeusa.com
November 2007 51
11sig2.QXD 9/21/07 9:23 AM Page 51
installation and setup. Numerous single servos
could drive ailerons this size with no trouble,
but because of structural factors I advise you
to go with the manufacturer’s
recommendations of two each.
Ganging multiple servos on one control
surface requires careful attention to controllinkage
geometry to assure that for a fixed
amount of servo travel from either servo there
is a corresponding amount of control-surface
deflection. Otherwise the servos will fight
each other, wasting battery capacity, reducing
control effectiveness, and possibly
overheating and damaging the servos.
Matching servo centering and travel endpoints
is required for the same reason.
Although there are several means of doing
this, including using devices such as the JR
MatchBox or using transmitter multipoint
mixes, a simple method that works is to use
sets of programmable digital servos, such as
those Hitec offers. Simplicity was one of the
goals of this project, so I chose this path.
Assembly: Overall the instructions were fairly
clear and matched what was provided with the
kit. Among the minor discrepancies was that
the control-horn-hole locations were supposed
to be partially drilled, but none of the hard
points had any locations marked.
It was not difficult to find the hard points,
but it did require that I carefully measure and
drill to achieve the correct control-arm offsets
for each location so the control-linkage
geometry was consistent.
There were only two misses to the model’s
construction, although neither was serious,
one of which was that the hole in the fuselage
to accept the aft antirotation pin for the left
wing was misaligned. Out of the box it was
impossible to mate the left wing to the
fuselage.
The fix was to pop off the plywood
doughnut inside the fuselage that anchors the
pin, and then slightly open the hole in the
fuselage side and reglue the plywood
doughnut in the correct location.
The other issue was that the left stabilizer
had a twist to it. However, it required only a
minor degree of trimming the elevator halves
to offset this irregularity. The flying qualities
were fine with that small adjustment.
Engine Mounting: The Brison 2.4 fit within
the recommended engine requirements, but
since it had a rear-mounting flange it was
impossible to use the mounting hardware
supplied. I made a set of equal-length
hardwood dowels and drilled through the
center as mounting spacers to permit proper
alignment of the engine. The engine box was
already set with the firewall at the correct
engine-thrust offset angle built in, so this work
went quickly.
I selected a Bisson 2.4 inverted muffler,
which fit easily inside the large cowl.
Since the Brison engine mounting
locations caused the mounting bolts to
impinge on the area where the tank was
designed to be, I made a different
mounting system. I was also able to place
the tank closer to the balance point.
Brison’s Walbro carburetor’s strong
pumping action meant that moving it back
from the factory location wouldn’t pose a
fuel-delivery problem.
General Flying Qualities and Trimming:
Most of the flying was done with a 20 x 8
APC propeller, which allowed the Brison 2.4
to operate in a comfortable range up to 7,700
rpm. With this setup the Yak’s vertical
penetration was good for moderately difficult
aerobatics.
It was easily capable of flying through
Scale Aerobatics schedules up through
Sportsman. With good attention to energy
management it could also handle
Intermediate-level schedules.
Other schedules place more demand on
the power plant/airframe combination, and
the model would not perform the vertical
snaps and very tall complex geometric figures
well. Different propeller selections may yield
better performance, but not to the extent that
this airplane would excel in the higher-class
sequences.
However, it fits the bill for the intended
use of sport aerobatics or the first few classes
of Scale Aerobatics competition. The Yak is
also capable of many 3-D maneuvers, with
some limitations caused by wing loading.
This airplane follows some popular design
trends for models that are 3-D capable,
including large control-surface areas and
hinge-line beveling to allow for the extreme
control throws required for 3-D. It also has a
large aerodynamic counterbalance on the
rudder, which is intended to reduce the
demand on the rudder servo for extreme
control deflections.
As with everything in aircraft design,
there are trade-offs. What you gain in control
effectiveness at extreme throws can
sometimes result in other issues around
neutral positions.
That proved to be the case with the Yak. I
noticed its tendency to fishtail at higher
cruising speeds and wander in either direction
in the roll axis because of roll-coupling
effects as the model yawed.
At first, suspecting that this might be a
rear balance-point issue, I determined that a
stronger rudder servo was the answer to all
the tracking and rolling issues. Even with a
168 ounce-inch HS-5645MG Hitec servo it
was unable to keep the rudder completely
neutralized because the air tends to grab the
large counterbalance surface and cause an
unwanted deflection in the rudder.
Switching to an available JR DS8611
servo with 296 ounce-inch of torque at 6 volts
instantly solved the yawing and roll-coupling
problems. At the same time knife-edge
control effectiveness improved noticeably.
