For the last fi ve years, I have been developing
a two-meter canard sailplane called a
Canarrow. Despite its unconventional
appearance, the model is stable and easy to fl y. It
launches and fl ies conventionally.
The Canarrow is a good choice for a
developing sailplane enthusiast looking for
something unique with better performance than
a typical beginner’s ARF. The model employs
traditional construction techniques and fl atbottomed
airfoils for ease of building. It is strong
enough to survive typical beginner mishaps.
The forward surface is swept to protect it if the
model were to fl ip over on landing.
The design has its origins in a stick glider I
made in the early 1980s. Canards were in fashion
then. I was reminded of it when I decided to
build something for a beginner-oriented contest
series the Silent Order of Aeromodeling by
Radio (S.O.A.R.) holds each year that is limited
to rudder/elevator/spoiler (RES) and Two-Meter
models.
That had me thinking about the classic twometer
dilemma of wing area versus aspect
ratio. I fi gured the best way to have open-class
fi gures for each was to start with an open-class
wing. The idea was to chop off the outer panels,
leaving a 2-meter center section, and then
attach the severed tips to the fuselage in a lifting
confi guration.
Using the spoiler causes the nose to pitch sharply up. A program mix
will keep the fuselage level. Here the spoiler is deployed for landing.
by Daniel Fritz
www.ModelAviation.com JULY 2013 Model Aviation 33
033-037_MA0713_Canarrow.indd 33 5/28/13 1:03 PM
Top: The ve canard structures are complete except for upper surface sheeting and tip blocks. The lower
spars are spruce, and the elevator servo bays have been cut out. The elevators are made from 2-inch
aileron stock.
Bottom: A view from below of the canard’s structure shows the upper surface sheeting, elevator servo
bays, nylon bolt hole, and servo wire hole.
The main wing center section only lacks the upper surface sheeting. The spar is a carbon-balsa laminate
I-beam with carbon caps. The entire spar is wrapped with Kevlar tow to prevent delamination.
The Canarrow is technically a canard because pitch
stability and control are provided by a forward lifting
surface, but it is more correctly a tandem-wing airplane. The
CG is entirely between the two lifting surfaces.
If one were to reassemble the forward wings to the tips
of the main wing, the result would span 112 inches, offer
752 square inches of wing area, and have an aspect ratio of
roughly 17. Of course, things are not so simple and drag is
higher (there are twice as many tip vortices); nevertheless,
this concept has proven successful.
The tip vortices from the forward wing fl ow over the top
of the main wing at the dihedral breaks where some energy
is recaptured. Sweeping the forward wing proved successful
in protecting it, as it
did on the old stick
glider.
The forward wing
lies behind two lines
drawn from the nose
to the tips of the main
wing.
Assuming the
model lands on a fl at
surface, something
else must break before
the canard will. The
vertical stabilizer is
tall enough to protect
the canard when the
model is inverted.
Construction
The fuselage is a semimonocoque
in that most of
its strength comes from a
thin, 1/16-inch skin, and the
shape is maintained by robust,
closely spaced formers. The
corner joints are reinforced
with triangle stock balsa that
contributes to the model’s
overall strength. It has proven
to be up to the job, despite
high bending forces during
contest landings.
The longest parts on the
entire model are the fuselage
side panels, which measure 48
inches and can be cut from a
single sheet of commercially
available balsa. These must
be accurately cut to ensure
that the wing and canard
are properly aligned when
everything is fi nished.
Install the forward plywood
doublers by drawing a line
3/16 inch from the nose on
the inside of both side panels.
Align the tops of the doublers with the tops of each side panel
and the front of the doublers with the line.
The plywood doublers set the angle of incidence for the
canard after removing the excess balsa above them. The
triangle stock balsa does not extend forward of the plywood
doublers. It should also end 3/16 inch from the tail.
Cut relief into the upper triangle stock for the doublers.
Glue formers B, C, and all four Ds to both sides in a single
gluing step using a slow-curing epoxy. Apply clamps or rubber
bands around the fuselage sides at each former. Before curing,
place the fuselage upside down on the building board and
apply weight so the upper surfaces are aligned in the same
plane.
34 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 34 5/20/13 4:51 PM
The fuselage a er covering
shows main wing and
canard nylon bolts, wires
for elevators and spoiler,
towhook, and rudder linkage.
The right side of the main wing center section
shows the upper surface sheeting in place. The
sheeting overrides only one of the doubled ribs
at the dihedral break, leaving the other half of
the ribs to accept sheeting from the wingtip
panels.
Photos and illustrations by the author
The upper sheeting is installed before the lower sheeting
to allow the mounting surfaces for the wing and canard to
be completed. For CG purposes, the battery and rudder
servo are mounted in the aft compartment below the
vertical fi n.
The main wing is conventionally built with an I-beam
spar, D-tube sheeting ahead of the spar, and open bay
construction behind it. All sheeting is 1/16 balsa with spanwise
grain. The spar is full-depth to keep the caps as far apart
as possible.
Accordingly, the D-tube does not overlie the spar, but
merely butt-joins the forward sides of the spar caps top and
bottom. The sheer webs are vertical-grain balsa. The TE is
1-inch solid balsa. The spars can be spruce or carbon/balsa
laminates. Carbon/balsa is lighter. Use at least 0.014-inch
carbon on the center section and 0.007 on the tips.
The laminated spar must be wrapped in carbon or Kevlar
tow to prevent delamination under load. There is limited
sheeting behind the spar to provide ease of handling/
covering and additional rigidity.
Lower surface sheeting behind the spar is cut to fi t into
the bays between the ribs, spar, and TE. All upper surface
sheeting overlies the ribs and butt-joins the spar and TEs.
On the upper surface, the middle three bays and the bays
immediately adjacent to the dihedral breaks (seven bays) are
sheeted. On the lower surface, the middle three bays and
inboard bays adjacent to the dihedral breaks (fi ve bays) are
sheeted.
The canard is built as three separate pieces. These are buttjoined
together and the joints are reinforced with fi berglass.
The center section is sheeted top and bottom and can either
be permanently fi xed to the fuselage or removable.
Each outer panel uses a single lower spar and a fully
sheeted upper surface that serves as the upper spar. Only the
bays immediately adjacent to the center section are sheeted
on the lower surface using cross-grained balsa between the
ribs and spars. The bays ahead of the spar are sheeted with
3/8 wood and sanded to conform to the airfoil.
Actuation of the elevators is complicated by the fact that
they move in different planes. The preferred method is
to use small servos (Hitec HS-65 or equivalent) mounted
in each outer panel behind the lower spar in the bays
immediately outboard of the center section.
The servos are mounted at an angle with their arms
aligned parallel to their respective elevator hinge lines.
Actuation of the surfaces is by a short, straight link to the
control horns, which
are also aligned
permendicular to the
hinge line.
The servo wires pass
through small holes
into the center section of the canard. This setup requires
either a computer radio or a Y harness.
Fiberglass
reinforcement
of the butt
joints cannot
be omitted
and should
be carried out
one full bay on
either side of the
center section
to ensure loads
are transmitted
across the
surface skin
joints.
The wing
and canard
are mounted
using 1/4 x 20
nylon bolts
with threaded
maple blocks to
ensure accurate
placement.
In the fl ying
surfaces,
these bolts
pass through
unthreaded
mounting blocks
made from a
sandwich of
balsa capped with 1/32 plywood measuring 3/4 x 17/8 and
spanning the middle rib bays.
The plywood reinforces the lower surface sheeting in the
event that a bolt sheers and accepts the loads from the bolt
head. This sandwich is fl at on the top and bottom. Make the
sandwiches so that the top plywood surface comes up to the
top of the ribs but does not exceed their contour. Install the
blocks onto the lower surface sheeting.
