80 MODEL AVIATION
THIS MONTH I’LL debut “the
condensation analogy.” This original
thermaling tip helps predict where the
base of thermals will be located relative to
the ground. I’ll also describe a gadget
called the LoLo, which is a tiny logging
altimeter for models.
Learning to thermal is a daunting task.
Besides being invisible, the shapes of
thermals are complicated and always
changing. They lean with the wind and
sometimes break off. Finding and coring
the thermal can be difficult.
“Coring” a thermal means finding a
circle center and diameter that result in a
maximum rate of climb. If the glider
climbs more on one side of the circle, shift
the center in that direction. If no
improvement is seen during the shifting
and your model is climbing well, you
either have it cored or it is huge and
gentle. In the latter case, try wider circles
to climb faster. If you can’t find a thermal
center that results in an even climb,
decrease the diameter and then recenter.
Thermals drift with the wind. Holding
a constant circle relative to the thermal
means that the center of the circle must
drift too. If you try to hold a constant
circle center relative to the ground, the
thermal will be lost as it travels
downwind. Thermals get larger in
diameter with increasing altitude. During
the climb, try periodically to widen the
circle a bit and see if the climb rate
improves.
Thermals are often described as being
shaped like trees with exposed roots or
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
The 10-gram LoLo altimeter is easy to carry, even in a Hand-Launched Glider.
multifunneled tornadoes. The trees
migrate downwind, sometimes pausing
over particularly strong generators of
warm air.
Several times I have cored a thermal
on one side of a field at nearly the same
time another experienced flier cored one
some distance away. We were fairly
confident that we had each cored a plume.
Any deviation in circle center resulted in a
lower climb rate. Each time this has
happened, the two thermal plumes
eventually joined at a much higher
altitude. The plumes were like tree roots.
We followed different tree roots (plumes)
up to the same trunk.
Most of the writing I have found about
thermals describes what happens at the
tree-trunk altitude. Winch launches and all
hand launches start in the surface layer,
usually well below the trunks of the
thermals.
There is very little good information
describing how to predict where the roots
01sig3.QXD 10/27/03 10:03 am Page 80
82 MODEL AVIATION
of the tree will start. Saying that the
thermals form over pavement and darker
ground falls short of predicting their
locations. After flying for 20 years I
developed an analogy that is useful in
predicting where the roots of the trees
(bases of the plumes) will be.
The Condensation Analogy: Have you
ever watched what condensation does on
the ceiling, say above a shower stall? The
droplets take shape uniformly at first, then
they start to move around and coalesce.
The small droplets stick to the ceiling
because of surface tension. When they get
bigger, gravity overcomes the surface
tension and they fall.
On a flat, smooth ceiling, the drops fall
from random locations. If the ceiling is a
hair unlevel or sags, the drops tend to
migrate toward the low side. When the
drops encounter a local low spot, they
follow it downward and stop there. After
enough small droplets have collected on
the low spot, it releases a drip.
Compare the behavior of the
condensation droplets to the blobs of warm
air that form above a relatively flat field.
The blobs of air tend to migrate along the
ground with the wind like the condensation
Tru-Turn now offers the popular Ultimate shape in EIGHT
different sizes! This Spinner looks great on your Cessna as well
as CAP, Edge, Extra, Giles, and many other aerobatic and sport
designs.
You'll find this Spinner available in "120-Slot" for the prop range
used on 4-stroke .91-1.50 motors and "Menz Cut" for use with
most european style props up to 22". Special Slotting is
available upon request too! Use our "Adapter Finder" online to
find an Adapter Kit and learn of any possible Spinner Backplate
modifications you may need at our website today!
See your Hobby dealer or call Tru-Turn direct:
(281) 479-9600 www.tru-turn.com
Made in the U.S.A.
by Romco Manufacturing, Inc.
100 West First Street, Deer Park, Texas 77536
Made in the U.S.A.
01sig3.QXD 10/27/03 10:04 am Page 82
drops migrate with a slight tilt of the
ceiling.
Maybe a more vivid picture is the way
condensation droplets flow down the sides of
a domed glass lid above a boiling pot. The
droplets coalesce when they bump into each
other and always head in the direction of
lower ground.
