Ellipsix - 2010/04

ApriAl 2p0ri1l 02 0 2170 27
Clean, curvy lines make this model an attractive choice for Catapult Glider. The day-glow
orange wingtips help find it at the field.
Lead
by Don DeLoach
This design provides
loads of enjoyment
for a bare-minimum
investment, and it
represents a perfect
introduction to FF
competition. Ellipsix
THE BEST THING about competition FF
is the wide variety of model types and sizes.
There are glow-powered gas aircraft that
span 10 feet and Indoor Rubber airplanes
that are as little as paper clips. Somewhere
between those extremes is handheld Outdoor
Catapult Glider (AMA event 142).
These models are compact, quick to
build, inexpensive, and easy to fly. In the
time-and-money-per-unit-of-fun department,
no event delivers as Catapult Glider does.
For the beginner, these aircraft are a
perfect entry point for experiencing the joys
of FF. Best of all, they can be made to fly
great with little experience or expertise on
the part of the builder.
Balsa for FF: Let’s start with wood
selection. Balsa varies widely in density,
from as much as 15 to as few as 4 pounds per
cubic foot. In FF, light balsa is crucial for top
performance, because our models are
generally smaller and less tolerant of high
wing loadings than the average 10-pound RC
aircraft.
In FF, we’re after the least-dense balsa
available. This is known in the industry as
“contest grade,” and it’s 6 pounds per square
foot and less. That is approximately half the
density of average balsa in a hobby shop or
RC kit.
I hope you have a good local hobby shop
with a decent selection of balsa and can take
time to sort through it. If not, mail-order
your wood from Mountain Models in
Colorado Springs. (Contact information is in
the source list at the end of this article.)
Owner Brian Eberwein weighs and sorts
every sheet of wood he receives from his
suppliers. When you buy a piece of “Contest”
balsa from Brian, you can be certain that it is
6 pounds per cubic foot in density or less.
CONSTRUCTION
For the wing, you’ll need one piece of
contest 3/16 balsa that is at least 31/2 x 18
inches. For the fin and horizontal stabilizer,
you’ll need roughly 8 inches of 1/16 x 3-inchwidth
balsa. The wood for the fin and
stabilizer should also be in the contest-density
range.
C-grain wood is preferable for all flight
surfaces, because it is the most warp-resistant.
It looks mottled, like mother-of-pearl, whereas
A- and B-grain have much straighter, parallel
grain patterns. It’s rare to find C-grain in
hobby shops, but you will if you sort through
enough sheets.
Above all, do not use balsa that is even
the slightest bit twisted. Catapult Gliders fly
extremely fast in the climb and cannot
tolerate warps.
Get your
hands on this
easy-to-build
FF Catapult
Glider
04sig1_00MSTRPG.QXD 2/23/10 9:06 AM Page 27
28 MODEL AVIATION
28 MODEL AVIATION
Above: Left front of nose area shows viscous-fluid badge timer
engaged with spring-loaded hold-on line. As the spring relaxes it
moves timer to roughly the 12:30 position, releasing the line and
engaging the DT. This causes the model to “parachute” down
from thermals at approximately 10 feet/second.
Left: The wing bottom is sprayed with Flat Black Design Master
spray paint, which is virtually weightless and greatly aids in-flight
visibility.
Underside of left wing shows small balsa washin wedge
th at is cr iti c al to t he G lider ’s t r i m . Th e w e dg e
provides additional left wing lift needed to prevent the
Ellipsix from spinning in during glide.
The rear grip is made from 1/32 birch plywood and a small plastic pinhead.
Notice pinholes in plywood where it meets carbon boom; this significantly
strengthens a CA bond.
Rear of the model shows slight stabilizer tilt (left tip high) that produces a left glide circle. Without stabilizer tilt, the airplane would
glide in a straight line and not stay centered in thermal lift.
04sig1_00MSTRPG.QXD 2/23/10 9:07 AM Page 28
April 2010 29
Top: The pop-up
tailboom DT is now
ubiquitous on small FF
Gliders. A 1/8-inch rivet
acts as a removable
hinge pin and tailboom
lifts via two #8 rubber
bands.