Center and drill the bolt holes through the bottom of the
lower sheeting before the upper sheeting is installed. Do not
attempt to glue the upper surface sheeting to the blocks,
which should lie immediately below the sheeting. After the
www.ModelAviation.com JULY 2013 Model Aviation 35
033-037_MA0713_Canarrow.indd 35 5/20/13 4:52 PM
The fuselage’s main structure shows both sides, forward
plywood doublers, triangle stock corner reinforcement, 3/8 x
3/16-inch tail stock, and all of the formers.
The author launches his
fourth Canarrow at the
beginning of its second
full season.
upper surface sheeting is on, complete preparation
for the nylon mounting bolts by drilling from the
bottom of the wing through the upper surface
sheeting.
Install the nylon wing bolt from the top and cut
around the head of the bolt through the upper
sheeting. After removing the cutout skin, the head
of the bolt will pass though the enlarged hole to
seat squarely against the top of the mounting block
and fl ush with the skin.
The fi rst prototypes used the popular S3021
airfoil for all lifting surfaces. I later modifi ed the
airfoil for the wingtips and the canard to optimize it for the
lower Reynolds Numbers I encountered. The modifi ed airfoil
is slightly thinned and the point of maximum thickness has
been moved forward. All airfoil work and rib plotting was
done with Profi li2 software.
The vertical stabilizer is the simplest structure on the
model. The only thing not immediately obvious is that the
entire structure is sheeted in 1/32 vertical grain balsa.
The sheeting is primarily for CG reasons. The vertical
stabilizer is easily damaged without it. The main vertical post,
which mates with the aft end of the fuselage, must be spruce
or carbon-laminated balsa.
A pine nose block is best to resist damage. All four wingtips
and the canopy are carved from balsa. The receiver and
switch/charging jack go in the canopy area.
The fi nished model will balance with little or no extra
balancing weight. Flying weights have varied from a weightoptimized
35 ounces to a strength-maximized 41 ounces.
Flying
The balance point is 203/8 inches ahead of the fuselage end
point (as marked on the plans). Balanced at this point, the
model will fl y stably and predictably from the fi rst hand toss.
The back of the towhook should be 1/8 inch ahead of the
CG. The model will pull hard during launch at that point,
but it will remain stable and resist popping off the line.
The recommended control throws are 30° up/down for the
elevators and 45° left/right for the rudder.
The Canarrow is strong enough for a winch, but as with
any other wooden sailplane, it can only take so much abuse.
It really comes into its own on a hi-start. I have used the
Northeast Sailplane Products medium-size Pinnacle and the
slightly less-powerful Dynafl ite standard hi-starts. The model
will get a full launch from either. It should not require any
elevator input on the line.
In the air, the Canarrow fl ies as though it’s larger than a
Two-Meter Sailplane. Its 750 square inches of wing area
compares favorably with traditional wooden Two-Meter
aircraft such as the Goldberg Gentle Lady and Great Planes
Spirit, which have roughly 670 square inches of wing area.
Handling is conventional for an RES Sailplane. The large
vertical stabilizer makes it responsive and helps indicate lift.
It’s buoyant and ranges well.
The biggest difference between the Canarrow and a
conventional design is that pitch does not vary as much with
changes in speed. Small changes in pitch trim will change the
fl ying speed. The deck angle of the fuselage stays remarkably
fl at even while climbing in lift.
The model has a single spoiler on the main wing. Deploying
the spoiler causes the nose to pitch sharply up. The elevator
moves in the opposite direction from a conventional design
(the elevator moves up for a nose-down command and vice
versa).
Accordingly, the pitch compensation for spoiler deployment
is to also spoil the forward wing with a down-elevator
command. A linear program mix will keep the fuselage level.
The combination is effective for descent and spot landings.
The Canarrow is a fun and rewarding model that will bring
a smile to anyone who builds it.
—Daniel Fritz
[email protected]
See bonus photos and a parts list in this
month’s tablet app and on www.ModelAviation.com.
36 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 36 5/20/13 4:52 PM
SPECIFICaTIONS
Type:
RC Sailplane
Intermediate builder; intermediate pilot
112 inches
55 inches
40 ounces
Four channels, four Hitec HS-65HB servos
Balsa, plywood
Oracover
Skill level:
Wingspan:
Length:
Weight:
Radio:
Construction:
Finish:
The only things missing on the Canarrow are
control horns, linkages, and lettering on the tail.
The solid-mahogany spoiler panel is nished in
clear, water-based urethane. This model is built to
the speci cations of the plans in the article and
the parts were laser cut. www.ModelAviation.com JULY 2013 Model Aviation 37
033-037_MA0713_Canarrow.indd 37 5/20/13 4:52 PM
Edition: Model Aviation - 2013/07
Page Numbers: 33,34,35,36,37
Edition: Model Aviation - 2013/07
Page Numbers: 33,34,35,36,37
For the last fi ve years, I have been developing
a two-meter canard sailplane called a
Canarrow. Despite its unconventional
appearance, the model is stable and easy to fl y. It
launches and fl ies conventionally.
The Canarrow is a good choice for a
developing sailplane enthusiast looking for
something unique with better performance than
a typical beginner’s ARF. The model employs
traditional construction techniques and fl atbottomed
airfoils for ease of building. It is strong
enough to survive typical beginner mishaps.
The forward surface is swept to protect it if the
model were to fl ip over on landing.
The design has its origins in a stick glider I
made in the early 1980s. Canards were in fashion
then. I was reminded of it when I decided to
build something for a beginner-oriented contest
series the Silent Order of Aeromodeling by
Radio (S.O.A.R.) holds each year that is limited
to rudder/elevator/spoiler (RES) and Two-Meter
models.
That had me thinking about the classic twometer
dilemma of wing area versus aspect
ratio. I fi gured the best way to have open-class
fi gures for each was to start with an open-class
wing. The idea was to chop off the outer panels,
leaving a 2-meter center section, and then
attach the severed tips to the fuselage in a lifting
confi guration.
Using the spoiler causes the nose to pitch sharply up. A program mix
will keep the fuselage level. Here the spoiler is deployed for landing.
by Daniel Fritz
www.ModelAviation.com JULY 2013 Model Aviation 33
033-037_MA0713_Canarrow.indd 33 5/28/13 1:03 PM
Top: The ve canard structures are complete except for upper surface sheeting and tip blocks. The lower
spars are spruce, and the elevator servo bays have been cut out. The elevators are made from 2-inch
aileron stock.
Bottom: A view from below of the canard’s structure shows the upper surface sheeting, elevator servo
bays, nylon bolt hole, and servo wire hole.
The main wing center section only lacks the upper surface sheeting. The spar is a carbon-balsa laminate
I-beam with carbon caps. The entire spar is wrapped with Kevlar tow to prevent delamination.
The Canarrow is technically a canard because pitch
stability and control are provided by a forward lifting
surface, but it is more correctly a tandem-wing airplane. The
CG is entirely between the two lifting surfaces.
If one were to reassemble the forward wings to the tips
of the main wing, the result would span 112 inches, offer
752 square inches of wing area, and have an aspect ratio of
roughly 17. Of course, things are not so simple and drag is
higher (there are twice as many tip vortices); nevertheless,
this concept has proven successful.
The tip vortices from the forward wing fl ow over the top
of the main wing at the dihedral breaks where some energy
is recaptured. Sweeping the forward wing proved successful
in protecting it, as it
did on the old stick
glider.
The forward wing
lies behind two lines
drawn from the nose
to the tips of the main
wing.
Assuming the
model lands on a fl at
surface, something
else must break before
the canard will. The
vertical stabilizer is
tall enough to protect
the canard when the
model is inverted.
