D.B. Mathews
F l y i n g f o r F u n
909 N. Maize Rd., Townhouse 734, Wichita KS 67212
THE INFORMATION in the February
column about micro 3-D Electrics contained
an error that requires some attention.
Contrary to what I wrote, Depron, fan fold,
and blue foam are not the same. I
misunderstood what I was told during an
interview with a builder and what I read on
the Web site.
The following is from an E-mail on the
subject from Tim Hart, who is responsible
for the designs featured in the February
column and maintenance of the Web site
www.foamyfactory.com.
“Blue foam is an expanded bead
polystyrene (similar to white ‘wing core’
foam) typically used in hot wire cut foam
core wings, then sheeted with balsa and
often fiberglassed. BlueCor is a brand name
manufactured by Dow and Georgia Pacific,
and is primarily used as insulation under
vinyl or aluminum siding. This is the stuff
referred to as fan fold, BlueCor, FFF, and
has a clear plastic coating on both sides of
the sheet.
“Fan fold is a generic term and has to do
with the manner in which the material is
packaged for shipment. The Dow product is
blue, the Owens Corning is pink, and the
Amocor is green. A few other brands are
also available. This foam is sold in 3⁄16 inch
and 3⁄8 inch sheets that are four feet tall and
fifty feet long. It is then ‘fan folded’ back
82 MODEL AVIATION
George Sauer’s Sig Astro-Hog has 21 2400 mAh Ni-Cd pack; Cobalt 40 motor;
AstroFlight Superbox; weighs 8 pounds, 2 ounces. All photos by George Sauer.
George replaced the Astro-Hog’s Ni-Cd pack with a 12-cell 6S (2P) Lithium-Polymer
pack, which resulted in a total aircraft weight of 6 pounds, 2 ounces.
and forth to create 35 four foot by two foot
sheets.
“A bundle that size usually sells for
about $25.00 and will build 10-20 airplanes,
depending on how much foam you waste
and how big the models are. The foam used
for posters etc. is called Foam Core or
Sturdy Board, and while it can be used for
models, the paper has to be peeled off and it
also gets pricey.
“Depron is a brand name and is only
widely available in Europe. All the Depron
used in modeling in the US is imported
from Europe. We have no source here in the
US that manufactures the material. In flat
sheets for modeling use, Depron is superior
to fan fold in many ways; it is more rigid,
stronger, and lighter, and it comes in 2-, 4-,
and 6mm thicknesses for modeling use. It
also does not have any coating on it!
“Both types of foam have their
advantages and disadvantages but work well
for constructing mini 3D Electrics.
Unfortunately, Depron is much more
expensive.”
There is no particular magic associated
with the name Depron. It is an expanded
bead polystyrene but is manufactured in a
closed mold to produce dense spacing and
smooth surfaces. This sort of product is
used in various fast-food containers that are
thermo-molded in the US. I recently learned
that Depron USA is importing the material;
go to www.depronusa.com for information.
A Web page that includes illustrated,
step-by-step construction articles for the
foamy fliers I showed in the February
06sig3.QXD 3/24/04 1:47 pm Page 82
84 MODEL AVIATION
column is www.rcgroups.com/forums/. This
site is also an open discussion forum.
Apples to Apples: In the fall of 2002 I had
the privilege of spending five days as a
guest of Fred Marks and his family (of FMA
Direct) in the Baltimore, Maryland, area.
The principal purpose of that visit was to
investigate the latest and greatest in
receivers and servos and the revolutionary
Li-Poly battery cells that they had just
begun to import from Korea.
To say I was impressed with these Li-
Poly cells is an understatement. They solved
the longtime major complaint about electricpowered
model airplanes: the fuel is too
heavy. If you have been reading the
excellent series by Bob Aberle or Bob
Kopski’s RC Electrics column in this
magazine, you are probably aware that Li-
Poly batteries can produce as much power at
increased duration as a Ni-Cd or NiMH
setup with one-third the dead weight.