This also made a significant improvement to
the Yak’s snap-roll handling.
With the lower-torque rudder servo the
model would wallow and usually end up
doing a tight barrel roll instead of a snap roll.
Snap rolls are “stalled” maneuvers, in which
autorotation occurs by forcing one wing to
stall by quickly yawing the model with rudder
as it is on the verge of a stall caused by a
quick pitch change (lots of elevator rapidly
applied). The advancing wing continues to fly
as the retreating wing stalls, so the model
rolls in the direction of the rudder applied.
A weak rudder response will not always
hit the spot where autorotation can occur
promptly, hence the improved snap-roll
performance with the DS8611 servo. Snap
rolls stop much better with a good rudder
servo too.
With the fishtail and roll-coupling issues
resolved, it was time to see what the Yak
would really do. Starting with the basics I
completed the standard aerobatic trimming
procedures I use for RC Aerobatics (Pattern)-
and IMAC (International Miniature Aerobatic
Club)-type models.
A typical set of small trim changes was
needed; most of the adjustments were
corrected with the slight twist of a clevis. I
put in two clevis turns of offset to the left
elevator to compensate for the left stabilizer
twist and got good tracking through positive
and negative looping figures.
I ended up carrying a small amount of
right rudder trim, which gave a good balance
of up-line tracking without causing unwanted
skidding during level flight. Some use of the
rudder to offset propeller spiral slipstream
effects is necessary during vertical
maneuvers, especially during the transition
from level to vertical, but it was a normal
amount and felt comfortable.
I added an 8% down-elevator mix at
throttle idle to prevent down-line shallowing
(pulling to the canopy). This percentage was
slightly higher than normal, most likely
because the Yak was a bit on the heavy side
at 16 pounds, which had it trimmed with
more pitch up force to hold upright, level
flight. This tends to contribute to down-line
shallowing.
The Yak also needed 8% rudder-to-aileron
mix to counteract a proverse roll in either
direction of rudder applied during knife edge.
However, pitch coupling was minimal; it was
so slight that I didn’t even bother to mix it
out.
Sport and Precision Aerobatics: I found that
tracking through inside and outside looping
figures was good as long as I started the
figures at a good cruising speed when entry
was from a horizontal attitude. Sharp-radius
figures were not as clean as larger figures
since the Yak tended to wallow a bit because
of its relatively high wing loading if the
radius was pulled fairly tight.
This model can present well with a
balance of speed and figure size that keeps
things moving at a moderate cruise and
doesn’t make maneuvers too tight or overly
large.
The Yak rolls nicely at moderate to high
cruising speeds with little work with the
rudder. I found that I didn’t need to adjust the
differential at all by using recommended
throws; i.e., the model rolled straight and true
with no tendency to wobble around its axis.
For finesse rolling maneuvers—that is,
with combinations of lower airspeeds and
extremely slow roll rates—the integrated
rudder and elevator workload is a bit high,
but good results are achievable.
The large rudder is extraordinarily
effective during Hammerheads, which can be
done easily within a half wingspan without
much tendency to tail wag after the yawing
over is finished. Carrying a bit of a fast idle
over the top was all that was needed.
With the correct rudder servo, knife-edge
flight at various speed ranges was good. The
Yak liked to be moving at a good cruising
speed to keep the fuselage angle reasonable
during knife edge, point rolls, or Slow Rolls
during sequence-type flying.
For show-off types of aerobatics you could
combine an extreme fuselage angle and
excessive rudder with plenty of throttle for an
impressive low-and-slow knife-edge pass. At
full power a series of knife-edge-to-knife-edge
snaps were fairly easy to catch accurately and
then continue along up to roughly 45° knifeedge
climbout.
Upright and inverted flat turns were
effective with the big rudder, and the Yak
could do some impressive tail-over-nose
tumbles integrated into those flat turns. This
required keeping a bit of power in, but they
were fun to do. Heligoin circles executed well
too, given at least a moderate airspeed.
The Yak snap-rolled well since everything
was set up right. I put it through many
combinations of Positive Snaps and Negative
Snaps in all attitudes, and it behaved nicely as
long as I had a decent amount of airspeed
going in and some power to pull through.
For vertical up-line snap rolls it worked
much better to keep the up-lines short before
and after the snap. They can use a great deal
of energy, but with proper technique the Yak
got through them fine with the Brison 2.4
pulling it along.
Unloading most of the elevator input after
the initial pitch break was the key. Otherwise
it would be difficult to get the model to come
out with a good line after the snap.
