Any sailplane pilots?

Larry wrote:

On an average day, a pilot will
spend a great deal of time attempting to "core" thermals. That
involves mentally visualizing the sailplane's position relative to the
thermal's vertical anticyclone column center, and guiding his
sailplane to circle as near to the center of it as he is able.

Why do you write "anticyclone" Larry. This would mean that all gliders would
circle righthanded to stay as close to the core as possible thereby using
the headwind of the thermal.
I have never found a meteorological reason to circle in a certain direction.
Most pilots circle lefthanded just because they were tought to do so in the
vicinity of their home field. However in x-country flights there is usually
no preference. In low situations the pilot usually circles in the direction
he feels most comfortable. Sometimes the gliders feels better when circling
to the right rather then to the left is my experience.

Karel, NL

"Eric Greenwell" schreef in bericht
...
Larry Dighera wrote:


The spectrum of soaring meteorological conditions ranges from flat
(little or no vertical movement of the air mass) to booming.

Eric Greenwell
Washington State
USA

On Fri, 26 Dec 2003 09:00:24 GMT, "K.P. Termaat" wrote
in Message-Id: :

Larry wrote:

On an average day, a pilot will
spend a great deal of time attempting to "core" thermals. That
involves mentally visualizing the sailplane's position relative to the
thermal's vertical anticyclone column center, and guiding his
sailplane to circle as near to the center of it as he is able.

Why do you write "anticyclone" Larry.

That was my recollection from my soaring experience in the early '70s.
However, it appears that the word 'cyclone' may have more correct now
that I have done some research:

The National Weather Service Glossary page here
http://www.wrh.noaa.gov/Phoenix/general/glossary/ has this to say:

ANTICYCLONE - A region of high atmospheric pressure around which
winds move in a clockwise direction in the northern hemisphere.
Generally associated with warm and dry weather

CYCLONE - An area of low pressure around which winds blow in a
counter-clockwise fashion in the northern hemisphere. Generally
associated with cool, wet and unsettled weather

On the other hand ...

This would mean that all gliders would circle righthanded to stay as close
to the core as possible thereby using the headwind of the thermal.

I'll defer to these sources:

http://www.rc-soar.com/tech/thermals.htm
Do thermals rotate?
They do, but not predictably. Even dust devils don't have a
preferred direction of rotation (see Stull, p.449). Thermals are
too small and too short-lived to be affected by the earth's
rotation (Coriolis force) or by the equator/pole thermal gradient.
Their rotation is determined by local terrain. Rotational velocity
in the core of a typical thermal is small compared to the vertical
velocity.


http://www.skynomad.com/articles/athermal10.html
THERMALS

Do Thermals Spin?
by Peter Gray

Of course, dust devils spin, so thermals probably do also, at
least when they're close to the ground. For many years, I was
convinced that dust devils rotated in random directions. However,
based on a few flights in northern Washington State, where I kept
more careful mental notes, I would guess that about 2/3 to 3/4 of
the dust devils there spin counterclockwise, in agreement with the
Coriolis Effect. Contrary to popular belief, the smaller-scale
equivalent, water going down a toilet or drain, is essentially
unaffected, and the rotation, if it is biased toward one spin
direction, is the result of the geometry of each such basin (check
it out for yourself!).

The dust devils formed by thermals seem to be just large
enough to be affected somewhat by the Coriolis Effect. If I have
the choice, I usually opt for circling against the dust devil's
rotation, most often to the right, in case this will produce a
better climb rate by reducing my circling ground speed, thus bank
angle and sinkrate.

However, when I have reversed direction several times in one
climb, I have rarely detected a significant advantage in one
direction. What little angular momentum thermals start with, they
seem to lose through drag in the surrounding air, and they
probably start with little spin anyway. As with water going down a
drain, very little spin momentum at a large radius can translate
to a rapid spin when the radius shrinks to that of a dust devil.

