132 MODEL AVIATION
The science and application of high-performance rubber
Free Flight Indoor John Kagan
[[email protected]]
Also included in this column:
• “THE SHEET”: an Indoor
Hand-Launched Glider story
• Indoor flying in Oklahoma City
• NS Wheels
Tony Asla’s Pistachio Scale Sportster. Terryl Asla photo.
Alan Pilcher and his scratch-built Martin at the Oklahoma City National Guard
Armory. Photo by Terryl Asla.
FRIENDS FREQUENTLY ASK me if we use special rubber bands
for our airplanes. The answer is, “Of course!” You don’t think we’d
have devoted all these hours to our toy airplanes without fully
exploring the nuances of extensible motors, do you?
And there is plenty to explore. What might seem as simple a power
source as possible actually has so many variables that a large amount
of knowledge falls into the categories of opinion and black art.
However, let’s start with a few facts.
The rubber we use is a special recipe that has significantly more
energy storage capacity than your basic, run-of-the-mill office rubber
bands. The best batches return more than 4,000 foot-pounds of energy
per pound of rubber with a stretch ratio of roughly 10:1.
We measure batches of rubber by winding or stretching, recording
force vs. distance or winds, and calculating the area under the resulting
curve. But even this scientific process has a bit of voodoo to it, because
you have to measure the energy the rubber gives back (hysteresis steals
part of what goes in) and put in close to as much as it will take without
breaking to find its max capacity. Understanding where that limit is is
an acquired feel and can have a dramatic impact on the results.
Rubber batches are identified by the date of production—similar to
fine wine. Indoorists talk about 5/99 Tan II the way wine connoisseurs
do a 1945 Mouton. It’s a great day when you get your hands on a batch
of 3/02, 2/99, 10/97, 8/95, or one of the other high-energy runs.
But the wine analogy doesn’t end there.
Preserving your prize rubber involves special
packaging (such as glassine envelopes or oven
bags, which don’t outgas acids) and climate
control (airtight darkness to reduce
degradation and freezer or refrigerator space
to slow vulcanizing chemical reactions).
The best batches came from a line that
FAI Model Supply called Tan II.
Unfortunately it has been out of production
since 7/02, when the supplier had to make a
permanent recipe modification prompted by
ingredient availability and demand changes.
FAI Model Supply calls the resulting new
products Tan Sport and Tan Super Sport.
On the plus side, the new line is
reportedly more consistent between batches
and compares favorably with some of the
decent Tan II runs, especially in Outdoor
events, in which choosing air plays a major
role in competition success. But for
Indoor, in which differences in energy
capacity correlate much more directly with
puts in the time required to get to a
level of competence, he or she
almost invariably
acquires at least a
small supply.
Third, this isn’t the
first time we’ve lost the best
rubber. As it reads on my investment
statements, “past performance is not an
indication of future performance.” But history
indicates that sooner or later we’ll have
something that outperforms Tan II.
Having one of the “good” batches doesn’t
necessarily simplify things though, thus
bringing us to some of the subtleties.
Different batches have different
characteristics, but it isn’t as simple as saying
one is better than another. A batch may have a
lot of energy-storage potential, but if much of
it is at high torque (the peak), it may not be as
useful for fixed-pitch events as a batch that
has a flatter torque curve.
However, many of the batches with a flat
curve are also very fragile. They won’t take a
great deal of peak torque and have to be
wound more carefully. A great instance of this
is 7/97. It had plenty of useful energy but was
so fragile that it frequently broke in flight.
Usually a rare occurrence, I witnessed a
handful at the 1997 F1D Team Selection,
most
with
catastrophic results.
We somewhat
affectionately labeled 7/97 the
“Fourth of July” batch for the fireworks it
generated.
Different sections of the same batch can
have different characteristics. My 3/02 might
not be as good as your 3/02 if they came from
different parts of the run. Even samples from
the same box can vary, especially if they
cross a splice in the strip.
When you fly a great deal, you start to
develop a feel for what the rubber should be
doing, such as how many turns and how
much torque it should take. The differences
aren’t as large as those between “good” and
“training” batches, but they can be important
at contest time.
Rubber takes a “set” when it is stretched
near its max and does not return to its original
size right away. The second and third winds
are similar to flying on a longer motor with a
thinner cross-section. Subsequent winds don’t
change much more, but nicks and abrasions
limit the number of times it can be wound.
As a result, some fliers let their motors
recover between uses, waiting up to an hour
for it to return to its original characteristics. I
July 2008 133
Jim Buxton’s reluctant new
Category II model. Buxton photo.
“I used ‘THE SHEET.’” Rob Romash’s
new Category II Hand-Launched
Glider. Romash photo.
Jim Buxton’s version of “THE SHEET.”
See text for the story.
NS Wheels, which look even better in
person. A Scale Mr. Mulligan Walnut waits its turn to fly. Terryl Asla photo.
flight times, Tan II is still highly desired.
However, all is not lost for the newcomer.
First, there is plenty to learn using the
currently available rubber. It may not
compare to the best Tan II if everything else
in your program is optimized, but that’s a big
“if.”
Sport and Super Sport are perfectly
suitable for tuning your models and
developing your flying technique. Many top
fliers use subpar batches for testing and
training, saving the good stuff for competition
days.
Second, good Tan II can still be obtained
sometimes, even though it is no longer
produced. For example, the Outdoor fliers go
through rubber by the truckload, and once in
awhile some of their stash goes on the market.
Even the Indoor fliers have been known to
share their coveted collections with someone
they see as having promise. Tan II is not
always easy to come by, but once someone
prefer to size the motors so that the size is
almost right from the second wind on. People
win contests both ways.
