Where is the next thermal?

[danlj]

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...

[Mike Bamberg]

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

[Nyal Williams[_2_]]

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
>
>
>

[Andy[_1_]]

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

[[email protected][_2_]]

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

[rlovinggood]

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

[Don[_4_]]

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

[BT]

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

[[email protected]]

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.

[[email protected]]

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!

[Derek Copeland[_2_]]

Can I agree with Andy. In the UK we often seem to get really strong
thermals close to a large lake or reservoir such as Grafham Water. The
thermals are coming off the surrounding land of course, but the
temperature contrast between the hotter ground and the cooler water seems
to act as a trigger mechanism or a mini front. I have often found that
discontinuities such as the edge of a forest, a ridge line (especially if
pointing into sun), or a ploughed field next to one with crop often seem
to give thermals. Provincial towns and active power stations are also good
ground sources.

However the most reliable thermal markers are circling birds of prey such
as buzzards or kites, or insect eaters such as swallows and swifts.

Derek Copeland


At 22:28 21 September 2009, Andy wrote:
>On Sep 21, 1:52=A0pm, 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
>

[Mike the Strike]

On Sep 22, 2:00*am, Derek Copeland > wrote:
> Can I agree with Andy. In the UK we often seem to get really strong
> thermals close to a large lake or reservoir such as Grafham Water. The
> thermals are coming off the surrounding land of course, but the
> temperature contrast between the hotter ground and the cooler water seems
> to act as a trigger mechanism or a mini front. I have often found that
> discontinuities such as the edge of a forest, a ridge line (especially if
> pointing into sun), or a ploughed field next to one with crop often seem
> to give thermals. Provincial towns and active power stations are also good
> ground sources.
>
> However the most reliable thermal markers are circling birds of prey such
> as buzzards or kites, or insect eaters such as swallows and swifts.
>
> Derek Copeland *
>
> At 22:28 21 September 2009, Andy wrote:
>
> >On Sep 21, 1:52=A0pm, 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

Andy's observation is a secret well-known to cross-country pilots in
Arizona. Sometimes the most ridiculously small and almost dry water
holes will be the source of strong thermals. My theory is that water
holes inject enough moisture into the hot dry air to significantly
increase its buoyancy. We also have small hills consisting of black
volcanic rock that are also good sources. Dry river beds (called
washes in the southwest US) also can be useful sources.

Another issue with clouds here is that on fairly dry days the top of
the lift is often a thousand feet or more below cloud base. However,
a strong thermal will often continue for a short time above the top of
lift fueled by the extra heat released by condensation and eventually
form a cumulus. Once this short thermal pulse has decayed, the area
immediately below the cloud then has no lift, although the original
thermal may still be found a few thousand feet below. I call these
clouds "cumulus decoyus" - decoy cumulus!


Mike

[Craig[_2_]]

On Sep 22, 11:40*am, Mike the Strike > wrote:
> On Sep 22, 2:00*am, Derek Copeland > wrote:
>
>
>
> > Can I agree with Andy. In the UK we often seem to get really strong
> > thermals close to a large lake or reservoir such as Grafham Water. The
> > thermals are coming off the surrounding land of course, but the
> > temperature contrast between the hotter ground and the cooler water seems
> > to act as a trigger mechanism or a mini front. I have often found that
> > discontinuities such as the edge of a forest, a ridge line (especially if
> > pointing into sun), or a ploughed field next to one with crop often seem
> > to give thermals. Provincial towns and active power stations are also good
> > ground sources.
>
> > However the most reliable thermal markers are circling birds of prey such
> > as buzzards or kites, or insect eaters such as swallows and swifts.
>
> > Derek Copeland *
>
> > At 22:28 21 September 2009, Andy wrote:
>
> > >On Sep 21, 1:52=A0pm, 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
>
> Andy's observation is a secret well-known *to cross-country pilots in
> Arizona. *Sometimes the most ridiculously small and almost dry water
> holes will be the source of strong thermals. *My theory is that water
> holes inject enough moisture into the hot dry air to significantly
> increase its buoyancy. *We also have small hills consisting of black
> volcanic rock that are also good sources. *Dry river beds (called
> washes in the southwest US) also can be useful sources.
>
> Another issue with clouds here is that on fairly dry days the top of
> the lift is often a thousand feet or more below cloud base. *However,
> a strong thermal will often continue for a short time above the top of
> lift fueled by the extra heat released by condensation and eventually
> form a cumulus. *Once this short thermal pulse has decayed, the area
> immediately below the cloud then has no lift, although the original
> thermal may still be found a few thousand feet below. *I call these
> clouds "cumulus decoyus" - decoy cumulus!
>
> Mike

Known in other parts of the world as "Cumulus no-liftus"

Craig

[cernauta]

On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy >
wrote:

>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

There was an article in S&G, a few years ago, about thermal origin and
how to guess their location.
It was under the title "Triggers and Feeders". Interesting reading
about the wide areas that collect warmer air, and features on the
ground that induce the bubbles to win adhesion and start soaring.

