90 MODEL AVIATION
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
THE THEME THIS month is thermaling.
I’ll give you a bunch of tips on how to find
and ride these finicky columns of rising air.
This month’s instructions and methods add to
the information from the January 2004
column about the “Condensation Analogy.”
As usual, I’ll start with basics and build to
more advanced ideas.
Bob Zimmerman submitted this month’s
illustration. Bob Sywassink took all the
pictures at the Misty Meadows soar-in, held
May 1-2 in Solon, Iowa.
Choosing the Model: If you are a new RC
glider pilot who wants to thermal, it is
especially important to choose a model that
has generous bend in the wing (dihedral or
Wayne Messner of West Liberty, Iowa, readies his Grande Esprit for a flight. His Space
Pro is sitting in the background.
Mike Fox scans the skies, deciding where to look first for lift. His dad Charlie is timing.
The sailplane is a light version of the Tragi 705.
Paul Haley of Lacrosse, Wisconsin,
launches his Waco Magic 6.
polyhedral). The bent wings will help
coordinate the yaw and roll in the thermal
turns; that is one less thing you will have to
worry about.
A classic good-thermaling polyhedral
sailplane is the Goldberg Gentle Lady. Gentle
Ladys are inexpensive and are now available
in ARF and kit form. Avoid aileron sailplanes
for learning; the vast majority of them have
exceptionally low dihedral angles, making
09sig3QXD 6/24/04 8:40 am Page 90
92 MODEL AVIATION
them more difficult to thermal.
To find thermals, it is critical that you
build the glider straight and true. It needs to
be able to fly straight in calm air. If a wing is
warped, you may be able to get the glider to
fly straight with rudder trim, but this only
works at one speed. Make sure your linkages
are slop free and repeatedly center well. Trim
your glider for straight, level flight with the
CG set so that the model is stable. When set
up correctly, it should fly straight on a calm
day with no pilot inputs.
Don’t move your transmitter sticks! To
find a thermal, you generally need to observe
a change in the sailplane’s direction, attitude,
or speed that you did not cause. The only way
to be certain that you did not cause a change is
to not move the sticks on the transmitter. This
is perfect for hunting thermals.
If you get the opportunity to watch an
expert glider pilot’s hands as he flies, do it.
While hunting for a thermal, you probably
will not see any movement of his or her
hands. Experts are attuned to any movement
Rich Burnoski of Bolingbrook, Illinois,
launches his Pike Superior at the Misty
Meadows Soaring Classic (Solon IA). He
won Unlimited.
Paul Haley’s Magic passes overhead. All photos by Bob Sywassink.
Some changes are coming to
Superior Balsa & Hobby Supply.
We’re starting with
www.superiorbalsa.com
09sig3QXD 6/24/04 8:40 am Page 92
of their gliders; they notice and react to tiny
pitch, roll, or yaw changes that most people
miss altogether.
There are certain times when thermals are
much more likely to form. Glider pilots like to
see a weather forecast that is sunny or partly
cloudy with winds from 5 to 15 mph. Light
and variable winds is another good forecast.
Thermals do form on windy days too, but they
tend to be less organized and are much harder
to work.
It is well known that warm air rises
relative to cold air. A less well-known fact is
that wet air is lighter than dry air. Anytime the
ground is drying, there will be some lift. The
day after a nighttime rain usually has good
thermals. The afternoon after a morning rain
also makes good lift.
A cold front followed by a mass of cold air
will provide contrast between the ground
temperature and the air temperature. I have
seen thermals and cumulus clouds form when
cold air masses arrive even on a winter
evening with a snow-covered ground.
When do the thermals start percolating?
The first opportunity for thermal lift in a day
is usually what I call the “morning burnoff.”
This is when the sun has risen enough to heat
and evaporate the morning dew on the grass.
In my area, the dew typically burns off at
roughly 9:30.
The morning-burnoff lift is usually weak
compared to later thermals. The dew may not
be causing the lift, but its disappearance is a
sure sign of ground heating, which does start
making lift. You can expect to find some
thermal activity anytime after the morning
burnoff.
The “noon balloon” occurs when the sun
is high in the sky. It is not really just at noon;
anytime between 11 a.m. and 3 p.m. is ideal
for finding thermals on a sunny day. This is
when you are most likely to find strong lift.
Early evening is not ideal for thermal
activity. If you fly after work on a weekday,
you have to make the most of the conditions.
Evening thermals tend to be wide, weak, and
smooth compared to midday thermals. If you
are lucky enough to find a thermal in the
evening, a couple clicks of rudder trim is
often perfect to trace huge circles with
minimum sink rate (thus maximum climb
rate).
The evening air often seems “buoyant,”
meaning that the lift may not be strong
enough to make the glider climb, but it is
enough to slow the descent or possibly hold
altitude. I have played “last man down” from
matched hi-starts in the evening. The pilot
who makes the fewest and most subtle control
inputs will usually win in this situation.
What to Look For: Most thermals are
invisible. The most obvious visual sign of
thermal activity is usually the formation of
cumulus clouds. These flat-bottomed cotton
balls sit on the top of thermals. Thermals can
be found in clear skies too, but young
(building) cumulus clouds guarantee it.
Thermals often carry flying insects.