Upright Spins or Inverted Spins, such as
those performed during a precision aerobatic
sequence, need planning if you are thinking of
doing more than one or two rotations. With its
relatively high wing loading, the Yak tended
to come down fairly quickly after the pitch
break and autorotation start, although its rate
of spin rotation was comfortable and easy to
time right, so it came out on heading.
I found that it was helpful to be partially
on the power during spin recovery to get
enough speed to make the transition back to
level flight crisp. Flat spins, such as what you
might do as part of a Blender maneuver, work
well with approximately half or more throttle
rolled in to reduce the rate of descent and keep
the rotation rate high. It’s important to have a
little power in already to help with a positive
recovery.
3-D Aerobatics: The Yak handles 3-D rolling
maneuvers well, although it has a slightly
heavy feel and requires that you keep the
power slightly more than halfway. It won’t get
down to the speed range that makes it look
like it’s filled with helium, but it works and
still looks good doing it.
It wasn’t too hard to manage transitions
from straight-line rollers to circling in either
direction, as long as the speed was kept up a
bit. The Yak is perhaps not the best learning
platform for 3-D rolling maneuvers, but it was
quite capable of them.
I was also able to take the model from a 3-
D Rolling Circle into three-quarters of a 3-D
Rolling Loop. I think it would have made it
through the bottom quarter of the 3-D Rolling
Loop, but I wasn’t brave enough to continue
all the way around that day.
The Yak did Walls without snapping
away, but it did mush through them a bit (not
a sudden stop). Controlling the aftermath of
the Wall required getting on the power fairly
quickly.
Parachutes also worked, although this
airplane didn’t exactly “stop and suspend.”
Instead it mushed through somewhat and
needed power applied fairly promptly to then
sustain an Elevator, 3-D roller, or some 3-D
maneuver transition.
Elevators had some wing rock and would
probably stabilize better with some crow mix
in the ailerons, even though I didn’t try that.
The wing rocking wasn’t so severe that it
couldn’t be dealt with with normal technique.
The Blenders the Yak could do were fairly
exciting. Starting with roughly 400 feet of
altitude, it wound up nicely as I banged it
from the aileron roll to negative snap
transition into the flat spin.
Hovering and torque rolls needed a fair bit
of power at this Yak’s weight. The setup was
capable, but I wouldn’t classify it as a good
learning setup. You need to get airspeed back
quickly at full throttle if a hovering maneuver
is aborted at low altitude, so being on your
toes is important.
I was unable to get the Yak to do more
than one consecutive Waterfall. Power to
weight was the issue in this case.
The Goldberg Yak 54 will give you the
capability to cross over between a good range
of 3-D maneuvers to medium-difficulty
precision sequence flying with the flip of a
few rate switches, without investing
megabucks to do it. MA
Ed Alt
[email protected]
Manufacturer/Distributor:
Carl Goldberg Models
Box 88
Oakwood GA 30566
(678) 450-0085
www.carlgoldbergproducts.com
Products Used In Review:
Radio:
JR
(217) 352-1913
www.horizonhobby.com
Servos:
Hitec
(858) 748-6948
www.hitecrcd.com
Other Printed Review Sources:
Non

BY ED ALT
Plane Talk: Carl Goldberg Products Yak 54 ARF
THE CARL GOLDBERG Yak 54 was delivered as a complete ARF,
with all the necessary hardware for control systems, engine mounting,
and fuel system. My first impressions were that the quality of
construction and finish were good overall. The model comprised balsa
and plywood formers, ribs, and sheeting.
This model was solidly constructed by today’s standards for ARFs,
especially with the integrated engine box and landing-gear design. A
great deal of attention was paid to detail, including a dowel-pinned
firewall. The control-surface/hinge-line beveling was quite good.
The covering job was above average. Relatively few spots required
tacking down and reshrinking, as is commonly necessary on an ARF.
That was especially surprising since the Yak had a good amount of
detail with many small pieces to complete its color scheme.
Some care was needed when removing the tape from the control
surfaces, to avoid lifting covering trim pieces, but nothing could not be
tacked back down effortlessly. The quality of the engine cowl’s and
wheel pants’ fiberglass was good, and those parts were reasonably
lightweight with a good paint finish.
Planning for Assembly: I weighed all the model’s parts and
hardware accessories in preparation for building. A big part of the
decision about engine choice, as well as the location of the rudder
servo, was made after I tallied the weight and did a trial balancepoint
estimate.