An antenna, a pond, a building, a moving object etc, all are excellent
triggers, but they're worth nothing without an adequate volume of warm
air being supplied by the feeder area.

Aldo Cernezzi

[[email protected][_2_]]

On Sep 22, 7:03*pm, cernauta > wrote:
> On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy >
> wrote:
>
> >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
>
> There was an article in S&G, a few years ago, about thermal origin and
> how to guess their location.
> It was under the title "Triggers and Feeders". Interesting reading
> about the wide areas that collect warmer air, and features on the
> ground that induce the bubbles to win adhesion and start soaring.
>
> An antenna, a pond, a building, a moving object etc, all are excellent
> triggers, but they're worth nothing without an adequate volume of warm
> air being supplied by the feeder area.
>
> Aldo Cernezzi

Many times in strong conditions (especially down low) there will a
strong downdraft to be crossed before you hit that (thank you god)
strong thermal.

Bill Snead

[Nyal Williams[_2_]]

I've heard pilots say that the departure of an aircraft will kick off a
thermal from the runway. Worth watching if you are relatively low over
the field and your timing is right to search it out.

At 00:03 23 September 2009, cernauta wrote:
>On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy
>wrote:
>
>>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
>
>There was an article in S&G, a few years ago, about thermal origin and
>how to guess their location.
>It was under the title "Triggers and Feeders". Interesting reading
>about the wide areas that collect warmer air, and features on the
>ground that induce the bubbles to win adhesion and start soaring.
>
>An antenna, a pond, a building, a moving object etc, all are excellent
>triggers, but they're worth nothing without an adequate volume of warm
>air being supplied by the feeder area.
>
>Aldo Cernezzi
>
>

[Martin Gregorie[_5_]]

On Wed, 23 Sep 2009 01:45:02 +0000, Nyal Williams wrote:

> I've heard pilots say that the departure of an aircraft will kick off a
> thermal from the runway. Worth watching if you are relatively low over
> the field and your timing is right to search it out.
>
Its well known in the free flight model flying world that in the right
conditions a few people running about flapping T-shirts can kick off a
thermal. I once made my own thermal just by running about circle towing
an F1A class competition glider in sparse foot-high dry grass on calm
early morning conditions. It wasn't strong though - just enough to make a
model with a 0.3 m/s min sink speed climb slowly.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Derek Copeland[_2_]]

I think this rather depends on the degree of instability in the air. On
relatively stable days the usual thermal sources often don't seem to
work. You need a large area to remain undisturbed for some time until
enough hot air is available to give a decent thermal when triggered. Often
things like towns and motorways don't work because there is too much
trigger activity going on and only tiny weak thermals will form that go to
no great height.

Derek Copeland

At 14:01 23 September 2009, Martin Gregorie wrote:
>On Wed, 23 Sep 2009 01:45:02 +0000, Nyal Williams wrote:
>
>> I've heard pilots say that the departure of an aircraft will kick off
a
>> thermal from the runway. Worth watching if you are relatively low
over
>> the field and your timing is right to search it out.
>>
>Its well known in the free flight model flying world that in the right
>conditions a few people running about flapping T-shirts can kick off a
>thermal. I once made my own thermal just by running about circle towing
>an F1A class competition glider in sparse foot-high dry grass on calm
>early morning conditions. It wasn't strong though - just enough to make
a
>model with a 0.3 m/s min sink speed climb slowly.
>
>
>--
>martin@ | Martin Gregorie
>gregorie. | Essex, UK
>org |
>

[mattm[_2_]]

On Sep 21, 7:09*pm, rlovinggood > wrote:
> 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

Yes, mine varies. I've found those shorter cell phone towers to be
reliable lift points when I'm lower. They act as a wick to dislodge
the warm air from the ground, I think. Reichmann points out that
the warm air at the surface has a surface tension that needs to be
broken. He relates the point by describing a case of finding a
thermal down low that was wicking from a roadside monument.