So there you have it. Keep your eyes out
for Tan II, but don’t let a lack of it keep you
from flying and competing.
Learn some of the energy-testing methods
so you can measure what you have. Develop
your airplanes and flying technique with
whatever rubber is available; you will pick up
the nuances with experience. And fly, fly, fly!
Everything should be this much fun.
Notes From the Glider Fliers (or “How to
Motivate Your Friends”): Hand-Launched
Glider expert Jim Buxton sent an interesting
account of events leading up to contest day:
“If you have ever seen Ferris Bueller’s
Day Off you may recall the scene where Ferris
repetitively calls Cameron to convince him to
get out of bed and drive over to the school to
take Ferris out for the ultimate skip day.
Cameron, sick at home, would rather not but
finally gives in knowing that Ferris will
continue to call and harass him until he does.
“For the past two spring seasons I have
reluctantly taken on the role as Cameron, with
Rob Romash playing the part of Ferris. It
starts in March. The phone rings ...
“Romash: ‘Buxton, what you building
for Kent?’
134 MODEL AVIATION
“Me: ‘Nothing, we just had a baby boy two
weeks ago, I am not even sleeping. Build
models? Good one.’
“Romash: ‘Quit being lazy, build
something new, don’t show up with the same
old stuff and baby poop on your shoulder.’
“Me: ‘Ben just spit up, I gotta go ... ’
“And so it continues, weekly, sometimes
daily calls, followed by messages. I get to the
point of ignoring the 719 area code all
together. Then he goes in for the kill. See the
photos for what appeared on my phone with
the text, ‘I used THE SHEET.’
“Every glider guy has a sheet of wood too
sacred to use. Mine is a beautiful sheet of 3.67
pound 1/4-inch C-grain. I have had it for almost
20 years. Sometimes I just take it out and look
at it, then store it back away.
“It seems all glider fanatics do this. I know
Romash and Jim Lewis both talk about having
‘THE SHEET’ as well. It gives us all comfort
to know we still have our best sheet in the rack.
One must not take the use of ‘THE SHEET’
lightly. See the pictures for mine.
“Even mice knew it was a good sheet.
Luckily they only got the corner which will not
limit the use of ‘THE SHEET.’ My balsa
storage is now rodent proof.
“With Kent looming a week away and a
picture of an impressive looking new glider on
my phone courtesy of Rob, what to do, what to
do? Sleep is a crutch. I dug out ‘THE SHEET’
and pulled a couple weekend all nighters. I
cannot let Rob do all the trash talking without a
shiny new glimmer of hope to call my own.
“Besides, there is something exciting about
going to a contest with a brand new stick. It
gives you something to think about, even
dream about the whole way there. A shiny new
glider that has yet to disappoint. Could it be the
one? Will it break the 60-second mark in a Cat
II building?
“There is just something about a glider that
has just emerged from a stack of balsa just
days before. Until the first flight, the glider is
perfect. After the first flight ... well, all faults
are known.
“The glider, well it is bigger, lighter and
sexier. That is exactly what Rob said he did, so
I did the same. See the pictures.
“So Rob can be considered a master
manipulator—of both balsa and people.
However, I still have ‘THE SHEET.’ At the
last second I chickened out and chose a slightly
less pretty, but already 4-inch wide sheet of 4.0 pound wood, no joining need, and time was an
issue.
“You always want to have one arrow left
in the quiver ... ”
Check out Jim’s contest report on the
136 MODEL AVIATION
Small Flying Arts Web site to see how things
turned out.
Local Scene: Terryl Asla sent in the
following report on the Oklahoma City,
Oklahoma, scene.
“Since they lost access to their fly-in
gymnasium about 18 months ago, the most
dedicated members of the Wichita, KS stick
and rubber free flight group—David
Aaronstein, Alan Pilcher, and Anthony
Asla—have been making the monthly 3 hour
trek south down Interstate 35 to the National
Guard Armory in Oklahoma City, where the
OK flyers gather.
“Aaronstein, an aeronautical engineer, is
no stranger to anyone familiar with stick and
tissue model building. Not surprisingly, he
continues to dominate the no-cal WWII mass
launches and to amaze with his new designs.
Pilcher, a graphic designer, creates and prints
his own tissue paper for covering his models.
“The results, like the Martin in this photo,
fly well and are arguably some of the most
attractive planes flying today. Asla, a school
psychiatrist, is making his mark in the
pistachio-scale class. His petite creations (he
often engineers his own plans from 3-views)
are usually among the top flyers in his class.
He also builds ‘half-stash’—one half pistachio
scale flyers with three-inch fuselages that are
ideal living room flyers.”
Thanks, Terryl!
NS Wheels: Alan Cohen is hand-producing a
new line of exquisite balsa-and-silk-thread
spoked wheels that are similar in design to the
famous Hungerford wheels. They range from
less than two-tenths of a gram to just less than
a gram, depending on the size, but they are
capable of supporting more than a pound of
axle weight.
These ultra-light 36-spoke gems are a
must-have for your next Scale project, and
they are even available with foam tires for
electric-powered RC models. Check out the
NS Wheels Web site for more details and
ordering information.