I have never found a meteorological reason to circle in a certain direction.
Most pilots circle lefthanded just because they were tought to do so in the
vicinity of their home field. However in x-country flights there is usually
no preference. In low situations the pilot usually circles in the direction
he feels most comfortable. Sometimes the gliders feels better when circling
to the right rather then to the left is my experience.

Karel, NL

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.

Thanks Larry for your interesting respons with your links to the articles.

As a matter of fact most members of our National Team (my son is one of
them) tend to circle to the right when low. They don't in effect know why.
They say, and I agree, that it usually feels better in getting up again. So
Peter Gray may be right in saying that most of the thermals have the
tendency to rotate to the left in the northern hemisphere, especially when
low when still having small diameters. Coriolis may be the cause then. Would
be interesting to know the experience in the southern hemisphere.

Talking about a drain and water brings me to the idea of telling that when
low and looking for a thermal I always try to locate small ponds in dry
areas. It looks to me that the water vapor rising from these ponds is an
excellent means of starting a thermal. Water vapor is lighter then air, so
it increases the boyancy of the air over the pond and off it goes. Starting
at about ground level, circling to the right may then generally be the
better option. Any experience with this Larry?

Karel, NL


"Larry Dighera" schreef in bericht
...
On Fri, 26 Dec 2003 09:00:24 GMT, "K.P. Termaat" wrote
in Message-Id: :

Larry wrote:

On an average day, a pilot will
spend a great deal of time attempting to "core" thermals. That
involves mentally visualizing the sailplane's position relative to the
thermal's vertical anticyclone column center, and guiding his
sailplane to circle as near to the center of it as he is able.

Why do you write "anticyclone" Larry.

That was my recollection from my soaring experience in the early '70s.
However, it appears that the word 'cyclone' may have more correct now
that I have done some research:

The National Weather Service Glossary page here
http://www.wrh.noaa.gov/Phoenix/general/glossary/ has this to say:

ANTICYCLONE - A region of high atmospheric pressure around which
winds move in a clockwise direction in the northern hemisphere.
Generally associated with warm and dry weather

CYCLONE - An area of low pressure around which winds blow in a
counter-clockwise fashion in the northern hemisphere. Generally
associated with cool, wet and unsettled weather

On the other hand ...

This would mean that all gliders would circle righthanded to stay as
close
to the core as possible thereby using the headwind of the thermal.

I'll defer to these sources:

http://www.rc-soar.com/tech/thermals.htm
Do thermals rotate?
They do, but not predictably. Even dust devils don't have a
preferred direction of rotation (see Stull, p.449). Thermals are
too small and too short-lived to be affected by the earth's
rotation (Coriolis force) or by the equator/pole thermal gradient.
Their rotation is determined by local terrain. Rotational velocity
in the core of a typical thermal is small compared to the vertical
velocity.


http://www.skynomad.com/articles/athermal10.html
THERMALS

Do Thermals Spin?
by Peter Gray

Of course, dust devils spin, so thermals probably do also, at
least when they're close to the ground. For many years, I was
convinced that dust devils rotated in random directions. However,
based on a few flights in northern Washington State, where I kept
more careful mental notes, I would guess that about 2/3 to 3/4 of
the dust devils there spin counterclockwise, in agreement with the
Coriolis Effect. Contrary to popular belief, the smaller-scale
equivalent, water going down a toilet or drain, is essentially
unaffected, and the rotation, if it is biased toward one spin
direction, is the result of the geometry of each such basin (check
it out for yourself!).

The dust devils formed by thermals seem to be just large
enough to be affected somewhat by the Coriolis Effect. If I have
the choice, I usually opt for circling against the dust devil's
rotation, most often to the right, in case this will produce a
better climb rate by reducing my circling ground speed, thus bank
angle and sinkrate.