On the thermal side of the analogy, the
bubbles of warm air are blown along the
ground with the wind. When they encounter a
high spot, they collect and break off. Any
ridge, hill, tree line, or building can be a
thermal trigger. These obstacles act much like
the low spots on the ceiling in the
condensation analogy.
Similar rules to predict the behavior apply.
The blobs drift with the wind, group together,
move to higher ground, and break off when
they can go no higher. The “higher-ground”
thermal effect is like the “lower-ground”
condensation effect turned upside down.
The wind and higher-ground effects are
additive. They can work with each other or
against each other, depending on their
magnitude. I don’t claim that any of the
physical forces on the two sides of the
analogy are the same. I do know that the
analogy is useful to predict the formation
of thermal plumes near the ground.
What does the analogy mean in
practice? Check the tree line or building
on the downwind side of a field. A plume
usually starts directly above the obstacle
downwind of the field. If the wind is not
perpendicular to the tree line, the blobs of
warm air will be corralled to the
downwind corner of the field, rise over the
tree line, and form a plume above the
corner.
If there is a high ridge line on lower
ground, thermal plumes frequently form at
the top of the ridge. You can verify that it
is not slope lift because you can climb
84 MODEL AVIATION
very high and the base of the plume is at
the peak of the ridge. Slope lift is
generally located out in front upwind at
approximately a 45° angle to the hill.
Ridge-top thermals are often strong and
break off suddenly. When I go sloping and
the wind is cycling from high to low, I
know that there are thermals climbing the
slope. If you understand the wind pattern
and catch the thermal, you can spec out
the glider during these lulls.
Some slopes are high enough to
intersect thermals that are already well
formed, like the trunks of trees. In this
case the whole tree will quickly dance up
the face of the slope, headed for higher
ground. It will peak in strength when the
base of the thermal “tree” hits the highest
point of the ridge. If you catch one of
these powerful thermals, core it quickly
because they tend to break off shortly
after reaching the top.
01sig3.QXD 10/27/03 10:04 am Page 84
86 MODEL AVIATION
The LoLo is a tiny data-logging altimeter
that you plug into a spare receiver
channel. It measures pressure and records
it, to be downloaded later. The LoLo
comes in a variety of sampling rates.
Mine can sample on 0.2-second intervals
for 32 minutes or 1.0-second intervals for
160 minutes. I select which sampling rate
is used with a jumper (removable bridge
between two places on the circuit).
The data is downloaded to a personal
computer with the included serial cable.
A Microsoft Excel spreadsheet catches
the data for graphing and review. My
wife bought me the LoLo for Christmas.
The data set graphed in this column
was from a lunch-hour flying session
with my discus glider (a flaperon XP-3). I
had the altimeter in the XP-3 most of this
year. The LoLo is light enough (10
grams) that I don’t notice it. Current
draw is not really an issue in my setup.
The 370 mAh Nickel Metal Hydride
flight-pack battery lasts me almost three
hours with the four servos and the LoLo,
which draws roughly 17 mAh.
The little spikes at the beginning of
the graph are discus launches. The first
warm-up launch is 100 feet; the best
launch on the graph is 132 feet. I was
sport flying, so I did stationary throws.
Running a few steps before spinning
results in higher launches. The second
and third launches were right into sinking
air.
Whenever I sport-fly I try hard to
really core the thermals. I get the greatest
satisfaction from knowing I located the
core of the plume and watching the glider
climb at a fast rate. You can see on the
graph that the XP-3 caught some lift and
climbed to 400 feet on the fourth launch.
After feeling a wind shift, I searched in
the direction it was sucking and found
stronger lift. Eventually I started tight,
slow circles in what appeared to be the
core of the thermal. The climb was
excellent for my part of the country,
averaging 565 feet per minute between
400 and 2,300 feet. I have had faster
apparent climb rates when flying over
desert regions.
The smooth, consistent climb and
high-altitude flying were made possible
by the stability that 7° of dihedral per
side (14° total bend) provided. I don’t
need to see my model well to fly it
efficiently. Dihedral also helped
maximize the climb rate. High-dihedral
airplanes can make slow, tight turns
without spiraling in.