Till next time. MA
Sources:
FAI Model Supply
(570) 882-9873
www.faimodelsupply.com
Small Flying Arts
(920) 420-2946
www.smallflyingarts.com
NS Wheels
2115A Route 31
Glen Gardner NJ 08826
www.nswheels.com
Edition: Model Aviation - 2008/07
Page Numbers: 132,133,134,136
Edition: Model Aviation - 2008/07
Page Numbers: 132,133,134,136
132 MODEL AVIATION
The science and application of high-performance rubber
Free Flight Indoor John Kagan
[[email protected]]
Also included in this column:
• “THE SHEET”: an Indoor
Hand-Launched Glider story
• Indoor flying in Oklahoma City
• NS Wheels
Tony Asla’s Pistachio Scale Sportster. Terryl Asla photo.
Alan Pilcher and his scratch-built Martin at the Oklahoma City National Guard
Armory. Photo by Terryl Asla.
FRIENDS FREQUENTLY ASK me if we use special rubber bands
for our airplanes. The answer is, “Of course!” You don’t think we’d
have devoted all these hours to our toy airplanes without fully
exploring the nuances of extensible motors, do you?
And there is plenty to explore. What might seem as simple a power
source as possible actually has so many variables that a large amount
of knowledge falls into the categories of opinion and black art.
However, let’s start with a few facts.
The rubber we use is a special recipe that has significantly more
energy storage capacity than your basic, run-of-the-mill office rubber
bands. The best batches return more than 4,000 foot-pounds of energy
per pound of rubber with a stretch ratio of roughly 10:1.
We measure batches of rubber by winding or stretching, recording
force vs. distance or winds, and calculating the area under the resulting
curve. But even this scientific process has a bit of voodoo to it, because
you have to measure the energy the rubber gives back (hysteresis steals
part of what goes in) and put in close to as much as it will take without
breaking to find its max capacity. Understanding where that limit is is
an acquired feel and can have a dramatic impact on the results.
Rubber batches are identified by the date of production—similar to
fine wine. Indoorists talk about 5/99 Tan II the way wine connoisseurs
do a 1945 Mouton. It’s a great day when you get your hands on a batch
of 3/02, 2/99, 10/97, 8/95, or one of the other high-energy runs.
But the wine analogy doesn’t end there.
Preserving your prize rubber involves special
packaging (such as glassine envelopes or oven
bags, which don’t outgas acids) and climate
control (airtight darkness to reduce
degradation and freezer or refrigerator space
to slow vulcanizing chemical reactions).
The best batches came from a line that
FAI Model Supply called Tan II.
Unfortunately it has been out of production
since 7/02, when the supplier had to make a
permanent recipe modification prompted by
ingredient availability and demand changes.
FAI Model Supply calls the resulting new
products Tan Sport and Tan Super Sport.
On the plus side, the new line is
reportedly more consistent between batches
and compares favorably with some of the
decent Tan II runs, especially in Outdoor
events, in which choosing air plays a major
role in competition success. But for
Indoor, in which differences in energy
capacity correlate much more directly with
puts in the time required to get to a
level of competence, he or she
almost invariably
acquires at least a
small supply.
Third, this isn’t the
first time we’ve lost the best
rubber. As it reads on my investment
statements, “past performance is not an
indication of future performance.” But history
indicates that sooner or later we’ll have
something that outperforms Tan II.
Having one of the “good” batches doesn’t
necessarily simplify things though, thus
bringing us to some of the subtleties.
Different batches have different
characteristics, but it isn’t as simple as saying
one is better than another. A batch may have a
lot of energy-storage potential, but if much of
it is at high torque (the peak), it may not be as
useful for fixed-pitch events as a batch that
has a flatter torque curve.
However, many of the batches with a flat
curve are also very fragile. They won’t take a
great deal of peak torque and have to be
wound more carefully. A great instance of this
is 7/97. It had plenty of useful energy but was
so fragile that it frequently broke in flight.
Usually a rare occurrence, I witnessed a
handful at the 1997 F1D Team Selection,
most
with
catastrophic results.
We somewhat
affectionately labeled 7/97 the
“Fourth of July” batch for the fireworks it
generated.
Different sections of the same batch can
have different characteristics. My 3/02 might
not be as good as your 3/02 if they came from
different parts of the run. Even samples from
the same box can vary, especially if they
cross a splice in the strip.
When you fly a great deal, you start to
develop a feel for what the rubber should be
doing, such as how many turns and how
much torque it should take. The differences
aren’t as large as those between “good” and
“training” batches, but they can be important
at contest time.
Rubber takes a “set” when it is stretched
near its max and does not return to its original
size right away. The second and third winds
are similar to flying on a longer motor with a
thinner cross-section. Subsequent winds don’t
change much more, but nicks and abrasions
limit the number of times it can be wound.
As a result, some fliers let their motors
recover between uses, waiting up to an hour
for it to return to its original characteristics. I
July 2008 133
Jim Buxton’s reluctant new
Category II model. Buxton photo.
“I used ‘THE SHEET.’” Rob Romash’s
new Category II Hand-Launched
Glider. Romash photo.
Jim Buxton’s version of “THE SHEET.”
See text for the story.
NS Wheels, which look even better in
person. A Scale Mr. Mulligan Walnut waits its turn to fly. Terryl Asla photo.
flight times, Tan II is still highly desired.
However, all is not lost for the newcomer.
First, there is plenty to learn using the
currently available rubber. It may not
compare to the best Tan II if everything else
in your program is optimized, but that’s a big
“if.”
Sport and Super Sport are perfectly
suitable for tuning your models and
developing your flying technique. Many top
fliers use subpar batches for testing and
training, saving the good stuff for competition
days.
Second, good Tan II can still be obtained
sometimes, even though it is no longer
produced. For example, the Outdoor fliers go
through rubber by the truckload, and once in
awhile some of their stash goes on the market.