Construction
The fuselage is a semimonocoque
in that most of
its strength comes from a
thin, 1/16-inch skin, and the
shape is maintained by robust,
closely spaced formers. The
corner joints are reinforced
with triangle stock balsa that
contributes to the model’s
overall strength. It has proven
to be up to the job, despite
high bending forces during
contest landings.
The longest parts on the
entire model are the fuselage
side panels, which measure 48
inches and can be cut from a
single sheet of commercially
available balsa. These must
be accurately cut to ensure
that the wing and canard
are properly aligned when
everything is fi nished.
Install the forward plywood
doublers by drawing a line
3/16 inch from the nose on
the inside of both side panels.
Align the tops of the doublers with the tops of each side panel
and the front of the doublers with the line.
The plywood doublers set the angle of incidence for the
canard after removing the excess balsa above them. The
triangle stock balsa does not extend forward of the plywood
doublers. It should also end 3/16 inch from the tail.
Cut relief into the upper triangle stock for the doublers.
Glue formers B, C, and all four Ds to both sides in a single
gluing step using a slow-curing epoxy. Apply clamps or rubber
bands around the fuselage sides at each former. Before curing,
place the fuselage upside down on the building board and
apply weight so the upper surfaces are aligned in the same
plane.
34 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 34 5/20/13 4:51 PM
The fuselage a er covering
shows main wing and
canard nylon bolts, wires
for elevators and spoiler,
towhook, and rudder linkage.
The right side of the main wing center section
shows the upper surface sheeting in place. The
sheeting overrides only one of the doubled ribs
at the dihedral break, leaving the other half of
the ribs to accept sheeting from the wingtip
panels.
Photos and illustrations by the author
The upper sheeting is installed before the lower sheeting
to allow the mounting surfaces for the wing and canard to
be completed. For CG purposes, the battery and rudder
servo are mounted in the aft compartment below the
vertical fi n.
The main wing is conventionally built with an I-beam
spar, D-tube sheeting ahead of the spar, and open bay
construction behind it. All sheeting is 1/16 balsa with spanwise
grain. The spar is full-depth to keep the caps as far apart
as possible.
Accordingly, the D-tube does not overlie the spar, but
merely butt-joins the forward sides of the spar caps top and
bottom. The sheer webs are vertical-grain balsa. The TE is
1-inch solid balsa. The spars can be spruce or carbon/balsa
laminates. Carbon/balsa is lighter. Use at least 0.014-inch
carbon on the center section and 0.007 on the tips.
The laminated spar must be wrapped in carbon or Kevlar
tow to prevent delamination under load. There is limited
sheeting behind the spar to provide ease of handling/
covering and additional rigidity.
Lower surface sheeting behind the spar is cut to fi t into
the bays between the ribs, spar, and TE. All upper surface
sheeting overlies the ribs and butt-joins the spar and TEs.
On the upper surface, the middle three bays and the bays
immediately adjacent to the dihedral breaks (seven bays) are
sheeted. On the lower surface, the middle three bays and
inboard bays adjacent to the dihedral breaks (fi ve bays) are
sheeted.
The canard is built as three separate pieces. These are buttjoined
together and the joints are reinforced with fi berglass.
The center section is sheeted top and bottom and can either
be permanently fi xed to the fuselage or removable.
Each outer panel uses a single lower spar and a fully
sheeted upper surface that serves as the upper spar. Only the
bays immediately adjacent to the center section are sheeted
on the lower surface using cross-grained balsa between the
ribs and spars. The bays ahead of the spar are sheeted with
3/8 wood and sanded to conform to the airfoil.
Actuation of the elevators is complicated by the fact that
they move in different planes. The preferred method is
to use small servos (Hitec HS-65 or equivalent) mounted
in each outer panel behind the lower spar in the bays
immediately outboard of the center section.
The servos are mounted at an angle with their arms
aligned parallel to their respective elevator hinge lines.
Actuation of the surfaces is by a short, straight link to the
control horns, which
are also aligned
permendicular to the
hinge line.
The servo wires pass
through small holes
into the center section of the canard. This setup requires
either a computer radio or a Y harness.
Fiberglass
reinforcement
of the butt
joints cannot
be omitted
and should
be carried out
one full bay on
either side of the
center section
to ensure loads
are transmitted
across the
surface skin
joints.
The wing
and canard
are mounted
using 1/4 x 20
nylon bolts
with threaded
maple blocks to
ensure accurate
placement.
In the fl ying
surfaces,
these bolts
pass through
unthreaded
mounting blocks
made from a
sandwich of
balsa capped with 1/32 plywood measuring 3/4 x 17/8 and
spanning the middle rib bays.
The plywood reinforces the lower surface sheeting in the
event that a bolt sheers and accepts the loads from the bolt
head. This sandwich is fl at on the top and bottom. Make the
sandwiches so that the top plywood surface comes up to the
top of the ribs but does not exceed their contour. Install the
blocks onto the lower surface sheeting.
Center and drill the bolt holes through the bottom of the
lower sheeting before the upper sheeting is installed. Do not
attempt to glue the upper surface sheeting to the blocks,
which should lie immediately below the sheeting. After the
www.ModelAviation.com JULY 2013 Model Aviation 35
033-037_MA0713_Canarrow.indd 35 5/20/13 4:52 PM
The fuselage’s main structure shows both sides, forward
plywood doublers, triangle stock corner reinforcement, 3/8 x
3/16-inch tail stock, and all of the formers.
The author launches his
fourth Canarrow at the
beginning of its second
full season.
upper surface sheeting is on, complete preparation
for the nylon mounting bolts by drilling from the
bottom of the wing through the upper surface
sheeting.
Install the nylon wing bolt from the top and cut
around the head of the bolt through the upper
sheeting. After removing the cutout skin, the head
of the bolt will pass though the enlarged hole to
seat squarely against the top of the mounting block
and fl ush with the skin.
The fi rst prototypes used the popular S3021
airfoil for all lifting surfaces. I later modifi ed the
airfoil for the wingtips and the canard to optimize it for the
lower Reynolds Numbers I encountered. The modifi ed airfoil
is slightly thinned and the point of maximum thickness has
been moved forward. All airfoil work and rib plotting was
done with Profi li2 software.
The vertical stabilizer is the simplest structure on the
model. The only thing not immediately obvious is that the
entire structure is sheeted in 1/32 vertical grain balsa.
The sheeting is primarily for CG reasons. The vertical
stabilizer is easily damaged without it. The main vertical post,
which mates with the aft end of the fuselage, must be spruce
or carbon-laminated balsa.
A pine nose block is best to resist damage. All four wingtips
and the canopy are carved from balsa. The receiver and
switch/charging jack go in the canopy area.
The fi nished model will balance with little or no extra
balancing weight. Flying weights have varied from a weightoptimized
35 ounces to a strength-maximized 41 ounces.
Flying
The balance point is 203/8 inches ahead of the fuselage end
point (as marked on the plans). Balanced at this point, the
model will fl y stably and predictably from the fi rst hand toss.
The back of the towhook should be 1/8 inch ahead of the
CG. The model will pull hard during launch at that point,
but it will remain stable and resist popping off the line.
The recommended control throws are 30° up/down for the
elevators and 45° left/right for the rudder.
The Canarrow is strong enough for a winch, but as with
any other wooden sailplane, it can only take so much abuse.
It really comes into its own on a hi-start. I have used the
Northeast Sailplane Products medium-size Pinnacle and the
slightly less-powerful Dynafl ite standard hi-starts. The model
will get a full launch from either. It should not require any
elevator input on the line.
In the air, the Canarrow fl ies as though it’s larger than a
Two-Meter Sailplane. Its 750 square inches of wing area
compares favorably with traditional wooden Two-Meter
aircraft such as the Goldberg Gentle Lady and Great Planes
Spirit, which have roughly 670 square inches of wing area.
Handling is conventional for an RES Sailplane. The large
vertical stabilizer makes it responsive and helps indicate lift.