Given the large control surfaces on the Yak’s tail, as well as the
large fuselage volume aft of the balance point, this model could
easily have come out tail-heavy if this kind of preparation was not
done. Although an option was to mount the rudder servo in the tail,
it seemed that that installation would work only with a heavy
engine-and-muffler combination.
I ultimately selected a Brison 2.4 (39cc) gas engine, Bisson
muffler, and cabin-mounted rudder servo. With that combination, in
addition to a relatively heavy APC 20 x 8 propeller and placing the
ignition and flight-pack batteries as far forward as was practical, the
balance point came out right on the money.
Servo Selection: There were no recommendations in the kit for
minimum servo torque for any of the control surfaces, although a servo
rated at 57 ounce-inch of torque at 6.0 volts was shown for the
elevators. My experience with models this size told me that something
with substantially more torque would be needed.
Since Hitec HS-5625MG servos (130 ounce-inch at 6 volts) were
available to me, I used those on the elevators. I used Hitec HS-
5645HBs (164 ounce-inch at 6 volts) for the ailerons, even though their
combined torque was a bit of overkill for the application. I chose an
HS-5645MG for the rudder, which proved to be inadequate.
Since the Yak’s ailerons were designed to be driven by two servos
each, I considered programmable servos to be an advantage for ease of
This sport-scale model is
great for sport aerobatics
or 3-D fun
48 MODEL AVIATION
11sig2.QXD 9/21/07 9:20 AM Page 48
November 2007 49
Photos by the author
Wood-dowel spacers were used to offset
the engine from the firewall. Notice the
simple throttle-linkage arrangement.
The author removed the neatly packaged Yak’s parts from their plastic bagging and set
them aside to acclimate. He touched up the small wrinkles in the covering a few days later.
To correct for any wing-incidence
variations, remove the autorotation
doubler, resize the opening, and then
replace the doubler.
The Yak was constructed from accurate and well-engineered laser-cut parts. The
stressed skin sheeting made the structure extraordinarily stiff.
The rudder servo is a tight fit between the wing tube and the aft
former. Install a servo with no less than 200 inch-ounce of torque.
The fuel tank was mounted aft, closer to the CG, on a custom-built
plywood mount. The offset also helps balance the model laterally.
11sig2.QXD 9/21/07 9:21 AM Page 49
50 MODEL AVIATION
Test-Model Details
Pluses and Minuses
Specifications
The model features sharp hinge lines that
permit a 3-D control-throw setup.
Hardwood plates are located at the
control-horn locations.
There’s plenty of room up front to clear
the APC 20-inch propeller. A 1/4-scale pilot
would set off the model nicely.
The oversized control surfaces make this
Yak ideal for slow-speed aerobatics. The
recommended CG is accurate.
The large top hatch makes the Yak easy to maintain and quick to assemble.
Ground handling is solid with its wide landing gear.
The author performs a
ground check of all control
surfaces before taxiing the
model out.
+
• Complete kit
• Good looks
• Easy assembly -• Heavier than advertised
• Antirotation pins required adjustment
Engine used: Brison 2.4
Propeller: APC 20 x 8
Fuel: 24-ounce tank, 93 octane fuel with
Amsoil 100:1 (after break-in)
Radio system: JR 10X transmitter with
frequency synthesis; JR R2000
synthesized receiver; six Hitec digital
servos; one Futaba 3004 servo; one JR
DS8611 servo; 2080 mAh, 7.4-volt Li-Ion
battery with dual ALR5 programmable 5-
amp regulators
Ready-to-fly weight: 16 pounds, 8
ounces
Wing loading: 32.4 ounces/square foot
Flight duration: 15 minutes
Type: RC aerobatic ARF
Pilot skill level: Intermediate to
advanced
Wingspan: 77 inches
Wing area: 1,139 square inches
Length: 72 inches
Weight: 13-14 pounds
Wing loading: 27 ounces/square
foot
Engine: 1.20-2.20 cu. in. (19.7-
36cc) two-stroke, 1.20-1.80 cu. in.
(19.7-29cc) four-stroke, or 2.4 cu.
in. (19.7-39cc) gasoline
Radio: Four channels (minimum),
eight servos
Construction: Balsa and plywood
Covering/finish: Polyester film,
painted fiberglass parts
Price: $389.99
11sig2.QXD 9/21/07 10:04 AM Page 50
Brison 2.4 Engine
IT WAS A pleasure to have a Brison 2.4
engine to review along with the Goldberg
Yak 54. Having owned other competition
gas engines in the 100- to 150cc range, this
was my first Brison and I was anxious to
see how it stacked up.
