Where is the next thermal?

I am writing this to ask experienced soaring pilots to correct me
where you have acquired different wisdom, or your local conditions are
different, or where you have something more to add.

I hope this turns into a thread on "How I keep going" - there must be
scores of pilots more excellent than I who can say more than me.

More than 20 years ago, before I had become able to pursue soaring (as
distinguished from gliding), a letter to the editor appeared in
Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self-
taught XC soaring, innocently thought that SSA members might have a
lot more wisdom that he, so he asked for clues on how to find
thermals. He never got a response that was printed in the magazine...

He did tell the one thing he knew about finding thermals: "The best
lift is at the most downwind corner of the field."

This, in my own experience, is the single most important clue on where
to go when scratching low, here over the prairies. Identifying what
is "the field", where the wind's coming from, and what's "a corner"
have sometimes been challenging, and figuring out just how small hills
and valleys will affect the thermals is always interesting (hills tend
to help, valleys tend to channel them - flying downwind up a valley
above ridgetop is usually a route to a save).

I've also noticed that any isolated sorta-bare hill or rock pile on
flat ground is a pretty reliable source...

On the negative side, being anywhere downwind of any lake wider than
about a mile, or wet river flood plain, is definitely associated with
a lack of organized thermals, sometimes for miles. Forests are bad,
but the clearings in them are good. Swamps in the prairie are often
bad (wet) but in the woods often create boomers due to the
differential, and moist air is buoyant.

I am not very good at identifying the best field when they all look
good (spring planting or fall harvest). On the first cold day after a
warm spell in the fall, some fields generate thermals on overcast
days: the best seem to be cut bean fields, covered with a thin layer
of stems and leaves.

Early in the day, thermal sources tend to be small (a single field or
parking lot) and late in the day, they tend to be very large (e.g., a
3-10 mile-diameter prairie).

And at the beginning of the day, all clouds have lift (of quite
variable strength), mid-day, as few as 20% do, and late in the day,
the appearance of the cloud is a reliable indicator of whether it's
"working."

When high, the corollary to the field is of course the flat cu: the
first place to look for the thermal is at the most upwind part of the
cloud. Although again, what's a "cloud", where the wind's coming from,
and the direction of the wind above cloudbase all affect what will be
found.

Clouds with flat bases are better that clouds with fuzzy bases, except
that a new wisp always has something, and an "old" flat cloud may be
dying.

Clouds with enthusiastic tops are sucking air, and under these, the
lift is usually under the tower (useful when aiming from a distance)
and there's often a dimple in the bottom where the suction is
greatest. I was once told that streamers usually indicate condensing
lift, but I've found this usually wrong -- except when the thermal is
unusually humid.

Clouds sometimes are lined up. My experience is that the streets are
fake (but not necessarily useless) if the surface wind is less than 10
kt, and usually real above that; but that all streets end.

The hardest time for me is when I'm sort of midway between cloud and
ground. Do I fly under the best part of the cloud and look up? Or do I
fly toward the thermal source? Or, how can I reliably identify a good
intermediate point?

In this regard, I've found that thermals are curved, sometimes
strongly (if imagined in "section"). This can be seen with swamp
fires, where the smoke skims along the ground for awhile, then begins
to rise in a great slow curve to the small cu created by the humidity
released from the ground by the fire's heat. This makes physical
sense, when one stops to think about it, for the wind first whisks the
thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The
warmed air must accelerate; this rate of acceleration depends on the
buoyancy of the thermal relative to the lapse rate. If it's a boomer,
say 900 ft/min, then the angle will go from nil to 45 degrees as it
accelerates, and this feels almost vertical. But down low, below about
1500 ft agl, the clouds are sometimes more a distraction than a help
because of this. The curvature of thermals, I think, is a special
mystery when trying to fly xwind on a blue day. I, at least, often
feel mystified.

More topics, about which I can't say much:

Staying alive late in the day (e.g., "there's zero-sink over
freeways")

Identifying mountain thermals

"Good terrain" in deserts

sea-breeze and dry-front lift

other...

