How To Do It The Performance EDF Experience - 2010/03

ELECTRIC-DUCTED-FAN (EDF)-
powered models have been around for
decades, but the last few years have seen the
hobby reach new levels of size and
performance, owing largely to the sudden
increase of brushless motors, high-discharge
Lithium battery packs, and advances in
lightweight composite construction.
Now that larger ducted-fan systems are
more viable, quite a few models that were
limited to more expensive turbine power can
successfully use electric power. And
airplanes that were designed around glowpowered
ducted fans can be converted—and
in most cases they can surpass previously
expected performance.
There are many factors to consider when
using EDFs and in choosing the correct
airframe and power system for a project.
Although numerous manufacturers offer kits
and power systems that are designed to work
together, many modelers prefer the
challenge of working out power systems and
configurations themselves.
Choosing a Fan System: With so many
sizes and types of fans available, making
selections can be confusing. Properly sizing
the fan is crucial to the aircraft’s
performance.
Unlike turbines, which use combustion to
create thrust, ducted fans accelerate air
through the fan unit to produce the thrust.
Therefore, it is necessary to provide the
proper amount of airflow, which means
obtaining efficient and correct-size ducting.
When referring to these concepts
regarding fans, we use the term “fan swept
area,” or FSA; that is the amount of area that
the fan’s blades cover. You can calculate
this by subtracting the amount of area that
the center body section of the fan occupies
from the area of the fan shroud.
Luckily the manufacturer typically
supplies us with the FSA. Knowing that, we
can look at what is available in terms of inlet
area and decide which fan is going to be
properly sized for the application.
For the purposes of this article, I will
assemble a larger ducted-fan-powered model
and use the preceding principles to illustrate
the steps I take when deciding what fan unit
to use. I’ll be building a Fox-Composites.com
BAe Hawk, which has been around in
various forms for more than 25 years.
Originally designed around a glow
ducted fan, this jet has also flown
successfully with turbine and electric
power. It is supplied more or less set up
for a 44- to 60-size turbine. The model
features a fiberglass fuselage, and the
latest version features hollow composite
wings.
The kit includes some generic ducting
that can be adapted to work with a variety of
power setups. I will build the Hawk
according to the instructions, except in the
areas that require attention for an electric
conversion.
The first thing I want to do is examine
the supplied ducting and fuselage intakes to
determine the amount of combined area with
which I have to work. Because of its glowducted-
fan origins, this model has largerthan-
scale intakes that will make powering
the Hawk with an electric fan a relatively
easy conversion.
The method I use to calculate the area of
the ducting is relatively simple. By tracing
the outline of the intake end of the ducting,
you can easily calculate the area.
Using graph paper with 1/4-inch squares,
trace the outline of the inlet side of the
ducting. Count the number of squares
within the perimeter of the lines. Divide that
total by 16, since 1/4-square-inch graph
paper is being used. This equals the intake
area in square inches.
So with 94.5 squares divided by 16, I get
5.91 square inches. Multiplying that by 2
intakes equals an available area of 11.82
square inches total. Knowing that, I can
inspect different fan units and figure out
which one will be a good choice.
Considering what I want in the way of
performance and flight time, there are
plenty of options for fans. For this article, I
narrowed my search to a few of the newer,
higher-powered systems that are near the
range required for the Hawk.
After considering the aforementioned
EDF setups’ sizes, battery requirements,
and ducting necessities, the best candidates
were the Schübeler DS-75-DIA HDT, the
Stumax SM110-52, and the Tam Jets TJ-
100. I also considered what equipment I
already had, including batteries and ESCs,
to economize as much as possible.
I currently use the Schübeler DS-75 and
the TJ-100 and have been satisfied with the
performance of both. With that in mind, I
decided that for this project I would go with
the Stumax SM110-52 setup. I was
interested in seeing firsthand what this fan
could do, and its unique sound would add
another level of realism to the Hawk.
Another thing you must take into
consideration on these larger models is the
main battery packs’ location. I’ll power the
Hawk with a 5S and 6S set of XPS
Professional series Li-Polys from Xtreme
Power Systems, configured as a single 11S
5000 mAh Li-Poly battery.
With that in mind, it’s important to make
sure that the 3.2 pounds of batteries can be
installed in a location that will allow the
recommended CG to be achieved. Ideally, I
can get them into the front area of the Hawk;
that offers the most area and good airflow, to
help keep the battery temperatures down.
In some cases it is necessary to use more
than two packs (saddle packs), to find a
location at which to install the batteries
while maintaining the CG. That won’t be
necessary in the Hawk; we have plenty of
room to work with inside.
Before installing the ducts, install the fan
to make sure that everything will line up
correctly. The Hawk comes from the factory
with fiberglass mounts for a turbine built into
the fuselage. With a slight modification, I
should be able to use it for the fan as well and
keep everything located similar to the
turbine-powered setup.