At medium levels you can sometimes relate a lift source with
its resulting cloud. At a contest a year and a half ago I was
getting lowish (2000ft or so) and was flying over some shaded
ground looking for a thermal. Ahead, I saw a large field in the
sunlight that was being plowed. To my left and even with the
field was a new and growing cu (downwind). I drew a mental line
between the two and pulled up into the strongest thermal of the
day (an honest 8kt climb to cloudbase).

-- Matt

[Brad[_2_]]

On Sep 23, 1:35*pm, mattm > wrote:
> On Sep 21, 7:09*pm, rlovinggood > wrote:
>
>
>
>
>
> > 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
>
> Yes, mine varies. *I've found those shorter cell phone towers to be
> reliable lift points when I'm lower. *They act as a wick to dislodge
> the warm air from the ground, I think. *Reichmann points out that
> the warm air at the surface has a surface tension that needs to be
> broken. *He relates the point by describing a case of finding a
> thermal down low that was wicking from a roadside monument.
>
> At medium levels you can sometimes relate a lift source with
> its resulting cloud. *At a contest a year and a half ago I was
> getting lowish (2000ft or so) and was flying over some shaded
> ground looking for a thermal. *Ahead, I saw a large field in the
> sunlight that was being plowed. *To my left and even with the
> field was a new and growing cu (downwind). *I drew a mental line
> between the two and pulled up into the strongest thermal of the
> day (an honest 8kt climb to cloudbase).
>
> -- Matt

High tension power lines act as triggers, and the dirt roads/gap in
the trees where the towers are located are generators. IMO.

Brad

[Martin Gregorie[_5_]]

On Wed, 23 Sep 2009 15:00:04 +0000, Derek Copeland wrote:

> I think this rather depends on the degree of instability in the air. On
> relatively stable days the usual thermal sources often don't seem to
> work. You need a large area to remain undisturbed for some time until
> enough hot air is available to give a decent thermal when triggered.
> Often things like towns and motorways don't work because there is too
> much trigger activity going on and only tiny weak thermals will form
> that go to no great height.
>
'Flapping' (as its called in FF jargon) only works in calm conditions
with weak lift. To be successful it requires an area of 'stuck-down' warm
air that can be broken loose by some vigorous milling about.

A few years ago at a WC we and the Russians, at adjacent poles, each had
one man still to fly in the last 5 mins of a round. We could feel a
thermal building and the thermal detectors showed the air temp was
building but it wasn't likely to go before the end of the round, so we
decided to try to break it loose and started flapping. The Russians saw
what we were doing and joined in. The thermal got broken loose and both
models climbed away in it just before the hooter at the end of the round.

Flapping is common at major Euro and World level events where the fliers
have retrieval teams available to flap, but that was the only time I've
seen or helped to get a thermal going before the model was launched. Its
more usual to flap under a model that's been launched before the bubble
has broken away and is coming down.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected][_2_]]

On Sep 23, 6:26*pm, Martin Gregorie >
wrote:
> On Wed, 23 Sep 2009 15:00:04 +0000, Derek Copeland wrote:
> > I think this rather depends on the degree of instability in the air. On
> > relatively stable days the usual thermal sources often don't seem to
> > work. You need a large area to remain undisturbed for some time until
> > enough hot air is available to give a decent thermal when triggered.
> > Often things like towns and motorways don't work because there is too
> > much trigger activity going on and only tiny weak thermals will form
> > that go to no great height.
>
> 'Flapping' (as its called in FF jargon) only works in calm conditions
> with weak lift. To be successful it requires an area of 'stuck-down' warm
> air that can be broken loose by some vigorous milling about.
>
> A few years ago at a WC we and the Russians, at adjacent poles, each had
> one man still to fly in the last 5 mins of a round. We could feel a
> thermal building and the thermal detectors showed the air temp was
> building but it wasn't likely to go before the end of the round, so we
> decided to try to break it loose and started flapping. The Russians saw
> what we were doing and joined in. The thermal got broken loose and both
> models climbed away in it just before the hooter at the end of the round.
>
> Flapping is common at major Euro and World level events where the fliers
> have retrieval teams available to flap, but that was the only time I've
> seen or helped to get a thermal going before the model was launched. Its
> more usual to flap under a model that's been launched before the bubble
> has broken away and is coming down.
>
> --
> martin@ * | Martin Gregorie
> gregorie. | Essex, UK
> org * * * |

Shat is a thermal detector?