Above: Underside
shows the 1/8-inch rivet
hinge pin, 1/32 plywood
launching hook, and
.009-inch music-wire
DT spring in relaxed
position.
Left: A trio of Ellipsix
models can easily be
built in a week of
evenings. AMA FF
Catapult Glider rules
allow up to three
gliders per competitor
per contest.
Photos by the author
Ellipsix
April 2010 29
Type: AMA (event 142) FF handheld
Catapult Glider
Skill level: Suitable for beginners
Wingspan (flat): 18 inches
Wingspan (projected): 16.3 inches
Wing area: 50 square inches
(projected)
Length: 18 inches
Weight range: 0.7-0.9 ounces
Wing loading: 2.3 ounces/square foot
Power: 7- to 9-inch loop of 1/4 x .042-
inch FAI Tan rubber, on 6-inch handle
Construction: Balsa, plywood, tubular
carbon tailboom
Finish: Nitrate dope or Minwax
Helmsman Spar Urethane
Cost to construct: $5-$10 in
materials, $10-15 DT timer
Time to construct: Four to six hours
(two evenings)
Flight Duration:
Two-minute
maximums
(“maxes”)
in competition
04sig1_00MSTRPG.QXD 2/23/10 9:09 AM Page 29
34 MODEL AVIATION
Others like to mix a small amount of
talcum power with the dope, for a sanding
sealer effect. Still others use a light coat of
clear Minwax polyurethane, mostly smeared
off with a paper towel.
Use your favorite finishing method, but
don’t forget to color the model for visibility. I
like Design Master spray paint from the
Michael’s chain of craft stores. It is extremely
bright and weighs next to nothing.
Design Master “Carnation Red” and
“Holiday Red” are excellent choices for the
top surfaces. For the underside of the wings, a
coat of Design Master “Flat Black” will
greatly aid in-flight visibility, especially on
cloudy days.
Final Touches: After tending to a few more
details, we’ll be ready to test-fly.
Securely attach the 1/32 plywood launching
and rear hooks with thin CA. Attach a 1/32
plywood doubler to one side of the nose. This
will give the nose area extra durability and
strength. Test your DT operation on the
ground several times, to make sure that it is
working reliably.
Turn your attention to rigging the
Spiderwire hold-down line that extends to the
timer. The line should capture the front portion
of the carbon tailboom and lock it into position
under the midchord point under the wing.
Now route the line back to the TE and up
over the top surface of the wing. Attach a 2- to
3-inch loop of the elastic thread that is
supplied with the timer, and experiment with
tension on the timer.
Ideally, you want the timer to rotate
approximately a half revolution in slightly
more than two minutes. This is perfect for the
two-minute “maxes” flown in Catapult Glider
competitions.
A better alternative to the elastic thread is a
metal spring. These are available from Stan
Buddenbohm, or you can wind one using .009
music wire on a .078 mandrel. Springs are
consistent across all temperatures and don’t
dry out and weaken with time, as does elastic.
Test the timer several times on the ground,
making sure that the tailboom is locked up
solidly under tension and that each timer
release results in the wing popping up every
time. If the tailboom is binding in the hinge
assembly, sand it a bit narrower or increase the
rubber band tension. DTs must work every
time; otherwise, they are simply an
aggravation.
Last, don’t forget the 1/16 balsa washin
wedge glued on the left main wing panel. This
is crucial, because it keeps the model from
spinning in to the left in the event of a
nosedive or turbulent air. The Ellipsix, as do
most Catapult Gliders, uses little incidence and
a rearward CG, so careful trimming is a must.
Flying: Balance your model at 55% per the
plans and head to the test field. Do a couple of
hand glides and observe the aircraft’s
tendencies. If it is stallish, take out some
incidence via the tailboom adjustment screw.
If the Glider dives, add incidence until the
nose comes up and it is near a stall. What you
are after is a nice floating glide on the verge of
a stall, with a left glide circle that is roughly
50-75 feet in diameter.
In preparation for the maiden catapult
launch, bend in a small amount of left rudder
(approximately 1/32-1/20). Set the DT to five to
10 seconds and hook up the Ellipsix to the
rubber.