A thrust tube is now required. As
previously discussed, ducted fans are
designed to accelerate air flowing through the
ducting and out the back of the fan, to
produce thrust. The thrust tube is used to
increase the velocity of the air coming out,
which is also known as the “efflux velocity.”
By decreasing the diameter of the output end
of the thrust tube, we can further accelerate
the air, but only to a point. Beyond that, we
start reducing performance.
For the SM110-52 fan, the manufacturer
suggests an exit diameter of 87mm. Knowing
that measurement, the fan shroud’s outside
diameter, and the distance between the back
of the fan and the end of the fuselage, I can
make the appropriate-size thrust tube.
A handy trick I picked up from another
kit is to make a simple fixture around which
to form the thrust tube. Some .010-inch
Mylar from a crafts store can be used to
make the thrust tube. To make the fixture, I
cut a 5/8-inch-diameter dowel and a 3/8-inchthick
length of balsa stock to the length
measured from the rear of the fan to the end
of the fuselage.
I cut two flat circles from a sheet of 1/8
plywood. For my project, the first one
measured 112.5mm—the same as the
shroud’s OD at the rear of the fan. The
second disk was 87mm—the dimension that
the manufacturer supplied. I glue the circles
to each end of the dowel and glue the length
of balsa to the fixture, lining up the outside
edge of the balsa with the outside edge of
both disks.
I tape the long edge of an appropriatesize
piece of Mylar to the balsa to hold it in
place, and then I can wrap the Mylar around
the fixture and overlap the taped edge. I use
a marker to trace the ends and the seam onto
While most people associate model jets
strictly with speed, many, including myself, try to
reach a balance between performance, flight
time, and weight. To do this, you must look
realistically at the aircraft and determine what the
airframe’s capabilities are.
A larger model such as Fox-Composites.com’s
BAe Hawk has a somewhat draggy airframe
compared to a purpose-built sport jet such as the
Composite-ARF Spark or BVM Electra.
You have to be realistic in your expectations
about performance. You quickly reach a point of
diminishing returns with power levels, because
most models will hit an aerodynamic wall, and
additional power yields marginal results in
overall performance.
Following are some options for you to
consider for electric-ducted-fan power.
• XPS Dynamax
Xtreme: This is an
electric version of
the Dynamax fan.
These fans have
been around for
years, but they are
regaining
popularity as
electric
conversions. One
of the main benefits is that the new unit is a dropin
replacement for many models that were
originally designed around the glow-enginepowered
Dynamax.
At 3.1 pounds including the Castle Creations
HV-110 controller, the Dynamax Xtreme is a
proven and well-built unit. XPS reports that it can
run on 10-18 Li-Poly cells, handles power levels
up to 10,000 watts, and develops well more than
22 pounds of thrust.
The unit’s FSA is right at 16 square inches,
and XPS recommends that an inlet providing
123% FSA is best. This works out to roughly
19.6 square inches.
Look to see this system powering some largescale
jets in the near future.
• Schübeler DS-94-
DIA HST and DS-
77-DIA-HST:
Daniel Schübeler
has been
manufacturing
some of the highestquality
ducted fans
for years. His allcarbon
designs are
lightweight yet incredibly strong, and they are
capable of absorbing huge amounts of power.
And the company’s customer service is topnotch.
The latest versions are “HST”s (High Static
Thrust) and are powered by Schübeler’s
proprietary motor—the DSM6740—a two-pole
design that is integrated into the fan’s center
body.
The DS-94 model has an inner shroud
diameter of 128mm, with an FSA of 94 square
cm (14.6 square inches). It features a 12-blade
rotor and can reportedly produce more than 22
pounds of thrust on a 14S Li-Poly. The plug-andplay
package that includes the HV-180 ESC
weighs a bit more than 3.5 pounds.
The DS-77 is a 120mm fan with an FSA of
77 square cm (11.9 square inches) and can
produce just less than 21 pounds of thrust on a
14S Li-Poly. This plug-and-play package
includes the HV-180 and weighs slightly less
than 3.5 pounds.
Compared with four-blade rotors, these
units’ 12-blade-rotor fans are quiet and produce
a much more jetlike sound.
• Schübeler DS-94-DIA
HDT and DS-75-DIA
HDT: This company
also offers an “HDT”
(High Dynamic
Thrust) line of fans that
are similar in size to
the HST models. The
four-blade HDT units
are designed to offer higher dynamic thrust
(top-end speed) than their HST counterparts.
The HDT fans don’t incorporate
Schübeler’s integrated motor system, so a wide
variety of motors can be used, depending on the
application. Plug-and-play versions are
available from the manufacturer.
The DS-94 has a fan diameter of 120mm.
The plug-and-play setup including the HV-120
ESC weighs 1.85 pounds, has an FSA of 94
square cm (14.5 square inches), and produces
13.5 pounds of thrust on a 10S Li-Poly.
