May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html
Edition: Model Aviation - 2008/05
Page Numbers: 47,48,49,50,51,52
May 2008 47
BY LEE ESTINGOY
The latest power systems
make Soaring a breeze
I HAVE THE rare privilege of working with the
best products available in RC; this makes it slightly
more difficult for a product or project to wow me.
That’s why a Supra electric-power conversion
project was a pleasant surprise.
In June 2006 Barry Kennedy—the US agent for
Vladimir’s Model—suggested that I attempt to make
an electric-launch version of the hot Supra Thermal
Duration (TD) sailplane. We wanted to convert a
standard Supra into a self-launching setup that sport
and competition pilots could fly without a winch or
bungee system for launches.
Electric-powered sailplanes offer incredible
convenience at the expense of a weight gain—
sometimes a significant weight gain. We wanted to
fashion a system that would offer the best of both
worlds: the convenience of electric launch and the
performance of a world-class TD sailplane.
I took Barry up on his dare and purchased a
Supra, which is designed and built with singleminded
attention to functionality. It is optimized for
excellent soaring.
The Supra offers cutting-edge aerodynamics
with a short list of options; the main one is
whether or not the owner wants to use a
lightweight wing that can handle gentle winch
launches or a version with extra carbon in the
build for insurance against the most brutal winchlaunching
stresses. This model would not see
winch launches as an electric-launched sailplane,
so there was no need to carry the extra weight or
incur the extra expense of the wing upgrade.
The electrified Supra is comparable in weight to the TD model and climbs as if it
were on a high-power winch.
05sig2.QXD 3/24/08 2:20 PM Page 47
48 MODEL AVIATION
Where to Begin With Electric Power Systems? I generally
select components for a power system by determining the
amount of power I need to achieve the performance I expect
from the project.
An electric system’s power is expressed in terms of watts
(756 watts = 1 horsepower). A total of 100 watts per pound is
good for brisk climbs for sailplanes.
I knew that the ballpark weight of this airframe and its
equipment was going to be 75 ounces, or roughly 4.5 pounds.
That would lead to the conclusion that more than 450 watts
would be needed.
I wanted to use a two-cell pack to meet the electriccompetition
rules; I knew I needed to achieve no less than a
65-amp draw (450 watts divided by 7 volts equals 65).
“Good climb” is never enough for sailplane fliers, so let’s
say I needed 70-100 amps on 2S. That means I needed to
find a way to fit two 2500-5000 mAh batteries.
I knew I needed 70-100 amps. Given a C rating of
approximately 20, I needed a baseline capacity of 3500-5000
mAh cells. If the C rating were
higher, say 30C, the required
capacity would shrink to only 2500
mAh.
Finding the Cells: I have the
distinct convenience of having
TanicPacks nearby, so I can motor
over and try sizes until I find one
that fits. I settled on a 4200 2S
pack. It is capable of putting out
more than 80 amps for a sailplane
Left: The RF 17 x 13 propeller system folds back to reduce drag
while in thermal mode.
Above: The 3-meter Supra, from Kennedy Composites, is an
expert TD competition model that, when under power, can also
fly like a sport model or as a trainer.
Airframe Version Weight
Fiberglass—Lightweight 62 ounces
Carbon-fiber center-section/lightweight tips 67 ounces
Full carbon wing 69 ounces
Electric conversion of fiberglass lightweight
airframe with 7-ounce 2S 4250 pack or 7-ounce
3S 2500 NeuEnergy pack and Castle Creations BEC 73 ounces
The Supra comes in a variety of layups that offer you a choice of
light weight or more stiffness at the expense of a few ounces. This table
contains the weights of those versions compared with the electricpowered
version. MA
Input Propeller Amps Watts Watts/Pound Pack Weight
2S 4250 Tanic 17 x 13 RFM 65.4 426 95 7.2 ounces
2S 4250 Tanic 18 x 16 RFM 72.1 495 110 7.2 ounces
3S 2500 NeuEnergy 17 x 13 RFM 96.1 799 178 7.6 ounces
This table shows the relative abilities of a 2S and a 3S setup. MA
05sig2.QXD 3/24/08 2:23 PM Page 48
May 2008 49
The Supra climbs to the moon. Setting up at the field is so much quicker without a winch
or hi-start required.
launch of no more than 20-30 seconds.