Bill Snead

[Mike Bamberg]

On Sep 23, 5:53*pm, wrote:
> On Sep 23, 6:26*pm, Martin Gregorie >
> wrote:
>
>
>
>
>
> > On Wed, 23 Sep 2009 15:00:04 +0000, Derek Copeland wrote:
> > > I think this rather depends on the degree of instability in the air. On
> > > relatively stable days the usual thermal sources often don't seem to
> > > work. You need a large area to remain undisturbed for some time until
> > > enough hot air is available to give a decent thermal when triggered.
> > > Often things like towns and motorways don't work because there is too
> > > much trigger activity going on and only tiny weak thermals will form
> > > that go to no great height.
>
> > 'Flapping' (as its called in FF jargon) only works in calm conditions
> > with weak lift. To be successful it requires an area of 'stuck-down' warm
> > air that can be broken loose by some vigorous milling about.
>
> > A few years ago at a WC we and the Russians, at adjacent poles, each had
> > one man still to fly in the last 5 mins of a round. We could feel a
> > thermal building and the thermal detectors showed the air temp was
> > building but it wasn't likely to go before the end of the round, so we
> > decided to try to break it loose and started flapping. The Russians saw
> > what we were doing and joined in. The thermal got broken loose and both
> > models climbed away in it just before the hooter at the end of the round.
>
> > Flapping is common at major Euro and World level events where the fliers
> > have retrieval teams available to flap, but that was the only time I've
> > seen or helped to get a thermal going before the model was launched. Its
> > more usual to flap under a model that's been launched before the bubble
> > has broken away and is coming down.
>
> > --
> > martin@ * | Martin Gregorie
> > gregorie. | Essex, UK
> > org * * * |
>
> Shat is a thermal detector?
>
> Bill Snead- Hide quoted text -
>
> - Show quoted text -

Bill,

In this case it's a long pole, mounted vertical, with temperature
sensors at the top and somewhat lower to measure the temperature
differential close to the ground.

In addition there is usually a long, light-weight mylar streamer
attached to the top that can show the inflow to the thermal as it
begins to rise.

here is a site that has pictures:

http://www.gallery.f1a.info/imgpage.php?dir=home/ff/2008/bulgaria/contest/img/img026.jpg

The long poles to the right and directly behind the guy with the model
are the thermal detectors.

Mike

[danlj]

On Sep 21, 3:52*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.

Thanks for passing on this thread, Dan. Interesting discussion. About
the only thing in addition that comes to mind is that my mind changed
recently on the forest issue. Not that I want to make a habit of
flying over large tracts of forest, but the conditions seemed right to
me at the time a month ago when I flew to Escanaba, MI. For the last
90 or so miles the terrain was 90% forest. There was also very nice
lift. I was by no means scratching as you can tell--
http://www.onlinecontest.org/olc-2.0/gliding/flightinfo.html?flightId=840249634.
Perhaps this was similar to one of the people commenting on your
thread about forests. With the exception that this was nearly purely
forest, and the lift was good. I wonder if indeed the lift was good
over this forest because it was later in the day?

Chris Prince

[Martin Gregorie[_5_]]

On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:

>
> Shat is a thermal detector?
>
Typically an DC amplifier watching a tiny, naked fast response thermistor
on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
it is fitted with a sunshade to keep direct or reflected sunlight off it.
They are also typically high resistance units (20K is a sensible minimum)
so the sensing voltage doesn't warm them. If this happens the detector is
sensitive to wind speed - something we don't want.

Output is normally an analogue dial or a chart recorder built from RC
servos though I have seen one with an audio output tone that rose and
fell with temperature.

Thermal detectors can be quite sensitive. Full scale deflection with a
0.8 C temperature change is not uncommon, so the better units are
designed to let the zero setting track average day temperature. All have
a gain control, needed because the temperature swing as a thermal blows
through rises during the day, peaking in mid-afternoon.

Some people use digital thermometers, but there are problems - the
sampling rate is often far too slow (usually every 3 or 10 seconds) and
the sensitivity to small temperature variations is limited by the
display. I've seen none that can show changes of less than 0.1 degree.

That's probably more than you wanted to know, but there you go.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[smithcorp]

Are you sure he wasn't being tongue-in-cheek? I regularly find that
the best thermals are found on my downwind leg right before i want to
turn on base. Perhaps that's what he meant by the "downwind corner of
the field" :)

smith

On Sep 22, 6:52*am, danlj > wrote:
>> He did tell the one thing he knew about finding thermals: "The best
> lift is at the most downwind corner of the field."