The DS-75 has a 110mm fan diameter. The
plug-and-play setup including the HV-120
weighs 1.75 pounds, has an FSA of 75 square
cm (11.6 square inches), and produces 12.5
pounds of thrust on a 10S Li-Poly.
• Stumax Aircraft
SM110-52: This unit
comes standard with a
Neu 1915 1Y motor and
is designed for 11S-12S
Li-Poly batteries. It has
an OD of 110mm and an
FSA of 73 square cm
(11.4 square inches).
The unique feature
that sets the 110-52 fan
apart from others is that it is an IGV—Inlet
Guide Vane—or “pusher” setup. The more
common fan configuration is for the rotor to be
in the front and the stators behind. The SM110-
52 is set up the opposite way.
Also, the center body and stators are a
one-piece aluminum heat sink. Stumax
carefully machines each unit so that the
motor fits snugly in the center-section,
increasing its ability to dissipate heat.
Another advantage of this design is the sound
it produces. Ducted fans have historically
been fairly loud and high-pitched, but the
Stumax unit is quiet.
More sound is heard from the fan’s thrust
than from the fan itself. Many pilots find this
desirable, because it adds a more realistic
sound to the model.
Powered by an 11S Li-Poly, the SM110-
42 produces approximately 3,500 watts and
nearly 11.5 pounds of thrust. On 12S the
output increases to 4,200 watts and 13.5
pounds of thrust.
• Jet Hangar
International ETurbax:
This is
another 130mm
fan that has gone
from nitro to
electric power with excellent results.
The company has been in business for
more than 30 years, and in 1980 it acquired
the rights to the Turbax fan. For the past few
years, Jet Hangar has been selling these units
as an electric conversion, or “E-Turbax.” It
offers the fan as a plug-and-play package
with power setups configured for 9S, 10S,
and 12S Li-Poly operation. This setup is a
drop-in replacement for several aircraft.
The RTF version is powered with a
NeuMotor unit and features an HV-110 ESC.
The E-Turbax is also sold bare as “ready to
assemble,” for those who want to use
different motor configurations.
The E-Turbax has an FSA of slightly
more than 96 square cm (15 square inches).
Depending on which motor/Li-Poly
configuration is installed, it produces 12-17
pounds of thrust.
• Tam Jets TJ-100:
This company has
entered the EDF
market with the TJ-
100. This 100mm
fan is made from
carbon fiber and
aluminum. The
aluminum center
body housing the
motor is, in effect, a
full-length heat
sink. Behind that, the ESC is mounted in the
rear fairing to aid in cooling.
The TJ-100 has an FSA of 75 square cm
(11.6 square inches) and weighs
approximately 1.75 pounds. On the upper end
of the power range, it produces an excess of
13 pounds of thrust.
Tam Jets offers a wide variety of plugand-
play setups featuring NeuMotor 15-
series power plants running six to 12 Li-Poly
setups and featuring 85- to 110-amp Castle
Creations HV controllers.
The company also sells a broad selection
of conversion kits that allow you to install the
TJ-100 in most of its turbine-powered aircraft
and a few other brands of models that are
designed for turbine and ducted-fan use.
With custom-fabricated ducting and
nacelles to fit many of today’s popular
aircraft, and power output ranging from
2,200 to 4,500 watts, this is probably one of
the easiest and most versatile setups to
integrate into an existing model.
• BVM VioFan:
With electric
power’s increasing
popularity, BVM
reintroduced the
Viojett a few years
ago as the VioFan.
Powered by a
NeuMotor 1524-series unit and 10-12 Li-
Poly cells, it will produce more than 5,000
watts and 14 pounds of thrust.
The VioFan comes factory-ready and
includes an HV-110 controller, which is
integrated into the rear fairing. This power
system weighs approximately 2.5 pounds and
has an FSA of approximately 13 square
inches.
The VioFan has proved to be an
extremely reliable EDF unit. BVM offers a
solution for upgrading many of its older
models and offers new aircraft that are
designed specifically for the VioFan. MA
—Roger McCormick
March 2010 51
the Mylar and trim away the excess.
Clear packing tape is sufficient to hold
the seam together on the inside and outside.
When the tube is completed, it can be
secured to the back of the fan with clear
tape.
I used a pair of curved Lexan scissors to
cut and trim the intake ducting so that it fits
into the inlets on the fuselage and lines up
evenly with the front of the fan. Tape the
ducting into place and make a coupler
section to connect the fan to the ducts.
I use poster board to create a template for
a short coupler piece to join the fan and
ducts, leaving an extra 1/4 inch on each end
to overlap when it’s glued together. Then I
trace it onto a .010-inch-thick fiberglass
sheet that I later roll into a tube. I use CA to
bond the overlap, and then I epoxy two
layers of 1/2-ounce fiberglass cloth over the
seam.
After that dries, I wrap it with carbon tow
to make it even stronger. I don’t want it to
collapse when I start pulling a vacuum on
the ducting.