On Sep 21, 1:52*pm, danlj wrote:
I am writing this to ask experienced soaring pilots to correct me
where you have acquired different wisdom, or your local conditions are
different, or where you have something more to add.

I hope this turns into a thread on "How I keep going" - there must be
scores of pilots more excellent than I who can say more than me.

More than 20 years ago, before I had become able to pursue soaring (as
distinguished from gliding), a letter to the editor appeared in
Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self-
taught XC soaring, innocently thought that SSA members might have a
lot more wisdom that he, so he asked for clues on how to find
thermals. He never got a response that was printed in the magazine...

He did tell the one thing he knew about finding thermals: "The best
lift is at the most downwind corner of the field."

This, in my own experience, is the single most important clue on where
to go when scratching low, here over the prairies. *Identifying what
is "the field", where the wind's coming from, and what's "a corner"
have sometimes been challenging, and figuring out just how small hills
and valleys will affect the thermals is always interesting (hills tend
to help, valleys tend to channel them - flying downwind up a valley
above ridgetop is usually a route to a save).

I've also noticed that any isolated sorta-bare hill or rock pile on
flat ground is a pretty reliable source...

On the negative side, being anywhere downwind of any lake wider than
about a mile, or wet river flood plain, is definitely associated with
a lack of organized thermals, sometimes for miles. Forests are bad,
but the clearings in them are good. Swamps in the prairie are often
bad (wet) but in the woods often create boomers due to the
differential, and moist air is buoyant.

I am not very good at identifying the best field when they all look
good (spring planting or fall harvest). On the first cold day after a
warm spell in the fall, some fields generate thermals on overcast
days: the best seem to be cut bean fields, covered with a thin layer
of stems and leaves.

Early in the day, thermal sources tend to be small (a single field or
parking lot) and late in the day, they tend to be very large (e.g., a
3-10 mile-diameter prairie).

And at the beginning of the day, all clouds have lift (of quite
variable strength), mid-day, as few as 20% do, and late in the day,
the appearance of the cloud is a reliable indicator of whether it's
"working."

When high, the corollary to the field is of course the flat cu: the
first place to look for the thermal is at the most upwind part of the
cloud. Although again, what's a "cloud", where the wind's coming from,
and the direction of the wind above cloudbase all affect what will be
found.

Clouds with flat bases are better that clouds with fuzzy bases, except
that a new wisp always has something, and an "old" flat cloud may be
dying.

Clouds with enthusiastic tops are sucking air, and under these, the
lift is usually under the tower (useful when aiming from a distance)
and there's often a dimple in the bottom where the suction is
greatest. I was once told that streamers usually indicate condensing
lift, but I've found this usually wrong -- except when the thermal is
unusually humid.

Clouds sometimes are lined up. My experience is that the streets are
fake (but not necessarily useless) if the surface wind is less than 10
kt, and usually real above that; but that all streets end.

The hardest time for me is when I'm sort of midway between cloud and
ground. Do I fly under the best part of the cloud and look up? Or do I
fly toward the thermal source? Or, how can I reliably identify a good
intermediate point?

In this regard, I've found that thermals are curved, sometimes
strongly (if imagined in "section"). This can be seen with swamp
fires, where the smoke skims along the ground for awhile, then begins
to rise in a great slow curve to the small cu created by the humidity
released from the ground by the fire's heat. This makes physical
sense, when one stops to think about it, for the wind first whisks the
thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The
warmed air must accelerate; this rate of acceleration depends on the
buoyancy of the thermal relative to the lapse rate. If it's a boomer,
say 900 ft/min, then the angle will go from nil to 45 degrees as it
accelerates, and this feels almost vertical. But down low, below about
1500 ft agl, the clouds are sometimes more a distraction than a help
because of this. *The curvature of thermals, I think, is a special
mystery when trying to fly xwind on a blue day. I, at least, often
feel mystified.

More topics, about which I can't say much:

Staying alive late in the day (e.g., "there's zero-sink over
freeways")

Identifying mountain thermals

"Good terrain" in deserts

sea-breeze and dry-front lift

other...

