54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]
Edition: Model Aviation - 2009/10
Page Numbers: 54,55,56,57,58,60
54 MODEL AVIATION
by Eric Henderson
Soar into the air with
ease, and bring a friend
Ken Flaer and Scott Bonomo fly off on another towing attempt. Only a few flights were needed for them to feel comfortable.
A HIGH-PERFORMANCE sailplane will
stay aloft for hours, once you can find the
right conditions. The problem that a glider
pilot faces, apart from finding a thermal, is
how to get enough altitude to enter one at the
right point. If entered at too low a point, the
slower-rising air/lift may not have enough
energy to help the airplane go upward.
Once in awhile, you might find a thermal
with a lot of energy near the ground into
which you could hand-launch a large
sailplane. These thermals are not too
common, so the model needs help to get to
that higher entry point.
There are several ways to help a glider
reach the right entry point. In most cases, it
involves a towline that is pulled by a runner
or a winch. In sailplane parlance, this is
called a “hand” or “winch tow.” A more
exciting way to give a model some operating
altitude is to copy the full-scale practice of
giving it an aerotow, by using a powered
airplane to do the pulling.
There are two places where a towline can
be attached to a glider. The hand or winch
towline is attached under the fuselage, just in
front of the CG. The aerotow line is hooked
up on the front of the nose.
I chose the Multiplex Cularis as the
subject to be towed. It is a full-function,
high-performance glider that comes designed
to be aerotowed by a powered airplane. I
selected the Multiplex Mentor (see the
review on page 42) to pull the Cularis aloft.
Both models’ boxes showed the electricpowered
Mentor towing the Cularis. The
latter ceased to be just a trainer and became
the tug.
The advantage of a motor is that it is
much more reliable than a glow or gas
engine. Since it runs on electricity, it can be
summoned to perform instantly at your
command. Glow and ignition engines have
been the power of choice, but brushless
motors and high-capacity Li-Poly batteries
can do the job as well, if not better.
This reliability is significant in
aerotowing. With a motor, you don’t have
the fear that an idling engine will decide to
quit at the wrong moment.
Before you attempt an aerotow, there are
many practices and much preparation you
need to be successful.
Setting It Up: With the two models selected,
you need to look at the towline mechanics
and the pilots’ roles. You must have the
ability to release the towline of the tug or
glider independently. This can save both in
bad situations.
There is always an opportunity for the
unexpected to happen when two working RC
airplanes are connected to each other by a
towline. The line could snag on takeoff or
the glider could get too close to the tug. If
the glider passes the tug, the line could get
caught in the propeller.
The aerotow line hookup and release for
the glider is in the nose. A release servo is
10sig2.QXD 8/21/09 1:34 PM Page 54
October 2009 55
Photos by the author
Above: The tow pilot should ease the takeoff power in as the
cable slack is removed. When the sailplane begins to move, the
tow model should be at full power.
Left: First-time tow pilot and glider tow pilots will be more
comfortable initiating the launch from this perspective. A 75- to
100-foot spread between the airplanes is healthy.
A recess on the port side of the Cularis’s
nose hides the tow-cable attach-andrelease
mechanism.
Right: The electric-powered Multiplex
Mentor is ready-made to suit the
aerotowing requirements of Two-Meterclass
sailplanes such as the Cularis.
The Multiplex Cularis’s box features an inspirational image that depicts a common RC
trainer towing the full-house sailplane.
wired to the retract switch, because it can be
“hit” easily.
If the tug or the glider has difficulties, an
aerotow-line hook release servo is also fitted
and wired to the tug radio retract switch. The
towline attachment point in this case is just
behind the Mentor’s wing saddle.
Take care to make sure that the line runs
out above the stabilizer at the rear of the tug.
If the aerotow wire gets caught under the
stabilizer, the tug will be unable to pull out
of a dive or make a turn. The flick of a
switch will free both parties and let each
make its own way to the ground.