Even the Indoor fliers have been known to
share their coveted collections with someone
they see as having promise. Tan II is not
always easy to come by, but once someone
prefer to size the motors so that the size is
almost right from the second wind on. People
win contests both ways.
So there you have it. Keep your eyes out
for Tan II, but don’t let a lack of it keep you
from flying and competing.
Learn some of the energy-testing methods
so you can measure what you have. Develop
your airplanes and flying technique with
whatever rubber is available; you will pick up
the nuances with experience. And fly, fly, fly!
Everything should be this much fun.
Notes From the Glider Fliers (or “How to
Motivate Your Friends”): Hand-Launched
Glider expert Jim Buxton sent an interesting
account of events leading up to contest day:
“If you have ever seen Ferris Bueller’s
Day Off you may recall the scene where Ferris
repetitively calls Cameron to convince him to
get out of bed and drive over to the school to
take Ferris out for the ultimate skip day.
Cameron, sick at home, would rather not but
finally gives in knowing that Ferris will
continue to call and harass him until he does.
“For the past two spring seasons I have
reluctantly taken on the role as Cameron, with
Rob Romash playing the part of Ferris. It
starts in March. The phone rings ...
“Romash: ‘Buxton, what you building
for Kent?’
134 MODEL AVIATION
“Me: ‘Nothing, we just had a baby boy two
weeks ago, I am not even sleeping. Build
models? Good one.’
“Romash: ‘Quit being lazy, build
something new, don’t show up with the same
old stuff and baby poop on your shoulder.’
“Me: ‘Ben just spit up, I gotta go ... ’
“And so it continues, weekly, sometimes
daily calls, followed by messages. I get to the
point of ignoring the 719 area code all
together. Then he goes in for the kill. See the
photos for what appeared on my phone with
the text, ‘I used THE SHEET.’
“Every glider guy has a sheet of wood too
sacred to use. Mine is a beautiful sheet of 3.67
pound 1/4-inch C-grain. I have had it for almost
20 years. Sometimes I just take it out and look
at it, then store it back away.
“It seems all glider fanatics do this. I know
Romash and Jim Lewis both talk about having
‘THE SHEET’ as well. It gives us all comfort
to know we still have our best sheet in the rack.
One must not take the use of ‘THE SHEET’
lightly. See the pictures for mine.
“Even mice knew it was a good sheet.
Luckily they only got the corner which will not
limit the use of ‘THE SHEET.’ My balsa
storage is now rodent proof.
“With Kent looming a week away and a
picture of an impressive looking new glider on
my phone courtesy of Rob, what to do, what to
do? Sleep is a crutch. I dug out ‘THE SHEET’
and pulled a couple weekend all nighters. I
cannot let Rob do all the trash talking without a
shiny new glimmer of hope to call my own.
“Besides, there is something exciting about
going to a contest with a brand new stick. It
gives you something to think about, even
dream about the whole way there. A shiny new
glider that has yet to disappoint. Could it be the
one? Will it break the 60-second mark in a Cat
II building?
“There is just something about a glider that
has just emerged from a stack of balsa just
days before. Until the first flight, the glider is
perfect. After the first flight ... well, all faults
are known.
“The glider, well it is bigger, lighter and
sexier. That is exactly what Rob said he did, so
I did the same. See the pictures.
“So Rob can be considered a master
manipulator—of both balsa and people.
However, I still have ‘THE SHEET.’ At the
last second I chickened out and chose a slightly
less pretty, but already 4-inch wide sheet of 4.0 pound wood, no joining need, and time was an
issue.
“You always want to have one arrow left
in the quiver ... ”
Check out Jim’s contest report on the
136 MODEL AVIATION
Small Flying Arts Web site to see how things
turned out.
Local Scene: Terryl Asla sent in the
following report on the Oklahoma City,
Oklahoma, scene.
“Since they lost access to their fly-in
gymnasium about 18 months ago, the most
dedicated members of the Wichita, KS stick
and rubber free flight group—David
Aaronstein, Alan Pilcher, and Anthony
Asla—have been making the monthly 3 hour
trek south down Interstate 35 to the National
Guard Armory in Oklahoma City, where the
OK flyers gather.
“Aaronstein, an aeronautical engineer, is
no stranger to anyone familiar with stick and
tissue model building. Not surprisingly, he
continues to dominate the no-cal WWII mass
launches and to amaze with his new designs.
Pilcher, a graphic designer, creates and prints
his own tissue paper for covering his models.
“The results, like the Martin in this photo,
fly well and are arguably some of the most
attractive planes flying today. Asla, a school
psychiatrist, is making his mark in the
pistachio-scale class. His petite creations (he
often engineers his own plans from 3-views)
are usually among the top flyers in his class.
He also builds ‘half-stash’—one half pistachio
scale flyers with three-inch fuselages that are
ideal living room flyers.”
Thanks, Terryl!
NS Wheels: Alan Cohen is hand-producing a
new line of exquisite balsa-and-silk-thread
spoked wheels that are similar in design to the
famous Hungerford wheels. They range from
less than two-tenths of a gram to just less than
a gram, depending on the size, but they are
capable of supporting more than a pound of
axle weight.
These ultra-light 36-spoke gems are a
must-have for your next Scale project, and
they are even available with foam tires for
electric-powered RC models. Check out the
NS Wheels Web site for more details and
ordering information.