It’s buoyant and ranges well.
The biggest difference between the Canarrow and a
conventional design is that pitch does not vary as much with
changes in speed. Small changes in pitch trim will change the
fl ying speed. The deck angle of the fuselage stays remarkably
fl at even while climbing in lift.
The model has a single spoiler on the main wing. Deploying
the spoiler causes the nose to pitch sharply up. The elevator
moves in the opposite direction from a conventional design
(the elevator moves up for a nose-down command and vice
versa).
Accordingly, the pitch compensation for spoiler deployment
is to also spoil the forward wing with a down-elevator
command. A linear program mix will keep the fuselage level.
The combination is effective for descent and spot landings.
The Canarrow is a fun and rewarding model that will bring
a smile to anyone who builds it.
—Daniel Fritz
[email protected]
See bonus photos and a parts list in this
month’s tablet app and on www.ModelAviation.com.
36 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 36 5/20/13 4:52 PM
SPECIFICaTIONS
Type:
RC Sailplane
Intermediate builder; intermediate pilot
112 inches
55 inches
40 ounces
Four channels, four Hitec HS-65HB servos
Balsa, plywood
Oracover
Skill level:
Wingspan:
Length:
Weight:
Radio:
Construction:
Finish:
The only things missing on the Canarrow are
control horns, linkages, and lettering on the tail.
The solid-mahogany spoiler panel is nished in
clear, water-based urethane. This model is built to
the speci cations of the plans in the article and
the parts were laser cut. www.ModelAviation.com JULY 2013 Model Aviation 37
033-037_MA0713_Canarrow.indd 37 5/20/13 4:52 PM
Edition: Model Aviation - 2013/07
Page Numbers: 33,34,35,36,37
For the last fi ve years, I have been developing
a two-meter canard sailplane called a
Canarrow. Despite its unconventional
appearance, the model is stable and easy to fl y. It
launches and fl ies conventionally.
The Canarrow is a good choice for a
developing sailplane enthusiast looking for
something unique with better performance than
a typical beginner’s ARF. The model employs
traditional construction techniques and fl atbottomed
airfoils for ease of building. It is strong
enough to survive typical beginner mishaps.
The forward surface is swept to protect it if the
model were to fl ip over on landing.
The design has its origins in a stick glider I
made in the early 1980s. Canards were in fashion
then. I was reminded of it when I decided to
build something for a beginner-oriented contest
series the Silent Order of Aeromodeling by
Radio (S.O.A.R.) holds each year that is limited
to rudder/elevator/spoiler (RES) and Two-Meter
models.
That had me thinking about the classic twometer
dilemma of wing area versus aspect
ratio. I fi gured the best way to have open-class
fi gures for each was to start with an open-class
wing. The idea was to chop off the outer panels,
leaving a 2-meter center section, and then
attach the severed tips to the fuselage in a lifting
confi guration.
Using the spoiler causes the nose to pitch sharply up. A program mix
will keep the fuselage level. Here the spoiler is deployed for landing.
by Daniel Fritz
www.ModelAviation.com JULY 2013 Model Aviation 33
033-037_MA0713_Canarrow.indd 33 5/28/13 1:03 PM
Top: The ve canard structures are complete except for upper surface sheeting and tip blocks. The lower
spars are spruce, and the elevator servo bays have been cut out. The elevators are made from 2-inch
aileron stock.
Bottom: A view from below of the canard’s structure shows the upper surface sheeting, elevator servo
bays, nylon bolt hole, and servo wire hole.
The main wing center section only lacks the upper surface sheeting. The spar is a carbon-balsa laminate
I-beam with carbon caps. The entire spar is wrapped with Kevlar tow to prevent delamination.
The Canarrow is technically a canard because pitch
stability and control are provided by a forward lifting
surface, but it is more correctly a tandem-wing airplane. The
CG is entirely between the two lifting surfaces.
If one were to reassemble the forward wings to the tips
of the main wing, the result would span 112 inches, offer
752 square inches of wing area, and have an aspect ratio of
roughly 17. Of course, things are not so simple and drag is
higher (there are twice as many tip vortices); nevertheless,
this concept has proven successful.
The tip vortices from the forward wing fl ow over the top
of the main wing at the dihedral breaks where some energy
is recaptured. Sweeping the forward wing proved successful
in protecting it, as it
did on the old stick
glider.
The forward wing
lies behind two lines
drawn from the nose
to the tips of the main
wing.
Assuming the
model lands on a fl at
surface, something
else must break before
the canard will. The
vertical stabilizer is
tall enough to protect
the canard when the
model is inverted.
Construction
The fuselage is a semimonocoque
in that most of
its strength comes from a
thin, 1/16-inch skin, and the
shape is maintained by robust,
closely spaced formers. The
corner joints are reinforced
with triangle stock balsa that
contributes to the model’s
overall strength. It has proven
to be up to the job, despite
high bending forces during
contest landings.
The longest parts on the
entire model are the fuselage
side panels, which measure 48
inches and can be cut from a
single sheet of commercially
available balsa. These must
be accurately cut to ensure
that the wing and canard
are properly aligned when
everything is fi nished.
Install the forward plywood
doublers by drawing a line
3/16 inch from the nose on
the inside of both side panels.
Align the tops of the doublers with the tops of each side panel
and the front of the doublers with the line.
The plywood doublers set the angle of incidence for the
canard after removing the excess balsa above them. The
triangle stock balsa does not extend forward of the plywood
doublers. It should also end 3/16 inch from the tail.
Cut relief into the upper triangle stock for the doublers.
Glue formers B, C, and all four Ds to both sides in a single
gluing step using a slow-curing epoxy. Apply clamps or rubber
bands around the fuselage sides at each former. Before curing,
place the fuselage upside down on the building board and
apply weight so the upper surfaces are aligned in the same
plane.
34 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 34 5/20/13 4:51 PM
The fuselage a er covering
shows main wing and
canard nylon bolts, wires
for elevators and spoiler,
towhook, and rudder linkage.
The right side of the main wing center section
shows the upper surface sheeting in place. The
sheeting overrides only one of the doubled ribs
at the dihedral break, leaving the other half of
the ribs to accept sheeting from the wingtip
panels.
Photos and illustrations by the author
The upper sheeting is installed before the lower sheeting
to allow the mounting surfaces for the wing and canard to
be completed. For CG purposes, the battery and rudder
servo are mounted in the aft compartment below the
vertical fi n.
The main wing is conventionally built with an I-beam
spar, D-tube sheeting ahead of the spar, and open bay
construction behind it. All sheeting is 1/16 balsa with spanwise
grain. The spar is full-depth to keep the caps as far apart
as possible.
Accordingly, the D-tube does not overlie the spar, but
merely butt-joins the forward sides of the spar caps top and
bottom. The sheer webs are vertical-grain balsa. The TE is
1-inch solid balsa. The spars can be spruce or carbon/balsa
laminates. Carbon/balsa is lighter. Use at least 0.014-inch
carbon on the center section and 0.007 on the tips.
The laminated spar must be wrapped in carbon or Kevlar
tow to prevent delamination under load. There is limited
sheeting behind the spar to provide ease of handling/
covering and additional rigidity.
Lower surface sheeting behind the spar is cut to fi t into
the bays between the ribs, spar, and TE. All upper surface
sheeting overlies the ribs and butt-joins the spar and TEs.
On the upper surface, the middle three bays and the bays
immediately adjacent to the dihedral breaks (seven bays) are
sheeted. On the lower surface, the middle three bays and
inboard bays adjacent to the dihedral breaks (fi ve bays) are
sheeted.
The canard is built as three separate pieces. These are buttjoined
together and the joints are reinforced with fi berglass.
The center section is sheeted top and bottom and can either
be permanently fi xed to the fuselage or removable.