The towline’s design can make a big
difference in your towing success rate. It
helps if you can see the line; small ribbons
tied and taped every 10 feet will do a fine
job. This way, too, the tension, or lack
thereof, in the towline has a visual indicator.
If the glider is going too fast or turning
too quickly, the line will be seen as a sagging
curve. You can also see how quickly your
glider is taking up the slack, and the tug pilot
can use judicious throttle management to
prevent sudden line whipping.
Towlines should have a weak link, to
cater to release failures, etc. The towline is
10sig2.QXD 8/21/09 1:34 PM Page 55
56 MODEL AVIATION
Above: The Mentor tug drags the tow cable once the sailplane
is released. To avoid snags, the tug should release the cable
before landing.
Left: The sailplane pilot is usually given priority for landing,
since the option to go around is unavailable. When the crow
condition is activated on the Cularis, spot landing is easy.
The sailplane is typically airborne before the tug. Red ribbons clearly show the slack in
the cable, which must be minimal at all times during the tow.
normally made from multistrand wire, similar
to what CL pilots use. A short loop of nylon
fishing wire that is roughly 30-pound
stress/strain will give you a good weak link.
Put this in the middle of the line so that the
release mechanisms’ metal rods don’t wear it
out.
Some pilots have tried using short
sections of bungee cord or surgical tubing as
a sort of shock absorber. This is a disastrous
route to take with aerotowing.
All the bungee does is stretch under load
and then catapult the glider forward toward
the tug. Then you get into a slack-line
situation that accelerates the tug, which
rapidly retightens and restretches the bungee
cord. This cycle will not stop repeating itself
until you release the towline or it releases
itself for you—most likely with a part of the
tug or glider attached to it.
The sailplane pilot needs to learn how to
keep his or her model just below the tug at all
times. The glider wings should be kept
Wingspan: 102.75 inches
Length: 49.6 inches
Flying weight: Approximately 49.38 ounces
Wing loading: Approximately 8-10 ounces/
square foot
Wing area: Approximately 853 square inches
Requires: Eight-channel radio, seven servos,
eight-channel receiver, 4.8-volt flight battery,
servo extensions
Options: Electric power system
available
Price: $184.99
Multiplex Cularis
ARF Glider
10sig2.QXD 8/21/09 1:34 PM Page 56
October 2009 57
The Multiplex Cularis can be built as an electric-assisted or
pure glider. To create the latter version, the motor is not fitted. To
create an aerotow version, the motor is replaced with a servo and
a towline release mechanism.
As a sailplane, the Cularis is a “full-house” design; it has two
outer ailerons and two inner ailerons/flaps. The four control
surfaces are normally operated as ailerons, but they can have
other glider-related capabilities. The same four control surfaces
can also be used to vary the wing’s camber, to provide
configurations for normal, high-speed, and high-lift wing
sections.
In addition, when the Cularis needs to lose a lot of airspeed,
such as in a diving landing approach, a “crow” configuration can
be selected. This is obtained when the two outer ailerons go up
and the two center flaps go down, to give maximum drag while
maintaining some effective aileron control.
The Cularis’s wings and stabilizer halves plug onto the
fuselage, to make the airplane easy to transport and store. The
mechanical retainer systems engage automatically when the
wings are plugged in. At the same time, the two servo leads per
wing panel automatically connect, using a hard-mounted
alignment for the plugs. This connection of the servo leads
eliminates the tedious task of connecting servo-lead extensions in
small, confined spaces.
The all-moving tailplane (AMT) is also removable and has an
automatic retainer system that clicks into place when the AMT is
fitted. This prevents the stabilizer from falling off during flight,
but it is easy to release for disassembly.
The manual is a series of high-quality diagrams that are easy
to follow. The Cularis is made mainly from molded Elapor foam,
which does not work well with foam-safe CA, white wood glue,
or epoxy. You are instructed to use only medium-thickness CA.
The good news is
that you can use a
spray activator
agent without
harming the Elapor.