Some problems with my vision
following the Baltimore visit prevented my
doing any “cut-and-fly” evaluations, but
since other writers have done such an
excellent job of analyzing the advantages
and special care and feeding of Li-Poly
batteries, there was no need for me to try to
add anything more.
I am not an engineer and admit to never
being fully comfortable with mathematical
formulas and equations to predict
performance of a new idea or product.
Consequently, I’ve avoided the subject until
now, leaving it to those who enjoy
crunching numbers to prove their points.
I’ve been waiting to explore the
advantages of the Li-Poly cells in an applesto-
apples-to-apples manner; I wanted to
compare the battery choices to each other
George powered a different Sig Astro-Hog with an O.S. 61 four-stroke engine. Fueled
and ready to fly, this model weighs 7 pounds, 10 ounces.
Large pack of 21 2400 mAh Ni-Cds weighs 3 pounds. Flat-cell pack roughly equivalent
in volts and amps uses 12 1500 mAh Li-Poly cells and weighs 1 pound.
and to “wet” (glow) power with all the other
variables constant. That is, use the same
airplane and motor, changing only the
battery type, and then doing side-by-side
flying comparisons. My longtime flying
buddy George Sauer has done that, and his
findings confirm the others’ theories, but in
a completely nuts-and-bolts comparison.
Months ago I wrote about a Sig Astro-
Hog that George powered with an
AstroFlight Cobalt 15 electric power plant
using Ni-Cd packs. That setup flew, but not
with any gusto or performance. George then
repowered the model with an AstroFlight
Cobalt 40 motor and an AstroFlight
Superbox gear drive. This version initially
used Ni-Cd packs (21 cells of 2400 mAh
capacity).
The electric-powered Astro-Hog flew
well and was comparable to the identical
Astro-Hog he had constructed that was
powered by an O.S. 60 four-stroke engine.
Performance was similar even though the
illusion of noise caused the glow-powered
model to seem to fly faster. Flying the
models side by side revealed that they were
closely matched. The glow version weighed
7 pounds, 10 ounces fueled, and the Ni-Cd
version weighed 8 pounds, 2 ounces.
When NiMH batteries of the same
amperage and voltage were substituted for
the Ni-Cd batteries, all the performance
variables remained nearly identical for the
electric version except that duration did
increase notably.
George is one of those enquiring minds
that are so common in this hobby. He is a
retired aeronautical engineer by education
and occupation. Perhaps since George’s
specialty is aircraft structures, he worships
at the altar of mathematics enough to design
a part but not be totally comfortable with it
until it has been fabricated and fitted to the
other structures.
From years of experience, George knows
that the part may look good on paper but
require adjustment when put into a practical
application. Because of that humility, he is a
delight to watch while he delves into the
new and untried.
After hearing me rave about Li-Poly
cells, George read everything he could find
on the subject (in print and online),
considered the subject thoroughly, and then
ordered Kokam Li-Poly High Discharge
batteries from FMA Direct.
To obtain the proper voltage (each cell
produces 3.7 volts), George assembled two
sets of six 1500 mAh, high-discharge cells
(8C) in series and then connected the two in
parallel to give 22.2 volts and 3000 mAh.
This sort of setup is referred to as 6S (2P).
Charging is accomplished using an FMA
Direct Li-Poly charger three cells at a time.
The Li-Poly-celled Astro-Hog weighs 6
pounds, 2 ounces, or a full 2 pounds less
than the Ni-Cd version and 1 pound, 8
ounces less than the glow-powered model.
Using a 16 x 8 propeller cut to 15.5 inches,
and drawing 25 amps, the Astro-Hog flies
12-15 minutes and is noticeably more
powerful than the Ni-Cd or glow version.
06sig3.QXD 3/24/04 1:47 pm Page 84
That’s not much of a surprise when one
considers that the model is a full 2 pounds
lighter than the other units, and a 16 x 8
propeller certainly provides more thrust.
This is the first time I’ve ever reported an
electric-powered model being superior to
an equivalent glow-powered model. Think
of the potential!