Each outer panel uses a single lower spar and a fully
sheeted upper surface that serves as the upper spar. Only the
bays immediately adjacent to the center section are sheeted
on the lower surface using cross-grained balsa between the
ribs and spars. The bays ahead of the spar are sheeted with
3/8 wood and sanded to conform to the airfoil.
Actuation of the elevators is complicated by the fact that
they move in different planes. The preferred method is
to use small servos (Hitec HS-65 or equivalent) mounted
in each outer panel behind the lower spar in the bays
immediately outboard of the center section.
The servos are mounted at an angle with their arms
aligned parallel to their respective elevator hinge lines.
Actuation of the surfaces is by a short, straight link to the
control horns, which
are also aligned
permendicular to the
hinge line.
The servo wires pass
through small holes
into the center section of the canard. This setup requires
either a computer radio or a Y harness.
Fiberglass
reinforcement
of the butt
joints cannot
be omitted
and should
be carried out
one full bay on
either side of the
center section
to ensure loads
are transmitted
across the
surface skin
joints.
The wing
and canard
are mounted
using 1/4 x 20
nylon bolts
with threaded
maple blocks to
ensure accurate
placement.
In the fl ying
surfaces,
these bolts
pass through
unthreaded
mounting blocks
made from a
sandwich of
balsa capped with 1/32 plywood measuring 3/4 x 17/8 and
spanning the middle rib bays.
The plywood reinforces the lower surface sheeting in the
event that a bolt sheers and accepts the loads from the bolt
head. This sandwich is fl at on the top and bottom. Make the
sandwiches so that the top plywood surface comes up to the
top of the ribs but does not exceed their contour. Install the
blocks onto the lower surface sheeting.
Center and drill the bolt holes through the bottom of the
lower sheeting before the upper sheeting is installed. Do not
attempt to glue the upper surface sheeting to the blocks,
which should lie immediately below the sheeting. After the
www.ModelAviation.com JULY 2013 Model Aviation 35
033-037_MA0713_Canarrow.indd 35 5/20/13 4:52 PM
The fuselage’s main structure shows both sides, forward
plywood doublers, triangle stock corner reinforcement, 3/8 x
3/16-inch tail stock, and all of the formers.
The author launches his
fourth Canarrow at the
beginning of its second
full season.
upper surface sheeting is on, complete preparation
for the nylon mounting bolts by drilling from the
bottom of the wing through the upper surface
sheeting.
Install the nylon wing bolt from the top and cut
around the head of the bolt through the upper
sheeting. After removing the cutout skin, the head
of the bolt will pass though the enlarged hole to
seat squarely against the top of the mounting block
and fl ush with the skin.
The fi rst prototypes used the popular S3021
airfoil for all lifting surfaces. I later modifi ed the
airfoil for the wingtips and the canard to optimize it for the
lower Reynolds Numbers I encountered. The modifi ed airfoil
is slightly thinned and the point of maximum thickness has
been moved forward. All airfoil work and rib plotting was
done with Profi li2 software.
The vertical stabilizer is the simplest structure on the
model. The only thing not immediately obvious is that the
entire structure is sheeted in 1/32 vertical grain balsa.
The sheeting is primarily for CG reasons. The vertical
stabilizer is easily damaged without it. The main vertical post,
which mates with the aft end of the fuselage, must be spruce
or carbon-laminated balsa.
A pine nose block is best to resist damage. All four wingtips
and the canopy are carved from balsa. The receiver and
switch/charging jack go in the canopy area.
The fi nished model will balance with little or no extra
balancing weight. Flying weights have varied from a weightoptimized
35 ounces to a strength-maximized 41 ounces.
Flying
The balance point is 203/8 inches ahead of the fuselage end
point (as marked on the plans). Balanced at this point, the
model will fl y stably and predictably from the fi rst hand toss.
The back of the towhook should be 1/8 inch ahead of the
CG. The model will pull hard during launch at that point,
but it will remain stable and resist popping off the line.
The recommended control throws are 30° up/down for the
elevators and 45° left/right for the rudder.
The Canarrow is strong enough for a winch, but as with
any other wooden sailplane, it can only take so much abuse.
It really comes into its own on a hi-start. I have used the
Northeast Sailplane Products medium-size Pinnacle and the
slightly less-powerful Dynafl ite standard hi-starts. The model
will get a full launch from either. It should not require any
elevator input on the line.
In the air, the Canarrow fl ies as though it’s larger than a
Two-Meter Sailplane. Its 750 square inches of wing area
compares favorably with traditional wooden Two-Meter
aircraft such as the Goldberg Gentle Lady and Great Planes
Spirit, which have roughly 670 square inches of wing area.
Handling is conventional for an RES Sailplane. The large
vertical stabilizer makes it responsive and helps indicate lift.
It’s buoyant and ranges well.
The biggest difference between the Canarrow and a
conventional design is that pitch does not vary as much with
changes in speed. Small changes in pitch trim will change the
fl ying speed. The deck angle of the fuselage stays remarkably
fl at even while climbing in lift.
The model has a single spoiler on the main wing. Deploying
the spoiler causes the nose to pitch sharply up. The elevator
moves in the opposite direction from a conventional design
(the elevator moves up for a nose-down command and vice
versa).
Accordingly, the pitch compensation for spoiler deployment
is to also spoil the forward wing with a down-elevator
command. A linear program mix will keep the fuselage level.
The combination is effective for descent and spot landings.
The Canarrow is a fun and rewarding model that will bring
a smile to anyone who builds it.
—Daniel Fritz
[email protected]
See bonus photos and a parts list in this
month’s tablet app and on www.ModelAviation.com.
36 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 36 5/20/13 4:52 PM
SPECIFICaTIONS
Type:
RC Sailplane
Intermediate builder; intermediate pilot
112 inches
55 inches
40 ounces
Four channels, four Hitec HS-65HB servos
Balsa, plywood
Oracover
Skill level:
Wingspan:
Length:
Weight:
Radio:
Construction:
Finish:
The only things missing on the Canarrow are
control horns, linkages, and lettering on the tail.
The solid-mahogany spoiler panel is nished in
clear, water-based urethane. This model is built to
the speci cations of the plans in the article and
the parts were laser cut. www.ModelAviation.com JULY 2013 Model Aviation 37
033-037_MA0713_Canarrow.indd 37 5/20/13 4:52 PM
Edition: Model Aviation - 2013/07
Page Numbers: 33,34,35,36,37
For the last fi ve years, I have been developing
a two-meter canard sailplane called a
Canarrow. Despite its unconventional
appearance, the model is stable and easy to fl y. It
launches and fl ies conventionally.
The Canarrow is a good choice for a
developing sailplane enthusiast looking for
something unique with better performance than
a typical beginner’s ARF. The model employs
traditional construction techniques and fl atbottomed
airfoils for ease of building. It is strong
enough to survive typical beginner mishaps.
The forward surface is swept to protect it if the
model were to fl ip over on landing.
The design has its origins in a stick glider I
made in the early 1980s. Canards were in fashion
then. I was reminded of it when I decided to
build something for a beginner-oriented contest
series the Silent Order of Aeromodeling by
Radio (S.O.A.R.) holds each year that is limited
to rudder/elevator/spoiler (RES) and Two-Meter
models.
That had me thinking about the classic twometer
dilemma of wing area versus aspect
ratio. I fi gured the best way to have open-class
fi gures for each was to start with an open-class
wing. The idea was to chop off the outer panels,
leaving a 2-meter center section, and then
attach the severed tips to the fuselage in a lifting
confi guration.