I hope you find the condensation
analogy useful in predicting where to
catch your next bus up to cloud base. MA
Sources:
LoLo manufacturer:
www.lomcovak.cz/eindex.html
LoLo US source:
www.yntdesign.com/
www.modelaircraft.org
01sig3.QXD 10/27/03 10:04 am Page 86
Edition: Model Aviation - 2004/01
Page Numbers: 80,82,84,86
Edition: Model Aviation - 2004/01
Page Numbers: 80,82,84,86
80 MODEL AVIATION
THIS MONTH I’LL debut “the
condensation analogy.” This original
thermaling tip helps predict where the
base of thermals will be located relative to
the ground. I’ll also describe a gadget
called the LoLo, which is a tiny logging
altimeter for models.
Learning to thermal is a daunting task.
Besides being invisible, the shapes of
thermals are complicated and always
changing. They lean with the wind and
sometimes break off. Finding and coring
the thermal can be difficult.
“Coring” a thermal means finding a
circle center and diameter that result in a
maximum rate of climb. If the glider
climbs more on one side of the circle, shift
the center in that direction. If no
improvement is seen during the shifting
and your model is climbing well, you
either have it cored or it is huge and
gentle. In the latter case, try wider circles
to climb faster. If you can’t find a thermal
center that results in an even climb,
decrease the diameter and then recenter.
Thermals drift with the wind. Holding
a constant circle relative to the thermal
means that the center of the circle must
drift too. If you try to hold a constant
circle center relative to the ground, the
thermal will be lost as it travels
downwind. Thermals get larger in
diameter with increasing altitude. During
the climb, try periodically to widen the
circle a bit and see if the climb rate
improves.
Thermals are often described as being
shaped like trees with exposed roots or
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
The 10-gram LoLo altimeter is easy to carry, even in a Hand-Launched Glider.
multifunneled tornadoes. The trees
migrate downwind, sometimes pausing
over particularly strong generators of
warm air.
Several times I have cored a thermal
on one side of a field at nearly the same
time another experienced flier cored one
some distance away. We were fairly
confident that we had each cored a plume.
Any deviation in circle center resulted in a
lower climb rate. Each time this has
happened, the two thermal plumes
eventually joined at a much higher
altitude. The plumes were like tree roots.
We followed different tree roots (plumes)
up to the same trunk.
Most of the writing I have found about
thermals describes what happens at the
tree-trunk altitude. Winch launches and all
hand launches start in the surface layer,
usually well below the trunks of the
thermals.
There is very little good information
describing how to predict where the roots
01sig3.QXD 10/27/03 10:03 am Page 80
82 MODEL AVIATION
of the tree will start. Saying that the
thermals form over pavement and darker
ground falls short of predicting their
locations. After flying for 20 years I
developed an analogy that is useful in
predicting where the roots of the trees
(bases of the plumes) will be.
The Condensation Analogy: Have you
ever watched what condensation does on
the ceiling, say above a shower stall? The
droplets take shape uniformly at first, then
they start to move around and coalesce.
The small droplets stick to the ceiling
because of surface tension. When they get
bigger, gravity overcomes the surface
tension and they fall.
On a flat, smooth ceiling, the drops fall
from random locations. If the ceiling is a
hair unlevel or sags, the drops tend to
migrate toward the low side. When the
drops encounter a local low spot, they
follow it downward and stop there. After
enough small droplets have collected on
the low spot, it releases a drip.
Compare the behavior of the
condensation droplets to the blobs of warm
air that form above a relatively flat field.
The blobs of air tend to migrate along the
ground with the wind like the condensation
Tru-Turn now offers the popular Ultimate shape in EIGHT
different sizes! This Spinner looks great on your Cessna as well
as CAP, Edge, Extra, Giles, and many other aerobatic and sport
designs.
You'll find this Spinner available in "120-Slot" for the prop range
used on 4-stroke .91-1.50 motors and "Menz Cut" for use with
most european style props up to 22". Special Slotting is
available upon request too! Use our "Adapter Finder" online to
find an Adapter Kit and learn of any possible Spinner Backplate
modifications you may need at our website today!
See your Hobby dealer or call Tru-Turn direct:
(281) 479-9600 www.tru-turn.com
Made in the U.S.A.
by Romco Manufacturing, Inc.
100 West First Street, Deer Park, Texas 77536
Made in the U.S.A.
01sig3.QXD 10/27/03 10:04 am Page 82
drops migrate with a slight tilt of the
ceiling.
