Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
Edition: Model Aviation - 2012/10
Page Numbers: 39,40,41,42,43,44
Last year, Halloween came around with its hordes
of witches and bats, and my mind was warped
more than normal! A bat’s wing shape is unique
and I wanted to incorporate it into an RC model. The
deep, scalloped LE wing shape seemed to be a natural
thing to add.
I thought there might be some interesting
aerodynamic results from the vortex action because
of the spikes and scallops. The TEs could be brought
to a point but I left them with some bluntness to help
alleviate hangar rash.
The prototype was called a Pink Bat, but I
thought that a name that would appeal to someone
other than a child would be more appropriate—
something mean, with fangs. Pink Bat is not going to
scare anyone and is defi nitely not indicative of the
performance of the airplane!
MA Editor-in-Chief Jay Smith suggested that
Borealis might be an appropriate name. Borealis is
the name of a carnivorous bat with red-tinted fur. It
doesn’t suck blood, but at least it is a carnivore with
sharp teeth, so Borealis became the name.
I had a second thought about
incorporating spikes into the design, but
not about the aerodynamics resulting
from their presence. The second thought
concerned the spike’s strength.
If I leave the foam spike in its natural
condition, it would be vulnerable to
accidental bumps, hangar rash, and
perhaps break on landing. However,
in a year of fl ying of the old prototype
without any reinforcement, the spike
only broke once. I fi xed it on the fi eld
with CA.
The airplane can be fl own easily into
a nose-high landing that prevents the
spikes from contacting the ground. If I
reinforced the spike too much it could
be a “pointy thing” on the airplane that
could potentially be dangerous.
I attached a layer of fabric with CA
to the top and bottom of the points,
which. This strengthened the points
as I expected, but not so much that I
thought they were dangerous.
The spike can still break during
unplanned contact with the ground or
an object, but it poses a lesser danger
to weak human fl esh than a pointed
spinner or sharp propeller, spinning or
otherwise.
The basic airplane can vary. The
vertical tail shapes are strictly for looks.
You could have two outboard fi ns or
one single fi n. If you want to make
the shapes more angular, that is fi ne. A
canopy similar to the F-117 could be
added or you could change the outer
wing curve to several straight segments.
I like the look of the three fi ns and the
scalloped, curved edges. I have always
been a Batman fan.
The inlets on each side of the nose are
functional and allow cooling air to fl ow
over the ESCs. The ducts give an area
to grip during the underhand launch.
You can launch overhand by holding the
battery area.
Building the Borealis is relatively
simple. All of the parts needed to make
the Borealis can be cut from one piece of
fan-fold foam. To generate foam-marking
templates, use pieces of transparent
paper and copy the main components
from the plans. Use these to mark the
fan-fold foam material with a ballpoint
pen. To stop the foam from tearing, use a
sharp blade or a small box cutter. Cut all
of the pieces at one time.
As it comes from the factory, the big
piece of fan-fold foam is warped, so that
problem needs to be addressed. Start
with the main wing by cutting out the
locations for the forward and aft wing
spars.
I used carbon-fi ber arrow shafts for
spars. The shaft’s diameter is slightly
larger than the thickness of the foam.
Glue the spars in place using CA. I built
the entire airplane with less than one
bottle of thick, foam-friendly CA.
The slow setting time allows you time
to arrange the parts and then set them
with foam-friendly CA accelerator. Add
fabric reinforcement on the top and
bottom of the wing spars as shown on
the plans. Add fabric reinforcement on
the top and bottom of the wingtips.
One photo shows where I used an
alternate method of capping the spar
with a piece of 1/32 balsa. Both balsa and
fabric work well.
To remove the forward-to-aft warping
we will use the stiffness properties of the
various foam assemblies that run from
the front to the rear of the airplane. We
need to make the main body fin, main
body inboard, and nose assembly. To do
this, glue one main body inboard to each
side of the main body fi n while bracing
the vertical tail upright; hold until the
glue hardens.
Add the nose assemblies to each side
of the front. Cut the nose to shape as
shown on the top view of the plans.
Then build up two subassemblies
consisting of the outboard nacelle and
the motor fairing parts. To form a motor
mount, add three pieces of balsa, glued
in a cross-grain fashion, to the front of
the outboard nacelle. Cut the motor
fairings to shape as shown on the top
view of the plans.
Now you can glue the above
assemblies to the main wing at the
locations shown on the plans. Also glue
the two main body outboard pieces to
the main wing. You will end up with no
warps in the wing. Glue the top nose
parts to the airplane. The foam bends
easily around the nose and you can
hold it until the accelerator sets the CA,
resulting in a nice, fl at-bottomed, foam
assembly.
The top tail part is removable to give
access to the electronics. Glue a small
piece of balsa under the forward part of
the top tail. This will let it slide under
the top nose and lock the forward part
of the top tail in place. A nylon bolt that
goes through the rear of the top tail,
going down to the wing, holds the top
tail in place.
The battery-holder section is made
from the chin parts and the chin fairing
parts. Stack them as shown on the
plans and add a small balsa triangle to
reinforce the inside corners where the
cross section is thin. Glue the completed
battery holder assembly to the bottom
of the wing.
Use a sharp knife and sandpaper to
shape the nose as desired. I didn’t round
the nose much and I left the fl ying
surfaces with square edges, although
you can round them. After shaping the
overall edges, cut a piece of fl exible
plastic (a milk jug would work nicely)
and using long screws, attach it to the
front of the battery holder assembly as
shown on the plans.