Till next time. MA
Sources:
FAI Model Supply
(570) 882-9873
www.faimodelsupply.com
Small Flying Arts
(920) 420-2946
www.smallflyingarts.com
NS Wheels
2115A Route 31
Glen Gardner NJ 08826
www.nswheels.com
Edition: Model Aviation - 2008/07
Page Numbers: 132,133,134,136
132 MODEL AVIATION
The science and application of high-performance rubber
Free Flight Indoor John Kagan
[[email protected]]
Also included in this column:
• “THE SHEET”: an Indoor
Hand-Launched Glider story
• Indoor flying in Oklahoma City
• NS Wheels
Tony Asla’s Pistachio Scale Sportster. Terryl Asla photo.
Alan Pilcher and his scratch-built Martin at the Oklahoma City National Guard
Armory. Photo by Terryl Asla.
FRIENDS FREQUENTLY ASK me if we use special rubber bands
for our airplanes. The answer is, “Of course!” You don’t think we’d
have devoted all these hours to our toy airplanes without fully
exploring the nuances of extensible motors, do you?
And there is plenty to explore. What might seem as simple a power
source as possible actually has so many variables that a large amount
of knowledge falls into the categories of opinion and black art.
However, let’s start with a few facts.
The rubber we use is a special recipe that has significantly more
energy storage capacity than your basic, run-of-the-mill office rubber
bands. The best batches return more than 4,000 foot-pounds of energy
per pound of rubber with a stretch ratio of roughly 10:1.
We measure batches of rubber by winding or stretching, recording
force vs. distance or winds, and calculating the area under the resulting
curve. But even this scientific process has a bit of voodoo to it, because
you have to measure the energy the rubber gives back (hysteresis steals
part of what goes in) and put in close to as much as it will take without
breaking to find its max capacity. Understanding where that limit is is
an acquired feel and can have a dramatic impact on the results.
Rubber batches are identified by the date of production—similar to
fine wine. Indoorists talk about 5/99 Tan II the way wine connoisseurs
do a 1945 Mouton. It’s a great day when you get your hands on a batch
of 3/02, 2/99, 10/97, 8/95, or one of the other high-energy runs.
But the wine analogy doesn’t end there.
Preserving your prize rubber involves special
packaging (such as glassine envelopes or oven
bags, which don’t outgas acids) and climate
control (airtight darkness to reduce
degradation and freezer or refrigerator space
to slow vulcanizing chemical reactions).
The best batches came from a line that
FAI Model Supply called Tan II.
Unfortunately it has been out of production
since 7/02, when the supplier had to make a
permanent recipe modification prompted by
ingredient availability and demand changes.
FAI Model Supply calls the resulting new
products Tan Sport and Tan Super Sport.
On the plus side, the new line is
reportedly more consistent between batches
and compares favorably with some of the
decent Tan II runs, especially in Outdoor
events, in which choosing air plays a major
role in competition success. But for
Indoor, in which differences in energy
capacity correlate much more directly with
puts in the time required to get to a
level of competence, he or she
almost invariably
acquires at least a
small supply.
Third, this isn’t the
first time we’ve lost the best
rubber. As it reads on my investment
statements, “past performance is not an
indication of future performance.” But history
indicates that sooner or later we’ll have
something that outperforms Tan II.
Having one of the “good” batches doesn’t
necessarily simplify things though, thus
bringing us to some of the subtleties.
Different batches have different
characteristics, but it isn’t as simple as saying
one is better than another. A batch may have a
lot of energy-storage potential, but if much of
it is at high torque (the peak), it may not be as
useful for fixed-pitch events as a batch that
has a flatter torque curve.
However, many of the batches with a flat
curve are also very fragile. They won’t take a
great deal of peak torque and have to be
wound more carefully. A great instance of this
is 7/97. It had plenty of useful energy but was
so fragile that it frequently broke in flight.
Usually a rare occurrence, I witnessed a
handful at the 1997 F1D Team Selection,
most
with
catastrophic results.
We somewhat
affectionately labeled 7/97 the
“Fourth of July” batch for the fireworks it
generated.
Different sections of the same batch can
have different characteristics. My 3/02 might
not be as good as your 3/02 if they came from
different parts of the run. Even samples from
the same box can vary, especially if they
cross a splice in the strip.
When you fly a great deal, you start to
develop a feel for what the rubber should be
doing, such as how many turns and how
much torque it should take. The differences
aren’t as large as those between “good” and
“training” batches, but they can be important
at contest time.
Rubber takes a “set” when it is stretched
near its max and does not return to its original
size right away. The second and third winds
are similar to flying on a longer motor with a
thinner cross-section. Subsequent winds don’t
change much more, but nicks and abrasions
limit the number of times it can be wound.
As a result, some fliers let their motors
recover between uses, waiting up to an hour
for it to return to its original characteristics. I
July 2008 133
Jim Buxton’s reluctant new
Category II model. Buxton photo.
“I used ‘THE SHEET.’” Rob Romash’s
new Category II Hand-Launched
Glider. Romash photo.
Jim Buxton’s version of “THE SHEET.”
See text for the story.
NS Wheels, which look even better in
person. A Scale Mr. Mulligan Walnut waits its turn to fly. Terryl Asla photo.
flight times, Tan II is still highly desired.
However, all is not lost for the newcomer.
First, there is plenty to learn using the
currently available rubber. It may not
compare to the best Tan II if everything else
in your program is optimized, but that’s a big
“if.”
Sport and Super Sport are perfectly
suitable for tuning your models and
developing your flying technique. Many top
fliers use subpar batches for testing and
training, saving the good stuff for competition
days.
Second, good Tan II can still be obtained
sometimes, even though it is no longer
produced. For example, the Outdoor fliers go
through rubber by the truckload, and once in
awhile some of their stash goes on the market.