With the coupler secured to the fan and
ducting and everything checked for
alignment, I glue the ducting to the inlets on
the fuselage with a mixture of epoxy and
microballoons. On the inside wall of the
fuselage, I used 1/2-ounce fiberglass cloth to
cover the overlap and help secure the inner
side of the ducting.
Ideally you want a smooth and clean
intake radius, to reduce turbulence of
incoming air. The stock ducting left some
large gaps and overlaps, so clean these up
and remove any excess with a Dremel tool.
Then fill with body filler, to blend it in. I’ll
use my airbrush to repaint the intakes.
The batteries need a tray. The kit came
with two plywood sections that glue to the
bottom of the fuselage the length of the nose
section to reinforce it. I added triangle stock
to the sides, and I’ll put a piece of 3/16 light
plywood over it to act as the battery tray.
The most common mounting solution for
the ESC in the majority of ducted fans is to
put it behind the engine in a fairing, so that it
receives plenty of cooling air. That approach
won’t work with the SM100-52 and its rearrotor
design.
To get proper airflow over the ESC, I
mounted it on the top of the ducting under
the rear hatch area. The Hawk has intake
scoops molded into the fuselage, as the fullscale
aircraft does, so I use those to get air to
the speed controller.
I also used a piece of lightweight plastic
to close off the underside of the hatch and
cut out a section to direct the air directly
over the ESC, where it’s then drawn out the
rear of the fuselage. In addition, I mounted a
temperature probe on the ESC so I can
monitor its temperature with the Eagle Tree
Systems data logging system.
As a rule of thumb, 250 watts per pound
is a good figure to apply when dealing with
ducted-fan models; we call that number
“good performance.” And take care when
static-testing any aircraft; safety glasses are
a good idea.
With the Hawk secured and the Eagle
Tree transmitting information back to the
laptop via the Seagull wireless setup, I ran
the fan to somewhat simulate a typical flight
by varying the throttle and working the
control surfaces for approximately five
minutes, with a short cooldown period at
low throttle for the motor.
The Eagle Tree system reported 3,429
watts at 83.54 amps. The model’s final
weight at 13.8 pounds works out to 248.5
watts per pound, so we should be good on
power.
The SM110-52 can also be run on 12S,
producing approximately 4,200 watts at
close to 100 amps. The 12S 5000 batteries
would raise the weight to slightly more than
14 pounds and push the power up to
approximately 295 watts per pound. So I
have a bit of room to work with if I feel like
I need more power, while remaining within
the specifications for fan, ESC, and
batteries.
Flying the Hawk:With everything ready and
all systems thoroughly tested, I headed to
Ohio a few days before the E-Jets
International event so I could do the Hawk’s
test flights at the TORKS (The Ohio Radio
Kontrol Society) field, which has a very nice
1,000-foot runway and plenty of room.
Pablo Hernandez, a Florida resident and
fellow pilot, was kind enough to do two
shakedown flights with me. He is a skilled
flier and has plenty of experience with larger
Hawks. We set the timer at 4:30 as a starting
point for the first flights, to ensure that the
batteries weren’t overdischarged.
In the air with other jets flying, you had to
listen closely to hear the Stumax unit. It
definitely lives up to its reputation as one of
the quietest fans available, and the model flew
nicely on the 11S 5000 mAh setup.
According to the Eagle Tree system, the
Hawk’s top speed was 137 mph. The 4:30
flight used 3800 mA of the 5000 mAh pack.
With the Eagle Tree system, I could see
that the main batteries reached a maximum
temperature of 128° and the ESC peaked at
121°. With its ability to monitor so many
components (temperature, watts, amps,
voltage, rpm), it’s a great tool for any aircraft.
As of this writing, the Hawk has made more
than 10 flights. After getting accustomed to
its characteristics, I can get five-minute
flights using slightly more than 4000 mAh
from the 11S 5000 packs.
With the ideas and concepts I’ve
presented in this article, you should
understand the basic principles of sizing and
implementing a ducted-fan setup. If you do
have questions, the manufacturers I have
mentioned are happy to offer guidance so
that your ducted-fan project is a success. MA
Roger McCormick
[email protected]
Sources:
Fox-Composites
http://fox-composites.com
Schübeler Modellsysteme (Germany)
49 (0)5251 873348
www.schuebeler-jets.com
Stumax Aircraft (Australia)
61 2 8819 4330
www.stumaxaircraft.com
Tam Jets R/C Model
(408) 224-7600
www.tamjets.com
XPS
2440 N. Kiowa Blvd.
Lake Havasu City AZ 86403
www.xtremepowersystems.net
Eagle Tree Systems
(425) 614-0450
www.eagletreesystems.com
BVM Jets
(407) 327-6333
www.bvmjets.com
Castle Creations
(913) 390-6939
www.castlecreations.com
Jet Hangar International, Inc.