As delivered this engine was a beautiful
piece of work. It had a polished-aluminum
crankcase, with an aluminum bellcrank to
operate the Walbro carburetor. There was
an idle return spring that could be
disconnected but not removed since it
acted as a spacer for assembly, ensuring
that the butterfly valve did not come loose
and possibly be ingested by the engine.
I would have preferred to keep the
return spring engaged as a safety backup in
case the throttle linkage ever came apart in
flight, but I felt that the constant load on
the throttle servo would not be a good
thing.
I would like to see milder springs used
for these applications. I have not yet seen a
gas engine with which I felt comfortable
leaving the return spring engaged for this
reason.
The Brison 2.4 came supplied with a
RevMaster ignition module, which featured
continuous spark advance throughout the
usable rpm range. This eliminated the
original mechanical timing advance,
although the mechanical advance is still
available from Brison for those who prefer
it.
My experience with the Brison/
RevMaster combination was positive, and I
would not hesitate to run it again.
The Brison had a Nikasil-lined
cylinder/piston assembly that is made in the
USA by Dolmar. The Nikasil lining is
designed for low wear throughout the life
of the engine.
Propeller mounting was quick and easy
with a single propeller bolt hub. It was
advertised as being suitable for models
ranging in weight from 12 to 21 pounds,
depending on wing loading.
For this application, which required
wringing out the full performance of an
intermediate- to advanced-skill-level
aerobatic model, it was right at the upper
limit of its performance capability. The Yak
54 weighed 16.5 pounds with fuel.
My best estimate is that the Brison 2.4
would excel at powering aerobatic models
that are kept at less than 15 pounds ready
to fuel. The weight of the engine itself was
reasonable, at only 2.75 pounds.
The weight of the ignition module and
battery and the Brison’s all-up weight
without a muffler was a shade heavier than
3 pounds. That is extremely competitive
with the weight of some popular glow
engines in a similar displacement and power
range.
Brison recommends using high-octane
gasoline with a good-quality synthetic twocycle
oil such as Amsoil or Klotz.
Petroleum-based oils are also permissible,
at a 64:1 fuel-to-oil ratio. The
recommended ratios for synthetic oils are
64:1-100:1. My experience with Amsoil is
that you use it at 100:1. I used 93-octane
gasoline throughout.
There is no prescribed break-in
procedure per se since this engine is
considered ready to fly as delivered.
However, the instructions do point out (as
most would recommend) that you run the
engine to avoid surprises, ensuring that it
will operate reliably at all rpm ranges,
before taking off for that first flight.
Expect the engine to take 40-50 hours
of operation before it is fully run in, during
which time maximum rpm should increase
gradually. Other handling qualities can be
expected to improve during this time as
well, such as slower, steadier idling and
improved transition. Also, cylinder-head
temperatures tend to diminish as the engine
completes its run-in period.
During flight testing for this review, only
approximately one-tenth of the prescribed
run-in period was achieved. However, I
clearly observed that the engine had
improved in all respects during that time
(accompanied by some mixture
adjustments).
By the eighth flight the APC 20 x 8
propeller was being turned at 7,600-7,650
static rpm when fully warmed up, indicating
that the engine was ready for more
propeller load. Brison’s recommended
range for best output torque was 6,500-
7,500 rpm.
Although the operating instructions
were firm about the needle settings being
optimally adjusted at the factory, I found it
necessary to lean out both the low and high
end after a few flights to realize more of
the engine’s potential and get a smooth,
reliable midrange and throttle transition in
flight.
The final settings used were still on the
rich side since this engine’s running-in
period was incomplete. All the flying was
done at field elevations of 195-450 feet
ASL, so the mixture adjustment was not a
result of a high-altitude environment.
Although everything ended up working
out wonderfully with the Brison after
getting past a learning curve and later
carburetor mixture adjustments, my first
attempts at starting and running the engine
were a little frustrating. Following the
recommended starting procedures simply
didn’t work.
During the course of those 100-plus
flip-start attempts, I checked the ignition,
fuel connections, plug, etc. Not a pop, but
I sure got some good exercise. Note that
this was before making any carburetor
adjustments.
It may have been that this particular
Walbro carburetor was a bit weak at
drawing fuel at idle setting, but it was
impossible to draw enough fuel with the
choke closed and the throttle set below
full throttle.
The starting procedure that worked for
me was the following: fully choked,
throttle wide open, ignition on, and a few
flips until it fired. After the first pop I
closed the throttle to idle, opened the
choke, and continued flipping until it
started and ran at idle.
That is not my favorite procedure—I
am accustomed to doing the entire choke
procedure at idle—but it definitely worked
reliably by following the preceding
technique. Of course this entire procedure
was done with a helper holding the model.