Although the insects may be too far away for
a ground-based pilot to see, the swallows or
other birds feeding on the bugs are more
visible. The presence of soaring birds is, of
course, a dead giveaway. In movies, circling
birds mean that something is dead. In real life,
it is much more likely to mean that they are
riding a thermal.
Note the frequency of the wind cycles. On
a day with light breezes, the wind repeatedly
dies and then picks up. When the wind dies,
the thermal is either just upwind of you or
right above you. When the wind picks up, the
thermal has just passed to the downwind side
of your location. By paying attention to the
wind velocity and direction on the ground,
you can get an excellent idea of which
direction the closest thermal is.
Think of the thermal as a vacuum sucking
in air near the ground from all directions.
When the thermal wind is superimposed on
the ambient wind, some components add up
and some cancel out.
Knowing the current wind and the average
or ambient component, you can use vector
math to solve for the thermal-induced wind.
This tells you the likely location of the bottom
of the thermal. No numbers are needed; just
use logic. Several-time world-champion pilot
Joe Wurts calls this “solving for the third
vector.”
Occasionally you can see a dust devil,
which is like a minitornado, kicking up dust
and dancing along the ground. I differentiate a
Specifications:
Displacement: .40 cubic inches
Bore: 0.82 inches
Stroke: 0.75 inches
Compression: 9:1 to 12:1
RPM Range: 2,000 to 17,000 rpm
Power: 1.4 hp @ 16,000 rpm
Fuel Consumption: 30 ounces/hour
Weight w/o muffler: 10.8 ounces
Weight w/ muffler: 13.1 ounces
Available from participating dealers for $109.99
“The AX-40 is a
revolutionary engine!”
Model Airplane News Magazine, January 2004
Norvel is exclusively distributed in North America by:
SIG Manufacturing Company, Inc. • P.O. Box 520 • Montezuma, IA 50171-0520 • Phone: 641-623-5154
www.norvel.com
We think so too. With a legendary Norvel heritage of superior
craftsmanship, state-of-the-art metallurgy and materials, coupled with rocksolid
reliability, the new AX-40 raises the bar for popularly sized glow engines.
Weighing ounces less than other similar engines, the Norvel
AX-40 sets the standard for power-to-weight ratios and fuel economy.
With our exclusive Revite™ cylinder technology with Sliktek™, engine
friction is not an issue and power is increased 20-40% on average.
What more could you want? How about a 2 needle carburetor
with an angled back design to help keep your fingers away from the
prop, and a lightweight, quiet yet power-efficient muffler designed
to keep the neighbors happy. All at a price you can’t afford to pass
up.
Join the revolution! Buy a AX-40 today and fly better
tomorrow.
94 MODEL AVIATION
09sig3QXD 6/24/04 8:41 am Page 94
dust devil from a normal thermal by its
rotation. The dirt in a dust devil can be seen
spinning. The dust devil also moves quickly
along the ground. Perhaps the high-velocity
rotation causes the dust devil to have the
energy to kick up dust. This rotation can be
violent and generally not good for RC gliders.
In reality, there is a continuous spectrum
of weather phenomena with varying amounts
of rotation. A good rule of thumb is that if
you can see rotating dust and movement of
the plume along the ground, keep your glider
away. The “friendly thermals” have a great
deal of rising velocity with little rotation.
The Initial Turn: When I am searching for
lift and turbulence banks my sailplane, I
assume it could be a thermal that I clipped
with one of the glider’s wings. I have an
original tip to share that has never be seen in
print; the initial turn diameter should be
inversely proportional to the severity of the
initial change in attitude.
If something strong rocks your model,
quickly start tight circles. If something
weakly disturbs the model, slowly start big
circles. If the thermal flips your model up to
knife-edge flight, whip the stick full over,
back into the thermal, and start tight circles
with a 45° bank angle.
At moderate altitudes, the large wind
shears needed to roll your sailplane over are
usually caused by fast-rising, small-diameter
thermals. By immediately getting your glider
back into the thermal and turning tightly, you
are likely to get in and stay with the fast-rising
air. If a thermal gently nudges your model, it
is likely weak and/or has a large diameter.
Smoothly turn your sailplane back in the
direction of the thermal and start a largediameter
(shallow-bank) test circle.
Drifting With Thermals: Beginners often
stumble into lift and then lose it after a few
circles. Experienced pilots let their circles
drift with the wind (thus with the thermal).
Instead of trying to circle a fixed point in the
sky, try to maintain a constant bank angle of
the wings. If you maintain a constant bank,
the (moving) center of the circle will take care
of itself. It is a safe bet that when you lose
your lift, the first place to check is straight
downwind of the glider. MA
96 MODEL AVIATION
The ANALYZER+ will test
the capacity of your 4 to
8-cell packs, and let you
know their condition.
Tests 2 packs at once and is highly
accurate.
Can be used stand-alone, or if
connected to the Charge+ TX/RX,
or similar charger, can re-charge
your batteries after testing.
Costs less than a new plane.
INTRODUCTORY OFFER
$14 9 95_ +S&H
Hughes RC 1-800-786-0802 www.hughesrc.com
What you don’t know
CAN hurt you!