However, when I have reversed direction several times in one
climb, I have rarely detected a significant advantage in one
direction. What little angular momentum thermals start with, they
seem to lose through drag in the surrounding air, and they
probably start with little spin anyway. As with water going down a
drain, very little spin momentum at a large radius can translate
to a rapid spin when the radius shrinks to that of a dust devil.

I have never found a meteorological reason to circle in a certain
direction.
Most pilots circle lefthanded just because they were tought to do so in
the
vicinity of their home field. However in x-country flights there is
usually
no preference. In low situations the pilot usually circles in the
direction
he feels most comfortable. Sometimes the gliders feels better when
circling
to the right rather then to the left is my experience.

Karel, NL

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.

Maybe it is simply an ergonomics thing --- I feel more comfortable
circling to the right in clutch situations simply because it is easier
to pull and adjust rather than push and adjust in right turns.

K.P. Termaat wrote:
Thanks Larry for your interesting respons with your links to the articles.

As a matter of fact most members of our National Team (my son is one of
them) tend to circle to the right when low. They don't in effect know why.
They say, and I agree, that it usually feels better in getting up again. So
Peter Gray may be right in saying that most of the thermals have the
tendency to rotate to the left in the northern hemisphere, especially when
low when still having small diameters. Coriolis may be the cause then. Would
be interesting to know the experience in the southern hemisphere.

Talking about a drain and water brings me to the idea of telling that when
low and looking for a thermal I always try to locate small ponds in dry
areas. It looks to me that the water vapor rising from these ponds is an
excellent means of starting a thermal. Water vapor is lighter then air, so
it increases the boyancy of the air over the pond and off it goes. Starting
at about ground level, circling to the right may then generally be the
better option. Any experience with this Larry?

Karel, NL


"Larry Dighera" schreef in bericht
...

On Fri, 26 Dec 2003 09:00:24 GMT, "K.P. Termaat" wrote
in Message-Id: :


Larry wrote:


On an average day, a pilot will
spend a great deal of time attempting to "core" thermals. That
involves mentally visualizing the sailplane's position relative to the
thermal's vertical anticyclone column center, and guiding his
sailplane to circle as near to the center of it as he is able.

Why do you write "anticyclone" Larry.

That was my recollection from my soaring experience in the early '70s.
However, it appears that the word 'cyclone' may have more correct now
that I have done some research:

The National Weather Service Glossary page here
http://www.wrh.noaa.gov/Phoenix/general/glossary/ has this to say:

ANTICYCLONE - A region of high atmospheric pressure around which
winds move in a clockwise direction in the northern hemisphere.
Generally associated with warm and dry weather

CYCLONE - An area of low pressure around which winds blow in a
counter-clockwise fashion in the northern hemisphere. Generally
associated with cool, wet and unsettled weather

On the other hand ...


This would mean that all gliders would circle righthanded to stay as

close

to the core as possible thereby using the headwind of the thermal.

I'll defer to these sources:

http://www.rc-soar.com/tech/thermals.htm
Do thermals rotate?
They do, but not predictably. Even dust devils don't have a
preferred direction of rotation (see Stull, p.449). Thermals are
too small and too short-lived to be affected by the earth's
rotation (Coriolis force) or by the equator/pole thermal gradient.
Their rotation is determined by local terrain. Rotational velocity
in the core of a typical thermal is small compared to the vertical
velocity.


http://www.skynomad.com/articles/athermal10.html
THERMALS

Do Thermals Spin?
by Peter Gray

Of course, dust devils spin, so thermals probably do also, at
least when they're close to the ground. For many years, I was
convinced that dust devils rotated in random directions. However,
based on a few flights in northern Washington State, where I kept
more careful mental notes, I would guess that about 2/3 to 3/4 of
the dust devils there spin counterclockwise, in agreement with the
Coriolis Effect. Contrary to popular belief, the smaller-scale
equivalent, water going down a toilet or drain, is essentially
unaffected, and the rotation, if it is biased toward one spin
direction, is the result of the geometry of each such basin (check
it out for yourself!).