Using the spoiler causes the nose to pitch sharply up. A program mix
will keep the fuselage level. Here the spoiler is deployed for landing.
by Daniel Fritz
www.ModelAviation.com JULY 2013 Model Aviation 33
033-037_MA0713_Canarrow.indd 33 5/28/13 1:03 PM
Top: The ve canard structures are complete except for upper surface sheeting and tip blocks. The lower
spars are spruce, and the elevator servo bays have been cut out. The elevators are made from 2-inch
aileron stock.
Bottom: A view from below of the canard’s structure shows the upper surface sheeting, elevator servo
bays, nylon bolt hole, and servo wire hole.
The main wing center section only lacks the upper surface sheeting. The spar is a carbon-balsa laminate
I-beam with carbon caps. The entire spar is wrapped with Kevlar tow to prevent delamination.
The Canarrow is technically a canard because pitch
stability and control are provided by a forward lifting
surface, but it is more correctly a tandem-wing airplane. The
CG is entirely between the two lifting surfaces.
If one were to reassemble the forward wings to the tips
of the main wing, the result would span 112 inches, offer
752 square inches of wing area, and have an aspect ratio of
roughly 17. Of course, things are not so simple and drag is
higher (there are twice as many tip vortices); nevertheless,
this concept has proven successful.
The tip vortices from the forward wing fl ow over the top
of the main wing at the dihedral breaks where some energy
is recaptured. Sweeping the forward wing proved successful
in protecting it, as it
did on the old stick
glider.
The forward wing
lies behind two lines
drawn from the nose
to the tips of the main
wing.
Assuming the
model lands on a fl at
surface, something
else must break before
the canard will. The
vertical stabilizer is
tall enough to protect
the canard when the
model is inverted.
Construction
The fuselage is a semimonocoque
in that most of
its strength comes from a
thin, 1/16-inch skin, and the
shape is maintained by robust,
closely spaced formers. The
corner joints are reinforced
with triangle stock balsa that
contributes to the model’s
overall strength. It has proven
to be up to the job, despite
high bending forces during
contest landings.
The longest parts on the
entire model are the fuselage
side panels, which measure 48
inches and can be cut from a
single sheet of commercially
available balsa. These must
be accurately cut to ensure
that the wing and canard
are properly aligned when
everything is fi nished.
Install the forward plywood
doublers by drawing a line
3/16 inch from the nose on
the inside of both side panels.
Align the tops of the doublers with the tops of each side panel
and the front of the doublers with the line.
The plywood doublers set the angle of incidence for the
canard after removing the excess balsa above them. The
triangle stock balsa does not extend forward of the plywood
doublers. It should also end 3/16 inch from the tail.
Cut relief into the upper triangle stock for the doublers.
Glue formers B, C, and all four Ds to both sides in a single
gluing step using a slow-curing epoxy. Apply clamps or rubber
bands around the fuselage sides at each former. Before curing,
place the fuselage upside down on the building board and
apply weight so the upper surfaces are aligned in the same
plane.
34 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 34 5/20/13 4:51 PM
The fuselage a er covering
shows main wing and
canard nylon bolts, wires
for elevators and spoiler,
towhook, and rudder linkage.
The right side of the main wing center section
shows the upper surface sheeting in place. The
sheeting overrides only one of the doubled ribs
at the dihedral break, leaving the other half of
the ribs to accept sheeting from the wingtip
panels.
Photos and illustrations by the author
The upper sheeting is installed before the lower sheeting
to allow the mounting surfaces for the wing and canard to
be completed. For CG purposes, the battery and rudder
servo are mounted in the aft compartment below the
vertical fi n.
The main wing is conventionally built with an I-beam
spar, D-tube sheeting ahead of the spar, and open bay
construction behind it. All sheeting is 1/16 balsa with spanwise
grain. The spar is full-depth to keep the caps as far apart
as possible.
Accordingly, the D-tube does not overlie the spar, but
merely butt-joins the forward sides of the spar caps top and
bottom. The sheer webs are vertical-grain balsa. The TE is
1-inch solid balsa. The spars can be spruce or carbon/balsa
laminates. Carbon/balsa is lighter. Use at least 0.014-inch
carbon on the center section and 0.007 on the tips.
The laminated spar must be wrapped in carbon or Kevlar
tow to prevent delamination under load. There is limited
sheeting behind the spar to provide ease of handling/
covering and additional rigidity.
Lower surface sheeting behind the spar is cut to fi t into
the bays between the ribs, spar, and TE. All upper surface
sheeting overlies the ribs and butt-joins the spar and TEs.
On the upper surface, the middle three bays and the bays
immediately adjacent to the dihedral breaks (seven bays) are
sheeted. On the lower surface, the middle three bays and
inboard bays adjacent to the dihedral breaks (fi ve bays) are
sheeted.
The canard is built as three separate pieces. These are buttjoined
together and the joints are reinforced with fi berglass.
The center section is sheeted top and bottom and can either
be permanently fi xed to the fuselage or removable.
Each outer panel uses a single lower spar and a fully
sheeted upper surface that serves as the upper spar. Only the
bays immediately adjacent to the center section are sheeted
on the lower surface using cross-grained balsa between the
ribs and spars. The bays ahead of the spar are sheeted with
3/8 wood and sanded to conform to the airfoil.
Actuation of the elevators is complicated by the fact that
they move in different planes. The preferred method is
to use small servos (Hitec HS-65 or equivalent) mounted
in each outer panel behind the lower spar in the bays
immediately outboard of the center section.
The servos are mounted at an angle with their arms
aligned parallel to their respective elevator hinge lines.
Actuation of the surfaces is by a short, straight link to the
control horns, which
are also aligned
permendicular to the
hinge line.
The servo wires pass
through small holes
into the center section of the canard. This setup requires
either a computer radio or a Y harness.
Fiberglass
reinforcement
of the butt
joints cannot
be omitted
and should
be carried out
one full bay on
either side of the
center section
to ensure loads
are transmitted
across the
surface skin
joints.
The wing
and canard
are mounted
using 1/4 x 20
nylon bolts
with threaded
maple blocks to
ensure accurate
placement.
In the fl ying
surfaces,
these bolts
pass through
unthreaded
mounting blocks
made from a
sandwich of
balsa capped with 1/32 plywood measuring 3/4 x 17/8 and
spanning the middle rib bays.
The plywood reinforces the lower surface sheeting in the
event that a bolt sheers and accepts the loads from the bolt
head. This sandwich is fl at on the top and bottom. Make the
sandwiches so that the top plywood surface comes up to the
top of the ribs but does not exceed their contour. Install the
blocks onto the lower surface sheeting.
Center and drill the bolt holes through the bottom of the
lower sheeting before the upper sheeting is installed. Do not
attempt to glue the upper surface sheeting to the blocks,
which should lie immediately below the sheeting. After the
www.ModelAviation.com JULY 2013 Model Aviation 35
033-037_MA0713_Canarrow.indd 35 5/20/13 4:52 PM
The fuselage’s main structure shows both sides, forward
plywood doublers, triangle stock corner reinforcement, 3/8 x
3/16-inch tail stock, and all of the formers.
The author launches his
fourth Canarrow at the
beginning of its second
full season.
upper surface sheeting is on, complete preparation
for the nylon mounting bolts by drilling from the
bottom of the wing through the upper surface
sheeting.
Install the nylon wing bolt from the top and cut
around the head of the bolt through the upper
sheeting. After removing the cutout skin, the head
of the bolt will pass though the enlarged hole to
seat squarely against the top of the mounting block
and fl ush with the skin.
The fi rst prototypes used the popular S3021
airfoil for all lifting surfaces. I later modifi ed the
airfoil for the wingtips and the canard to optimize it for the
lower Reynolds Numbers I encountered. The modifi ed airfoil
is slightly thinned and the point of maximum thickness has
been moved forward. All airfoil work and rib plotting was
done with Profi li2 software.
The vertical stabilizer is the simplest structure on the
model. The only thing not immediately obvious is that the
entire structure is sheeted in 1/32 vertical grain balsa.