This setup’s performance is different
from what is predicted using any of the
popular formulas. This is good, oldfashioned,
practical, in-the-field
information. George believes that the
popular formulas apply to small electricpowered
models and are inappropriate for
larger models.
When one considers the variance in
larger wet-powered models’ power
requirements and flying manners when
compared to small models, this all seems
more logical. Compare a 40-size model to
a Jumbo.
The change to Li-Poly cells in this
model altered it from nice to
extraordinary. These cells are expensive,
but they are certainly worth the
investment. As is almost always the case
with model airplanes, you get what you
pay for. George got the same or slightly
more power, increased duration, one-third
the weight, and proven results—not
mathematically, but in actual use. That is
exciting!
If you have one of those climb-andglide
models that were sold in the early
days of electric RC and you became
totally disillusioned with it, remove the
cheap can motor and batteries that came
with it, substitute a good, modern geared
motor and Li-Poly cells, and you’ll have a
model that performs well and gives you a
great deal of pleasure.
Some confusing stories about charging
Li-Poly cells are making the rounds. The
chargers used for Ni-Cd or NiMH cells are
unsafe for Li-Poly cells because the latter
must be charged initially at a constant
current, switched to a constant voltage
before they are fully charged, and then
shut down when a certain voltage is
reached. If you understand how a Ni-Cd
charger works, you realize that the voltage
varies throughout the charge, and the
current is constant as the pack charges. A
Ni-Cd charger will possibly ignite a Li-
Poly pack.
Buy an appropriate Li-Poly charger and
read the instructions until you completely
understand the principles involved. Proper
understanding and management is
essential in charging any battery,
regardless of type.
Space is short, and there is little reason
to present addresses for the suppliers I
have mentioned in this text. Most, if not
all, of them advertise in this magazine.
Consider converting one of those
numerous Scale 60-size glow-powered
warbird kits to the electric setup George
is using. Imagine the project turning out
lighter than the engine-powered version
and probably flying better. Some
modelers are also switching to electric
power for very large models. How about
that?
Li-Poly batteries may be the missing piece
of the puzzle and may bring electric RC to
where it is equal to, or even better than, wet
power, and may also solve many of the
flying-site problems I’ve mention in the last
two columns. Now that is exciting! MA
(Editor’s note: For the complete story
on Li-Poly cells, their use and care, and
especially the safety aspects involved with
their use, please read Bob Aberle’s
“Introduction to Lithium-Polymer
Batteries” article in the May 2004 MA.)
86 MODEL AVIATION
06sig3.QXD 3/24/04 1:48 pm Page 86
Edition: Model Aviation - 2004/06
Page Numbers: 82,84,86
Edition: Model Aviation - 2004/06
Page Numbers: 82,84,86
D.B. Mathews
F l y i n g f o r F u n
909 N. Maize Rd., Townhouse 734, Wichita KS 67212
THE INFORMATION in the February
column about micro 3-D Electrics contained
an error that requires some attention.
Contrary to what I wrote, Depron, fan fold,
and blue foam are not the same. I
misunderstood what I was told during an
interview with a builder and what I read on
the Web site.
The following is from an E-mail on the
subject from Tim Hart, who is responsible
for the designs featured in the February
column and maintenance of the Web site
www.foamyfactory.com.
“Blue foam is an expanded bead
polystyrene (similar to white ‘wing core’
foam) typically used in hot wire cut foam
core wings, then sheeted with balsa and
often fiberglassed. BlueCor is a brand name
manufactured by Dow and Georgia Pacific,
and is primarily used as insulation under
vinyl or aluminum siding. This is the stuff
referred to as fan fold, BlueCor, FFF, and
has a clear plastic coating on both sides of
the sheet.