The dust devils formed by thermals seem to be just large
enough to be affected somewhat by the Coriolis Effect. If I have
the choice, I usually opt for circling against the dust devil's
rotation, most often to the right, in case this will produce a
better climb rate by reducing my circling ground speed, thus bank
angle and sinkrate.

However, when I have reversed direction several times in one
climb, I have rarely detected a significant advantage in one
direction. What little angular momentum thermals start with, they
seem to lose through drag in the surrounding air, and they
probably start with little spin anyway. As with water going down a
drain, very little spin momentum at a large radius can translate
to a rapid spin when the radius shrinks to that of a dust devil.


I have never found a meteorological reason to circle in a certain

direction.

Most pilots circle lefthanded just because they were tought to do so in

the

vicinity of their home field. However in x-country flights there is

usually

no preference. In low situations the pilot usually circles in the

direction

he feels most comfortable. Sometimes the gliders feels better when

circling

to the right rather then to the left is my experience.

Karel, NL

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.


The protocol I was taught was that unless you are first into the
thermal, you follow the left or right pattern of the gliders already there.
I've never had a preference of right or left. I was taught to turn into
whichever wingtip went up.
I was also taught that the most efficient technique, that is the
highest rate of altitude gain, is in a 45-degree bank turn hopefully
"coring" the thermal.
Up here in the Mojave Desert flying out of IYK, I've been in a couple of
10 Knot thermals but 5 to 6 is the most common. I can't ever remember any
kind of cyclonic rotation of any of them.
That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

Casey Wilson wrote:

That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

No dust, no dust devil! But, of course, the thermal can still be there.
Coming into one low can be dangerous, but up here in eastern Washington
State, we use them frequently, especially on blue days. They are usually
quite tame. Only the biggest are potentially dangerous, and then only
when "near" the ground (say, less then 1500 feet AGL).

What you are flying makes a difference, too: a 1-26 is going to be
tossed around a lot more than an ASW 20 with ballast. Flying faster than
the normal thermalling speed helps quite a bit if the thermal is rough.


--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

That is how I found my best thermal ever. Flying my HP16T at a Region
8 contest in Eric's stomping grounds. It was about 2 hours into a 3
Hour post task and front started moving into the area. I decided that
getting home might score better than trying to make the minimum time
and landing out so I headed back to the airport under the cloud deck.
The Glide was totally smooth and I arrived back at the airport at
about 1500 AGL. (~3000MSL) on the far side of the airport the sun was
shining and I could see two large dust devils up on the hill from the
airport. As I approached closer dust devil I could see cheat grass,
tumble weeds and garbage bags floating around in it. I put my left
wing into the dust devil and turned hard left. My 10kt vario pegged. I
switched the scale to 20kts and it pegged again. It would occasionall
drop to as low as 16kts. I went from 3000MSL to 11000MSL in about 4
minutes averaging right at 20kts. I had to stop the climb due to cloud
bases. From there I did a final glide out to a turnpoint and back to
the airport to finish within a few minutes of the 3 hour minimum.
Looking out on the wing I could see cheat grass draped all along the
leading edge of the wing. I am sure it didn't due anything good to my
glide ratio. As I rolled to a stop at the airport all the Cheat grass
dropped off the wing onto the tarmac, which made for a great story
"There I was, so low that..."

Brian
HP16T



Eric Greenwell wrote in message ...
Casey Wilson wrote:

That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

No dust, no dust devil! But, of course, the thermal can still be there.
Coming into one low can be dangerous, but up here in eastern Washington
State, we use them frequently, especially on blue days. They are usually
quite tame. Only the biggest are potentially dangerous, and then only
when "near" the ground (say, less then 1500 feet AGL).

What you are flying makes a difference, too: a 1-26 is going to be
tossed around a lot more than an ASW 20 with ballast. Flying faster than
the normal thermalling speed helps quite a bit if the thermal is rough.