09sig3QXD 6/24/04 8:41 am Page 96
Edition: Model Aviation - 2004/09
Page Numbers: 90,92,94,96
Edition: Model Aviation - 2004/09
Page Numbers: 90,92,94,96
90 MODEL AVIATION
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
THE THEME THIS month is thermaling.
I’ll give you a bunch of tips on how to find
and ride these finicky columns of rising air.
This month’s instructions and methods add to
the information from the January 2004
column about the “Condensation Analogy.”
As usual, I’ll start with basics and build to
more advanced ideas.
Bob Zimmerman submitted this month’s
illustration. Bob Sywassink took all the
pictures at the Misty Meadows soar-in, held
May 1-2 in Solon, Iowa.
Choosing the Model: If you are a new RC
glider pilot who wants to thermal, it is
especially important to choose a model that
has generous bend in the wing (dihedral or
Wayne Messner of West Liberty, Iowa, readies his Grande Esprit for a flight. His Space
Pro is sitting in the background.
Mike Fox scans the skies, deciding where to look first for lift. His dad Charlie is timing.
The sailplane is a light version of the Tragi 705.
Paul Haley of Lacrosse, Wisconsin,
launches his Waco Magic 6.
polyhedral). The bent wings will help
coordinate the yaw and roll in the thermal
turns; that is one less thing you will have to
worry about.
A classic good-thermaling polyhedral
sailplane is the Goldberg Gentle Lady. Gentle
Ladys are inexpensive and are now available
in ARF and kit form. Avoid aileron sailplanes
for learning; the vast majority of them have
exceptionally low dihedral angles, making
09sig3QXD 6/24/04 8:40 am Page 90
92 MODEL AVIATION
them more difficult to thermal.
To find thermals, it is critical that you
build the glider straight and true. It needs to
be able to fly straight in calm air. If a wing is
warped, you may be able to get the glider to
fly straight with rudder trim, but this only
works at one speed. Make sure your linkages
are slop free and repeatedly center well. Trim
your glider for straight, level flight with the
CG set so that the model is stable. When set
up correctly, it should fly straight on a calm
day with no pilot inputs.
Don’t move your transmitter sticks! To
find a thermal, you generally need to observe
a change in the sailplane’s direction, attitude,
or speed that you did not cause. The only way
to be certain that you did not cause a change is
to not move the sticks on the transmitter. This
is perfect for hunting thermals.
If you get the opportunity to watch an
expert glider pilot’s hands as he flies, do it.
While hunting for a thermal, you probably
will not see any movement of his or her
hands. Experts are attuned to any movement
Rich Burnoski of Bolingbrook, Illinois,
launches his Pike Superior at the Misty
Meadows Soaring Classic (Solon IA). He
won Unlimited.
Paul Haley’s Magic passes overhead. All photos by Bob Sywassink.
Some changes are coming to
Superior Balsa & Hobby Supply.
We’re starting with
www.superiorbalsa.com
09sig3QXD 6/24/04 8:40 am Page 92
of their gliders; they notice and react to tiny
pitch, roll, or yaw changes that most people
miss altogether.
There are certain times when thermals are
much more likely to form. Glider pilots like to
see a weather forecast that is sunny or partly
cloudy with winds from 5 to 15 mph. Light
and variable winds is another good forecast.
Thermals do form on windy days too, but they
tend to be less organized and are much harder
to work.
It is well known that warm air rises
relative to cold air. A less well-known fact is
that wet air is lighter than dry air. Anytime the
ground is drying, there will be some lift. The
day after a nighttime rain usually has good
thermals. The afternoon after a morning rain
also makes good lift.
A cold front followed by a mass of cold air
will provide contrast between the ground
temperature and the air temperature. I have
seen thermals and cumulus clouds form when
cold air masses arrive even on a winter
evening with a snow-covered ground.
When do the thermals start percolating?
The first opportunity for thermal lift in a day
is usually what I call the “morning burnoff.”
This is when the sun has risen enough to heat
and evaporate the morning dew on the grass.
In my area, the dew typically burns off at
roughly 9:30.
The morning-burnoff lift is usually weak
compared to later thermals. The dew may not
be causing the lift, but its disappearance is a
sure sign of ground heating, which does start
making lift. You can expect to find some
thermal activity anytime after the morning
burnoff.
The “noon balloon” occurs when the sun
is high in the sky. It is not really just at noon;
anytime between 11 a.m. and 3 p.m. is ideal
for finding thermals on a sunny day. This is
when you are most likely to find strong lift.
Early evening is not ideal for thermal
activity. If you fly after work on a weekday,
you have to make the most of the conditions.
Evening thermals tend to be wide, weak, and
smooth compared to midday thermals. If you
are lucky enough to find a thermal in the
evening, a couple clicks of rudder trim is
often perfect to trace huge circles with
minimum sink rate (thus maximum climb
rate).
The evening air often seems “buoyant,”
meaning that the lift may not be strong
enough to make the glider climb, but it is
enough to slow the descent or possibly hold
altitude. I have played “last man down” from
matched hi-starts in the evening. The pilot
who makes the fewest and most subtle control
inputs will usually win in this situation.
What to Look For: Most thermals are
invisible. The most obvious visual sign of
thermal activity is usually the formation of
cumulus clouds. These flat-bottomed cotton
balls sit on the top of thermals. Thermals can
be found in clear skies too, but young
(building) cumulus clouds guarantee it.