Danlj

A very nice collection of ideas for finding thermals. Many of the
same Ideas that I have noticed and shared with students. They work
better in farmland and wooded areas than desert as the triggers are
less distinct in the dessert and more of the surface are is being
heated to the same temperature.

Regarding the "downwind corner", I also note that where the ground
surface changes; dry to wet, low to high, plowed to growing. At each
of these areas especially if you can identify that the downwind
surface is colder or denser, there will be the necessary upward push
to start a thermal. I describe them as "discontinuities" in the
surface. They form an edge, if you will, that can trigger the thermal.

Thanks for the list.

Mike

A bare field just downwind of a patch of trees has time to heat up more
owing to the windbreak and it can kick off a thermal sometimes down
lower.

Also, wooded areas serve well late in the day. Surrounding open land will
cool off more quickly and then the woods will begin to give up its heat in
a soft thermal that won't go very high, but can serve to hang on for a
bit and as a place from which to jump to the next woods patch while trying
to get home.

Not an expert by r.a.s. standards.


At 21:13 21 September 2009, Mike Bamberg wrote:
On Sep 21, 1:52=A0pm, danlj wrote:
I am writing this to ask experienced soaring pilots to correct me
where you have acquired different wisdom, or your local conditions are
different, or where you have something more to add.

I hope this turns into a thread on "How I keep going" - there must
be
scores of pilots more excellent than I who can say more than me.

More than 20 years ago, before I had become able to pursue soaring (as
distinguished from gliding), a letter to the editor appeared in
Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of
self-
taught XC soaring, innocently thought that SSA members might have a
lot more wisdom that he, so he asked for clues on how to find
thermals. He never got a response that was printed in the magazine...

He did tell the one thing he knew about finding thermals: "The best
lift is at the most downwind corner of the field."

This, in my own experience, is the single most important clue on where
to go when scratching low, here over the prairies. =A0Identifying what
is "the field", where the wind's coming from, and what's "a
corner"
have sometimes been challenging, and figuring out just how small hills
and valleys will affect the thermals is always interesting (hills tend
to help, valleys tend to channel them - flying downwind up a valley
above ridgetop is usually a route to a save).

I've also noticed that any isolated sorta-bare hill or rock pile on
flat ground is a pretty reliable source...

On the negative side, being anywhere downwind of any lake wider than
about a mile, or wet river flood plain, is definitely associated with
a lack of organized thermals, sometimes for miles. Forests are bad,
but the clearings in them are good. Swamps in the prairie are often
bad (wet) but in the woods often create boomers due to the
differential, and moist air is buoyant.

I am not very good at identifying the best field when they all look
good (spring planting or fall harvest). On the first cold day after a
warm spell in the fall, some fields generate thermals on overcast
days: the best seem to be cut bean fields, covered with a thin layer
of stems and leaves.

Early in the day, thermal sources tend to be small (a single field or
parking lot) and late in the day, they tend to be very large (e.g., a
3-10 mile-diameter prairie).

And at the beginning of the day, all clouds have lift (of quite
variable strength), mid-day, as few as 20% do, and late in the day,
the appearance of the cloud is a reliable indicator of whether it's
"working."

When high, the corollary to the field is of course the flat cu: the
first place to look for the thermal is at the most upwind part of the
cloud. Although again, what's a "cloud", where the wind's coming
from,
and the direction of the wind above cloudbase all affect what will be
found.

Clouds with flat bases are better that clouds with fuzzy bases, except
that a new wisp always has something, and an "old" flat cloud may be
dying.

Clouds with enthusiastic tops are sucking air, and under these, the
lift is usually under the tower (useful when aiming from a distance)
and there's often a dimple in the bottom where the suction is
greatest. I was once told that streamers usually indicate condensing
lift, but I've found this usually wrong -- except when the thermal is
unusually humid.

Clouds sometimes are lined up. My experience is that the streets are
fake (but not necessarily useless) if the surface wind is less than 10
kt, and usually real above that; but that all streets end.

The hardest time for me is when I'm sort of midway between cloud and
ground. Do I fly under the best part of the cloud and look up? Or do I
fly toward the thermal source? Or, how can I reliably identify a good
intermediate point?