“Fan fold is a generic term and has to do
with the manner in which the material is
packaged for shipment. The Dow product is
blue, the Owens Corning is pink, and the
Amocor is green. A few other brands are
also available. This foam is sold in 3⁄16 inch
and 3⁄8 inch sheets that are four feet tall and
fifty feet long. It is then ‘fan folded’ back
82 MODEL AVIATION
George Sauer’s Sig Astro-Hog has 21 2400 mAh Ni-Cd pack; Cobalt 40 motor;
AstroFlight Superbox; weighs 8 pounds, 2 ounces. All photos by George Sauer.
George replaced the Astro-Hog’s Ni-Cd pack with a 12-cell 6S (2P) Lithium-Polymer
pack, which resulted in a total aircraft weight of 6 pounds, 2 ounces.
and forth to create 35 four foot by two foot
sheets.
“A bundle that size usually sells for
about $25.00 and will build 10-20 airplanes,
depending on how much foam you waste
and how big the models are. The foam used
for posters etc. is called Foam Core or
Sturdy Board, and while it can be used for
models, the paper has to be peeled off and it
also gets pricey.
“Depron is a brand name and is only
widely available in Europe. All the Depron
used in modeling in the US is imported
from Europe. We have no source here in the
US that manufactures the material. In flat
sheets for modeling use, Depron is superior
to fan fold in many ways; it is more rigid,
stronger, and lighter, and it comes in 2-, 4-,
and 6mm thicknesses for modeling use. It
also does not have any coating on it!
“Both types of foam have their
advantages and disadvantages but work well
for constructing mini 3D Electrics.
Unfortunately, Depron is much more
expensive.”
There is no particular magic associated
with the name Depron. It is an expanded
bead polystyrene but is manufactured in a
closed mold to produce dense spacing and
smooth surfaces. This sort of product is
used in various fast-food containers that are
thermo-molded in the US. I recently learned
that Depron USA is importing the material;
go to www.depronusa.com for information.
A Web page that includes illustrated,
step-by-step construction articles for the
foamy fliers I showed in the February
06sig3.QXD 3/24/04 1:47 pm Page 82
84 MODEL AVIATION
column is www.rcgroups.com/forums/. This
site is also an open discussion forum.
Apples to Apples: In the fall of 2002 I had
the privilege of spending five days as a
guest of Fred Marks and his family (of FMA
Direct) in the Baltimore, Maryland, area.
The principal purpose of that visit was to
investigate the latest and greatest in
receivers and servos and the revolutionary
Li-Poly battery cells that they had just
begun to import from Korea.
To say I was impressed with these Li-
Poly cells is an understatement. They solved
the longtime major complaint about electricpowered
model airplanes: the fuel is too
heavy. If you have been reading the
excellent series by Bob Aberle or Bob
Kopski’s RC Electrics column in this
magazine, you are probably aware that Li-
Poly batteries can produce as much power at
increased duration as a Ni-Cd or NiMH
setup with one-third the dead weight.
Some problems with my vision
following the Baltimore visit prevented my
doing any “cut-and-fly” evaluations, but
since other writers have done such an
excellent job of analyzing the advantages
and special care and feeding of Li-Poly
batteries, there was no need for me to try to
add anything more.
I am not an engineer and admit to never
being fully comfortable with mathematical
formulas and equations to predict
performance of a new idea or product.
Consequently, I’ve avoided the subject until
now, leaving it to those who enjoy
crunching numbers to prove their points.
I’ve been waiting to explore the
advantages of the Li-Poly cells in an applesto-
apples-to-apples manner; I wanted to
compare the battery choices to each other
George powered a different Sig Astro-Hog with an O.S. 61 four-stroke engine. Fueled
and ready to fly, this model weighs 7 pounds, 10 ounces.
Large pack of 21 2400 mAh Ni-Cds weighs 3 pounds. Flat-cell pack roughly equivalent
in volts and amps uses 12 1500 mAh Li-Poly cells and weighs 1 pound.
and to “wet” (glow) power with all the other
variables constant. That is, use the same
airplane and motor, changing only the
battery type, and then doing side-by-side
flying comparisons. My longtime flying
buddy George Sauer has done that, and his
findings confirm the others’ theories, but in
a completely nuts-and-bolts comparison.