A one-piece,
molded fixture is
included to build
the wing panels.
The underneath is
molded to perfectly
fit both the right- and left-hand wing panels. Almost all of the
required work prepares the fuselage before the halves are joined.
The only modification was to fit a towhook under the fuselage,
to allow for hand-towing to test the glider before it was given an
aerotow. This option was well illustrated in the manual. When the
wings and stabilizers were plugged in, they lined up perfectly
with each other. There was nothing to adjust or glue.
The Cularis Six required six servos: two for ailerons, two for
flaps, one for rudder, and one for elevator. A seventh servo is
used to release the towline.
A JR 10X 2.4 GHz transmitter and an R9000 nine-channel
receiver were used. The transmitter has terrific glider mixing
features that allow many wing-configuration options. A sevenchannel
receiver could have been used, but the R9000 permits
fail-safe options to be set. The control throws used were per the
manual.
You can just hand-launch the Cularis to see if it will fly
straight. A medium push with wings level into the wind will give
it a 50-yard shallow glide. This is plenty of time to see what is
happening.
With a hand tow using the conventional towhook position, it
was easy to take the sailplane up and test the control settings.
More down-elevator down-trim was added when the crow was
engaged, to prevent ballooning on landing approach.
The Multiplex Cularis performed very well with the
recommended throws. It is a delight to fly and can be looped
easily and gracefully from a shallow dive. To do a roll, you will
need a lot of airspeed and plenty of room.
Where this glider excels is in its ability to climb in a thermal
with the wing in high-lift mode. Then as that thermal recedes, the
wing can be switched to the high-speed wing section, to let the
model fly rapidly to find the next one. Landings are easy and can
be done with pinpoint accuracy, with judicious use of the crow
option. MA
—Eric Henderson
Manufacturer/Distributor:
Multiplex Modelsport USA
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.multiplexusa.com
Multiplex Cularis ARF
10sig2.QXD 8/21/09 1:35 PM Page 57
level—not banked toward the inside or
outside of the turn that the tug is making.
That is because the tug will lead the glider
around the sky, similar to how a speedboat
pulls an inner tube. If you have ever waterskied,
you will notice that if the skier turns
too much into the boat, the tow rope goes
slack. It is the same for the glider. By
keeping the wing level, you keep the glider
“out there” and under good line tension.
The sailplane pilot needs strong mental
discipline, because it is instinctive and
tempting to turn in toward the tug. This
probably comes from the natural desire to
fall into formation with the lead airplane.
If the line goes loose, the tug is
“unloaded” and will accelerate until the line
goes “doing!” It will be like the proverbial
guard dog running after the mailman until the
chain reaches its limit.
The tug pilot can practice without the
glider. A good drill is to fly around while
pulling a 1-foot-diameter balloon, to get used
to slower tug speed and the effects of another
model’s weight and drag. Apart from hand
or winch towing, the glider guider can do
little but prepare mentally.
Landing with a towline attached is asking
for a line snag and a bad nose-in prang for
the sailplane. The tug can also get caught out
when dragging a line.
The glider can fly with the towline still in
place, but it will be a bit sluggish and prone
to losing height quickly. In that case, dump
the aerotow line at the earliest practical
opportunity; that depends on how much
time/height was left after the unscheduled
tug release took place. It is much less
expensive to replace a towline than an
airplane.
However, we must be environmentally
conscious when it comes to metal wires and
our wild furry/feathered friends out there.
Please make every effort to find your
towlines in the event of an emergency line
dump.
In general, the tug has power and should
give landing preference to the sailplane in an
emergency, unless it’s also in trouble; e.g.,
there is no battery power left.
Secrets of Aerotowing Success: Following
is an expanded checklist of what you need to
know and do to make aerotowing work for
you.
• Pretest and trim both airplanes. This
should be obvious but is often omitted.
• Have a flight plan. If both pilots know
what is expected of them, the chances of
success go up dramatically.