Spending a little time on Steve Neu’s
Web site revealed that I needed a 1406 2D
motor with the 6.7:1 gear ratio to give the
best performance for the given volts and
amps. This motor would also work well if I
upped the ante and used a 3S Li-Poly pack.
A bit of “basement flying” with the
pieces and components taped to the airframe
to get a feel for the CG convinced me that
the usual layout of the elevator and/or
rudder servo in the tail would result in an
extremely tail-heavy airplane. The servos
would need to be placed in the nose to
maintain effective balance. This was great
news; I didn’t want to have to cut up the
vertical stabilizer or make a subfin for the
servos.
I found it painful to take the saw to such
a beautiful model. I shortened the inner nose
to allow clearance for the motor and spinner,
which are mounted on the outer nose cone.
The remaining stub section was still sturdy
because it was a complete tube-in crosssection.
I decided to keep that deck intact to
support the outer nose cone as much as
possible.
Although the standard method for
mounting servos in this type of fuselage is to
position them in the top of the deck, I found
that I needed to lay them on their sides and
place them under the little deck that is
normally used for servo mounting, to
provide room for battery removal. Putting
both servo pushrods on the same side of the
sailplane gave the largest usable space for
the cells inside the fuselage.
I used a longer servo arm on the rudder
servo and placed it in the front position so
the pushrod would clear the elevator servo
arm and pushrod by passing over the top of
the other servo arm.
The airframe plans suggest affixing the
pushrods to the outside of the tailboom. I
chose to place them inside the fuselage; I
couldn’t bear for such a beautiful airplane to
have its hosiery out for all to see.
The “bulkhead” at the front of the larger
fuselage section needed to be opened to
accommodate the batteries. I started small
and wound up with as large an opening as it
was possible to make. A 2.5-inch rotary
sanding drum made this a tidy procedure.
I left as much of the front of the inner
fuselage as possible; I felt that the nose cone
could use the added support. The nose cone
was not designed to be a structural member,
and support from the inside is prudent. I
used a small block of wood to support the
front servo and accept the nose-cone support
screw.
After I assembled everything, it was time
to check the CG position. The Supra was a
bit nose-heavy, but electric flight
components offer a great deal of flexibility
in these situations.
I elected to use 2/3 A cells for the
receiver pack. I mounted them on a stick and
slid them into the proper position in the pod
to achieve the balance I needed. I placed a
bit of Velcro on the front of the stick and in
the fuselage to secure the receiver pack. I
05sig2.QXD 3/24/08 2:24 PM Page 49
50 MODEL AVIATION
CG requirements are easily met by placing the receiver battery (four 2/3A) cells in a long,
skinny configuration and mounting them to a stick.
The power system: NeuMotors 1506 2D with 6.7:1 gearing, Castle Phoenix-80 ESC, and
either a Tanic 2S 4250 or NeuEnergy 3S 2500 Li-Poly pack.
There is just enough room for the motor battery pack to fit. The
fuselage’s taper prevents it from going too far back. Placing
Velcro on the sides is a good idea.
Both the elevator and rudder servos are located in the nose with
the pushrods on the same side. The rudder servo is in the front
with the longer arm.
intend to replace the pack with a Castle
Creations BEC to reduce the weight a bit.
I used a Castle Creations Phoenix-80
brushless ESC in this project. I recommend
using the Castle Link software to set the
brake to a moderate level so the propeller
stops without torquing the nose too much.
Because I am hammering the cells a bit
more than normal, I set the voltage cutoff to
an extraordinarily low number—generally
less than 3 volts per cell. I also set the
throttle to fixed endpoints, which makes the
start and full-throttle positions more exact
than when using the auto-calibrate default
setting.
I find the Berg 7PH 72 MHz receiver to
be a good fit for this sailplane because light
weight is important for this sort of project.
The Supra has a good amount of carbon in
the fuselage, so I generally run the antenna
through a small hole to the outside of the
boom. The antenna wire on the Berg receiver
is not tuned to a particular length, so I like to
add a bit of length to the antenna and let the
excess—maybe 18 inches—dangle behind
the rudder.
Flying: Test flights were a blast! The system
worked well.
I tried a few sizes of RFM folding
propellers (available from ShredAir) on this
setup. I settled on the 17 x 13 because it
worked better empirically for 2S. There are
certainly more aggressive motors in the Neu
catalog and more aggressive propellers by
RFM; the one I chose just seemed like it
would be the most flexible in terms of 2S
and 3S use.