Pull back all the way (that’s right—full
power). Bank the model 45° to the right
(holding the launch stick in your left hand),
and pitch the nose 45° up. Let go and observe
the flight path. Chances are, you will see the
Glider pitch up to nearly vertical while doing
the desired wide left roll, transitioning to the
glide at close to 100 feet.
Rolling the aircraft on launch burns a little
energy that could otherwise be used for
altitude gain, but a consistent transition is more
important than 10% or 20% more altitude.
The left rudder controls this left launch roll.
If you are feeling brave as you continue
trimming, you can take out some left rudder
and incidence until the model launches nearly
vertical with little or no roll.
Be prepared for spotty transitions and the
occasional death dive. The Ellipsix will go
higher this way, however.
Anytime you make an incidence change,
you must retrim the glide using CG shift. It is
that simple. And if your Glider won’t
transition well no matter what you do, add a bit
of clay to the left wingtip.
Trimming a Catapult Glider for top
performance is an individualized process.
That’s because your arm span and length of
rubber loop determine how much power you
have at launch.
Long-armed fliers are at an advantage. But
what is more important is that your rubber loop
is short enough to be near breaking when it is
in full launch extension.
The 9-inch maximum loop that the AMA
rules allow is too long for anyone with a
normal arm span. I have found 7-inch loops to
be perfect for my average arm span.
Make your launch stick from a largediameter
dowel, such as a length of
broomstick. Its bigger diameter gives you extra
gripping power to extend it an extra couple
inches forward for maximum stretch.
I use a 1/2-inch-OD screw eyelet in the top
of my dowel, taking care that the entire length
of the launch stick doesn’t extend past 6
inches. In preparation for a contest, I often tie
four or five fresh loops, because they wear out
after four or five full-power launches. MA
Don DeLoach
[email protected]
Sources:
Mountain Models
(719) 630-3186
www.mountainmodels.com
Stan Buddenbohm (He has a catalog of
excellent FF Glider stuff, including DT
fuselages and timer springs, hosted on the
informative Krempetz FF Glider site.)
Box 1177
Boulevard CA 91905
www.schnable.net/hosted/amaglider/index.h
tml
Michael’s Craft Stores
(800) 642-4235
www.michaels.com
Cabela’s (for 20-pound-test Spiderwire
fishing line)
(800) 237-4444
www.cabelas.com
FAI Model Supply (for Badge BL-7 DT
timers, Master Airscrew razor planes, Zona
razor saws, 1/4-inch-wide rubber)
(570) 882-9873
www.faimodelsupply.com
Don DeLoach
831 E. Willamette Ave.
Colorado Springs CO 80903
Peck-Polymers (for loads of great FF items,
scalpels and blades, razor planes, carbon
tubing, balsa)
(720) 833-9300
www.peck-polymers.com
04sig2.QXD_00MSTRPG.QXD 2/23/10 9:14 AM Page 34

ApriAl 2p0ri1l 02 0 2170 27
Clean, curvy lines make this model an attractive choice for Catapult Glider. The day-glow
orange wingtips help find it at the field.
Lead
by Don DeLoach
This design provides
loads of enjoyment
for a bare-minimum
investment, and it
represents a perfect
introduction to FF
competition. Ellipsix
THE BEST THING about competition FF
is the wide variety of model types and sizes.
There are glow-powered gas aircraft that
span 10 feet and Indoor Rubber airplanes
that are as little as paper clips. Somewhere
between those extremes is handheld Outdoor
Catapult Glider (AMA event 142).
These models are compact, quick to
build, inexpensive, and easy to fly. In the
time-and-money-per-unit-of-fun department,
no event delivers as Catapult Glider does.
For the beginner, these aircraft are a
perfect entry point for experiencing the joys
of FF. Best of all, they can be made to fly
great with little experience or expertise on
the part of the builder.
Balsa for FF: Let’s start with wood
selection. Balsa varies widely in density,
from as much as 15 to as few as 4 pounds per
cubic foot. In FF, light balsa is crucial for top
performance, because our models are
generally smaller and less tolerant of high
wing loadings than the average 10-pound RC
aircraft.