Months ago I wrote about a Sig Astro-
Hog that George powered with an
AstroFlight Cobalt 15 electric power plant
using Ni-Cd packs. That setup flew, but not
with any gusto or performance. George then
repowered the model with an AstroFlight
Cobalt 40 motor and an AstroFlight
Superbox gear drive. This version initially
used Ni-Cd packs (21 cells of 2400 mAh
capacity).
The electric-powered Astro-Hog flew
well and was comparable to the identical
Astro-Hog he had constructed that was
powered by an O.S. 60 four-stroke engine.
Performance was similar even though the
illusion of noise caused the glow-powered
model to seem to fly faster. Flying the
models side by side revealed that they were
closely matched. The glow version weighed
7 pounds, 10 ounces fueled, and the Ni-Cd
version weighed 8 pounds, 2 ounces.
When NiMH batteries of the same
amperage and voltage were substituted for
the Ni-Cd batteries, all the performance
variables remained nearly identical for the
electric version except that duration did
increase notably.
George is one of those enquiring minds
that are so common in this hobby. He is a
retired aeronautical engineer by education
and occupation. Perhaps since George’s
specialty is aircraft structures, he worships
at the altar of mathematics enough to design
a part but not be totally comfortable with it
until it has been fabricated and fitted to the
other structures.
From years of experience, George knows
that the part may look good on paper but
require adjustment when put into a practical
application. Because of that humility, he is a
delight to watch while he delves into the
new and untried.
After hearing me rave about Li-Poly
cells, George read everything he could find
on the subject (in print and online),
considered the subject thoroughly, and then
ordered Kokam Li-Poly High Discharge
batteries from FMA Direct.
To obtain the proper voltage (each cell
produces 3.7 volts), George assembled two
sets of six 1500 mAh, high-discharge cells
(8C) in series and then connected the two in
parallel to give 22.2 volts and 3000 mAh.
This sort of setup is referred to as 6S (2P).
Charging is accomplished using an FMA
Direct Li-Poly charger three cells at a time.
The Li-Poly-celled Astro-Hog weighs 6
pounds, 2 ounces, or a full 2 pounds less
than the Ni-Cd version and 1 pound, 8
ounces less than the glow-powered model.
Using a 16 x 8 propeller cut to 15.5 inches,
and drawing 25 amps, the Astro-Hog flies
12-15 minutes and is noticeably more
powerful than the Ni-Cd or glow version.
06sig3.QXD 3/24/04 1:47 pm Page 84
That’s not much of a surprise when one
considers that the model is a full 2 pounds
lighter than the other units, and a 16 x 8
propeller certainly provides more thrust.
This is the first time I’ve ever reported an
electric-powered model being superior to
an equivalent glow-powered model. Think
of the potential!
This setup’s performance is different
from what is predicted using any of the
popular formulas. This is good, oldfashioned,
practical, in-the-field
information. George believes that the
popular formulas apply to small electricpowered
models and are inappropriate for
larger models.
When one considers the variance in
larger wet-powered models’ power
requirements and flying manners when
compared to small models, this all seems
more logical. Compare a 40-size model to
a Jumbo.
The change to Li-Poly cells in this
model altered it from nice to
extraordinary. These cells are expensive,
but they are certainly worth the
investment. As is almost always the case
with model airplanes, you get what you
pay for. George got the same or slightly
more power, increased duration, one-third
the weight, and proven results—not
mathematically, but in actual use. That is
exciting!
If you have one of those climb-andglide
models that were sold in the early
days of electric RC and you became
totally disillusioned with it, remove the
cheap can motor and batteries that came
with it, substitute a good, modern geared
motor and Li-Poly cells, and you’ll have a
model that performs well and gives you a
great deal of pleasure.
Some confusing stories about charging
Li-Poly cells are making the rounds. The
chargers used for Ni-Cd or NiMH cells are
unsafe for Li-Poly cells because the latter
must be charged initially at a constant
current, switched to a constant voltage
before they are fully charged, and then
shut down when a certain voltage is
reached. If you understand how a Ni-Cd
charger works, you realize that the voltage
varies throughout the charge, and the
current is constant as the pack charges. A
Ni-Cd charger will possibly ignite a Li-
Poly pack.