Even the Indoor fliers have been known to
share their coveted collections with someone
they see as having promise. Tan II is not
always easy to come by, but once someone
prefer to size the motors so that the size is
almost right from the second wind on. People
win contests both ways.
So there you have it. Keep your eyes out
for Tan II, but don’t let a lack of it keep you
from flying and competing.
Learn some of the energy-testing methods
so you can measure what you have. Develop
your airplanes and flying technique with
whatever rubber is available; you will pick up
the nuances with experience. And fly, fly, fly!
Everything should be this much fun.
Notes From the Glider Fliers (or “How to
Motivate Your Friends”): Hand-Launched
Glider expert Jim Buxton sent an interesting
account of events leading up to contest day:
“If you have ever seen Ferris Bueller’s
Day Off you may recall the scene where Ferris
repetitively calls Cameron to convince him to
get out of bed and drive over to the school to
take Ferris out for the ultimate skip day.
Cameron, sick at home, would rather not but
finally gives in knowing that Ferris will
continue to call and harass him until he does.
“For the past two spring seasons I have
reluctantly taken on the role as Cameron, with
Rob Romash playing the part of Ferris. It
starts in March. The phone rings ...
“Romash: ‘Buxton, what you building
for Kent?’
134 MODEL AVIATION
“Me: ‘Nothing, we just had a baby boy two
weeks ago, I am not even sleeping. Build
models? Good one.’
“Romash: ‘Quit being lazy, build
something new, don’t show up with the same
old stuff and baby poop on your shoulder.’
“Me: ‘Ben just spit up, I gotta go ... ’
“And so it continues, weekly, sometimes
daily calls, followed by messages. I get to the
point of ignoring the 719 area code all
together. Then he goes in for the kill. See the
photos for what appeared on my phone with
the text, ‘I used THE SHEET.’
“Every glider guy has a sheet of wood too
sacred to use. Mine is a beautiful sheet of 3.67
pound 1/4-inch C-grain. I have had it for almost
20 years. Sometimes I just take it out and look
at it, then store it back away.
“It seems all glider fanatics do this. I know
Romash and Jim Lewis both talk about having
‘THE SHEET’ as well. It gives us all comfort
to know we still have our best sheet in the rack.
One must not take the use of ‘THE SHEET’
lightly. See the pictures for mine.
“Even mice knew it was a good sheet.
Luckily they only got the corner which will not
limit the use of ‘THE SHEET.’ My balsa
storage is now rodent proof.
“With Kent looming a week away and a
picture of an impressive looking new glider on
my phone courtesy of Rob, what to do, what to
do? Sleep is a crutch. I dug out ‘THE SHEET’
and pulled a couple weekend all nighters. I
cannot let Rob do all the trash talking without a
shiny new glimmer of hope to call my own.
“Besides, there is something exciting about
going to a contest with a brand new stick. It
gives you something to think about, even
dream about the whole way there. A shiny new
glider that has yet to disappoint. Could it be the
one? Will it break the 60-second mark in a Cat
II building?
“There is just something about a glider that
has just emerged from a stack of balsa just
days before. Until the first flight, the glider is
perfect. After the first flight ... well, all faults
are known.
“The glider, well it is bigger, lighter and
sexier. That is exactly what Rob said he did, so
I did the same. See the pictures.
“So Rob can be considered a master
manipulator—of both balsa and people.
However, I still have ‘THE SHEET.’ At the
last second I chickened out and chose a slightly
less pretty, but already 4-inch wide sheet of 4.0 pound wood, no joining need, and time was an
issue.
“You always want to have one arrow left
in the quiver ... ”
Check out Jim’s contest report on the
136 MODEL AVIATION
Small Flying Arts Web site to see how things
turned out.
Local Scene: Terryl Asla sent in the
following report on the Oklahoma City,
Oklahoma, scene.
“Since they lost access to their fly-in
gymnasium about 18 months ago, the most
dedicated members of the Wichita, KS stick
and rubber free flight group—David
Aaronstein, Alan Pilcher, and Anthony
Asla—have been making the monthly 3 hour
trek south down Interstate 35 to the National
Guard Armory in Oklahoma City, where the
OK flyers gather.
“Aaronstein, an aeronautical engineer, is
no stranger to anyone familiar with stick and
tissue model building. Not surprisingly, he
continues to dominate the no-cal WWII mass
launches and to amaze with his new designs.
Pilcher, a graphic designer, creates and prints
his own tissue paper for covering his models.
“The results, like the Martin in this photo,
fly well and are arguably some of the most
attractive planes flying today. Asla, a school
psychiatrist, is making his mark in the
pistachio-scale class. His petite creations (he
often engineers his own plans from 3-views)
are usually among the top flyers in his class.
He also builds ‘half-stash’—one half pistachio
scale flyers with three-inch fuselages that are
ideal living room flyers.”
Thanks, Terryl!
NS Wheels: Alan Cohen is hand-producing a
new line of exquisite balsa-and-silk-thread
spoked wheels that are similar in design to the
famous Hungerford wheels. They range from
less than two-tenths of a gram to just less than
a gram, depending on the size, but they are
capable of supporting more than a pound of
axle weight.
These ultra-light 36-spoke gems are a
must-have for your next Scale project, and
they are even available with foam tires for
electric-powered RC models. Check out the
NS Wheels Web site for more details and
ordering information.