Maybe a more vivid picture is the way
condensation droplets flow down the sides of
a domed glass lid above a boiling pot. The
droplets coalesce when they bump into each
other and always head in the direction of
lower ground.
On the thermal side of the analogy, the
bubbles of warm air are blown along the
ground with the wind. When they encounter a
high spot, they collect and break off. Any
ridge, hill, tree line, or building can be a
thermal trigger. These obstacles act much like
the low spots on the ceiling in the
condensation analogy.
Similar rules to predict the behavior apply.
The blobs drift with the wind, group together,
move to higher ground, and break off when
they can go no higher. The “higher-ground”
thermal effect is like the “lower-ground”
condensation effect turned upside down.
The wind and higher-ground effects are
additive. They can work with each other or
against each other, depending on their
magnitude. I don’t claim that any of the
physical forces on the two sides of the
analogy are the same. I do know that the
analogy is useful to predict the formation
of thermal plumes near the ground.
What does the analogy mean in
practice? Check the tree line or building
on the downwind side of a field. A plume
usually starts directly above the obstacle
downwind of the field. If the wind is not
perpendicular to the tree line, the blobs of
warm air will be corralled to the
downwind corner of the field, rise over the
tree line, and form a plume above the
corner.
If there is a high ridge line on lower
ground, thermal plumes frequently form at
the top of the ridge. You can verify that it
is not slope lift because you can climb
84 MODEL AVIATION
very high and the base of the plume is at
the peak of the ridge. Slope lift is
generally located out in front upwind at
approximately a 45° angle to the hill.
Ridge-top thermals are often strong and
break off suddenly. When I go sloping and
the wind is cycling from high to low, I
know that there are thermals climbing the
slope. If you understand the wind pattern
and catch the thermal, you can spec out
the glider during these lulls.
Some slopes are high enough to
intersect thermals that are already well
formed, like the trunks of trees. In this
case the whole tree will quickly dance up
the face of the slope, headed for higher
ground. It will peak in strength when the
base of the thermal “tree” hits the highest
point of the ridge. If you catch one of
these powerful thermals, core it quickly
because they tend to break off shortly
after reaching the top.
01sig3.QXD 10/27/03 10:04 am Page 84
86 MODEL AVIATION
The LoLo is a tiny data-logging altimeter
that you plug into a spare receiver
channel. It measures pressure and records
it, to be downloaded later. The LoLo
comes in a variety of sampling rates.
Mine can sample on 0.2-second intervals
for 32 minutes or 1.0-second intervals for
160 minutes. I select which sampling rate
is used with a jumper (removable bridge
between two places on the circuit).
The data is downloaded to a personal
computer with the included serial cable.
A Microsoft Excel spreadsheet catches
the data for graphing and review. My
wife bought me the LoLo for Christmas.
The data set graphed in this column
was from a lunch-hour flying session
with my discus glider (a flaperon XP-3). I
had the altimeter in the XP-3 most of this
year. The LoLo is light enough (10
grams) that I don’t notice it. Current
draw is not really an issue in my setup.
The 370 mAh Nickel Metal Hydride
flight-pack battery lasts me almost three
hours with the four servos and the LoLo,
which draws roughly 17 mAh.
The little spikes at the beginning of
the graph are discus launches. The first
warm-up launch is 100 feet; the best
launch on the graph is 132 feet. I was
sport flying, so I did stationary throws.
Running a few steps before spinning
results in higher launches. The second
and third launches were right into sinking
air.
Whenever I sport-fly I try hard to
really core the thermals. I get the greatest
satisfaction from knowing I located the
core of the plume and watching the glider
climb at a fast rate. You can see on the
graph that the XP-3 caught some lift and
climbed to 400 feet on the fourth launch.
After feeling a wind shift, I searched in
the direction it was sucking and found
stronger lift. Eventually I started tight,
slow circles in what appeared to be the
core of the thermal. The climb was
excellent for my part of the country,
averaging 565 feet per minute between
400 and 2,300 feet. I have had faster
apparent climb rates when flying over
desert regions.
The smooth, consistent climb and
high-altitude flying were made possible
by the stability that 7° of dihedral per
side (14° total bend) provided. I don’t
need to see my model well to fly it
efficiently. Dihedral also helped
maximize the climb rate. High-dihedral
airplanes can make slow, tight turns
without spiraling in.