Buy an appropriate Li-Poly charger and
read the instructions until you completely
understand the principles involved. Proper
understanding and management is
essential in charging any battery,
regardless of type.
Space is short, and there is little reason
to present addresses for the suppliers I
have mentioned in this text. Most, if not
all, of them advertise in this magazine.
Consider converting one of those
numerous Scale 60-size glow-powered
warbird kits to the electric setup George
is using. Imagine the project turning out
lighter than the engine-powered version
and probably flying better. Some
modelers are also switching to electric
power for very large models. How about
that?
Li-Poly batteries may be the missing piece
of the puzzle and may bring electric RC to
where it is equal to, or even better than, wet
power, and may also solve many of the
flying-site problems I’ve mention in the last
two columns. Now that is exciting! MA
(Editor’s note: For the complete story
on Li-Poly cells, their use and care, and
especially the safety aspects involved with
their use, please read Bob Aberle’s
“Introduction to Lithium-Polymer
Batteries” article in the May 2004 MA.)
86 MODEL AVIATION
06sig3.QXD 3/24/04 1:48 pm Page 86
Edition: Model Aviation - 2004/06
Page Numbers: 82,84,86
D.B. Mathews
F l y i n g f o r F u n
909 N. Maize Rd., Townhouse 734, Wichita KS 67212
THE INFORMATION in the February
column about micro 3-D Electrics contained
an error that requires some attention.
Contrary to what I wrote, Depron, fan fold,
and blue foam are not the same. I
misunderstood what I was told during an
interview with a builder and what I read on
the Web site.
The following is from an E-mail on the
subject from Tim Hart, who is responsible
for the designs featured in the February
column and maintenance of the Web site
www.foamyfactory.com.
“Blue foam is an expanded bead
polystyrene (similar to white ‘wing core’
foam) typically used in hot wire cut foam
core wings, then sheeted with balsa and
often fiberglassed. BlueCor is a brand name
manufactured by Dow and Georgia Pacific,
and is primarily used as insulation under
vinyl or aluminum siding. This is the stuff
referred to as fan fold, BlueCor, FFF, and
has a clear plastic coating on both sides of
the sheet.
“Fan fold is a generic term and has to do
with the manner in which the material is
packaged for shipment. The Dow product is
blue, the Owens Corning is pink, and the
Amocor is green. A few other brands are
also available. This foam is sold in 3⁄16 inch
and 3⁄8 inch sheets that are four feet tall and
fifty feet long. It is then ‘fan folded’ back
82 MODEL AVIATION
George Sauer’s Sig Astro-Hog has 21 2400 mAh Ni-Cd pack; Cobalt 40 motor;
AstroFlight Superbox; weighs 8 pounds, 2 ounces. All photos by George Sauer.
George replaced the Astro-Hog’s Ni-Cd pack with a 12-cell 6S (2P) Lithium-Polymer
pack, which resulted in a total aircraft weight of 6 pounds, 2 ounces.
and forth to create 35 four foot by two foot
sheets.
“A bundle that size usually sells for
about $25.00 and will build 10-20 airplanes,
depending on how much foam you waste
and how big the models are. The foam used
for posters etc. is called Foam Core or
Sturdy Board, and while it can be used for
models, the paper has to be peeled off and it
also gets pricey.
“Depron is a brand name and is only
widely available in Europe. All the Depron
used in modeling in the US is imported
from Europe. We have no source here in the
US that manufactures the material. In flat
sheets for modeling use, Depron is superior
to fan fold in many ways; it is more rigid,
stronger, and lighter, and it comes in 2-, 4-,
and 6mm thicknesses for modeling use. It
also does not have any coating on it!
“Both types of foam have their
advantages and disadvantages but work well
for constructing mini 3D Electrics.