In this regard, I've found that thermals are curved, sometimes
strongly (if imagined in "section"). This can be seen with swamp
fires, where the smoke skims along the ground for awhile, then begins
to rise in a great slow curve to the small cu created by the humidity
released from the ground by the fire's heat. This makes physical
sense, when one stops to think about it, for the wind first whisks the
thermal bubble along horizontally (at, say, 10 mph =3D 900 ft/min).
The
warmed air must accelerate; this rate of acceleration depends on the
buoyancy of the thermal relative to the lapse rate. If it's a boomer,
say 900 ft/min, then the angle will go from nil to 45 degrees as it
accelerates, and this feels almost vertical. But down low, below about
1500 ft agl, the clouds are sometimes more a distraction than a help
because of this. =A0The curvature of thermals, I think, is a special
mystery when trying to fly xwind on a blue day. I, at least, often
feel mystified.

More topics, about which I can't say much:

Staying alive late in the day (e.g., "there's zero-sink over
freeways")

Identifying mountain thermals

"Good terrain" in deserts

sea-breeze and dry-front lift

other...

Danlj

A very nice collection of ideas for finding thermals. Many of the
same Ideas that I have noticed and shared with students. They work
better in farmland and wooded areas than desert as the triggers are
less distinct in the dessert and more of the surface are is being
heated to the same temperature.

Regarding the "downwind corner", I also note that where the ground
surface changes; dry to wet, low to high, plowed to growing. At each
of these areas especially if you can identify that the downwind
surface is colder or denser, there will be the necessary upward push
to start a thermal. I describe them as "discontinuities" in the
surface. They form an edge, if you will, that can trigger the thermal.

Thanks for the list.

Mike

On Sep 21, 1:52*pm, danlj wrote:
I hope this turns into a thread on "How I keep going" - there must be
scores of pilots more excellent than I who can say more than me.

I well remember that years ago when a visiting German pilot asked for
advice on finding thermals in Arizona I told him to look above and
downwind of cattle tanks. These are known as stock ponds in other
places. His reaction, that I must be a complete idiot for suggesting
that pools of water could trigger thermals, has made me cautious about
offering that advice to anyone. I hoped he landed out but I don't
think he did.

Andy

I've noticed that there seems to be a time in the afternoon when the
lift gets "soft" and previously reliable clouds become much less
reliable. Then, after an hour or so, the lift seems to pick up again,
not usually as strong but good enough to get home.

My totally uneducated guess is that at some point, the reserve of lift
that is breaking loose and forming thermals gets exhausted and isn't
replenished fast enough, so it takes a while to build up again and
start making reliable thermals.

This is really noticable where I often fly in Illinois, where you have
to slow down and be real careful not to get too low mid afternoon,
even though the day still looks great with cu's all over the place -
around 2 to 3 in the afternoon it gets real soft and you have to slow
down and stay high and wait for the lift to cycle back on. Then you
can stay up till the sun goes down!

Kirk
66

Two items:

1. Junkyards

2. Radio transmission antennas.

I can understand the junkyards. It's a good "discontinuity" in the
surrounding area and has the wrecked cars packed tightly together,
more so than the typical parking lot.

As for the antennas, we speculate it's not the antenna itself, but the
ground they're on. They are probably most likely on the highest spot
around, even though it all looks quite flat to us. And, we're talking
about the 2,000' tall, cable stayed antennas and not the little cell
phone towers. But I guess any water tower and radio antennas are
placed on the highest ground in the local area.

Remember, Your Mileage May Vary...

Ray Lovinggood
Carrboro, North Carolina, USA

I have very good luck going right over the center of a town.

Downwind at the edge of the dry lake.
Dry hot air moving across the lake bed get triggered to release and rise
when encountering the scrub.

On an open desert floor, look for darker areas. The darker areas are most
likely elevated hard rock that is hotter than the surrounding sand and dirt.

I have also found thermals coming up from broad open "dry washes", the
exposed rock in the dry wash gets hotter than the surrounding soils.