Till next time. MA
Sources:
FAI Model Supply
(570) 882-9873
www.faimodelsupply.com
Small Flying Arts
(920) 420-2946
www.smallflyingarts.com
NS Wheels
2115A Route 31
Glen Gardner NJ 08826
www.nswheels.com
Edition: Model Aviation - 2008/07
Page Numbers: 132,133,134,136
132 MODEL AVIATION
The science and application of high-performance rubber
Free Flight Indoor John Kagan
[[email protected]]
Also included in this column:
• “THE SHEET”: an Indoor
Hand-Launched Glider story
• Indoor flying in Oklahoma City
• NS Wheels
Tony Asla’s Pistachio Scale Sportster. Terryl Asla photo.
Alan Pilcher and his scratch-built Martin at the Oklahoma City National Guard
Armory. Photo by Terryl Asla.
FRIENDS FREQUENTLY ASK me if we use special rubber bands
for our airplanes. The answer is, “Of course!” You don’t think we’d
have devoted all these hours to our toy airplanes without fully
exploring the nuances of extensible motors, do you?
And there is plenty to explore. What might seem as simple a power
source as possible actually has so many variables that a large amount
of knowledge falls into the categories of opinion and black art.
However, let’s start with a few facts.
The rubber we use is a special recipe that has significantly more
energy storage capacity than your basic, run-of-the-mill office rubber
bands. The best batches return more than 4,000 foot-pounds of energy
per pound of rubber with a stretch ratio of roughly 10:1.
We measure batches of rubber by winding or stretching, recording
force vs. distance or winds, and calculating the area under the resulting
curve. But even this scientific process has a bit of voodoo to it, because
you have to measure the energy the rubber gives back (hysteresis steals
part of what goes in) and put in close to as much as it will take without
breaking to find its max capacity. Understanding where that limit is is
an acquired feel and can have a dramatic impact on the results.
Rubber batches are identified by the date of production—similar to
fine wine. Indoorists talk about 5/99 Tan II the way wine connoisseurs
do a 1945 Mouton. It’s a great day when you get your hands on a batch
of 3/02, 2/99, 10/97, 8/95, or one of the other high-energy runs.
But the wine analogy doesn’t end there.
Preserving your prize rubber involves special
packaging (such as glassine envelopes or oven
bags, which don’t outgas acids) and climate
control (airtight darkness to reduce
degradation and freezer or refrigerator space
to slow vulcanizing chemical reactions).
The best batches came from a line that
FAI Model Supply called Tan II.
Unfortunately it has been out of production
since 7/02, when the supplier had to make a
permanent recipe modification prompted by
ingredient availability and demand changes.
FAI Model Supply calls the resulting new
products Tan Sport and Tan Super Sport.
On the plus side, the new line is
reportedly more consistent between batches
and compares favorably with some of the
decent Tan II runs, especially in Outdoor
events, in which choosing air plays a major
role in competition success. But for
Indoor, in which differences in energy
capacity correlate much more directly with
puts in the time required to get to a
level of competence, he or she
almost invariably
acquires at least a
small supply.
Third, this isn’t the
first time we’ve lost the best
rubber. As it reads on my investment
statements, “past performance is not an
indication of future performance.” But history
indicates that sooner or later we’ll have
something that outperforms Tan II.
Having one of the “good” batches doesn’t
necessarily simplify things though, thus
bringing us to some of the subtleties.
Different batches have different
characteristics, but it isn’t as simple as saying
one is better than another. A batch may have a
lot of energy-storage potential, but if much of
it is at high torque (the peak), it may not be as
useful for fixed-pitch events as a batch that
has a flatter torque curve.
However, many of the batches with a flat
curve are also very fragile. They won’t take a
great deal of peak torque and have to be
wound more carefully. A great instance of this
is 7/97. It had plenty of useful energy but was
so fragile that it frequently broke in flight.
Usually a rare occurrence, I witnessed a
handful at the 1997 F1D Team Selection,
most
with
catastrophic results.
We somewhat
affectionately labeled 7/97 the
“Fourth of July” batch for the fireworks it
generated.
Different sections of the same batch can
have different characteristics. My 3/02 might
not be as good as your 3/02 if they came from
different parts of the run. Even samples from
the same box can vary, especially if they
cross a splice in the strip.
When you fly a great deal, you start to
develop a feel for what the rubber should be
doing, such as how many turns and how
much torque it should take. The differences
aren’t as large as those between “good” and
“training” batches, but they can be important
at contest time.
Rubber takes a “set” when it is stretched
near its max and does not return to its original
size right away. The second and third winds
are similar to flying on a longer motor with a
thinner cross-section. Subsequent winds don’t
change much more, but nicks and abrasions
limit the number of times it can be wound.
As a result, some fliers let their motors
recover between uses, waiting up to an hour
for it to return to its original characteristics. I
July 2008 133
Jim Buxton’s reluctant new
Category II model. Buxton photo.
“I used ‘THE SHEET.’” Rob Romash’s
new Category II Hand-Launched
Glider. Romash photo.
Jim Buxton’s version of “THE SHEET.”
See text for the story.
NS Wheels, which look even better in
person. A Scale Mr. Mulligan Walnut waits its turn to fly. Terryl Asla photo.
flight times, Tan II is still highly desired.
However, all is not lost for the newcomer.
First, there is plenty to learn using the
currently available rubber. It may not
compare to the best Tan II if everything else
in your program is optimized, but that’s a big
“if.”
Sport and Super Sport are perfectly
suitable for tuning your models and
developing your flying technique. Many top
fliers use subpar batches for testing and
training, saving the good stuff for competition
days.
Second, good Tan II can still be obtained
sometimes, even though it is no longer
produced. For example, the Outdoor fliers go
through rubber by the truckload, and once in
awhile some of their stash goes on the market.