In FF, we’re after the least-dense balsa
available. This is known in the industry as
“contest grade,” and it’s 6 pounds per square
foot and less. That is approximately half the
density of average balsa in a hobby shop or
RC kit.
I hope you have a good local hobby shop
with a decent selection of balsa and can take
time to sort through it. If not, mail-order
your wood from Mountain Models in
Colorado Springs. (Contact information is in
the source list at the end of this article.)
Owner Brian Eberwein weighs and sorts
every sheet of wood he receives from his
suppliers. When you buy a piece of “Contest”
balsa from Brian, you can be certain that it is
6 pounds per cubic foot in density or less.
CONSTRUCTION
For the wing, you’ll need one piece of
contest 3/16 balsa that is at least 31/2 x 18
inches. For the fin and horizontal stabilizer,
you’ll need roughly 8 inches of 1/16 x 3-inchwidth
balsa. The wood for the fin and
stabilizer should also be in the contest-density
range.
C-grain wood is preferable for all flight
surfaces, because it is the most warp-resistant.
It looks mottled, like mother-of-pearl, whereas
A- and B-grain have much straighter, parallel
grain patterns. It’s rare to find C-grain in
hobby shops, but you will if you sort through
enough sheets.
Above all, do not use balsa that is even
the slightest bit twisted. Catapult Gliders fly
extremely fast in the climb and cannot
tolerate warps.
Get your
hands on this
easy-to-build
FF Catapult
Glider
04sig1_00MSTRPG.QXD 2/23/10 9:06 AM Page 27
28 MODEL AVIATION
28 MODEL AVIATION
Above: Left front of nose area shows viscous-fluid badge timer
engaged with spring-loaded hold-on line. As the spring relaxes it
moves timer to roughly the 12:30 position, releasing the line and
engaging the DT. This causes the model to “parachute” down
from thermals at approximately 10 feet/second.
Left: The wing bottom is sprayed with Flat Black Design Master
spray paint, which is virtually weightless and greatly aids in-flight
visibility.
Underside of left wing shows small balsa washin wedge
th at is cr iti c al to t he G lider ’s t r i m . Th e w e dg e
provides additional left wing lift needed to prevent the
Ellipsix from spinning in during glide.
The rear grip is made from 1/32 birch plywood and a small plastic pinhead.
Notice pinholes in plywood where it meets carbon boom; this significantly
strengthens a CA bond.
Rear of the model shows slight stabilizer tilt (left tip high) that produces a left glide circle. Without stabilizer tilt, the airplane would
glide in a straight line and not stay centered in thermal lift.
04sig1_00MSTRPG.QXD 2/23/10 9:07 AM Page 28
April 2010 29
Top: The pop-up
tailboom DT is now
ubiquitous on small FF
Gliders. A 1/8-inch rivet
acts as a removable
hinge pin and tailboom
lifts via two #8 rubber
bands.
Above: Underside
shows the 1/8-inch rivet
hinge pin, 1/32 plywood
launching hook, and
.009-inch music-wire
DT spring in relaxed
position.
Left: A trio of Ellipsix
models can easily be
built in a week of
evenings. AMA FF
Catapult Glider rules
allow up to three
gliders per competitor
per contest.
Photos by the author
Ellipsix
April 2010 29
Type: AMA (event 142) FF handheld
Catapult Glider
Skill level: Suitable for beginners
Wingspan (flat): 18 inches
Wingspan (projected): 16.3 inches
Wing area: 50 square inches
(projected)
Length: 18 inches
Weight range: 0.7-0.9 ounces
Wing loading: 2.3 ounces/square foot
Power: 7- to 9-inch loop of 1/4 x .042-
inch FAI Tan rubber, on 6-inch handle
Construction: Balsa, plywood, tubular
carbon tailboom
Finish: Nitrate dope or Minwax
Helmsman Spar Urethane
Cost to construct: $5-$10 in
materials, $10-15 DT timer
Time to construct: Four to six hours
(two evenings)
Flight Duration:
Two-minute
maximums
(“maxes”)
in competition
04sig1_00MSTRPG.QXD 2/23/10 9:09 AM Page 29
34 MODEL AVIATION
Others like to mix a small amount of
talcum power with the dope, for a sanding
sealer effect. Still others use a light coat of
clear Minwax polyurethane, mostly smeared
off with a paper towel.