[[email protected][_2_]]

On Sep 24, 5:02*pm, Martin Gregorie >
wrote:
> On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>
> > Shat is a thermal detector?
>
> Typically an DC amplifier watching a tiny, naked fast response thermistor
> on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
> it is fitted with a sunshade to keep direct or reflected sunlight off it.
> They are also typically high resistance units (20K is a sensible minimum)
> so the sensing voltage doesn't warm them. If this happens the detector is
> sensitive to wind speed - something we don't want.
>
> Output is normally an analogue dial or a chart recorder built from RC
> servos though I have seen one with an audio output tone that rose and
> fell with temperature.
>
> Thermal detectors can be quite sensitive. Full scale deflection with a
> 0.8 C temperature change is not uncommon, so the better units are
> designed to let the zero setting track average day temperature. All have
> a gain control, needed because the temperature swing as a thermal blows
> through rises during the day, peaking in mid-afternoon.
>
> Some people use digital thermometers, but there are problems - the
> sampling rate is often far too slow (usually every 3 or 10 seconds) and
> the sensitivity to small temperature variations is limited by the
> display. I've seen none that can show changes of less than 0.1 degree.
>
> That's probably more than you wanted to know, but there you go.
>
> --
> martin@ * | Martin Gregorie
> gregorie. | Essex, UK
> org * * * |

Does anyone have experience with using thermal detectors to increase
the "get away rate" when auto or winch towing full size gliders?

Bill

[Frank Whiteley]

On Sep 25, 5:08*pm, wrote:
> On Sep 24, 5:02*pm, Martin Gregorie >
> wrote:
>
>
>
> > On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>
> > > Shat is a thermal detector?
>
> > Typically an DC amplifier watching a tiny, naked fast response thermistor
> > on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
> > it is fitted with a sunshade to keep direct or reflected sunlight off it.

[Brad[_2_]]

> I regularly find that
> the best thermals are found on my downwind leg right before i want to
> turn on base. Perhaps that's what he meant by the "downwind corner of
> the field" :)

your field is like that too eh? hmmmmmmmm................

Brad

[Martin Gregorie[_5_]]

On Fri, 25 Sep 2009 16:08:02 -0700, snead1 wrote:

> On Sep 24, 5:02Â*pm, Martin Gregorie >
> wrote:
>> On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>>
>> > Shat is a thermal detector?
>>
>> Typically an DC amplifier watching a tiny, naked fast response
>> thermistor on a 5m (15ft) pole. The thermistor should be sensitive to
>> air temp, so it is fitted with a sunshade to keep direct or reflected
>> sunlight off it. They are also typically high resistance units (20K is
>> a sensible minimum) so the sensing voltage doesn't warm them. If this
>> happens the detector is sensitive to wind speed - something we don't
>> want.
>>
>> Output is normally an analogue dial or a chart recorder built from RC
>> servos though I have seen one with an audio output tone that rose and
>> fell with temperature.
>>
>> Thermal detectors can be quite sensitive. Full scale deflection with a
>> 0.8 C temperature change is not uncommon, so the better units are
>> designed to let the zero setting track average day temperature. All
>> have a gain control, needed because the temperature swing as a thermal
>> blows through rises during the day, peaking in mid-afternoon.
>>
>> Some people use digital thermometers, but there are problems - the
>> sampling rate is often far too slow (usually every 3 or 10 seconds) and
>> the sensitivity to small temperature variations is limited by the
>> display. I've seen none that can show changes of less than 0.1 degree.
>>
>> That's probably more than you wanted to know, but there you go.
>>
>> --
>> martin@ Â* | Martin Gregorie
>> gregorie. | Essex, UK
>> org Â* Â* Â* |
>
> Does anyone have experience with using thermal detectors to increase the
> "get away rate" when auto or winch towing full size gliders?
>
I should have added that photos and circuits of the thermal detectors
I've built are here:

http://www.gregorie.org/freeflight/thermal_detector/thermal_detector.html

The article mentions 'mylar ribbon' in passing. This is another low-tech
way of finding thermals. 5-10m of the thin aluminised ribbon out of a
mylar capacitor (it is around 25mm [1 inch] wide and 0.5 microns thick)
is attached to the top of a 5m fishing pole. When the ribbon is lifted
horizontal and you see big waves running along the ribbon and/or it
points upwards a thermal is passing over the pole. If there are several
mylars on the field and the day is calm, they will all point at the
thermal - though this arrangement doesn't really belong on a glider
field!