As I noted, it was necessary to lean out
the low- and high-end mixture settings to
really let the Brison 2.4 perform. It had a
distinct tendency to load up in the
midrange and actually quit in flight once
because of this condition (at the factory
settings).
That was enough for me. I switched
into my normal mode of setting a gas
engine by ear and with a tachometer and
infrared temperature gauge to correlate
what I was hearing.
Once adjusted, which took only a
couple flights to tweak, the Brison became
one sweet-running engine. It is easily the
smoothest-running single-cylinder gas
engine I have flown and has a linear, rapid
throttle response. The idle is extremely
stable down to approximately 1,600 rpm
and is still exceedingly smooth at that
speed.
No doubt that others’ experiences
with the recommended starting
procedures will vary from my own, as will
what was found with the performance on
factory needle settings. But that goes to
show that I did the review with an off-theshelf
engine “by the book” and illustrates
what can happen with any manufacturer’s
product.
This is not a unique result; you have to
be ready to apply some of your own
experience to get things going just right
with any manufacturer’s power plant. The
Brison 2.4 is a great little gas engine and I
can recommend it without hesitation. MA
—Ed Alt
Manufacturer/Distributor:
Cimmaster Inc./Kangke Industrial USA
Inc.
49 E. Industry Ct. Unit N
Deer Park NY 11729
(631) 274-3058
www.kangkeusa.com
November 2007 51
11sig2.QXD 9/21/07 9:23 AM Page 51
installation and setup. Numerous single servos
could drive ailerons this size with no trouble,
but because of structural factors I advise you
to go with the manufacturer’s
recommendations of two each.
Ganging multiple servos on one control
surface requires careful attention to controllinkage
geometry to assure that for a fixed
amount of servo travel from either servo there
is a corresponding amount of control-surface
deflection. Otherwise the servos will fight
each other, wasting battery capacity, reducing
control effectiveness, and possibly
overheating and damaging the servos.
Matching servo centering and travel endpoints
is required for the same reason.
Although there are several means of doing
this, including using devices such as the JR
MatchBox or using transmitter multipoint
mixes, a simple method that works is to use
sets of programmable digital servos, such as
those Hitec offers. Simplicity was one of the
goals of this project, so I chose this path.
Assembly: Overall the instructions were fairly
clear and matched what was provided with the
kit. Among the minor discrepancies was that
the control-horn-hole locations were supposed
to be partially drilled, but none of the hard
points had any locations marked.
It was not difficult to find the hard points,
but it did require that I carefully measure and
drill to achieve the correct control-arm offsets
for each location so the control-linkage
geometry was consistent.
There were only two misses to the model’s
construction, although neither was serious,
one of which was that the hole in the fuselage
to accept the aft antirotation pin for the left
wing was misaligned. Out of the box it was
impossible to mate the left wing to the
fuselage.
The fix was to pop off the plywood
doughnut inside the fuselage that anchors the
pin, and then slightly open the hole in the
fuselage side and reglue the plywood
doughnut in the correct location.
The other issue was that the left stabilizer
had a twist to it. However, it required only a
minor degree of trimming the elevator halves
to offset this irregularity. The flying qualities
were fine with that small adjustment.
Engine Mounting: The Brison 2.4 fit within
the recommended engine requirements, but
since it had a rear-mounting flange it was
impossible to use the mounting hardware
supplied. I made a set of equal-length
hardwood dowels and drilled through the
center as mounting spacers to permit proper
alignment of the engine. The engine box was
already set with the firewall at the correct
engine-thrust offset angle built in, so this work
went quickly.
I selected a Bisson 2.4 inverted muffler,
which fit easily inside the large cowl.
Since the Brison engine mounting
locations caused the mounting bolts to
impinge on the area where the tank was
designed to be, I made a different
mounting system. I was also able to place
the tank closer to the balance point.
Brison’s Walbro carburetor’s strong
pumping action meant that moving it back
from the factory location wouldn’t pose a
fuel-delivery problem.
General Flying Qualities and Trimming:
Most of the flying was done with a 20 x 8
APC propeller, which allowed the Brison 2.4
to operate in a comfortable range up to 7,700
rpm. With this setup the Yak’s vertical
penetration was good for moderately difficult
aerobatics.
It was easily capable of flying through
Scale Aerobatics schedules up through
Sportsman. With good attention to energy
management it could also handle
Intermediate-level schedules.
Other schedules place more demand on
the power plant/airframe combination, and
the model would not perform the vertical
snaps and very tall complex geometric figures
well. Different propeller selections may yield
better performance, but not to the extent that
this airplane would excel in the higher-class
sequences.