Thermals often carry flying insects.
Although the insects may be too far away for
a ground-based pilot to see, the swallows or
other birds feeding on the bugs are more
visible. The presence of soaring birds is, of
course, a dead giveaway. In movies, circling
birds mean that something is dead. In real life,
it is much more likely to mean that they are
riding a thermal.
Note the frequency of the wind cycles. On
a day with light breezes, the wind repeatedly
dies and then picks up. When the wind dies,
the thermal is either just upwind of you or
right above you. When the wind picks up, the
thermal has just passed to the downwind side
of your location. By paying attention to the
wind velocity and direction on the ground,
you can get an excellent idea of which
direction the closest thermal is.
Think of the thermal as a vacuum sucking
in air near the ground from all directions.
When the thermal wind is superimposed on
the ambient wind, some components add up
and some cancel out.
Knowing the current wind and the average
or ambient component, you can use vector
math to solve for the thermal-induced wind.
This tells you the likely location of the bottom
of the thermal. No numbers are needed; just
use logic. Several-time world-champion pilot
Joe Wurts calls this “solving for the third
vector.”
Occasionally you can see a dust devil,
which is like a minitornado, kicking up dust
and dancing along the ground. I differentiate a
Specifications:
Displacement: .40 cubic inches
Bore: 0.82 inches
Stroke: 0.75 inches
Compression: 9:1 to 12:1
RPM Range: 2,000 to 17,000 rpm
Power: 1.4 hp @ 16,000 rpm
Fuel Consumption: 30 ounces/hour
Weight w/o muffler: 10.8 ounces
Weight w/ muffler: 13.1 ounces
Available from participating dealers for $109.99
“The AX-40 is a
revolutionary engine!”
Model Airplane News Magazine, January 2004
Norvel is exclusively distributed in North America by:
SIG Manufacturing Company, Inc. • P.O. Box 520 • Montezuma, IA 50171-0520 • Phone: 641-623-5154
www.norvel.com
We think so too. With a legendary Norvel heritage of superior
craftsmanship, state-of-the-art metallurgy and materials, coupled with rocksolid
reliability, the new AX-40 raises the bar for popularly sized glow engines.
Weighing ounces less than other similar engines, the Norvel
AX-40 sets the standard for power-to-weight ratios and fuel economy.
With our exclusive Revite™ cylinder technology with Sliktek™, engine
friction is not an issue and power is increased 20-40% on average.
What more could you want? How about a 2 needle carburetor
with an angled back design to help keep your fingers away from the
prop, and a lightweight, quiet yet power-efficient muffler designed
to keep the neighbors happy. All at a price you can’t afford to pass
up.
Join the revolution! Buy a AX-40 today and fly better
tomorrow.
94 MODEL AVIATION
09sig3QXD 6/24/04 8:41 am Page 94
dust devil from a normal thermal by its
rotation. The dirt in a dust devil can be seen
spinning. The dust devil also moves quickly
along the ground. Perhaps the high-velocity
rotation causes the dust devil to have the
energy to kick up dust. This rotation can be
violent and generally not good for RC gliders.
In reality, there is a continuous spectrum
of weather phenomena with varying amounts
of rotation. A good rule of thumb is that if
you can see rotating dust and movement of
the plume along the ground, keep your glider
away. The “friendly thermals” have a great
deal of rising velocity with little rotation.
The Initial Turn: When I am searching for
lift and turbulence banks my sailplane, I
assume it could be a thermal that I clipped
with one of the glider’s wings. I have an
original tip to share that has never be seen in
print; the initial turn diameter should be
inversely proportional to the severity of the
initial change in attitude.
If something strong rocks your model,
quickly start tight circles. If something
weakly disturbs the model, slowly start big
circles. If the thermal flips your model up to
knife-edge flight, whip the stick full over,
back into the thermal, and start tight circles
with a 45° bank angle.
At moderate altitudes, the large wind
shears needed to roll your sailplane over are
usually caused by fast-rising, small-diameter
thermals. By immediately getting your glider
back into the thermal and turning tightly, you
are likely to get in and stay with the fast-rising
air. If a thermal gently nudges your model, it
is likely weak and/or has a large diameter.
Smoothly turn your sailplane back in the
direction of the thermal and start a largediameter
(shallow-bank) test circle.
Drifting With Thermals: Beginners often
stumble into lift and then lose it after a few
circles. Experienced pilots let their circles
drift with the wind (thus with the thermal).
Instead of trying to circle a fixed point in the
sky, try to maintain a constant bank angle of
the wings. If you maintain a constant bank,
the (moving) center of the circle will take care
of itself. It is a safe bet that when you lose
your lift, the first place to check is straight
downwind of the glider. MA
96 MODEL AVIATION
The ANALYZER+ will test
the capacity of your 4 to
8-cell packs, and let you
know their condition.
Tests 2 packs at once and is highly
accurate.
Can be used stand-alone, or if
connected to the Charge+ TX/RX,
or similar charger, can re-charge
your batteries after testing.
Costs less than a new plane.
INTRODUCTORY OFFER
$14 9 95_ +S&H
Hughes RC 1-800-786-0802 www.hughesrc.com
What you don’t know
CAN hurt you!