Use your favorite finishing method, but
don’t forget to color the model for visibility. I
like Design Master spray paint from the
Michael’s chain of craft stores. It is extremely
bright and weighs next to nothing.
Design Master “Carnation Red” and
“Holiday Red” are excellent choices for the
top surfaces. For the underside of the wings, a
coat of Design Master “Flat Black” will
greatly aid in-flight visibility, especially on
cloudy days.
Final Touches: After tending to a few more
details, we’ll be ready to test-fly.
Securely attach the 1/32 plywood launching
and rear hooks with thin CA. Attach a 1/32
plywood doubler to one side of the nose. This
will give the nose area extra durability and
strength. Test your DT operation on the
ground several times, to make sure that it is
working reliably.
Turn your attention to rigging the
Spiderwire hold-down line that extends to the
timer. The line should capture the front portion
of the carbon tailboom and lock it into position
under the midchord point under the wing.
Now route the line back to the TE and up
over the top surface of the wing. Attach a 2- to
3-inch loop of the elastic thread that is
supplied with the timer, and experiment with
tension on the timer.
Ideally, you want the timer to rotate
approximately a half revolution in slightly
more than two minutes. This is perfect for the
two-minute “maxes” flown in Catapult Glider
competitions.
A better alternative to the elastic thread is a
metal spring. These are available from Stan
Buddenbohm, or you can wind one using .009
music wire on a .078 mandrel. Springs are
consistent across all temperatures and don’t
dry out and weaken with time, as does elastic.
Test the timer several times on the ground,
making sure that the tailboom is locked up
solidly under tension and that each timer
release results in the wing popping up every
time. If the tailboom is binding in the hinge
assembly, sand it a bit narrower or increase the
rubber band tension. DTs must work every
time; otherwise, they are simply an
aggravation.
Last, don’t forget the 1/16 balsa washin
wedge glued on the left main wing panel. This
is crucial, because it keeps the model from
spinning in to the left in the event of a
nosedive or turbulent air. The Ellipsix, as do
most Catapult Gliders, uses little incidence and
a rearward CG, so careful trimming is a must.
Flying: Balance your model at 55% per the
plans and head to the test field. Do a couple of
hand glides and observe the aircraft’s
tendencies. If it is stallish, take out some
incidence via the tailboom adjustment screw.
If the Glider dives, add incidence until the
nose comes up and it is near a stall. What you
are after is a nice floating glide on the verge of
a stall, with a left glide circle that is roughly
50-75 feet in diameter.
In preparation for the maiden catapult
launch, bend in a small amount of left rudder
(approximately 1/32-1/20). Set the DT to five to
10 seconds and hook up the Ellipsix to the
rubber.
Pull back all the way (that’s right—full
power). Bank the model 45° to the right
(holding the launch stick in your left hand),
and pitch the nose 45° up. Let go and observe
the flight path. Chances are, you will see the
Glider pitch up to nearly vertical while doing
the desired wide left roll, transitioning to the
glide at close to 100 feet.
Rolling the aircraft on launch burns a little
energy that could otherwise be used for
altitude gain, but a consistent transition is more
important than 10% or 20% more altitude.
The left rudder controls this left launch roll.
If you are feeling brave as you continue
trimming, you can take out some left rudder
and incidence until the model launches nearly
vertical with little or no roll.
Be prepared for spotty transitions and the
occasional death dive. The Ellipsix will go
higher this way, however.
Anytime you make an incidence change,
you must retrim the glide using CG shift. It is
that simple. And if your Glider won’t
transition well no matter what you do, add a bit
of clay to the left wingtip.
Trimming a Catapult Glider for top
performance is an individualized process.
That’s because your arm span and length of
rubber loop determine how much power you
have at launch.
Long-armed fliers are at an advantage. But
what is more important is that your rubber loop
is short enough to be near breaking when it is
in full launch extension.
The 9-inch maximum loop that the AMA
rules allow is too long for anyone with a
normal arm span. I have found 7-inch loops to
be perfect for my average arm span.