Unfortunately, Depron is much more
expensive.”
There is no particular magic associated
with the name Depron. It is an expanded
bead polystyrene but is manufactured in a
closed mold to produce dense spacing and
smooth surfaces. This sort of product is
used in various fast-food containers that are
thermo-molded in the US. I recently learned
that Depron USA is importing the material;
go to www.depronusa.com for information.
A Web page that includes illustrated,
step-by-step construction articles for the
foamy fliers I showed in the February
06sig3.QXD 3/24/04 1:47 pm Page 82
84 MODEL AVIATION
column is www.rcgroups.com/forums/. This
site is also an open discussion forum.
Apples to Apples: In the fall of 2002 I had
the privilege of spending five days as a
guest of Fred Marks and his family (of FMA
Direct) in the Baltimore, Maryland, area.
The principal purpose of that visit was to
investigate the latest and greatest in
receivers and servos and the revolutionary
Li-Poly battery cells that they had just
begun to import from Korea.
To say I was impressed with these Li-
Poly cells is an understatement. They solved
the longtime major complaint about electricpowered
model airplanes: the fuel is too
heavy. If you have been reading the
excellent series by Bob Aberle or Bob
Kopski’s RC Electrics column in this
magazine, you are probably aware that Li-
Poly batteries can produce as much power at
increased duration as a Ni-Cd or NiMH
setup with one-third the dead weight.
Some problems with my vision
following the Baltimore visit prevented my
doing any “cut-and-fly” evaluations, but
since other writers have done such an
excellent job of analyzing the advantages
and special care and feeding of Li-Poly
batteries, there was no need for me to try to
add anything more.
I am not an engineer and admit to never
being fully comfortable with mathematical
formulas and equations to predict
performance of a new idea or product.
Consequently, I’ve avoided the subject until
now, leaving it to those who enjoy
crunching numbers to prove their points.
I’ve been waiting to explore the
advantages of the Li-Poly cells in an applesto-
apples-to-apples manner; I wanted to
compare the battery choices to each other
George powered a different Sig Astro-Hog with an O.S. 61 four-stroke engine. Fueled
and ready to fly, this model weighs 7 pounds, 10 ounces.
Large pack of 21 2400 mAh Ni-Cds weighs 3 pounds. Flat-cell pack roughly equivalent
in volts and amps uses 12 1500 mAh Li-Poly cells and weighs 1 pound.
and to “wet” (glow) power with all the other
variables constant. That is, use the same
airplane and motor, changing only the
battery type, and then doing side-by-side
flying comparisons. My longtime flying
buddy George Sauer has done that, and his
findings confirm the others’ theories, but in
a completely nuts-and-bolts comparison.
Months ago I wrote about a Sig Astro-
Hog that George powered with an
AstroFlight Cobalt 15 electric power plant
using Ni-Cd packs. That setup flew, but not
with any gusto or performance. George then
repowered the model with an AstroFlight
Cobalt 40 motor and an AstroFlight
Superbox gear drive. This version initially
used Ni-Cd packs (21 cells of 2400 mAh
capacity).
The electric-powered Astro-Hog flew
well and was comparable to the identical
Astro-Hog he had constructed that was
powered by an O.S. 60 four-stroke engine.
Performance was similar even though the
illusion of noise caused the glow-powered
model to seem to fly faster. Flying the
models side by side revealed that they were
closely matched. The glow version weighed
7 pounds, 10 ounces fueled, and the Ni-Cd
version weighed 8 pounds, 2 ounces.
When NiMH batteries of the same
amperage and voltage were substituted for
the Ni-Cd batteries, all the performance
variables remained nearly identical for the
electric version except that duration did
increase notably.
George is one of those enquiring minds
that are so common in this hobby. He is a
retired aeronautical engineer by education
and occupation. Perhaps since George’s
specialty is aircraft structures, he worships
at the altar of mathematics enough to design
a part but not be totally comfortable with it
until it has been fabricated and fitted to the
other structures.