I hope you find the condensation
analogy useful in predicting where to
catch your next bus up to cloud base. MA
Sources:
LoLo manufacturer:
www.lomcovak.cz/eindex.html
LoLo US source:
www.yntdesign.com/
www.modelaircraft.org
01sig3.QXD 10/27/03 10:04 am Page 86
Edition: Model Aviation - 2004/01
Page Numbers: 80,82,84,86
80 MODEL AVIATION
THIS MONTH I’LL debut “the
condensation analogy.” This original
thermaling tip helps predict where the
base of thermals will be located relative to
the ground. I’ll also describe a gadget
called the LoLo, which is a tiny logging
altimeter for models.
Learning to thermal is a daunting task.
Besides being invisible, the shapes of
thermals are complicated and always
changing. They lean with the wind and
sometimes break off. Finding and coring
the thermal can be difficult.
“Coring” a thermal means finding a
circle center and diameter that result in a
maximum rate of climb. If the glider
climbs more on one side of the circle, shift
the center in that direction. If no
improvement is seen during the shifting
and your model is climbing well, you
either have it cored or it is huge and
gentle. In the latter case, try wider circles
to climb faster. If you can’t find a thermal
center that results in an even climb,
decrease the diameter and then recenter.
Thermals drift with the wind. Holding
a constant circle relative to the thermal
means that the center of the circle must
drift too. If you try to hold a constant
circle center relative to the ground, the
thermal will be lost as it travels
downwind. Thermals get larger in
diameter with increasing altitude. During
the climb, try periodically to widen the
circle a bit and see if the climb rate
improves.
Thermals are often described as being
shaped like trees with exposed roots or
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
The 10-gram LoLo altimeter is easy to carry, even in a Hand-Launched Glider.
multifunneled tornadoes. The trees
migrate downwind, sometimes pausing
over particularly strong generators of
warm air.
Several times I have cored a thermal
on one side of a field at nearly the same
time another experienced flier cored one
some distance away. We were fairly
confident that we had each cored a plume.
Any deviation in circle center resulted in a
lower climb rate. Each time this has
happened, the two thermal plumes
eventually joined at a much higher
altitude. The plumes were like tree roots.
We followed different tree roots (plumes)
up to the same trunk.
Most of the writing I have found about
thermals describes what happens at the
tree-trunk altitude. Winch launches and all
hand launches start in the surface layer,
usually well below the trunks of the
thermals.
There is very little good information
describing how to predict where the roots
01sig3.QXD 10/27/03 10:03 am Page 80
82 MODEL AVIATION
of the tree will start. Saying that the
thermals form over pavement and darker
ground falls short of predicting their
locations. After flying for 20 years I
developed an analogy that is useful in
predicting where the roots of the trees
(bases of the plumes) will be.
The Condensation Analogy: Have you
ever watched what condensation does on
the ceiling, say above a shower stall? The
droplets take shape uniformly at first, then
they start to move around and coalesce.
The small droplets stick to the ceiling
because of surface tension. When they get
bigger, gravity overcomes the surface
tension and they fall.
On a flat, smooth ceiling, the drops fall
from random locations. If the ceiling is a
hair unlevel or sags, the drops tend to
migrate toward the low side. When the
drops encounter a local low spot, they
follow it downward and stop there. After
enough small droplets have collected on
the low spot, it releases a drip.
Compare the behavior of the
condensation droplets to the blobs of warm
air that form above a relatively flat field.
The blobs of air tend to migrate along the
ground with the wind like the condensation
Tru-Turn now offers the popular Ultimate shape in EIGHT
different sizes! This Spinner looks great on your Cessna as well
as CAP, Edge, Extra, Giles, and many other aerobatic and sport
designs.
You'll find this Spinner available in "120-Slot" for the prop range
used on 4-stroke .91-1.50 motors and "Menz Cut" for use with
most european style props up to 22". Special Slotting is
available upon request too! Use our "Adapter Finder" online to
find an Adapter Kit and learn of any possible Spinner Backplate
modifications you may need at our website today!
See your Hobby dealer or call Tru-Turn direct:
(281) 479-9600 www.tru-turn.com
Made in the U.S.A.
by Romco Manufacturing, Inc.