(562) 467-0260
www.jethangar.com
03sig2.QXD_00MSTRPG.QXD 1/25/10 1:15 PM Page 51

ELECTRIC-DUCTED-FAN (EDF)-
powered models have been around for
decades, but the last few years have seen the
hobby reach new levels of size and
performance, owing largely to the sudden
increase of brushless motors, high-discharge
Lithium battery packs, and advances in
lightweight composite construction.
Now that larger ducted-fan systems are
more viable, quite a few models that were
limited to more expensive turbine power can
successfully use electric power. And
airplanes that were designed around glowpowered
ducted fans can be converted—and
in most cases they can surpass previously
expected performance.
There are many factors to consider when
using EDFs and in choosing the correct
airframe and power system for a project.
Although numerous manufacturers offer kits
and power systems that are designed to work
together, many modelers prefer the
challenge of working out power systems and
configurations themselves.
Choosing a Fan System: With so many
sizes and types of fans available, making
selections can be confusing. Properly sizing
the fan is crucial to the aircraft’s
performance.
Unlike turbines, which use combustion to
create thrust, ducted fans accelerate air
through the fan unit to produce the thrust.
Therefore, it is necessary to provide the
proper amount of airflow, which means
obtaining efficient and correct-size ducting.
When referring to these concepts
regarding fans, we use the term “fan swept
area,” or FSA; that is the amount of area that
the fan’s blades cover. You can calculate
this by subtracting the amount of area that
the center body section of the fan occupies
from the area of the fan shroud.
Luckily the manufacturer typically
supplies us with the FSA. Knowing that, we
can look at what is available in terms of inlet
area and decide which fan is going to be
properly sized for the application.
For the purposes of this article, I will
assemble a larger ducted-fan-powered model
and use the preceding principles to illustrate
the steps I take when deciding what fan unit
to use. I’ll be building a Fox-Composites.com
BAe Hawk, which has been around in
various forms for more than 25 years.
Originally designed around a glow
ducted fan, this jet has also flown
successfully with turbine and electric
power. It is supplied more or less set up
for a 44- to 60-size turbine. The model
features a fiberglass fuselage, and the
latest version features hollow composite
wings.
The kit includes some generic ducting
that can be adapted to work with a variety of
power setups. I will build the Hawk
according to the instructions, except in the
areas that require attention for an electric
conversion.
The first thing I want to do is examine
the supplied ducting and fuselage intakes to
determine the amount of combined area with
which I have to work. Because of its glowducted-
fan origins, this model has largerthan-
scale intakes that will make powering
the Hawk with an electric fan a relatively
easy conversion.
The method I use to calculate the area of
the ducting is relatively simple. By tracing
the outline of the intake end of the ducting,
you can easily calculate the area.
Using graph paper with 1/4-inch squares,
trace the outline of the inlet side of the
ducting. Count the number of squares
within the perimeter of the lines. Divide that
total by 16, since 1/4-square-inch graph
paper is being used. This equals the intake
area in square inches.
So with 94.5 squares divided by 16, I get
5.91 square inches. Multiplying that by 2
intakes equals an available area of 11.82
square inches total. Knowing that, I can
inspect different fan units and figure out
which one will be a good choice.
Considering what I want in the way of
performance and flight time, there are
plenty of options for fans. For this article, I
narrowed my search to a few of the newer,
higher-powered systems that are near the
range required for the Hawk.
After considering the aforementioned
EDF setups’ sizes, battery requirements,
and ducting necessities, the best candidates
were the Schübeler DS-75-DIA HDT, the
Stumax SM110-52, and the Tam Jets TJ-
100. I also considered what equipment I
already had, including batteries and ESCs,
to economize as much as possible.
I currently use the Schübeler DS-75 and
the TJ-100 and have been satisfied with the
performance of both. With that in mind, I
decided that for this project I would go with
the Stumax SM110-52 setup. I was
interested in seeing firsthand what this fan
could do, and its unique sound would add
another level of realism to the Hawk.
Another thing you must take into
consideration on these larger models is the
main battery packs’ location. I’ll power the
Hawk with a 5S and 6S set of XPS
Professional series Li-Polys from Xtreme
Power Systems, configured as a single 11S
5000 mAh Li-Poly battery.
With that in mind, it’s important to make
sure that the 3.2 pounds of batteries can be
installed in a location that will allow the
recommended CG to be achieved. Ideally, I
can get them into the front area of the Hawk;
that offers the most area and good airflow, to
help keep the battery temperatures down.
In some cases it is necessary to use more
than two packs (saddle packs), to find a
location at which to install the batteries
while maintaining the CG. That won’t be
necessary in the Hawk; we have plenty of
room to work with inside.
Before installing the ducts, install the fan
to make sure that everything will line up
correctly. The Hawk comes from the factory
with fiberglass mounts for a turbine built into
the fuselage. With a slight modification, I
should be able to use it for the fan as well and
keep everything located similar to the
turbine-powered setup.