Make your launch stick from a largediameter
dowel, such as a length of
broomstick. Its bigger diameter gives you extra
gripping power to extend it an extra couple
inches forward for maximum stretch.
I use a 1/2-inch-OD screw eyelet in the top
of my dowel, taking care that the entire length
of the launch stick doesn’t extend past 6
inches. In preparation for a contest, I often tie
four or five fresh loops, because they wear out
after four or five full-power launches. MA
Don DeLoach
[email protected]
Sources:
Mountain Models
(719) 630-3186
www.mountainmodels.com
Stan Buddenbohm (He has a catalog of
excellent FF Glider stuff, including DT
fuselages and timer springs, hosted on the
informative Krempetz FF Glider site.)
Box 1177
Boulevard CA 91905
www.schnable.net/hosted/amaglider/index.h
tml
Michael’s Craft Stores
(800) 642-4235
www.michaels.com
Cabela’s (for 20-pound-test Spiderwire
fishing line)
(800) 237-4444
www.cabelas.com
FAI Model Supply (for Badge BL-7 DT
timers, Master Airscrew razor planes, Zona
razor saws, 1/4-inch-wide rubber)
(570) 882-9873
www.faimodelsupply.com
Don DeLoach
831 E. Willamette Ave.
Colorado Springs CO 80903
Peck-Polymers (for loads of great FF items,
scalpels and blades, razor planes, carbon
tubing, balsa)
(720) 833-9300
www.peck-polymers.com
04sig2.QXD_00MSTRPG.QXD 2/23/10 9:14 AM Page 34

ApriAl 2p0ri1l 02 0 2170 27
Clean, curvy lines make this model an attractive choice for Catapult Glider. The day-glow
orange wingtips help find it at the field.
Lead
by Don DeLoach
This design provides
loads of enjoyment
for a bare-minimum
investment, and it
represents a perfect
introduction to FF
competition. Ellipsix
THE BEST THING about competition FF
is the wide variety of model types and sizes.
There are glow-powered gas aircraft that
span 10 feet and Indoor Rubber airplanes
that are as little as paper clips. Somewhere
between those extremes is handheld Outdoor
Catapult Glider (AMA event 142).
These models are compact, quick to
build, inexpensive, and easy to fly. In the
time-and-money-per-unit-of-fun department,
no event delivers as Catapult Glider does.
For the beginner, these aircraft are a
perfect entry point for experiencing the joys
of FF. Best of all, they can be made to fly
great with little experience or expertise on
the part of the builder.
Balsa for FF: Let’s start with wood
selection. Balsa varies widely in density,
from as much as 15 to as few as 4 pounds per
cubic foot. In FF, light balsa is crucial for top
performance, because our models are
generally smaller and less tolerant of high
wing loadings than the average 10-pound RC
aircraft.
In FF, we’re after the least-dense balsa
available. This is known in the industry as
“contest grade,” and it’s 6 pounds per square
foot and less. That is approximately half the
density of average balsa in a hobby shop or
RC kit.
I hope you have a good local hobby shop
with a decent selection of balsa and can take
time to sort through it. If not, mail-order
your wood from Mountain Models in
Colorado Springs. (Contact information is in
the source list at the end of this article.)
Owner Brian Eberwein weighs and sorts
every sheet of wood he receives from his
suppliers. When you buy a piece of “Contest”
balsa from Brian, you can be certain that it is
6 pounds per cubic foot in density or less.
CONSTRUCTION
For the wing, you’ll need one piece of
contest 3/16 balsa that is at least 31/2 x 18
inches. For the fin and horizontal stabilizer,
you’ll need roughly 8 inches of 1/16 x 3-inchwidth
balsa. The wood for the fin and
stabilizer should also be in the contest-density
range.
C-grain wood is preferable for all flight
surfaces, because it is the most warp-resistant.
It looks mottled, like mother-of-pearl, whereas
A- and B-grain have much straighter, parallel
grain patterns. It’s rare to find C-grain in
hobby shops, but you will if you sort through
enough sheets.
Above all, do not use balsa that is even
the slightest bit twisted. Catapult Gliders fly
extremely fast in the climb and cannot
tolerate warps.