100 West First Street, Deer Park, Texas 77536
Made in the U.S.A.
01sig3.QXD 10/27/03 10:04 am Page 82
drops migrate with a slight tilt of the
ceiling.
Maybe a more vivid picture is the way
condensation droplets flow down the sides of
a domed glass lid above a boiling pot. The
droplets coalesce when they bump into each
other and always head in the direction of
lower ground.
On the thermal side of the analogy, the
bubbles of warm air are blown along the
ground with the wind. When they encounter a
high spot, they collect and break off. Any
ridge, hill, tree line, or building can be a
thermal trigger. These obstacles act much like
the low spots on the ceiling in the
condensation analogy.
Similar rules to predict the behavior apply.
The blobs drift with the wind, group together,
move to higher ground, and break off when
they can go no higher. The “higher-ground”
thermal effect is like the “lower-ground”
condensation effect turned upside down.
The wind and higher-ground effects are
additive. They can work with each other or
against each other, depending on their
magnitude. I don’t claim that any of the
physical forces on the two sides of the
analogy are the same. I do know that the
analogy is useful to predict the formation
of thermal plumes near the ground.
What does the analogy mean in
practice? Check the tree line or building
on the downwind side of a field. A plume
usually starts directly above the obstacle
downwind of the field. If the wind is not
perpendicular to the tree line, the blobs of
warm air will be corralled to the
downwind corner of the field, rise over the
tree line, and form a plume above the
corner.
If there is a high ridge line on lower
ground, thermal plumes frequently form at
the top of the ridge. You can verify that it
is not slope lift because you can climb
84 MODEL AVIATION
very high and the base of the plume is at
the peak of the ridge. Slope lift is
generally located out in front upwind at
approximately a 45° angle to the hill.
Ridge-top thermals are often strong and
break off suddenly. When I go sloping and
the wind is cycling from high to low, I
know that there are thermals climbing the
slope. If you understand the wind pattern
and catch the thermal, you can spec out
the glider during these lulls.
Some slopes are high enough to
intersect thermals that are already well
formed, like the trunks of trees. In this
case the whole tree will quickly dance up
the face of the slope, headed for higher
ground. It will peak in strength when the
base of the thermal “tree” hits the highest
point of the ridge. If you catch one of
these powerful thermals, core it quickly
because they tend to break off shortly
after reaching the top.
01sig3.QXD 10/27/03 10:04 am Page 84
86 MODEL AVIATION
The LoLo is a tiny data-logging altimeter
that you plug into a spare receiver
channel. It measures pressure and records
it, to be downloaded later. The LoLo
comes in a variety of sampling rates.
Mine can sample on 0.2-second intervals
for 32 minutes or 1.0-second intervals for
160 minutes. I select which sampling rate
is used with a jumper (removable bridge
between two places on the circuit).
The data is downloaded to a personal
computer with the included serial cable.
A Microsoft Excel spreadsheet catches
the data for graphing and review. My
wife bought me the LoLo for Christmas.
The data set graphed in this column
was from a lunch-hour flying session
with my discus glider (a flaperon XP-3). I
had the altimeter in the XP-3 most of this
year. The LoLo is light enough (10
grams) that I don’t notice it. Current
draw is not really an issue in my setup.
The 370 mAh Nickel Metal Hydride
flight-pack battery lasts me almost three
hours with the four servos and the LoLo,
which draws roughly 17 mAh.
The little spikes at the beginning of
the graph are discus launches. The first
warm-up launch is 100 feet; the best
launch on the graph is 132 feet. I was
sport flying, so I did stationary throws.
Running a few steps before spinning
results in higher launches. The second
and third launches were right into sinking
air.
Whenever I sport-fly I try hard to
really core the thermals. I get the greatest
satisfaction from knowing I located the
core of the plume and watching the glider
climb at a fast rate. You can see on the
graph that the XP-3 caught some lift and
climbed to 400 feet on the fourth launch.
After feeling a wind shift, I searched in
the direction it was sucking and found
stronger lift. Eventually I started tight,
slow circles in what appeared to be the
core of the thermal. The climb was
excellent for my part of the country,
averaging 565 feet per minute between
400 and 2,300 feet. I have had faster
apparent climb rates when flying over
desert regions.