However, it fits the bill for the intended
use of sport aerobatics or the first few classes
of Scale Aerobatics competition. The Yak is
also capable of many 3-D maneuvers, with
some limitations caused by wing loading.
This airplane follows some popular design
trends for models that are 3-D capable,
including large control-surface areas and
hinge-line beveling to allow for the extreme
control throws required for 3-D. It also has a
large aerodynamic counterbalance on the
rudder, which is intended to reduce the
demand on the rudder servo for extreme
control deflections.
As with everything in aircraft design,
there are trade-offs. What you gain in control
effectiveness at extreme throws can
sometimes result in other issues around
neutral positions.
That proved to be the case with the Yak. I
noticed its tendency to fishtail at higher
cruising speeds and wander in either direction
in the roll axis because of roll-coupling
effects as the model yawed.
At first, suspecting that this might be a
rear balance-point issue, I determined that a
stronger rudder servo was the answer to all
the tracking and rolling issues. Even with a
168 ounce-inch HS-5645MG Hitec servo it
was unable to keep the rudder completely
neutralized because the air tends to grab the
large counterbalance surface and cause an
unwanted deflection in the rudder.
Switching to an available JR DS8611
servo with 296 ounce-inch of torque at 6 volts
instantly solved the yawing and roll-coupling
problems. At the same time knife-edge
control effectiveness improved noticeably.
This also made a significant improvement to
the Yak’s snap-roll handling.
With the lower-torque rudder servo the
model would wallow and usually end up
doing a tight barrel roll instead of a snap roll.
Snap rolls are “stalled” maneuvers, in which
autorotation occurs by forcing one wing to
stall by quickly yawing the model with rudder
as it is on the verge of a stall caused by a
quick pitch change (lots of elevator rapidly
applied). The advancing wing continues to fly
as the retreating wing stalls, so the model
rolls in the direction of the rudder applied.
A weak rudder response will not always
hit the spot where autorotation can occur
promptly, hence the improved snap-roll
performance with the DS8611 servo. Snap
rolls stop much better with a good rudder
servo too.
With the fishtail and roll-coupling issues
resolved, it was time to see what the Yak
would really do. Starting with the basics I
completed the standard aerobatic trimming
procedures I use for RC Aerobatics (Pattern)-
and IMAC (International Miniature Aerobatic
Club)-type models.
A typical set of small trim changes was
needed; most of the adjustments were
corrected with the slight twist of a clevis. I
put in two clevis turns of offset to the left
elevator to compensate for the left stabilizer
twist and got good tracking through positive
and negative looping figures.
I ended up carrying a small amount of
right rudder trim, which gave a good balance
of up-line tracking without causing unwanted
skidding during level flight. Some use of the
rudder to offset propeller spiral slipstream
effects is necessary during vertical
maneuvers, especially during the transition
from level to vertical, but it was a normal
amount and felt comfortable.
I added an 8% down-elevator mix at
throttle idle to prevent down-line shallowing
(pulling to the canopy). This percentage was
slightly higher than normal, most likely
because the Yak was a bit on the heavy side
at 16 pounds, which had it trimmed with
more pitch up force to hold upright, level
flight. This tends to contribute to down-line
shallowing.
The Yak also needed 8% rudder-to-aileron
mix to counteract a proverse roll in either
direction of rudder applied during knife edge.
However, pitch coupling was minimal; it was
so slight that I didn’t even bother to mix it
out.
Sport and Precision Aerobatics: I found that
tracking through inside and outside looping
figures was good as long as I started the
figures at a good cruising speed when entry
was from a horizontal attitude. Sharp-radius
figures were not as clean as larger figures
since the Yak tended to wallow a bit because
of its relatively high wing loading if the
radius was pulled fairly tight.
This model can present well with a
balance of speed and figure size that keeps
things moving at a moderate cruise and
doesn’t make maneuvers too tight or overly
large.
The Yak rolls nicely at moderate to high
cruising speeds with little work with the
rudder. I found that I didn’t need to adjust the
differential at all by using recommended
throws; i.e., the model rolled straight and true
with no tendency to wobble around its axis.
For finesse rolling maneuvers—that is,
with combinations of lower airspeeds and
extremely slow roll rates—the integrated
rudder and elevator workload is a bit high,
but good results are achievable.
The large rudder is extraordinarily
effective during Hammerheads, which can be
done easily within a half wingspan without
much tendency to tail wag after the yawing
over is finished. Carrying a bit of a fast idle
over the top was all that was needed.