A thrust tube is now required. As
previously discussed, ducted fans are
designed to accelerate air flowing through the
ducting and out the back of the fan, to
produce thrust. The thrust tube is used to
increase the velocity of the air coming out,
which is also known as the “efflux velocity.”
By decreasing the diameter of the output end
of the thrust tube, we can further accelerate
the air, but only to a point. Beyond that, we
start reducing performance.
For the SM110-52 fan, the manufacturer
suggests an exit diameter of 87mm. Knowing
that measurement, the fan shroud’s outside
diameter, and the distance between the back
of the fan and the end of the fuselage, I can
make the appropriate-size thrust tube.
A handy trick I picked up from another
kit is to make a simple fixture around which
to form the thrust tube. Some .010-inch
Mylar from a crafts store can be used to
make the thrust tube. To make the fixture, I
cut a 5/8-inch-diameter dowel and a 3/8-inchthick
length of balsa stock to the length
measured from the rear of the fan to the end
of the fuselage.
I cut two flat circles from a sheet of 1/8
plywood. For my project, the first one
measured 112.5mm—the same as the
shroud’s OD at the rear of the fan. The
second disk was 87mm—the dimension that
the manufacturer supplied. I glue the circles
to each end of the dowel and glue the length
of balsa to the fixture, lining up the outside
edge of the balsa with the outside edge of
both disks.
I tape the long edge of an appropriatesize
piece of Mylar to the balsa to hold it in
place, and then I can wrap the Mylar around
the fixture and overlap the taped edge. I use
a marker to trace the ends and the seam onto
While most people associate model jets
strictly with speed, many, including myself, try to
reach a balance between performance, flight
time, and weight. To do this, you must look
realistically at the aircraft and determine what the
airframe’s capabilities are.
A larger model such as Fox-Composites.com’s
BAe Hawk has a somewhat draggy airframe
compared to a purpose-built sport jet such as the
Composite-ARF Spark or BVM Electra.
You have to be realistic in your expectations
about performance. You quickly reach a point of
diminishing returns with power levels, because
most models will hit an aerodynamic wall, and
additional power yields marginal results in
overall performance.
Following are some options for you to
consider for electric-ducted-fan power.
• XPS Dynamax
Xtreme: This is an
electric version of
the Dynamax fan.
These fans have
been around for
years, but they are
regaining
popularity as
electric
conversions. One
of the main benefits is that the new unit is a dropin
replacement for many models that were
originally designed around the glow-enginepowered
Dynamax.
At 3.1 pounds including the Castle Creations
HV-110 controller, the Dynamax Xtreme is a
proven and well-built unit. XPS reports that it can
run on 10-18 Li-Poly cells, handles power levels
up to 10,000 watts, and develops well more than
22 pounds of thrust.
The unit’s FSA is right at 16 square inches,
and XPS recommends that an inlet providing
123% FSA is best. This works out to roughly
19.6 square inches.
Look to see this system powering some largescale
jets in the near future.
• Schübeler DS-94-
DIA HST and DS-
77-DIA-HST:
Daniel Schübeler
has been
manufacturing
some of the highestquality
ducted fans
for years. His allcarbon
designs are
lightweight yet incredibly strong, and they are
capable of absorbing huge amounts of power.
And the company’s customer service is topnotch.
The latest versions are “HST”s (High Static
Thrust) and are powered by Schübeler’s
proprietary motor—the DSM6740—a two-pole
design that is integrated into the fan’s center
body.
The DS-94 model has an inner shroud
diameter of 128mm, with an FSA of 94 square
cm (14.6 square inches). It features a 12-blade
rotor and can reportedly produce more than 22
pounds of thrust on a 14S Li-Poly. The plug-andplay
package that includes the HV-180 ESC
weighs a bit more than 3.5 pounds.
The DS-77 is a 120mm fan with an FSA of
77 square cm (11.9 square inches) and can
produce just less than 21 pounds of thrust on a
14S Li-Poly. This plug-and-play package
includes the HV-180 and weighs slightly less
than 3.5 pounds.
Compared with four-blade rotors, these
units’ 12-blade-rotor fans are quiet and produce
a much more jetlike sound.
• Schübeler DS-94-DIA
HDT and DS-75-DIA
HDT: This company
also offers an “HDT”
(High Dynamic
Thrust) line of fans that
are similar in size to
the HST models. The
four-blade HDT units
are designed to offer higher dynamic thrust
(top-end speed) than their HST counterparts.
The HDT fans don’t incorporate
Schübeler’s integrated motor system, so a wide
variety of motors can be used, depending on the
application. Plug-and-play versions are
available from the manufacturer.
The DS-94 has a fan diameter of 120mm.
The plug-and-play setup including the HV-120
ESC weighs 1.85 pounds, has an FSA of 94
square cm (14.5 square inches), and produces
13.5 pounds of thrust on a 10S Li-Poly.