The smooth, consistent climb and
high-altitude flying were made possible
by the stability that 7° of dihedral per
side (14° total bend) provided. I don’t
need to see my model well to fly it
efficiently. Dihedral also helped
maximize the climb rate. High-dihedral
airplanes can make slow, tight turns
without spiraling in.
I hope you find the condensation
analogy useful in predicting where to
catch your next bus up to cloud base. MA
Sources:
LoLo manufacturer:
www.lomcovak.cz/eindex.html
LoLo US source:
www.yntdesign.com/
www.modelaircraft.org
01sig3.QXD 10/27/03 10:04 am Page 86
Edition: Model Aviation - 2004/01
Page Numbers: 80,82,84,86
80 MODEL AVIATION
THIS MONTH I’LL debut “the
condensation analogy.” This original
thermaling tip helps predict where the
base of thermals will be located relative to
the ground. I’ll also describe a gadget
called the LoLo, which is a tiny logging
altimeter for models.
Learning to thermal is a daunting task.
Besides being invisible, the shapes of
thermals are complicated and always
changing. They lean with the wind and
sometimes break off. Finding and coring
the thermal can be difficult.
“Coring” a thermal means finding a
circle center and diameter that result in a
maximum rate of climb. If the glider
climbs more on one side of the circle, shift
the center in that direction. If no
improvement is seen during the shifting
and your model is climbing well, you
either have it cored or it is huge and
gentle. In the latter case, try wider circles
to climb faster. If you can’t find a thermal
center that results in an even climb,
decrease the diameter and then recenter.
Thermals drift with the wind. Holding
a constant circle relative to the thermal
means that the center of the circle must
drift too. If you try to hold a constant
circle center relative to the ground, the
thermal will be lost as it travels
downwind. Thermals get larger in
diameter with increasing altitude. During
the climb, try periodically to widen the
circle a bit and see if the climb rate
improves.
Thermals are often described as being
shaped like trees with exposed roots or
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
The 10-gram LoLo altimeter is easy to carry, even in a Hand-Launched Glider.
multifunneled tornadoes. The trees
migrate downwind, sometimes pausing
over particularly strong generators of
warm air.
Several times I have cored a thermal
on one side of a field at nearly the same
time another experienced flier cored one
some distance away. We were fairly
confident that we had each cored a plume.
Any deviation in circle center resulted in a
lower climb rate. Each time this has
happened, the two thermal plumes
eventually joined at a much higher
altitude. The plumes were like tree roots.
We followed different tree roots (plumes)
up to the same trunk.
Most of the writing I have found about
thermals describes what happens at the
tree-trunk altitude. Winch launches and all
hand launches start in the surface layer,
usually well below the trunks of the
thermals.
There is very little good information
describing how to predict where the roots
01sig3.QXD 10/27/03 10:03 am Page 80
82 MODEL AVIATION
of the tree will start. Saying that the
thermals form over pavement and darker
ground falls short of predicting their
locations. After flying for 20 years I
developed an analogy that is useful in
predicting where the roots of the trees
(bases of the plumes) will be.
The Condensation Analogy: Have you
ever watched what condensation does on
the ceiling, say above a shower stall? The
droplets take shape uniformly at first, then
they start to move around and coalesce.
The small droplets stick to the ceiling
because of surface tension. When they get
bigger, gravity overcomes the surface
tension and they fall.
On a flat, smooth ceiling, the drops fall
from random locations. If the ceiling is a
hair unlevel or sags, the drops tend to
migrate toward the low side. When the
drops encounter a local low spot, they
follow it downward and stop there. After
enough small droplets have collected on
the low spot, it releases a drip.
Compare the behavior of the
condensation droplets to the blobs of warm
air that form above a relatively flat field.
The blobs of air tend to migrate along the
ground with the wind like the condensation
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01sig3.QXD 10/27/03 10:04 am Page 82
drops migrate with a slight tilt of the
ceiling.
Maybe a more vivid picture is the way
condensation droplets flow down the sides of
a domed glass lid above a boiling pot. The
droplets coalesce when they bump into each
other and always head in the direction of
lower ground.
On the thermal side of the analogy, the
bubbles of warm air are blown along the
ground with the wind. When they encounter a
high spot, they collect and break off. Any
ridge, hill, tree line, or building can be a
thermal trigger. These obstacles act much like
the low spots on the ceiling in the
condensation analogy.