• Have a spotter to watch the tug and another
to watch the glider. Listen to your spotter; if
you hear a release command, comply first
and ask questions later.
• Practice bailout signals and responses.
• Use a towline that is designed for the job.
A few well-positioned ribbons will allow
you to see the line at a distance.
• Practice flying the tug with a loaded
towline before taking on a model; e.g., with
a balloon as drag.
• For takeoff positioning, place the tow and
sailplane directly into the wind, even if that
is not straight down the runway. Ensure that
the towline is above the tug’s stabilizer.
• A primary rule of an aerotow is to gain
height as quickly as possible without stalling
the tug.
• Keep the glider wing level at all times
during the tow.
• Always keep the sailplane lower than the
tug.
• Do not let the glider catch up with the tug.
Steer to the side with the rudder and keep
the wings level to fix the problem.
• Practice postrelease towline management.
Do one pass to drop the line, and then land.
• Try to fly when the sky is clear of other
models—especially loud ones. They can
make it hard to hear what your spotter is
calling. Also, the towline can easily become
a hazard to other pilots, who are totally
focused on their own aircraft.
• If you are the tug pilot, do not watch the
glider once you are disconnected.
Concentrate on getting the airplane down
and clearing the towline for your glider
buddy, and other pilots, to land. After that is
done is the time to watch the results of your
aerotow work.
Remember to switch off the tug’s
electrics. It is easy to forget electric-powered
models’ shutdowns, because they are so quiet.
Flight Report: With an empty sky, the
aerotow team was ready to go. Scott
Bonomo was the glider guider and Ken Flaer,
the New Jersey Pine Barons club instructor,
was the willing tug captain. Neither had done
towing before, but both were more than
happy to try something different.
With all other club pilots watching, and
their models on the ground, the Mentor and
the Cularis were placed out on the center of
the runway and aimed into the wind. The
motor hummed to life, and the tug took up
the tension on the aerotow line.
All you could hear was a slight rustling as
the towline began to roll through the grass.
The Cularis gently started to move and
twitched straight as the aerotow line came up
to full tension, causing the nose to start
following the tug.
Gliders, by nature, sit with one wing
resting on the runway before they get
moving. The good news is that the sailplane
wing begins to “work” at exceptionally low
airspeeds. The Cularis’s low wing dragged
only a little and then picked itself up as the air
started to flow over it. It is easy to pick up a
dragging wing if you momentarily use inside
rudder.
If the glider is dragging the left wingtip,
turn into the tip by giving it left rudder for a
moment. This will cause the fuselage to act
like a sailboat’s keel and roll the airplane
over slightly, which will immediately pick up
the dragging wing.
As is common with gliders, the Cularis’s
takeoff run was much shorter than its tug’s.
The Cularis pilot flew lower to the ground as
full power was added to get the Mentor
airborne.
The glider pilot had selected the standard
wing camber section, which was previously
established in a regular towline test. This
gave the Cularis a little more drag. Some
down-elevator was pushed in, to prevent it
from getting too high.
The tug made a slow left-hand climbing
turn at approximately 100 feet. The sailplane
gently skidded around behind, with the wings
kept level.
The Cularis pilot hit the retract switch at
roughly 400 feet, releasing the towline and
starting to fly on his own. This was going to
be a deliberately short flight, to get in a proof
of concept.
The tug pilot did not need to be told that
the glider was gone, because the Mentor
increased in speed. He throttled back to half
speed, made a circuit, and landed. The
Cularis pilot later made a controlled “crow”
landing in the middle of the runway.
The pilots and I (author/cameraman)
celebrated with big grins and soon lined up
the models for a second flight. Both men
found their airplanes easy to fly and were
impressed with the Multiplex combination of
foam and electric power.
Aerotowing is fun and adds a new
dimension to what you can do with a
couple of radio-controlled models.
Everything worked perfectly and, best of all,
we had a bunch of pictures to prove it. MA
Eric Henderson
[email protected]