The sheeting is primarily for CG reasons. The vertical
stabilizer is easily damaged without it. The main vertical post,
which mates with the aft end of the fuselage, must be spruce
or carbon-laminated balsa.
A pine nose block is best to resist damage. All four wingtips
and the canopy are carved from balsa. The receiver and
switch/charging jack go in the canopy area.
The fi nished model will balance with little or no extra
balancing weight. Flying weights have varied from a weightoptimized
35 ounces to a strength-maximized 41 ounces.
Flying
The balance point is 203/8 inches ahead of the fuselage end
point (as marked on the plans). Balanced at this point, the
model will fl y stably and predictably from the fi rst hand toss.
The back of the towhook should be 1/8 inch ahead of the
CG. The model will pull hard during launch at that point,
but it will remain stable and resist popping off the line.
The recommended control throws are 30° up/down for the
elevators and 45° left/right for the rudder.
The Canarrow is strong enough for a winch, but as with
any other wooden sailplane, it can only take so much abuse.
It really comes into its own on a hi-start. I have used the
Northeast Sailplane Products medium-size Pinnacle and the
slightly less-powerful Dynafl ite standard hi-starts. The model
will get a full launch from either. It should not require any
elevator input on the line.
In the air, the Canarrow fl ies as though it’s larger than a
Two-Meter Sailplane. Its 750 square inches of wing area
compares favorably with traditional wooden Two-Meter
aircraft such as the Goldberg Gentle Lady and Great Planes
Spirit, which have roughly 670 square inches of wing area.
Handling is conventional for an RES Sailplane. The large
vertical stabilizer makes it responsive and helps indicate lift.
It’s buoyant and ranges well.
The biggest difference between the Canarrow and a
conventional design is that pitch does not vary as much with
changes in speed. Small changes in pitch trim will change the
fl ying speed. The deck angle of the fuselage stays remarkably
fl at even while climbing in lift.
The model has a single spoiler on the main wing. Deploying
the spoiler causes the nose to pitch sharply up. The elevator
moves in the opposite direction from a conventional design
(the elevator moves up for a nose-down command and vice
versa).
Accordingly, the pitch compensation for spoiler deployment
is to also spoil the forward wing with a down-elevator
command. A linear program mix will keep the fuselage level.
The combination is effective for descent and spot landings.
The Canarrow is a fun and rewarding model that will bring
a smile to anyone who builds it.
—Daniel Fritz
[email protected]
See bonus photos and a parts list in this
month’s tablet app and on www.ModelAviation.com.
36 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 36 5/20/13 4:52 PM
SPECIFICaTIONS
Type:
RC Sailplane
Intermediate builder; intermediate pilot
112 inches
55 inches
40 ounces
Four channels, four Hitec HS-65HB servos
Balsa, plywood
Oracover
Skill level:
Wingspan:
Length:
Weight:
Radio:
Construction:
Finish:
The only things missing on the Canarrow are
control horns, linkages, and lettering on the tail.
The solid-mahogany spoiler panel is nished in
clear, water-based urethane. This model is built to
the speci cations of the plans in the article and
the parts were laser cut. www.ModelAviation.com JULY 2013 Model Aviation 37
033-037_MA0713_Canarrow.indd 37 5/20/13 4:52 PM
Edition: Model Aviation - 2013/07
Page Numbers: 33,34,35,36,37
For the last fi ve years, I have been developing
a two-meter canard sailplane called a
Canarrow. Despite its unconventional
appearance, the model is stable and easy to fl y. It
launches and fl ies conventionally.
The Canarrow is a good choice for a
developing sailplane enthusiast looking for
something unique with better performance than
a typical beginner’s ARF. The model employs
traditional construction techniques and fl atbottomed
airfoils for ease of building. It is strong
enough to survive typical beginner mishaps.
The forward surface is swept to protect it if the
model were to fl ip over on landing.
The design has its origins in a stick glider I
made in the early 1980s. Canards were in fashion
then. I was reminded of it when I decided to
build something for a beginner-oriented contest
series the Silent Order of Aeromodeling by
Radio (S.O.A.R.) holds each year that is limited
to rudder/elevator/spoiler (RES) and Two-Meter
models.
That had me thinking about the classic twometer
dilemma of wing area versus aspect
ratio. I fi gured the best way to have open-class
fi gures for each was to start with an open-class
wing. The idea was to chop off the outer panels,
leaving a 2-meter center section, and then
attach the severed tips to the fuselage in a lifting
confi guration.
Using the spoiler causes the nose to pitch sharply up. A program mix
will keep the fuselage level. Here the spoiler is deployed for landing.
by Daniel Fritz
www.ModelAviation.com JULY 2013 Model Aviation 33
033-037_MA0713_Canarrow.indd 33 5/28/13 1:03 PM
Top: The ve canard structures are complete except for upper surface sheeting and tip blocks. The lower
spars are spruce, and the elevator servo bays have been cut out. The elevators are made from 2-inch
aileron stock.
Bottom: A view from below of the canard’s structure shows the upper surface sheeting, elevator servo
bays, nylon bolt hole, and servo wire hole.
The main wing center section only lacks the upper surface sheeting. The spar is a carbon-balsa laminate
I-beam with carbon caps. The entire spar is wrapped with Kevlar tow to prevent delamination.
The Canarrow is technically a canard because pitch
stability and control are provided by a forward lifting
surface, but it is more correctly a tandem-wing airplane. The
CG is entirely between the two lifting surfaces.
If one were to reassemble the forward wings to the tips
of the main wing, the result would span 112 inches, offer
752 square inches of wing area, and have an aspect ratio of
roughly 17. Of course, things are not so simple and drag is
higher (there are twice as many tip vortices); nevertheless,
this concept has proven successful.
The tip vortices from the forward wing fl ow over the top
of the main wing at the dihedral breaks where some energy
is recaptured. Sweeping the forward wing proved successful
in protecting it, as it
did on the old stick
glider.
The forward wing
lies behind two lines
drawn from the nose
to the tips of the main
wing.
Assuming the
model lands on a fl at
surface, something
else must break before
the canard will. The
vertical stabilizer is
tall enough to protect
the canard when the
model is inverted.
Construction
The fuselage is a semimonocoque
in that most of
its strength comes from a
thin, 1/16-inch skin, and the
shape is maintained by robust,
closely spaced formers. The
corner joints are reinforced
with triangle stock balsa that
contributes to the model’s
overall strength. It has proven
to be up to the job, despite
high bending forces during
contest landings.
The longest parts on the
entire model are the fuselage
side panels, which measure 48
inches and can be cut from a
single sheet of commercially
available balsa. These must
be accurately cut to ensure
that the wing and canard
are properly aligned when
everything is fi nished.
Install the forward plywood
doublers by drawing a line
3/16 inch from the nose on
the inside of both side panels.
Align the tops of the doublers with the tops of each side panel
and the front of the doublers with the line.
The plywood doublers set the angle of incidence for the
canard after removing the excess balsa above them. The
triangle stock balsa does not extend forward of the plywood
doublers. It should also end 3/16 inch from the tail.
Cut relief into the upper triangle stock for the doublers.
Glue formers B, C, and all four Ds to both sides in a single
gluing step using a slow-curing epoxy. Apply clamps or rubber
bands around the fuselage sides at each former. Before curing,
place the fuselage upside down on the building board and
apply weight so the upper surfaces are aligned in the same
plane.
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The fuselage a er covering
shows main wing and
canard nylon bolts, wires
for elevators and spoiler,
towhook, and rudder linkage.
The right side of the main wing center section
shows the upper surface sheeting in place. The
sheeting overrides only one of the doubled ribs
at the dihedral break, leaving the other half of
the ribs to accept sheeting from the wingtip
panels.