The DS-75 has a 110mm fan diameter. The
plug-and-play setup including the HV-120
weighs 1.75 pounds, has an FSA of 75 square
cm (11.6 square inches), and produces 12.5
pounds of thrust on a 10S Li-Poly.
• Stumax Aircraft
SM110-52: This unit
comes standard with a
Neu 1915 1Y motor and
is designed for 11S-12S
Li-Poly batteries. It has
an OD of 110mm and an
FSA of 73 square cm
(11.4 square inches).
The unique feature
that sets the 110-52 fan
apart from others is that it is an IGV—Inlet
Guide Vane—or “pusher” setup. The more
common fan configuration is for the rotor to be
in the front and the stators behind. The SM110-
52 is set up the opposite way.
Also, the center body and stators are a
one-piece aluminum heat sink. Stumax
carefully machines each unit so that the
motor fits snugly in the center-section,
increasing its ability to dissipate heat.
Another advantage of this design is the sound
it produces. Ducted fans have historically
been fairly loud and high-pitched, but the
Stumax unit is quiet.
More sound is heard from the fan’s thrust
than from the fan itself. Many pilots find this
desirable, because it adds a more realistic
sound to the model.
Powered by an 11S Li-Poly, the SM110-
42 produces approximately 3,500 watts and
nearly 11.5 pounds of thrust. On 12S the
output increases to 4,200 watts and 13.5
pounds of thrust.
• Jet Hangar
International ETurbax:
This is
another 130mm
fan that has gone
from nitro to
electric power with excellent results.
The company has been in business for
more than 30 years, and in 1980 it acquired
the rights to the Turbax fan. For the past few
years, Jet Hangar has been selling these units
as an electric conversion, or “E-Turbax.” It
offers the fan as a plug-and-play package
with power setups configured for 9S, 10S,
and 12S Li-Poly operation. This setup is a
drop-in replacement for several aircraft.
The RTF version is powered with a
NeuMotor unit and features an HV-110 ESC.
The E-Turbax is also sold bare as “ready to
assemble,” for those who want to use
different motor configurations.
The E-Turbax has an FSA of slightly
more than 96 square cm (15 square inches).
Depending on which motor/Li-Poly
configuration is installed, it produces 12-17
pounds of thrust.
• Tam Jets TJ-100:
This company has
entered the EDF
market with the TJ-
100. This 100mm
fan is made from
carbon fiber and
aluminum. The
aluminum center
body housing the
motor is, in effect, a
full-length heat
sink. Behind that, the ESC is mounted in the
rear fairing to aid in cooling.
The TJ-100 has an FSA of 75 square cm
(11.6 square inches) and weighs
approximately 1.75 pounds. On the upper end
of the power range, it produces an excess of
13 pounds of thrust.
Tam Jets offers a wide variety of plugand-
play setups featuring NeuMotor 15-
series power plants running six to 12 Li-Poly
setups and featuring 85- to 110-amp Castle
Creations HV controllers.
The company also sells a broad selection
of conversion kits that allow you to install the
TJ-100 in most of its turbine-powered aircraft
and a few other brands of models that are
designed for turbine and ducted-fan use.
With custom-fabricated ducting and
nacelles to fit many of today’s popular
aircraft, and power output ranging from
2,200 to 4,500 watts, this is probably one of
the easiest and most versatile setups to
integrate into an existing model.
• BVM VioFan:
With electric
power’s increasing
popularity, BVM
reintroduced the
Viojett a few years
ago as the VioFan.
Powered by a
NeuMotor 1524-series unit and 10-12 Li-
Poly cells, it will produce more than 5,000
watts and 14 pounds of thrust.
The VioFan comes factory-ready and
includes an HV-110 controller, which is
integrated into the rear fairing. This power
system weighs approximately 2.5 pounds and
has an FSA of approximately 13 square
inches.
The VioFan has proved to be an
extremely reliable EDF unit. BVM offers a
solution for upgrading many of its older
models and offers new aircraft that are
designed specifically for the VioFan. MA
—Roger McCormick
March 2010 51
the Mylar and trim away the excess.
Clear packing tape is sufficient to hold
the seam together on the inside and outside.
When the tube is completed, it can be
secured to the back of the fan with clear
tape.
I used a pair of curved Lexan scissors to
cut and trim the intake ducting so that it fits
into the inlets on the fuselage and lines up
evenly with the front of the fan. Tape the
ducting into place and make a coupler
section to connect the fan to the ducts.
I use poster board to create a template for
a short coupler piece to join the fan and
ducts, leaving an extra 1/4 inch on each end
to overlap when it’s glued together. Then I
trace it onto a .010-inch-thick fiberglass
sheet that I later roll into a tube. I use CA to
bond the overlap, and then I epoxy two
layers of 1/2-ounce fiberglass cloth over the
seam.
After that dries, I wrap it with carbon tow
to make it even stronger. I don’t want it to
collapse when I start pulling a vacuum on
the ducting.