The climb on 2S was totally usable—not
competition level but great for sport use. On
3S the climb was much more impressive. If
this model were going to be used for serious
competition, a motor more closely matched
to the task—either a 2S or an Unlimited—
might be a better choice. The motor I
selected is forgiving on all components,
which is perfect for sport flying.
A few weekends later I flew the sailplane
against some capable competition in the
Kansas City RC Soaring and Electric Club’s
electric contest. The model wowed all those
present and made me look better than I had a
right to look.
The electric-powered Supra performs like
a high-end TD aircraft—not like a heavy
electric model. It signals lift well and can
transit bad air without much altitude loss.
The airframe, with motor, controller, and
BEC, weighs 66 ounces ready to fly. The
battery packs I settled on weigh an
additional 7 ounces each, for an all-up
weight of 73 ounces.
As I mentioned at the beginning, the
Supra comes in a variety of layups that offer
you a choice of lightweight or higher
stiffness at the expense of a few ounces. An
accompanying table contains the weights of
those versions compared with the electricpowered
version.
I did not give up much by choosing the
electric launch. The weight was only 4
05sig2.QXD 3/25/08 8:57 AM Page 50
The elevator does not need as much throw; therefore, a short arm
is all that is needed. This arrangement yields the most room inside
the fuselage for batteries.
A comparison of the factory electric nose, the standard sailplane
nose, and the finished electric conversion.
Top to bottom: The factory electric fuselage, the converted
version, and the standard sailplane fuselage.
ounces heavier than the most popular carbon wing. I have a second
fuselage for making a TD version. I sincerely doubt I’ll use it for that
purpose because this model is too convenient.
Pick Your Preference—Mild or Wild: The 2S motor/battery setup is
not intended to be wild. You can achieve a normal TD winch-launch
height in roughly 15 seconds, and 30 seconds will put your model
nearly out of comfortable sight.
A 15-second climb uses approximately 350 mAh, so with the
4200 mAh capacity onboard you can make more than 10 launches on
a single charge. The pack is not terribly expensive because of the low
cell count, so it is reasonable to expect to take two charged packs to
the field and literally fly all day without fussing with the batteries.
Pilots should be able to use this model in an AMA Class A
electric sailplane event with only slight changes to the motor-andpropeller
setup.
Those who fly according to some of the newer evolutions of the
Limited Motor Run (LMR) rules, in which brute power is a
requirement, or who simply like the razzle-dazzle of an aggressive
climb will likely prefer the 3S setup. The NeuEnergy 3S 2500 mAh
pack fits easily in the fuselage and offers zippy climb.
I don’t get quite as many climbs with the 3S setup as I do with
the 2S system. The 3S will probably take the airplane out of the
Class A LMR category and move it to the Unlimited Class, in which
it will be a capable competitor.
I must admit that I left the same propeller on this setup as I used
for two cells. Steve Neu has assured me that the resulting amp draw
is well within the permissible range for these cells. It’s unbelievably
easy to choose 2S or 3S and then go fly.
One of the benefits of a long-term project is that many of the
technologies used can improve during the intervening period. Li-
Poly technology has certainly progressed since I started this project.
Cells now offer a higher discharge ability, so pilots can use
smaller cells to achieve higher wattage outputs via higher
amperages for a given form factor. Be aware that higher current
The Berg receiver (not shown) is placed under the wing pylon in
the fuselage. The antenna wire is routed out of the fuselage,
outside of the carbon boom.
May 2008 51
05sig2.QXD 3/24/08 2:28 PM Page 51
draw may yield a shorter useful lifetime
for the cells.
The Supra is great and has proven to be a
top performer in competitions worldwide.
The lightweight version of this airframe
makes an incredible electric sailplane that
is perfect for both the discerning sport flier
and the avid competitor.
The electric-launch version gains little
weight, and its performance will spoil you.
You have the convenience of electric
launch and the performance of a worldclass,
winch-launched sailplane.
Now an electric nose is available.
Kennedy Composites and Vladimir Model
have an electric nose in production that
eliminates quite a bit of the surgery that
was needed to convert the sailplane. MA
Lee Estingoy
[email protected]
Sources:
Kennedy Composites
(972) 602-3144
www.kennedycomposites.com/
TanicPacks
(800) 728-6976
www.tanicpacks.com
NeuMotors
(858) 674-2250
www.neumotors.com
Castle Creations
(913) 390-6939
www.castlecreations.com
ShredAir
(541) 954-6842
www.shredair.com/props.html