Photos and illustrations by the author
The upper sheeting is installed before the lower sheeting
to allow the mounting surfaces for the wing and canard to
be completed. For CG purposes, the battery and rudder
servo are mounted in the aft compartment below the
vertical fi n.
The main wing is conventionally built with an I-beam
spar, D-tube sheeting ahead of the spar, and open bay
construction behind it. All sheeting is 1/16 balsa with spanwise
grain. The spar is full-depth to keep the caps as far apart
as possible.
Accordingly, the D-tube does not overlie the spar, but
merely butt-joins the forward sides of the spar caps top and
bottom. The sheer webs are vertical-grain balsa. The TE is
1-inch solid balsa. The spars can be spruce or carbon/balsa
laminates. Carbon/balsa is lighter. Use at least 0.014-inch
carbon on the center section and 0.007 on the tips.
The laminated spar must be wrapped in carbon or Kevlar
tow to prevent delamination under load. There is limited
sheeting behind the spar to provide ease of handling/
covering and additional rigidity.
Lower surface sheeting behind the spar is cut to fi t into
the bays between the ribs, spar, and TE. All upper surface
sheeting overlies the ribs and butt-joins the spar and TEs.
On the upper surface, the middle three bays and the bays
immediately adjacent to the dihedral breaks (seven bays) are
sheeted. On the lower surface, the middle three bays and
inboard bays adjacent to the dihedral breaks (fi ve bays) are
sheeted.
The canard is built as three separate pieces. These are buttjoined
together and the joints are reinforced with fi berglass.
The center section is sheeted top and bottom and can either
be permanently fi xed to the fuselage or removable.
Each outer panel uses a single lower spar and a fully
sheeted upper surface that serves as the upper spar. Only the
bays immediately adjacent to the center section are sheeted
on the lower surface using cross-grained balsa between the
ribs and spars. The bays ahead of the spar are sheeted with
3/8 wood and sanded to conform to the airfoil.
Actuation of the elevators is complicated by the fact that
they move in different planes. The preferred method is
to use small servos (Hitec HS-65 or equivalent) mounted
in each outer panel behind the lower spar in the bays
immediately outboard of the center section.
The servos are mounted at an angle with their arms
aligned parallel to their respective elevator hinge lines.
Actuation of the surfaces is by a short, straight link to the
control horns, which
are also aligned
permendicular to the
hinge line.
The servo wires pass
through small holes
into the center section of the canard. This setup requires
either a computer radio or a Y harness.
Fiberglass
reinforcement
of the butt
joints cannot
be omitted
and should
be carried out
one full bay on
either side of the
center section
to ensure loads
are transmitted
across the
surface skin
joints.
The wing
and canard
are mounted
using 1/4 x 20
nylon bolts
with threaded
maple blocks to
ensure accurate
placement.
In the fl ying
surfaces,
these bolts
pass through
unthreaded
mounting blocks
made from a
sandwich of
balsa capped with 1/32 plywood measuring 3/4 x 17/8 and
spanning the middle rib bays.
The plywood reinforces the lower surface sheeting in the
event that a bolt sheers and accepts the loads from the bolt
head. This sandwich is fl at on the top and bottom. Make the
sandwiches so that the top plywood surface comes up to the
top of the ribs but does not exceed their contour. Install the
blocks onto the lower surface sheeting.
Center and drill the bolt holes through the bottom of the
lower sheeting before the upper sheeting is installed. Do not
attempt to glue the upper surface sheeting to the blocks,
which should lie immediately below the sheeting. After the
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The fuselage’s main structure shows both sides, forward
plywood doublers, triangle stock corner reinforcement, 3/8 x
3/16-inch tail stock, and all of the formers.
The author launches his
fourth Canarrow at the
beginning of its second
full season.
upper surface sheeting is on, complete preparation
for the nylon mounting bolts by drilling from the
bottom of the wing through the upper surface
sheeting.
Install the nylon wing bolt from the top and cut
around the head of the bolt through the upper
sheeting. After removing the cutout skin, the head
of the bolt will pass though the enlarged hole to
seat squarely against the top of the mounting block
and fl ush with the skin.
The fi rst prototypes used the popular S3021
airfoil for all lifting surfaces. I later modifi ed the
airfoil for the wingtips and the canard to optimize it for the
lower Reynolds Numbers I encountered. The modifi ed airfoil
is slightly thinned and the point of maximum thickness has
been moved forward. All airfoil work and rib plotting was
done with Profi li2 software.
The vertical stabilizer is the simplest structure on the
model. The only thing not immediately obvious is that the
entire structure is sheeted in 1/32 vertical grain balsa.
The sheeting is primarily for CG reasons. The vertical
stabilizer is easily damaged without it. The main vertical post,
which mates with the aft end of the fuselage, must be spruce
or carbon-laminated balsa.
A pine nose block is best to resist damage. All four wingtips
and the canopy are carved from balsa. The receiver and
switch/charging jack go in the canopy area.
The fi nished model will balance with little or no extra
balancing weight. Flying weights have varied from a weightoptimized
35 ounces to a strength-maximized 41 ounces.
Flying
The balance point is 203/8 inches ahead of the fuselage end
point (as marked on the plans). Balanced at this point, the
model will fl y stably and predictably from the fi rst hand toss.
The back of the towhook should be 1/8 inch ahead of the
CG. The model will pull hard during launch at that point,
but it will remain stable and resist popping off the line.
The recommended control throws are 30° up/down for the
elevators and 45° left/right for the rudder.
The Canarrow is strong enough for a winch, but as with
any other wooden sailplane, it can only take so much abuse.
It really comes into its own on a hi-start. I have used the
Northeast Sailplane Products medium-size Pinnacle and the
slightly less-powerful Dynafl ite standard hi-starts. The model
will get a full launch from either. It should not require any
elevator input on the line.
In the air, the Canarrow fl ies as though it’s larger than a
Two-Meter Sailplane. Its 750 square inches of wing area
compares favorably with traditional wooden Two-Meter
aircraft such as the Goldberg Gentle Lady and Great Planes
Spirit, which have roughly 670 square inches of wing area.
Handling is conventional for an RES Sailplane. The large
vertical stabilizer makes it responsive and helps indicate lift.
It’s buoyant and ranges well.
The biggest difference between the Canarrow and a
conventional design is that pitch does not vary as much with
changes in speed. Small changes in pitch trim will change the
fl ying speed. The deck angle of the fuselage stays remarkably
fl at even while climbing in lift.
The model has a single spoiler on the main wing. Deploying
the spoiler causes the nose to pitch sharply up. The elevator
moves in the opposite direction from a conventional design
(the elevator moves up for a nose-down command and vice
versa).
Accordingly, the pitch compensation for spoiler deployment
is to also spoil the forward wing with a down-elevator
command. A linear program mix will keep the fuselage level.
The combination is effective for descent and spot landings.
The Canarrow is a fun and rewarding model that will bring
a smile to anyone who builds it.
—Daniel Fritz
[email protected]
See bonus photos and a parts list in this
month’s tablet app and on www.ModelAviation.com.
36 Model Aviation JULY 2013 www.ModelAviation.com
033-037_MA0713_Canarrow.indd 36 5/20/13 4:52 PM
SPECIFICaTIONS
Type:
RC Sailplane
Intermediate builder; intermediate pilot
112 inches
55 inches
40 ounces
Four channels, four Hitec HS-65HB servos
Balsa, plywood
Oracover
Skill level:
Wingspan:
Length:
Weight:
Radio:
Construction:
Finish:
The only things missing on the Canarrow are
control horns, linkages, and lettering on the tail.
The solid-mahogany spoiler panel is nished in
clear, water-based urethane. This model is built to
the speci cations of the plans in the article and
the parts were laser cut. www.ModelAviation.com JULY 2013 Model Aviation 37
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