Get your
hands on this
easy-to-build
FF Catapult
Glider
04sig1_00MSTRPG.QXD 2/23/10 9:06 AM Page 27
28 MODEL AVIATION
28 MODEL AVIATION
Above: Left front of nose area shows viscous-fluid badge timer
engaged with spring-loaded hold-on line. As the spring relaxes it
moves timer to roughly the 12:30 position, releasing the line and
engaging the DT. This causes the model to “parachute” down
from thermals at approximately 10 feet/second.
Left: The wing bottom is sprayed with Flat Black Design Master
spray paint, which is virtually weightless and greatly aids in-flight
visibility.
Underside of left wing shows small balsa washin wedge
th at is cr iti c al to t he G lider ’s t r i m . Th e w e dg e
provides additional left wing lift needed to prevent the
Ellipsix from spinning in during glide.
The rear grip is made from 1/32 birch plywood and a small plastic pinhead.
Notice pinholes in plywood where it meets carbon boom; this significantly
strengthens a CA bond.
Rear of the model shows slight stabilizer tilt (left tip high) that produces a left glide circle. Without stabilizer tilt, the airplane would
glide in a straight line and not stay centered in thermal lift.
04sig1_00MSTRPG.QXD 2/23/10 9:07 AM Page 28
April 2010 29
Top: The pop-up
tailboom DT is now
ubiquitous on small FF
Gliders. A 1/8-inch rivet
acts as a removable
hinge pin and tailboom
lifts via two #8 rubber
bands.
Above: Underside
shows the 1/8-inch rivet
hinge pin, 1/32 plywood
launching hook, and
.009-inch music-wire
DT spring in relaxed
position.
Left: A trio of Ellipsix
models can easily be
built in a week of
evenings. AMA FF
Catapult Glider rules
allow up to three
gliders per competitor
per contest.
Photos by the author
Ellipsix
April 2010 29
Type: AMA (event 142) FF handheld
Catapult Glider
Skill level: Suitable for beginners
Wingspan (flat): 18 inches
Wingspan (projected): 16.3 inches
Wing area: 50 square inches
(projected)
Length: 18 inches
Weight range: 0.7-0.9 ounces
Wing loading: 2.3 ounces/square foot
Power: 7- to 9-inch loop of 1/4 x .042-
inch FAI Tan rubber, on 6-inch handle
Construction: Balsa, plywood, tubular
carbon tailboom
Finish: Nitrate dope or Minwax
Helmsman Spar Urethane
Cost to construct: $5-$10 in
materials, $10-15 DT timer
Time to construct: Four to six hours
(two evenings)
Flight Duration:
Two-minute
maximums
(“maxes”)
in competition
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34 MODEL AVIATION
Others like to mix a small amount of
talcum power with the dope, for a sanding
sealer effect. Still others use a light coat of
clear Minwax polyurethane, mostly smeared
off with a paper towel.
Use your favorite finishing method, but
don’t forget to color the model for visibility. I
like Design Master spray paint from the
Michael’s chain of craft stores. It is extremely
bright and weighs next to nothing.
Design Master “Carnation Red” and
“Holiday Red” are excellent choices for the
top surfaces. For the underside of the wings, a
coat of Design Master “Flat Black” will
greatly aid in-flight visibility, especially on
cloudy days.
Final Touches: After tending to a few more
details, we’ll be ready to test-fly.
Securely attach the 1/32 plywood launching
and rear hooks with thin CA. Attach a 1/32
plywood doubler to one side of the nose. This
will give the nose area extra durability and
strength. Test your DT operation on the
ground several times, to make sure that it is
working reliably.
Turn your attention to rigging the
Spiderwire hold-down line that extends to the
timer. The line should capture the front portion
of the carbon tailboom and lock it into position
under the midchord point under the wing.
Now route the line back to the TE and up
over the top surface of the wing. Attach a 2- to
3-inch loop of the elastic thread that is
supplied with the timer, and experiment with
tension on the timer.
Ideally, you want the timer to rotate
approximately a half revolution in slightly
more than two minutes. This is perfect for the
two-minute “maxes” flown in Catapult Glider
competitions.