With the coupler secured to the fan and
ducting and everything checked for
alignment, I glue the ducting to the inlets on
the fuselage with a mixture of epoxy and
microballoons. On the inside wall of the
fuselage, I used 1/2-ounce fiberglass cloth to
cover the overlap and help secure the inner
side of the ducting.
Ideally you want a smooth and clean
intake radius, to reduce turbulence of
incoming air. The stock ducting left some
large gaps and overlaps, so clean these up
and remove any excess with a Dremel tool.
Then fill with body filler, to blend it in. I’ll
use my airbrush to repaint the intakes.
The batteries need a tray. The kit came
with two plywood sections that glue to the
bottom of the fuselage the length of the nose
section to reinforce it. I added triangle stock
to the sides, and I’ll put a piece of 3/16 light
plywood over it to act as the battery tray.
The most common mounting solution for
the ESC in the majority of ducted fans is to
put it behind the engine in a fairing, so that it
receives plenty of cooling air. That approach
won’t work with the SM100-52 and its rearrotor
design.
To get proper airflow over the ESC, I
mounted it on the top of the ducting under
the rear hatch area. The Hawk has intake
scoops molded into the fuselage, as the fullscale
aircraft does, so I use those to get air to
the speed controller.
I also used a piece of lightweight plastic
to close off the underside of the hatch and
cut out a section to direct the air directly
over the ESC, where it’s then drawn out the
rear of the fuselage. In addition, I mounted a
temperature probe on the ESC so I can
monitor its temperature with the Eagle Tree
Systems data logging system.
As a rule of thumb, 250 watts per pound
is a good figure to apply when dealing with
ducted-fan models; we call that number
“good performance.” And take care when
static-testing any aircraft; safety glasses are
a good idea.
With the Hawk secured and the Eagle
Tree transmitting information back to the
laptop via the Seagull wireless setup, I ran
the fan to somewhat simulate a typical flight
by varying the throttle and working the
control surfaces for approximately five
minutes, with a short cooldown period at
low throttle for the motor.
The Eagle Tree system reported 3,429
watts at 83.54 amps. The model’s final
weight at 13.8 pounds works out to 248.5
watts per pound, so we should be good on
power.
The SM110-52 can also be run on 12S,
producing approximately 4,200 watts at
close to 100 amps. The 12S 5000 batteries
would raise the weight to slightly more than
14 pounds and push the power up to
approximately 295 watts per pound. So I
have a bit of room to work with if I feel like
I need more power, while remaining within
the specifications for fan, ESC, and
batteries.
Flying the Hawk:With everything ready and
all systems thoroughly tested, I headed to
Ohio a few days before the E-Jets
International event so I could do the Hawk’s
test flights at the TORKS (The Ohio Radio
Kontrol Society) field, which has a very nice
1,000-foot runway and plenty of room.
Pablo Hernandez, a Florida resident and
fellow pilot, was kind enough to do two
shakedown flights with me. He is a skilled
flier and has plenty of experience with larger
Hawks. We set the timer at 4:30 as a starting
point for the first flights, to ensure that the
batteries weren’t overdischarged.
In the air with other jets flying, you had to
listen closely to hear the Stumax unit. It
definitely lives up to its reputation as one of
the quietest fans available, and the model flew
nicely on the 11S 5000 mAh setup.
According to the Eagle Tree system, the
Hawk’s top speed was 137 mph. The 4:30
flight used 3800 mA of the 5000 mAh pack.
With the Eagle Tree system, I could see
that the main batteries reached a maximum
temperature of 128° and the ESC peaked at
121°. With its ability to monitor so many
components (temperature, watts, amps,
voltage, rpm), it’s a great tool for any aircraft.
As of this writing, the Hawk has made more
than 10 flights. After getting accustomed to
its characteristics, I can get five-minute
flights using slightly more than 4000 mAh
from the 11S 5000 packs.
With the ideas and concepts I’ve
presented in this article, you should
understand the basic principles of sizing and
implementing a ducted-fan setup. If you do
have questions, the manufacturers I have
mentioned are happy to offer guidance so
that your ducted-fan project is a success. MA
Roger McCormick
[email protected]
Sources:
Fox-Composites
http://fox-composites.com
Schübeler Modellsysteme (Germany)
49 (0)5251 873348
www.schuebeler-jets.com
Stumax Aircraft (Australia)
61 2 8819 4330
www.stumaxaircraft.com
Tam Jets R/C Model
(408) 224-7600
www.tamjets.com
XPS
2440 N. Kiowa Blvd.
Lake Havasu City AZ 86403
www.xtremepowersystems.net
Eagle Tree Systems
(425) 614-0450
www.eagletreesystems.com
BVM Jets
(407) 327-6333
www.bvmjets.com
Castle Creations
(913) 390-6939
www.castlecreations.com
Jet Hangar International, Inc.
(562) 467-0260
www.jethangar.com
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