09sig3QXD 6/24/04 8:41 am Page 96
Edition: Model Aviation - 2004/09
Page Numbers: 90,92,94,96
90 MODEL AVIATION
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
THE THEME THIS month is thermaling.
I’ll give you a bunch of tips on how to find
and ride these finicky columns of rising air.
This month’s instructions and methods add to
the information from the January 2004
column about the “Condensation Analogy.”
As usual, I’ll start with basics and build to
more advanced ideas.
Bob Zimmerman submitted this month’s
illustration. Bob Sywassink took all the
pictures at the Misty Meadows soar-in, held
May 1-2 in Solon, Iowa.
Choosing the Model: If you are a new RC
glider pilot who wants to thermal, it is
especially important to choose a model that
has generous bend in the wing (dihedral or
Wayne Messner of West Liberty, Iowa, readies his Grande Esprit for a flight. His Space
Pro is sitting in the background.
Mike Fox scans the skies, deciding where to look first for lift. His dad Charlie is timing.
The sailplane is a light version of the Tragi 705.
Paul Haley of Lacrosse, Wisconsin,
launches his Waco Magic 6.
polyhedral). The bent wings will help
coordinate the yaw and roll in the thermal
turns; that is one less thing you will have to
worry about.
A classic good-thermaling polyhedral
sailplane is the Goldberg Gentle Lady. Gentle
Ladys are inexpensive and are now available
in ARF and kit form. Avoid aileron sailplanes
for learning; the vast majority of them have
exceptionally low dihedral angles, making
09sig3QXD 6/24/04 8:40 am Page 90
92 MODEL AVIATION
them more difficult to thermal.
To find thermals, it is critical that you
build the glider straight and true. It needs to
be able to fly straight in calm air. If a wing is
warped, you may be able to get the glider to
fly straight with rudder trim, but this only
works at one speed. Make sure your linkages
are slop free and repeatedly center well. Trim
your glider for straight, level flight with the
CG set so that the model is stable. When set
up correctly, it should fly straight on a calm
day with no pilot inputs.
Don’t move your transmitter sticks! To
find a thermal, you generally need to observe
a change in the sailplane’s direction, attitude,
or speed that you did not cause. The only way
to be certain that you did not cause a change is
to not move the sticks on the transmitter. This
is perfect for hunting thermals.
If you get the opportunity to watch an
expert glider pilot’s hands as he flies, do it.
While hunting for a thermal, you probably
will not see any movement of his or her
hands. Experts are attuned to any movement
Rich Burnoski of Bolingbrook, Illinois,
launches his Pike Superior at the Misty
Meadows Soaring Classic (Solon IA). He
won Unlimited.
Paul Haley’s Magic passes overhead. All photos by Bob Sywassink.
Some changes are coming to
Superior Balsa & Hobby Supply.
We’re starting with
www.superiorbalsa.com
09sig3QXD 6/24/04 8:40 am Page 92
of their gliders; they notice and react to tiny
pitch, roll, or yaw changes that most people
miss altogether.
There are certain times when thermals are
much more likely to form. Glider pilots like to
see a weather forecast that is sunny or partly
cloudy with winds from 5 to 15 mph. Light
and variable winds is another good forecast.
Thermals do form on windy days too, but they
tend to be less organized and are much harder
to work.
It is well known that warm air rises
relative to cold air. A less well-known fact is
that wet air is lighter than dry air. Anytime the
ground is drying, there will be some lift. The
day after a nighttime rain usually has good
thermals. The afternoon after a morning rain
also makes good lift.
A cold front followed by a mass of cold air
will provide contrast between the ground
temperature and the air temperature. I have
seen thermals and cumulus clouds form when
cold air masses arrive even on a winter
evening with a snow-covered ground.
When do the thermals start percolating?
The first opportunity for thermal lift in a day
is usually what I call the “morning burnoff.”
This is when the sun has risen enough to heat
and evaporate the morning dew on the grass.
In my area, the dew typically burns off at
roughly 9:30.
The morning-burnoff lift is usually weak
compared to later thermals. The dew may not
be causing the lift, but its disappearance is a
sure sign of ground heating, which does start
making lift. You can expect to find some
thermal activity anytime after the morning
burnoff.
The “noon balloon” occurs when the sun
is high in the sky. It is not really just at noon;
anytime between 11 a.m. and 3 p.m. is ideal
for finding thermals on a sunny day. This is
when you are most likely to find strong lift.
Early evening is not ideal for thermal
activity. If you fly after work on a weekday,
you have to make the most of the conditions.
Evening thermals tend to be wide, weak, and
smooth compared to midday thermals. If you
are lucky enough to find a thermal in the
evening, a couple clicks of rudder trim is
often perfect to trace huge circles with
minimum sink rate (thus maximum climb
rate).
The evening air often seems “buoyant,”
meaning that the lift may not be strong
enough to make the glider climb, but it is
enough to slow the descent or possibly hold
altitude. I have played “last man down” from
matched hi-starts in the evening. The pilot
who makes the fewest and most subtle control
inputs will usually win in this situation.
What to Look For: Most thermals are
invisible. The most obvious visual sign of
thermal activity is usually the formation of
cumulus clouds. These flat-bottomed cotton
balls sit on the top of thermals. Thermals can
be found in clear skies too, but young
(building) cumulus clouds guarantee it.