On the other hand I can't tell you how many times(numerous) I
intercepted a dust devil at 1000-1500 AGL and climbed out at less then
1kt or even did not climb. Most times however I get 3-6 kts out of
them. I have see dust devils go to 7-8000 feet up. Hate to tell the
one gentleman this that wouldn't fly into a dust devil, but if he flys
using thermals he is just flying into dustless dust devils, As far as
I can tell the only difference is if it is lifting air over an area
were it can pick dust up or not.

Brian
HP16T



Eric Greenwell wrote in message ...
Casey Wilson wrote:

That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

No dust, no dust devil! But, of course, the thermal can still be there.
Coming into one low can be dangerous, but up here in eastern Washington
State, we use them frequently, especially on blue days. They are usually
quite tame. Only the biggest are potentially dangerous, and then only
when "near" the ground (say, less then 1500 feet AGL).

What you are flying makes a difference, too: a 1-26 is going to be
tossed around a lot more than an ASW 20 with ballast. Flying faster than
the normal thermalling speed helps quite a bit if the thermal is rough.

I didn't receive any direction about which way to circle. Common sense
would rule out going against the traffic in an established pattern.

If there is a "standard" I wonder if it is related to the default for holds
(right) in airplanes. I used to wonder why the default for holds is to the
right but the default for VFR patterns at airports is left. --Bill



"Casey Wilson" wrote in message
...

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.


The protocol I was taught was that unless you are first into the
thermal, you follow the left or right pattern of the gliders already
there.
I've never had a preference of right or left. I was taught to turn
into
whichever wingtip went up.
I was also taught that the most efficient technique, that is the
highest rate of altitude gain, is in a 45-degree bank turn hopefully
"coring" the thermal.
Up here in the Mojave Desert flying out of IYK, I've been in a couple
of
10 Knot thermals but 5 to 6 is the most common. I can't ever remember any
kind of cyclonic rotation of any of them.
That said, I did once, inadvertantly fly into a dust-devil. I NEVER
want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

The "standard" is to circle to the left. Usually this is a must near glider
airfields, especially with a competition going on. This is for safety
reasons.
While on x-country and joining other gliders, the circle direction is given
by these other gliders in the same thermal.
When alone and hitting a thermal, the direction to turn into is where you
suspect the thermal to be. Some experience is required for that. It always
makes sense to circle towards the direction of rotation of the thermal if
there is any rotation. Some pilots have the idea that 2/3 of the thermals
rotate counter clockwise looking from below. I have the idea that this may
be true, but only at low altitudes. That's why quite a lot of pilots, and I
am one of them, circle to the right when low. Some other pilots think that
there is no rotation at all, except in very narrow dust devils which are
unsuitable to fly in.

Karel, NL
"William W. Plummer" schreef in bericht
news:gCWHb.163786$8y1.490686@attbi_s52...
I didn't receive any direction about which way to circle. Common sense
would rule out going against the traffic in an established pattern.

If there is a "standard" I wonder if it is related to the default for
holds
(right) in airplanes. I used to wonder why the default for holds is to
the
right but the default for VFR patterns at airports is left. --Bill



"Casey Wilson" wrote in message
...

Agreed. Circling direction is more often dictated by other gliders
in
the thermal than meteorological phenomena and physics.


The protocol I was taught was that unless you are first into the
thermal, you follow the left or right pattern of the gliders already
there.
I've never had a preference of right or left. I was taught to turn
into
whichever wingtip went up.
I was also taught that the most efficient technique, that is the
highest rate of altitude gain, is in a 45-degree bank turn hopefully
"coring" the thermal.
Up here in the Mojave Desert flying out of IYK, I've been in a
couple
of
10 Knot thermals but 5 to 6 is the most common. I can't ever remember
any
kind of cyclonic rotation of any of them.
That said, I did once, inadvertantly fly into a dust-devil. I NEVER
want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.