Similar rules to predict the behavior apply.
The blobs drift with the wind, group together,
move to higher ground, and break off when
they can go no higher. The “higher-ground”
thermal effect is like the “lower-ground”
condensation effect turned upside down.
The wind and higher-ground effects are
additive. They can work with each other or
against each other, depending on their
magnitude. I don’t claim that any of the
physical forces on the two sides of the
analogy are the same. I do know that the
analogy is useful to predict the formation
of thermal plumes near the ground.
What does the analogy mean in
practice? Check the tree line or building
on the downwind side of a field. A plume
usually starts directly above the obstacle
downwind of the field. If the wind is not
perpendicular to the tree line, the blobs of
warm air will be corralled to the
downwind corner of the field, rise over the
tree line, and form a plume above the
corner.
If there is a high ridge line on lower
ground, thermal plumes frequently form at
the top of the ridge. You can verify that it
is not slope lift because you can climb
84 MODEL AVIATION
very high and the base of the plume is at
the peak of the ridge. Slope lift is
generally located out in front upwind at
approximately a 45° angle to the hill.
Ridge-top thermals are often strong and
break off suddenly. When I go sloping and
the wind is cycling from high to low, I
know that there are thermals climbing the
slope. If you understand the wind pattern
and catch the thermal, you can spec out
the glider during these lulls.
Some slopes are high enough to
intersect thermals that are already well
formed, like the trunks of trees. In this
case the whole tree will quickly dance up
the face of the slope, headed for higher
ground. It will peak in strength when the
base of the thermal “tree” hits the highest
point of the ridge. If you catch one of
these powerful thermals, core it quickly
because they tend to break off shortly
after reaching the top.
01sig3.QXD 10/27/03 10:04 am Page 84
86 MODEL AVIATION
The LoLo is a tiny data-logging altimeter
that you plug into a spare receiver
channel. It measures pressure and records
it, to be downloaded later. The LoLo
comes in a variety of sampling rates.
Mine can sample on 0.2-second intervals
for 32 minutes or 1.0-second intervals for
160 minutes. I select which sampling rate
is used with a jumper (removable bridge
between two places on the circuit).
The data is downloaded to a personal
computer with the included serial cable.
A Microsoft Excel spreadsheet catches
the data for graphing and review. My
wife bought me the LoLo for Christmas.
The data set graphed in this column
was from a lunch-hour flying session
with my discus glider (a flaperon XP-3). I
had the altimeter in the XP-3 most of this
year. The LoLo is light enough (10
grams) that I don’t notice it. Current
draw is not really an issue in my setup.
The 370 mAh Nickel Metal Hydride
flight-pack battery lasts me almost three
hours with the four servos and the LoLo,
which draws roughly 17 mAh.
The little spikes at the beginning of
the graph are discus launches. The first
warm-up launch is 100 feet; the best
launch on the graph is 132 feet. I was
sport flying, so I did stationary throws.
Running a few steps before spinning
results in higher launches. The second
and third launches were right into sinking
air.
Whenever I sport-fly I try hard to
really core the thermals. I get the greatest
satisfaction from knowing I located the
core of the plume and watching the glider
climb at a fast rate. You can see on the
graph that the XP-3 caught some lift and
climbed to 400 feet on the fourth launch.
After feeling a wind shift, I searched in
the direction it was sucking and found
stronger lift. Eventually I started tight,
slow circles in what appeared to be the
core of the thermal. The climb was
excellent for my part of the country,
averaging 565 feet per minute between
400 and 2,300 feet. I have had faster
apparent climb rates when flying over
desert regions.
The smooth, consistent climb and
high-altitude flying were made possible
by the stability that 7° of dihedral per
side (14° total bend) provided. I don’t
need to see my model well to fly it
efficiently. Dihedral also helped
maximize the climb rate. High-dihedral
airplanes can make slow, tight turns
without spiraling in.
I hope you find the condensation
analogy useful in predicting where to
catch your next bus up to cloud base. MA
Sources:
LoLo manufacturer:
www.lomcovak.cz/eindex.html
LoLo US source:
www.yntdesign.com/
www.modelaircraft.org
01sig3.QXD 10/27/03 10:04 am Page 86