Even the Indoor fliers have been known to
share their coveted collections with someone
they see as having promise. Tan II is not
always easy to come by, but once someone
prefer to size the motors so that the size is
almost right from the second wind on. People
win contests both ways.
So there you have it. Keep your eyes out
for Tan II, but don’t let a lack of it keep you
from flying and competing.
Learn some of the energy-testing methods
so you can measure what you have. Develop
your airplanes and flying technique with
whatever rubber is available; you will pick up
the nuances with experience. And fly, fly, fly!
Everything should be this much fun.
Notes From the Glider Fliers (or “How to
Motivate Your Friends”): Hand-Launched
Glider expert Jim Buxton sent an interesting
account of events leading up to contest day:
“If you have ever seen Ferris Bueller’s
Day Off you may recall the scene where Ferris
repetitively calls Cameron to convince him to
get out of bed and drive over to the school to
take Ferris out for the ultimate skip day.
Cameron, sick at home, would rather not but
finally gives in knowing that Ferris will
continue to call and harass him until he does.
“For the past two spring seasons I have
reluctantly taken on the role as Cameron, with
Rob Romash playing the part of Ferris. It
starts in March. The phone rings ...
“Romash: ‘Buxton, what you building
for Kent?’
134 MODEL AVIATION
“Me: ‘Nothing, we just had a baby boy two
weeks ago, I am not even sleeping. Build
models? Good one.’
“Romash: ‘Quit being lazy, build
something new, don’t show up with the same
old stuff and baby poop on your shoulder.’
“Me: ‘Ben just spit up, I gotta go ... ’
“And so it continues, weekly, sometimes
daily calls, followed by messages. I get to the
point of ignoring the 719 area code all
together. Then he goes in for the kill. See the
photos for what appeared on my phone with
the text, ‘I used THE SHEET.’
“Every glider guy has a sheet of wood too
sacred to use. Mine is a beautiful sheet of 3.67
pound 1/4-inch C-grain. I have had it for almost
20 years. Sometimes I just take it out and look
at it, then store it back away.
“It seems all glider fanatics do this. I know
Romash and Jim Lewis both talk about having
‘THE SHEET’ as well. It gives us all comfort
to know we still have our best sheet in the rack.
One must not take the use of ‘THE SHEET’
lightly. See the pictures for mine.
“Even mice knew it was a good sheet.
Luckily they only got the corner which will not
limit the use of ‘THE SHEET.’ My balsa
storage is now rodent proof.
“With Kent looming a week away and a
picture of an impressive looking new glider on
my phone courtesy of Rob, what to do, what to
do? Sleep is a crutch. I dug out ‘THE SHEET’
and pulled a couple weekend all nighters. I
cannot let Rob do all the trash talking without a
shiny new glimmer of hope to call my own.
“Besides, there is something exciting about
going to a contest with a brand new stick. It
gives you something to think about, even
dream about the whole way there. A shiny new
glider that has yet to disappoint. Could it be the
one? Will it break the 60-second mark in a Cat
II building?
“There is just something about a glider that
has just emerged from a stack of balsa just
days before. Until the first flight, the glider is
perfect. After the first flight ... well, all faults
are known.
“The glider, well it is bigger, lighter and
sexier. That is exactly what Rob said he did, so
I did the same. See the pictures.
“So Rob can be considered a master
manipulator—of both balsa and people.
However, I still have ‘THE SHEET.’ At the
last second I chickened out and chose a slightly
less pretty, but already 4-inch wide sheet of 4.0 pound wood, no joining need, and time was an
issue.
“You always want to have one arrow left
in the quiver ... ”
Check out Jim’s contest report on the
136 MODEL AVIATION
Small Flying Arts Web site to see how things
turned out.
Local Scene: Terryl Asla sent in the
following report on the Oklahoma City,
Oklahoma, scene.
“Since they lost access to their fly-in
gymnasium about 18 months ago, the most
dedicated members of the Wichita, KS stick
and rubber free flight group—David
Aaronstein, Alan Pilcher, and Anthony
Asla—have been making the monthly 3 hour
trek south down Interstate 35 to the National
Guard Armory in Oklahoma City, where the
OK flyers gather.
“Aaronstein, an aeronautical engineer, is
no stranger to anyone familiar with stick and
tissue model building. Not surprisingly, he
continues to dominate the no-cal WWII mass
launches and to amaze with his new designs.
Pilcher, a graphic designer, creates and prints
his own tissue paper for covering his models.
“The results, like the Martin in this photo,
fly well and are arguably some of the most
attractive planes flying today. Asla, a school
psychiatrist, is making his mark in the
pistachio-scale class. His petite creations (he
often engineers his own plans from 3-views)
are usually among the top flyers in his class.
He also builds ‘half-stash’—one half pistachio
scale flyers with three-inch fuselages that are
ideal living room flyers.”
Thanks, Terryl!
NS Wheels: Alan Cohen is hand-producing a
new line of exquisite balsa-and-silk-thread
spoked wheels that are similar in design to the
famous Hungerford wheels. They range from
less than two-tenths of a gram to just less than
a gram, depending on the size, but they are
capable of supporting more than a pound of
axle weight.
These ultra-light 36-spoke gems are a
must-have for your next Scale project, and
they are even available with foam tires for
electric-powered RC models. Check out the
NS Wheels Web site for more details and
ordering information.
Till next time. MA
Sources:
FAI Model Supply
(570) 882-9873
www.faimodelsupply.com
Small Flying Arts
(920) 420-2946
www.smallflyingarts.com
NS Wheels
2115A Route 31
Glen Gardner NJ 08826
www.nswheels.com