Thermals often carry flying insects.
Although the insects may be too far away for
a ground-based pilot to see, the swallows or
other birds feeding on the bugs are more
visible. The presence of soaring birds is, of
course, a dead giveaway. In movies, circling
birds mean that something is dead. In real life,
it is much more likely to mean that they are
riding a thermal.
Note the frequency of the wind cycles. On
a day with light breezes, the wind repeatedly
dies and then picks up. When the wind dies,
the thermal is either just upwind of you or
right above you. When the wind picks up, the
thermal has just passed to the downwind side
of your location. By paying attention to the
wind velocity and direction on the ground,
you can get an excellent idea of which
direction the closest thermal is.
Think of the thermal as a vacuum sucking
in air near the ground from all directions.
When the thermal wind is superimposed on
the ambient wind, some components add up
and some cancel out.
Knowing the current wind and the average
or ambient component, you can use vector
math to solve for the thermal-induced wind.
This tells you the likely location of the bottom
of the thermal. No numbers are needed; just
use logic. Several-time world-champion pilot
Joe Wurts calls this “solving for the third
vector.”
Occasionally you can see a dust devil,
which is like a minitornado, kicking up dust
and dancing along the ground. I differentiate a
Specifications:
Displacement: .40 cubic inches
Bore: 0.82 inches
Stroke: 0.75 inches
Compression: 9:1 to 12:1
RPM Range: 2,000 to 17,000 rpm
Power: 1.4 hp @ 16,000 rpm
Fuel Consumption: 30 ounces/hour
Weight w/o muffler: 10.8 ounces
Weight w/ muffler: 13.1 ounces
Available from participating dealers for $109.99
“The AX-40 is a
revolutionary engine!”
Model Airplane News Magazine, January 2004
Norvel is exclusively distributed in North America by:
SIG Manufacturing Company, Inc. • P.O. Box 520 • Montezuma, IA 50171-0520 • Phone: 641-623-5154
www.norvel.com
We think so too. With a legendary Norvel heritage of superior
craftsmanship, state-of-the-art metallurgy and materials, coupled with rocksolid
reliability, the new AX-40 raises the bar for popularly sized glow engines.
Weighing ounces less than other similar engines, the Norvel
AX-40 sets the standard for power-to-weight ratios and fuel economy.
With our exclusive Revite™ cylinder technology with Sliktek™, engine
friction is not an issue and power is increased 20-40% on average.
What more could you want? How about a 2 needle carburetor
with an angled back design to help keep your fingers away from the
prop, and a lightweight, quiet yet power-efficient muffler designed
to keep the neighbors happy. All at a price you can’t afford to pass
up.
Join the revolution! Buy a AX-40 today and fly better
tomorrow.
94 MODEL AVIATION
09sig3QXD 6/24/04 8:41 am Page 94
dust devil from a normal thermal by its
rotation. The dirt in a dust devil can be seen
spinning. The dust devil also moves quickly
along the ground. Perhaps the high-velocity
rotation causes the dust devil to have the
energy to kick up dust. This rotation can be
violent and generally not good for RC gliders.
In reality, there is a continuous spectrum
of weather phenomena with varying amounts
of rotation. A good rule of thumb is that if
you can see rotating dust and movement of
the plume along the ground, keep your glider
away. The “friendly thermals” have a great
deal of rising velocity with little rotation.
The Initial Turn: When I am searching for
lift and turbulence banks my sailplane, I
assume it could be a thermal that I clipped
with one of the glider’s wings. I have an
original tip to share that has never be seen in
print; the initial turn diameter should be
inversely proportional to the severity of the
initial change in attitude.
If something strong rocks your model,
quickly start tight circles. If something
weakly disturbs the model, slowly start big
circles. If the thermal flips your model up to
knife-edge flight, whip the stick full over,
back into the thermal, and start tight circles
with a 45° bank angle.
At moderate altitudes, the large wind
shears needed to roll your sailplane over are
usually caused by fast-rising, small-diameter
thermals. By immediately getting your glider
back into the thermal and turning tightly, you
are likely to get in and stay with the fast-rising
air. If a thermal gently nudges your model, it
is likely weak and/or has a large diameter.
Smoothly turn your sailplane back in the
direction of the thermal and start a largediameter
(shallow-bank) test circle.
Drifting With Thermals: Beginners often
stumble into lift and then lose it after a few
circles. Experienced pilots let their circles
drift with the wind (thus with the thermal).
Instead of trying to circle a fixed point in the
sky, try to maintain a constant bank angle of
the wings. If you maintain a constant bank,
the (moving) center of the circle will take care
of itself. It is a safe bet that when you lose
your lift, the first place to check is straight
downwind of the glider. MA
96 MODEL AVIATION
The ANALYZER+ will test
the capacity of your 4 to
8-cell packs, and let you
know their condition.
Tests 2 packs at once and is highly
accurate.
Can be used stand-alone, or if
connected to the Charge+ TX/RX,
or similar charger, can re-charge
your batteries after testing.
Costs less than a new plane.
INTRODUCTORY OFFER
$14 9 95_ +S&H
Hughes RC 1-800-786-0802 www.hughesrc.com
What you don’t know
CAN hurt you!