From years of experience, George knows
that the part may look good on paper but
require adjustment when put into a practical
application. Because of that humility, he is a
delight to watch while he delves into the
new and untried.
After hearing me rave about Li-Poly
cells, George read everything he could find
on the subject (in print and online),
considered the subject thoroughly, and then
ordered Kokam Li-Poly High Discharge
batteries from FMA Direct.
To obtain the proper voltage (each cell
produces 3.7 volts), George assembled two
sets of six 1500 mAh, high-discharge cells
(8C) in series and then connected the two in
parallel to give 22.2 volts and 3000 mAh.
This sort of setup is referred to as 6S (2P).
Charging is accomplished using an FMA
Direct Li-Poly charger three cells at a time.
The Li-Poly-celled Astro-Hog weighs 6
pounds, 2 ounces, or a full 2 pounds less
than the Ni-Cd version and 1 pound, 8
ounces less than the glow-powered model.
Using a 16 x 8 propeller cut to 15.5 inches,
and drawing 25 amps, the Astro-Hog flies
12-15 minutes and is noticeably more
powerful than the Ni-Cd or glow version.
06sig3.QXD 3/24/04 1:47 pm Page 84
That’s not much of a surprise when one
considers that the model is a full 2 pounds
lighter than the other units, and a 16 x 8
propeller certainly provides more thrust.
This is the first time I’ve ever reported an
electric-powered model being superior to
an equivalent glow-powered model. Think
of the potential!
This setup’s performance is different
from what is predicted using any of the
popular formulas. This is good, oldfashioned,
practical, in-the-field
information. George believes that the
popular formulas apply to small electricpowered
models and are inappropriate for
larger models.
When one considers the variance in
larger wet-powered models’ power
requirements and flying manners when
compared to small models, this all seems
more logical. Compare a 40-size model to
a Jumbo.
The change to Li-Poly cells in this
model altered it from nice to
extraordinary. These cells are expensive,
but they are certainly worth the
investment. As is almost always the case
with model airplanes, you get what you
pay for. George got the same or slightly
more power, increased duration, one-third
the weight, and proven results—not
mathematically, but in actual use. That is
exciting!
If you have one of those climb-andglide
models that were sold in the early
days of electric RC and you became
totally disillusioned with it, remove the
cheap can motor and batteries that came
with it, substitute a good, modern geared
motor and Li-Poly cells, and you’ll have a
model that performs well and gives you a
great deal of pleasure.
Some confusing stories about charging
Li-Poly cells are making the rounds. The
chargers used for Ni-Cd or NiMH cells are
unsafe for Li-Poly cells because the latter
must be charged initially at a constant
current, switched to a constant voltage
before they are fully charged, and then
shut down when a certain voltage is
reached. If you understand how a Ni-Cd
charger works, you realize that the voltage
varies throughout the charge, and the
current is constant as the pack charges. A
Ni-Cd charger will possibly ignite a Li-
Poly pack.
Buy an appropriate Li-Poly charger and
read the instructions until you completely
understand the principles involved. Proper
understanding and management is
essential in charging any battery,
regardless of type.
Space is short, and there is little reason
to present addresses for the suppliers I
have mentioned in this text. Most, if not
all, of them advertise in this magazine.
Consider converting one of those
numerous Scale 60-size glow-powered
warbird kits to the electric setup George
is using. Imagine the project turning out
lighter than the engine-powered version
and probably flying better. Some
modelers are also switching to electric
power for very large models. How about
that?
Li-Poly batteries may be the missing piece
of the puzzle and may bring electric RC to
where it is equal to, or even better than, wet
power, and may also solve many of the
flying-site problems I’ve mention in the last
two columns. Now that is exciting! MA
(Editor’s note: For the complete story
on Li-Poly cells, their use and care, and
especially the safety aspects involved with
their use, please read Bob Aberle’s
“Introduction to Lithium-Polymer
Batteries” article in the May 2004 MA.)
86 MODEL AVIATION
06sig3.QXD 3/24/04 1:48 pm Page 86