A better alternative to the elastic thread is a
metal spring. These are available from Stan
Buddenbohm, or you can wind one using .009
music wire on a .078 mandrel. Springs are
consistent across all temperatures and don’t
dry out and weaken with time, as does elastic.
Test the timer several times on the ground,
making sure that the tailboom is locked up
solidly under tension and that each timer
release results in the wing popping up every
time. If the tailboom is binding in the hinge
assembly, sand it a bit narrower or increase the
rubber band tension. DTs must work every
time; otherwise, they are simply an
aggravation.
Last, don’t forget the 1/16 balsa washin
wedge glued on the left main wing panel. This
is crucial, because it keeps the model from
spinning in to the left in the event of a
nosedive or turbulent air. The Ellipsix, as do
most Catapult Gliders, uses little incidence and
a rearward CG, so careful trimming is a must.
Flying: Balance your model at 55% per the
plans and head to the test field. Do a couple of
hand glides and observe the aircraft’s
tendencies. If it is stallish, take out some
incidence via the tailboom adjustment screw.
If the Glider dives, add incidence until the
nose comes up and it is near a stall. What you
are after is a nice floating glide on the verge of
a stall, with a left glide circle that is roughly
50-75 feet in diameter.
In preparation for the maiden catapult
launch, bend in a small amount of left rudder
(approximately 1/32-1/20). Set the DT to five to
10 seconds and hook up the Ellipsix to the
rubber.
Pull back all the way (that’s right—full
power). Bank the model 45° to the right
(holding the launch stick in your left hand),
and pitch the nose 45° up. Let go and observe
the flight path. Chances are, you will see the
Glider pitch up to nearly vertical while doing
the desired wide left roll, transitioning to the
glide at close to 100 feet.
Rolling the aircraft on launch burns a little
energy that could otherwise be used for
altitude gain, but a consistent transition is more
important than 10% or 20% more altitude.
The left rudder controls this left launch roll.
If you are feeling brave as you continue
trimming, you can take out some left rudder
and incidence until the model launches nearly
vertical with little or no roll.
Be prepared for spotty transitions and the
occasional death dive. The Ellipsix will go
higher this way, however.
Anytime you make an incidence change,
you must retrim the glide using CG shift. It is
that simple. And if your Glider won’t
transition well no matter what you do, add a bit
of clay to the left wingtip.
Trimming a Catapult Glider for top
performance is an individualized process.
That’s because your arm span and length of
rubber loop determine how much power you
have at launch.
Long-armed fliers are at an advantage. But
what is more important is that your rubber loop
is short enough to be near breaking when it is
in full launch extension.
The 9-inch maximum loop that the AMA
rules allow is too long for anyone with a
normal arm span. I have found 7-inch loops to
be perfect for my average arm span.
Make your launch stick from a largediameter
dowel, such as a length of
broomstick. Its bigger diameter gives you extra
gripping power to extend it an extra couple
inches forward for maximum stretch.
I use a 1/2-inch-OD screw eyelet in the top
of my dowel, taking care that the entire length
of the launch stick doesn’t extend past 6
inches. In preparation for a contest, I often tie
four or five fresh loops, because they wear out
after four or five full-power launches. MA
Don DeLoach
[email protected]
Sources:
Mountain Models
(719) 630-3186
www.mountainmodels.com
Stan Buddenbohm (He has a catalog of
excellent FF Glider stuff, including DT
fuselages and timer springs, hosted on the
informative Krempetz FF Glider site.)
Box 1177
Boulevard CA 91905
www.schnable.net/hosted/amaglider/index.h
tml
Michael’s Craft Stores
(800) 642-4235
www.michaels.com
Cabela’s (for 20-pound-test Spiderwire
fishing line)
(800) 237-4444
www.cabelas.com
FAI Model Supply (for Badge BL-7 DT
timers, Master Airscrew razor planes, Zona
razor saws, 1/4-inch-wide rubber)
(570) 882-9873
www.faimodelsupply.com
Don DeLoach
831 E. Willamette Ave.
Colorado Springs CO 80903
Peck-Polymers (for loads of great FF items,
scalpels and blades, razor planes, carbon
tubing, balsa)
(720) 833-9300
www.peck-polymers.com
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