09sig3QXD 6/24/04 8:41 am Page 96
Edition: Model Aviation - 2004/09
Page Numbers: 90,92,94,96
90 MODEL AVIATION
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
THE THEME THIS month is thermaling.
I’ll give you a bunch of tips on how to find
and ride these finicky columns of rising air.
This month’s instructions and methods add to
the information from the January 2004
column about the “Condensation Analogy.”
As usual, I’ll start with basics and build to
more advanced ideas.
Bob Zimmerman submitted this month’s
illustration. Bob Sywassink took all the
pictures at the Misty Meadows soar-in, held
May 1-2 in Solon, Iowa.
Choosing the Model: If you are a new RC
glider pilot who wants to thermal, it is
especially important to choose a model that
has generous bend in the wing (dihedral or
Wayne Messner of West Liberty, Iowa, readies his Grande Esprit for a flight. His Space
Pro is sitting in the background.
Mike Fox scans the skies, deciding where to look first for lift. His dad Charlie is timing.
The sailplane is a light version of the Tragi 705.
Paul Haley of Lacrosse, Wisconsin,
launches his Waco Magic 6.
polyhedral). The bent wings will help
coordinate the yaw and roll in the thermal
turns; that is one less thing you will have to
worry about.
A classic good-thermaling polyhedral
sailplane is the Goldberg Gentle Lady. Gentle
Ladys are inexpensive and are now available
in ARF and kit form. Avoid aileron sailplanes
for learning; the vast majority of them have
exceptionally low dihedral angles, making
09sig3QXD 6/24/04 8:40 am Page 90
92 MODEL AVIATION
them more difficult to thermal.
To find thermals, it is critical that you
build the glider straight and true. It needs to
be able to fly straight in calm air. If a wing is
warped, you may be able to get the glider to
fly straight with rudder trim, but this only
works at one speed. Make sure your linkages
are slop free and repeatedly center well. Trim
your glider for straight, level flight with the
CG set so that the model is stable. When set
up correctly, it should fly straight on a calm
day with no pilot inputs.
Don’t move your transmitter sticks! To
find a thermal, you generally need to observe
a change in the sailplane’s direction, attitude,
or speed that you did not cause. The only way
to be certain that you did not cause a change is
to not move the sticks on the transmitter. This
is perfect for hunting thermals.
If you get the opportunity to watch an
expert glider pilot’s hands as he flies, do it.
While hunting for a thermal, you probably
will not see any movement of his or her
hands. Experts are attuned to any movement
Rich Burnoski of Bolingbrook, Illinois,
launches his Pike Superior at the Misty
Meadows Soaring Classic (Solon IA). He
won Unlimited.
Paul Haley’s Magic passes overhead. All photos by Bob Sywassink.
Some changes are coming to
Superior Balsa & Hobby Supply.
We’re starting with
www.superiorbalsa.com
09sig3QXD 6/24/04 8:40 am Page 92
of their gliders; they notice and react to tiny
pitch, roll, or yaw changes that most people
miss altogether.
There are certain times when thermals are
much more likely to form. Glider pilots like to
see a weather forecast that is sunny or partly
cloudy with winds from 5 to 15 mph. Light
and variable winds is another good forecast.
Thermals do form on windy days too, but they
tend to be less organized and are much harder
to work.
It is well known that warm air rises
relative to cold air. A less well-known fact is
that wet air is lighter than dry air. Anytime the
ground is drying, there will be some lift. The
day after a nighttime rain usually has good
thermals. The afternoon after a morning rain
also makes good lift.
A cold front followed by a mass of cold air
will provide contrast between the ground
temperature and the air temperature. I have
seen thermals and cumulus clouds form when
cold air masses arrive even on a winter
evening with a snow-covered ground.
When do the thermals start percolating?
The first opportunity for thermal lift in a day
is usually what I call the “morning burnoff.”
This is when the sun has risen enough to heat
and evaporate the morning dew on the grass.
In my area, the dew typically burns off at
roughly 9:30.
The morning-burnoff lift is usually weak
compared to later thermals. The dew may not
be causing the lift, but its disappearance is a
sure sign of ground heating, which does start
making lift. You can expect to find some
thermal activity anytime after the morning
burnoff.
The “noon balloon” occurs when the sun
is high in the sky. It is not really just at noon;
anytime between 11 a.m. and 3 p.m. is ideal
for finding thermals on a sunny day. This is
when you are most likely to find strong lift.
Early evening is not ideal for thermal
activity. If you fly after work on a weekday,
you have to make the most of the conditions.
Evening thermals tend to be wide, weak, and
smooth compared to midday thermals. If you
are lucky enough to find a thermal in the
evening, a couple clicks of rudder trim is
often perfect to trace huge circles with
minimum sink rate (thus maximum climb
rate).
The evening air often seems “buoyant,”
meaning that the lift may not be strong
enough to make the glider climb, but it is
enough to slow the descent or possibly hold
altitude. I have played “last man down” from
matched hi-starts in the evening. The pilot
who makes the fewest and most subtle control
inputs will usually win in this situation.
What to Look For: Most thermals are
invisible. The most obvious visual sign of
thermal activity is usually the formation of
cumulus clouds. These flat-bottomed cotton
balls sit on the top of thermals. Thermals can
be found in clear skies too, but young
(building) cumulus clouds guarantee it.