To hold down the rear of the fl exible
plastic during fl ight, make a Velcro
hold-down assembly. Glue a piece of
balsa across the back of the battery
holder assembly and attach a piece
of loop Velcro to it. Attach the hook
Velcro to the fl exible plastic piece.
Recess the balsa piece as shown on
the plans to allow the plastic to fl atten
against the bottom of the battery area.
Add loop Velcro to the bottom of the
wing inside of the battery assembly
to provide a place to anchor the
fl ight battery (which has hook Velcro
attached.)
The fl exible elevons need a piece of
1/16-inch hard balsa reinforcement glued
spanwise across their bottom. Add some
balsa on the top where the control horn
attaches to stiffen the elevons.
Place the E-fl ite Park 370 motors
as shown on the plans. These produce
much power and work well on this
airplane. Park 400 powerplants would
work well and provide more power.
Route the wires going to the ESC
along the motor fairings and along the
wing into the equipment area. I used
masking tape to cover the loose wires
on the motor fairings. I used a piece of
hollowed-out foam to cover the loose
wires on the top of the wing and painted
the tape to look better.
Locate the E-fl ite 20-amp ESCs and
receiver to the wing as shown on the
plans. You can spot glue them down or
use Velcro.
I used a Spektrum AR7000 receiver,
but I recommend the less-expensive
Spektrum AR600. Route the wiring as
needed through the cutout in the main
body fi n. I use the BEC receiver power
output from both ESCs instead of
removing one of the power leads.
Notch the main body outboard
pieces to accept the servos. I added the
grommets to the servos and used CA on
the grommet/foam interface to hold the
servo in place. The JR DS368BB servos I
used may be overkill in terms of torque,
but I had them available, and the metal
gears won’t break. Don’t use micro
servos in this application. I doubt that
they have suffi cient torque.
Finally add some small pieces of balsa
across the equipment bays to hold the
wiring down. I used string hinges to
attach the elevons to the wing. They
have no binding issues and are easy to
install. Drill holes through the wing in
front of the aft spar and in each elevon.
Stiffen the ends of the string with
CA and thread it through the wing and
elevon. Install the control horns with
bolts through the elevons. Assemble
and attach the pushrod assemblies
from the servos to the elevons. Start
with a control surface position of
approximately 1/8-inch up-elevon and
adjust during fl ight to maintain level
fl ight. The Borealis shown in the photos
has a rudder, but I haven’t convinced
myself it is worth the effort because I
rarely use it.
If you decide to add a rudder, be
sure to brace the vertical tail on each
side with a strong string that runs at
roughly a 45° angle from the vertical
tail down to the surface of the wing.
Pull the string tight and CA it in place.
If you don’t, the bending moment from
the defl ected rudder may break the
glue joint between the vertical tail and
the wing.
With an E-fl ite 3s 2100 mAh
LiPo battery positioned against the
forward part of the battery area, the
model should balance at the CG
location shown on the plans. This is a
conservative CG location and a good
starting place.
You may want to experiment with
the CG position as you gain experience
with the airplane’s characteristics.
Moving the CG aft will make the
airplane more responsive to control
inputs until an unstable point is
reached.
The Borealis can be fl own with
the simplest of transmitters. If your
transmitter has an elevon-mixing
capability, that is all that you need.
If not, you can use a standard elevon
mixer with your receiver. Exotic
features such as control rate switching
capability and exponential are
unnecessary.
Although I fl y my Borealis with a JR
12X 2.4 GHz, which has triple rate
settings on each surface, I usually use
one rate setting for the entire fl ight.
Little or no exponential is needed in
pitch or roll; the foam will defl ect
slightly and soften the control inputs,
which makes the airplane great for the
simpler radio systems.
Set initial elevon, up and down,
and low rate defl ections equal to 5/8
inch when the transmitter roll stick
input is zero. You can adjust the fi nal
defl ections to suit your preferences.
Set the high rate defl ections as high as
your servos will allow for some exciting
fl ying times.
The fi nished airplane with a battery
weighed exactly 2 pounds and the
power level was measured at more
than 250 watts. This gives a power
loading of well beyond 100 watts per
pound and promises good performance.
I fl y the airplane with Landing
Products electric propellers ranging
from 8 x 6 to 9 x 6. I recommend
starting with 9 x 6 counterrotating
propellers, which will eliminate torque
effects. This will give maximum thrust
and speed. The motor temperatures at
the end of a flight are cool, so the setup
is fine.
I have flown the airplane with
propellers rotating in the same
direction—all that I had available at
the time—and the Borealis flew fine. It
only needed a bit of roll trim.
The airplane has no bad traits and
looks great in the air. It is an unusuallooking
planform and is a nice change
from the usual airplanes seen at the
flying field.
Possessing a 36-inch wingspan,
Borealis is a large flying wing and it
grooves well. With the power available,
the airplane will launch nicely with a
smooth underhand launch; hold the
nose up at roughly 30° and give it a
toss.
You may need to give a bit of
additional up elevon during the initial
part of the launch when the airspeed is
low. I recommend that a friend provide
the first launch for you, although I
launched the airplane myself.
The Borealis is a fast, maneuverable
airplane that is easy to fly, and it looks
delightful in the air. Before flying
Borealis on your own, you should
be able to fly a typical sport airplane
without much effort.
The Borealis’ low-speed handling
is nice, possibly because of the spikes
and the resulting vortex action.
During landing the pilot can set up
an approach angle of attack, or pitch
angle, and control the exact touchdown
spot with throttle control. Actual
touchdown speed is slow.
The Borealis has an interesting look
in the air and it is a nice-flying airplane
with no bad habits.