BT

"Mike Bamberg" wrote in message
...
On Sep 21, 1:52 pm, danlj wrote:
I am writing this to ask experienced soaring pilots to correct me
where you have acquired different wisdom, or your local conditions are
different, or where you have something more to add.

I hope this turns into a thread on "How I keep going" - there must be
scores of pilots more excellent than I who can say more than me.

More than 20 years ago, before I had become able to pursue soaring (as
distinguished from gliding), a letter to the editor appeared in
Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self-
taught XC soaring, innocently thought that SSA members might have a
lot more wisdom that he, so he asked for clues on how to find
thermals. He never got a response that was printed in the magazine...

He did tell the one thing he knew about finding thermals: "The best
lift is at the most downwind corner of the field."

This, in my own experience, is the single most important clue on where
to go when scratching low, here over the prairies. Identifying what
is "the field", where the wind's coming from, and what's "a corner"
have sometimes been challenging, and figuring out just how small hills
and valleys will affect the thermals is always interesting (hills tend
to help, valleys tend to channel them - flying downwind up a valley
above ridgetop is usually a route to a save).

I've also noticed that any isolated sorta-bare hill or rock pile on
flat ground is a pretty reliable source...

On the negative side, being anywhere downwind of any lake wider than
about a mile, or wet river flood plain, is definitely associated with
a lack of organized thermals, sometimes for miles. Forests are bad,
but the clearings in them are good. Swamps in the prairie are often
bad (wet) but in the woods often create boomers due to the
differential, and moist air is buoyant.

I am not very good at identifying the best field when they all look
good (spring planting or fall harvest). On the first cold day after a
warm spell in the fall, some fields generate thermals on overcast
days: the best seem to be cut bean fields, covered with a thin layer
of stems and leaves.

Early in the day, thermal sources tend to be small (a single field or
parking lot) and late in the day, they tend to be very large (e.g., a
3-10 mile-diameter prairie).

And at the beginning of the day, all clouds have lift (of quite
variable strength), mid-day, as few as 20% do, and late in the day,
the appearance of the cloud is a reliable indicator of whether it's
"working."

When high, the corollary to the field is of course the flat cu: the
first place to look for the thermal is at the most upwind part of the
cloud. Although again, what's a "cloud", where the wind's coming from,
and the direction of the wind above cloudbase all affect what will be
found.

Clouds with flat bases are better that clouds with fuzzy bases, except
that a new wisp always has something, and an "old" flat cloud may be
dying.

Clouds with enthusiastic tops are sucking air, and under these, the
lift is usually under the tower (useful when aiming from a distance)
and there's often a dimple in the bottom where the suction is
greatest. I was once told that streamers usually indicate condensing
lift, but I've found this usually wrong -- except when the thermal is
unusually humid.

Clouds sometimes are lined up. My experience is that the streets are
fake (but not necessarily useless) if the surface wind is less than 10
kt, and usually real above that; but that all streets end.

The hardest time for me is when I'm sort of midway between cloud and
ground. Do I fly under the best part of the cloud and look up? Or do I
fly toward the thermal source? Or, how can I reliably identify a good
intermediate point?

In this regard, I've found that thermals are curved, sometimes
strongly (if imagined in "section"). This can be seen with swamp
fires, where the smoke skims along the ground for awhile, then begins
to rise in a great slow curve to the small cu created by the humidity
released from the ground by the fire's heat. This makes physical
sense, when one stops to think about it, for the wind first whisks the
thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The
warmed air must accelerate; this rate of acceleration depends on the
buoyancy of the thermal relative to the lapse rate. If it's a boomer,
say 900 ft/min, then the angle will go from nil to 45 degrees as it
accelerates, and this feels almost vertical. But down low, below about
1500 ft agl, the clouds are sometimes more a distraction than a help
because of this. The curvature of thermals, I think, is a special
mystery when trying to fly xwind on a blue day. I, at least, often
feel mystified.

More topics, about which I can't say much:

Staying alive late in the day (e.g., "there's zero-sink over
freeways")

Identifying mountain thermals

"Good terrain" in deserts

sea-breeze and dry-front lift

other...