Thermals often carry flying insects.
Although the insects may be too far away for
a ground-based pilot to see, the swallows or
other birds feeding on the bugs are more
visible. The presence of soaring birds is, of
course, a dead giveaway. In movies, circling
birds mean that something is dead. In real life,
it is much more likely to mean that they are
riding a thermal.
Note the frequency of the wind cycles. On
a day with light breezes, the wind repeatedly
dies and then picks up. When the wind dies,
the thermal is either just upwind of you or
right above you. When the wind picks up, the
thermal has just passed to the downwind side
of your location. By paying attention to the
wind velocity and direction on the ground,
you can get an excellent idea of which
direction the closest thermal is.
Think of the thermal as a vacuum sucking
in air near the ground from all directions.
When the thermal wind is superimposed on
the ambient wind, some components add up
and some cancel out.
Knowing the current wind and the average
or ambient component, you can use vector
math to solve for the thermal-induced wind.
This tells you the likely location of the bottom
of the thermal. No numbers are needed; just
use logic. Several-time world-champion pilot
Joe Wurts calls this “solving for the third
vector.”
Occasionally you can see a dust devil,
which is like a minitornado, kicking up dust
and dancing along the ground. I differentiate a
Specifications:
Displacement: .40 cubic inches
Bore: 0.82 inches
Stroke: 0.75 inches
Compression: 9:1 to 12:1
RPM Range: 2,000 to 17,000 rpm
Power: 1.4 hp @ 16,000 rpm
Fuel Consumption: 30 ounces/hour
Weight w/o muffler: 10.8 ounces
Weight w/ muffler: 13.1 ounces
Available from participating dealers for $109.99
“The AX-40 is a
revolutionary engine!”
Model Airplane News Magazine, January 2004
Norvel is exclusively distributed in North America by:
SIG Manufacturing Company, Inc. • P.O. Box 520 • Montezuma, IA 50171-0520 • Phone: 641-623-5154
www.norvel.com
We think so too. With a legendary Norvel heritage of superior
craftsmanship, state-of-the-art metallurgy and materials, coupled with rocksolid
reliability, the new AX-40 raises the bar for popularly sized glow engines.
Weighing ounces less than other similar engines, the Norvel
AX-40 sets the standard for power-to-weight ratios and fuel economy.
With our exclusive Revite™ cylinder technology with Sliktek™, engine
friction is not an issue and power is increased 20-40% on average.
What more could you want? How about a 2 needle carburetor
with an angled back design to help keep your fingers away from the
prop, and a lightweight, quiet yet power-efficient muffler designed
to keep the neighbors happy. All at a price you can’t afford to pass
up.
Join the revolution! Buy a AX-40 today and fly better
tomorrow.
94 MODEL AVIATION
09sig3QXD 6/24/04 8:41 am Page 94
dust devil from a normal thermal by its
rotation. The dirt in a dust devil can be seen
spinning. The dust devil also moves quickly
along the ground. Perhaps the high-velocity
rotation causes the dust devil to have the
energy to kick up dust. This rotation can be
violent and generally not good for RC gliders.
In reality, there is a continuous spectrum
of weather phenomena with varying amounts
of rotation. A good rule of thumb is that if
you can see rotating dust and movement of
the plume along the ground, keep your glider
away. The “friendly thermals” have a great
deal of rising velocity with little rotation.
The Initial Turn: When I am searching for
lift and turbulence banks my sailplane, I
assume it could be a thermal that I clipped
with one of the glider’s wings. I have an
original tip to share that has never be seen in
print; the initial turn diameter should be
inversely proportional to the severity of the
initial change in attitude.
If something strong rocks your model,
quickly start tight circles. If something
weakly disturbs the model, slowly start big
circles. If the thermal flips your model up to
knife-edge flight, whip the stick full over,
back into the thermal, and start tight circles
with a 45° bank angle.
At moderate altitudes, the large wind
shears needed to roll your sailplane over are
usually caused by fast-rising, small-diameter
thermals. By immediately getting your glider
back into the thermal and turning tightly, you
are likely to get in and stay with the fast-rising
air. If a thermal gently nudges your model, it
is likely weak and/or has a large diameter.
Smoothly turn your sailplane back in the
direction of the thermal and start a largediameter
(shallow-bank) test circle.
Drifting With Thermals: Beginners often
stumble into lift and then lose it after a few
circles. Experienced pilots let their circles
drift with the wind (thus with the thermal).
Instead of trying to circle a fixed point in the
sky, try to maintain a constant bank angle of
the wings. If you maintain a constant bank,
the (moving) center of the circle will take care
of itself. It is a safe bet that when you lose
your lift, the first place to check is straight
downwind of the glider. MA
96 MODEL AVIATION
The ANALYZER+ will test
the capacity of your 4 to
8-cell packs, and let you
know their condition.
Tests 2 packs at once and is highly
accurate.
Can be used stand-alone, or if
connected to the Charge+ TX/RX,
or similar charger, can re-charge
your batteries after testing.
Costs less than a new plane.
INTRODUCTORY OFFER
$14 9 95_ +S&H
Hughes RC 1-800-786-0802 www.hughesrc.com
What you don’t know
CAN hurt you!
09sig3QXD 6/24/04 8:41 am Page 96