With the correct rudder servo, knife-edge
flight at various speed ranges was good. The
Yak liked to be moving at a good cruising
speed to keep the fuselage angle reasonable
during knife edge, point rolls, or Slow Rolls
during sequence-type flying.
For show-off types of aerobatics you could
combine an extreme fuselage angle and
excessive rudder with plenty of throttle for an
impressive low-and-slow knife-edge pass. At
full power a series of knife-edge-to-knife-edge
snaps were fairly easy to catch accurately and
then continue along up to roughly 45° knifeedge
climbout.
Upright and inverted flat turns were
effective with the big rudder, and the Yak
could do some impressive tail-over-nose
tumbles integrated into those flat turns. This
required keeping a bit of power in, but they
were fun to do. Heligoin circles executed well
too, given at least a moderate airspeed.
The Yak snap-rolled well since everything
was set up right. I put it through many
combinations of Positive Snaps and Negative
Snaps in all attitudes, and it behaved nicely as
long as I had a decent amount of airspeed
going in and some power to pull through.
For vertical up-line snap rolls it worked
much better to keep the up-lines short before
and after the snap. They can use a great deal
of energy, but with proper technique the Yak
got through them fine with the Brison 2.4
pulling it along.
Unloading most of the elevator input after
the initial pitch break was the key. Otherwise
it would be difficult to get the model to come
out with a good line after the snap.
Upright Spins or Inverted Spins, such as
those performed during a precision aerobatic
sequence, need planning if you are thinking of
doing more than one or two rotations. With its
relatively high wing loading, the Yak tended
to come down fairly quickly after the pitch
break and autorotation start, although its rate
of spin rotation was comfortable and easy to
time right, so it came out on heading.
I found that it was helpful to be partially
on the power during spin recovery to get
enough speed to make the transition back to
level flight crisp. Flat spins, such as what you
might do as part of a Blender maneuver, work
well with approximately half or more throttle
rolled in to reduce the rate of descent and keep
the rotation rate high. It’s important to have a
little power in already to help with a positive
recovery.
3-D Aerobatics: The Yak handles 3-D rolling
maneuvers well, although it has a slightly
heavy feel and requires that you keep the
power slightly more than halfway. It won’t get
down to the speed range that makes it look
like it’s filled with helium, but it works and
still looks good doing it.
It wasn’t too hard to manage transitions
from straight-line rollers to circling in either
direction, as long as the speed was kept up a
bit. The Yak is perhaps not the best learning
platform for 3-D rolling maneuvers, but it was
quite capable of them.
I was also able to take the model from a 3-
D Rolling Circle into three-quarters of a 3-D
Rolling Loop. I think it would have made it
through the bottom quarter of the 3-D Rolling
Loop, but I wasn’t brave enough to continue
all the way around that day.
The Yak did Walls without snapping
away, but it did mush through them a bit (not
a sudden stop). Controlling the aftermath of
the Wall required getting on the power fairly
quickly.
Parachutes also worked, although this
airplane didn’t exactly “stop and suspend.”
Instead it mushed through somewhat and
needed power applied fairly promptly to then
sustain an Elevator, 3-D roller, or some 3-D
maneuver transition.
Elevators had some wing rock and would
probably stabilize better with some crow mix
in the ailerons, even though I didn’t try that.
The wing rocking wasn’t so severe that it
couldn’t be dealt with with normal technique.
The Blenders the Yak could do were fairly
exciting. Starting with roughly 400 feet of
altitude, it wound up nicely as I banged it
from the aileron roll to negative snap
transition into the flat spin.
Hovering and torque rolls needed a fair bit
of power at this Yak’s weight. The setup was
capable, but I wouldn’t classify it as a good
learning setup. You need to get airspeed back
quickly at full throttle if a hovering maneuver
is aborted at low altitude, so being on your
toes is important.
I was unable to get the Yak to do more
than one consecutive Waterfall. Power to
weight was the issue in this case.
The Goldberg Yak 54 will give you the
capability to cross over between a good range
of 3-D maneuvers to medium-difficulty
precision sequence flying with the flip of a
few rate switches, without investing
megabucks to do it. MA
Ed Alt
[email protected]
Manufacturer/Distributor:
Carl Goldberg Models
Box 88
Oakwood GA 30566
(678) 450-0085
www.carlgoldbergproducts.com
Products Used In Review:
Radio:
JR
(217) 352-1913
www.horizonhobby.com
Servos:
Hitec
(858) 748-6948
www.hitecrcd.com
Other Printed Review Sources:
Non