Danlj

A very nice collection of ideas for finding thermals. Many of the
same Ideas that I have noticed and shared with students. They work
better in farmland and wooded areas than desert as the triggers are
less distinct in the dessert and more of the surface are is being
heated to the same temperature.

Regarding the "downwind corner", I also note that where the ground
surface changes; dry to wet, low to high, plowed to growing. At each
of these areas especially if you can identify that the downwind
surface is colder or denser, there will be the necessary upward push
to start a thermal. I describe them as "discontinuities" in the
surface. They form an edge, if you will, that can trigger the thermal.

Thanks for the list.

Mike

Flying in the Midwest farm country of the USA I find the vast majority
of thermals by simply blundering into them blindly.

Below 1500AGL ground clues MAY help you find lift but just as likely
not. In rocky mountainous terrain it's a different story.

Determine what altitude is half way to cloudbase (if there are
clouds); Below that ignore the clouds and just go, above that the
clouds MAY help you find lift.

Real cloudstreets DO exist as do lift streets with no clouds. Keep an
open mind at all times.

Many people fly too slow in sink or even turn in sink trying to decide
what to do. Even at 800agl if the vario says 500 or 1000 down go FAST
and go straight. You are much more likely to hit a thermal on your
way to your landing field than if you fly around maneuvering slow.

Fly SLOW in lift or zero sink. Pull back on the stick to min sink and
do it immediately. Many people turn too shallow and too late in
thermals. Circle just about as tight as you can fly slow in most
thermals for the best climb rate.

Keep a positive attitude. Keep a couple landing fields in sight but
keep a positive attitude. Many XC flights have been saved on
downwind. Once you turn base give it up. Hear the theme to Star Trek
in your mind and boldly go where no one has gone before.

Here is my methodology, most of which is found in Reichmann's
excellent book.

1. Develop testable 3-D models of the lift in your mind, based on
topography, wind, sun aspect and previous experience. This is my
version of "strolling along the ground to find where it is hot" in
Reichmann's definitive text.

2. Test the model by putting the glider in what you hypothesize as
the best energy lines.

3. Fly as precisely and efficiently as you can and in an direct
correlation to the intensity of lift/sink/turbulence: Smooth and easy
inputs in light, smooth lift. Firm and aggressive when it is rock-and
rolling. The flight paths of world-class pilots can appear as though
they are drunk or very sloppy as they weave about. This is in direct
opposition to wings lifting and can be used to locate in featureless,
cloudless terrain.

3. Adjust your mental image and flight path based on test results and
observation of other ships, birds, dust, etc. I believe AJ Smith and/
or Dick Schreder said that 90% of what you need to know is outside
the cockpit and if you have not made a decision in the last 5 minutes,
you are not working hard enough. Electron Slingers allow you to
direct your attention and energy where it matters: OUTSIDE THE
COCKPIT. A glance at the moving map periodically is all that is
required to affirm your location and that you have suitable fields in
a reasonable glide, how you are doing on task and what you need for
final glide.

3. Repeat this decision-action loop every 1/2 hour or so based on
changing wind direction and intensity, sun aspect, and terrain and
what is 20-50 miles down the road.

I would also echo what others have said:

When close to clouds, use them as the primary reference. And not just
"sort of under a cloud". You need to determine which side of the
cloud and what cloud phase is optimal and what height below base.
Target and test the clouds you select and adjust your selection
process. As one gets lower, lift hunting is more and more attached to
the terrain + wind + sun aspect.

Finally, be mentally Tough and never quit "soaring" until you commit
to landing. As someone said previously, many flights have been
"sucked off the ground", mostly due to the pilot's persistence and
willingness to fight until a safe landing is inevitably necessary.
"Giving up" is very seductive and absolutely ensures you will land.
Both of these behaviors are self-reinforcing; both become easier with
repetition. "Grinding it out" is where our hang glider brothers
really excel.

The paradoxical situation we find ourselves in when low and facing an
off-field landing is one of the many things I find interesting in X-C
soaring. Just when we are under maximum stress and with minimal
options, we need to be at our absolute technical best and most
creative. Gotta love it!