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[bildan]

On Sep 25, 6:51*pm, Frank Whiteley > wrote:
> On Sep 25, 5:08*pm, wrote:
>
>
>
> > On Sep 24, 5:02*pm, Martin Gregorie >
> > wrote:
>
> > > On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>
> > > > Shat is a thermal detector?
>
> > > Typically an DC amplifier watching a tiny, naked fast response thermistor
> > > on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
> > > it is fitted with a sunshade to keep direct or reflected sunlight off it.
> > > They are also typically high resistance units (20K is a sensible minimum)
> > > so the sensing voltage doesn't warm them. If this happens the detector is
> > > sensitive to wind speed - something we don't want.
>
> > > Output is normally an analogue dial or a chart recorder built from RC
> > > servos though I have seen one with an audio output tone that rose and
> > > fell with temperature.
>
> > > Thermal detectors can be quite sensitive. Full scale deflection with a
> > > 0.8 C temperature change is not uncommon, so the better units are
> > > designed to let the zero setting track average day temperature. All have
> > > a gain control, needed because the temperature swing as a thermal blows
> > > through rises during the day, peaking in mid-afternoon.
>
> > > Some people use digital thermometers, but there are problems - the
> > > sampling rate is often far too slow (usually every 3 or 10 seconds) and
> > > the sensitivity to small temperature variations is limited by the
> > > display. I've seen none that can show changes of less than 0.1 degree..
>
> > > That's probably more than you wanted to know, but there you go.
>
> > > --
> > > martin@ * | Martin Gregorie
> > > gregorie. | Essex, UK
> > > org * * * |
>
> > Does anyone have experience with using thermal detectors to increase
> > the "get away rate" when auto or winch towing full size gliders?
>
> > Bill
>
> When driving the winch, I often advise whether to turn left or right
> at the top of the launch. *Most don't listen.
>
> Frank

Radio exchange immediately after winch launch:-)

Frank: "Why are you circling right? I said turn left.
Me: "I'm climbing at 8 knots."
Frank: "Oh."

Actually, a system which could reliably locate thermals in the
vicinity of a winch would be extremely useful even though most pilots
find a thermal and soar away on better than 50% of their launches in
thermic conditions.

AFAIK, there are three methods that show promise.

The cheapest is anemometer/wind vanes on the four corners of the
airfield which can show surface inflow to a thermal. Connecting these
with radio modems and plotting the wind vectors on a laptop screen
should indicate the surface location of a thermal. Wireless weather
stations are off-the-shelf items.

Both lasers (LIDAR) and microwave (RADAR) can directly detect vertical
air motion by reflecting the beam off entrained dust, pollen and/or
insects. None of these are exactly cheap but that has to be weighed
against the utility of reliably finding thermals from a cheap winch
launch.

[Frank Whiteley]

On Sep 26, 1:13*pm, bildan > wrote:
> On Sep 25, 6:51*pm, Frank Whiteley > wrote:
>
>
>
> > On Sep 25, 5:08*pm, wrote:
>
> > > On Sep 24, 5:02*pm, Martin Gregorie >
> > > wrote:
>
> > > > On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>
> > > > > Shat is a thermal detector?
>
> > > > Typically an DC amplifier watching a tiny, naked fast response thermistor
> > > > on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
> > > > it is fitted with a sunshade to keep direct or reflected sunlight off it.
> > > > They are also typically high resistance units (20K is a sensible minimum)
> > > > so the sensing voltage doesn't warm them. If this happens the detector is
> > > > sensitive to wind speed - something we don't want.
>
> > > > Output is normally an analogue dial or a chart recorder built from RC
> > > > servos though I have seen one with an audio output tone that rose and
> > > > fell with temperature.
>
> > > > Thermal detectors can be quite sensitive. Full scale deflection with a
> > > > 0.8 C temperature change is not uncommon, so the better units are
> > > > designed to let the zero setting track average day temperature. All have
> > > > a gain control, needed because the temperature swing as a thermal blows
> > > > through rises during the day, peaking in mid-afternoon.
>
> > > > Some people use digital thermometers, but there are problems - the
> > > > sampling rate is often far too slow (usually every 3 or 10 seconds) and
> > > > the sensitivity to small temperature variations is limited by the
> > > > display. I've seen none that can show changes of less than 0.1 degree.
>
> > > > That's probably more than you wanted to know, but there you go.
>
> > > > --
> > > > martin@ * | Martin Gregorie
> > > > gregorie. | Essex, UK
> > > > org * * * |
>
> > > Does anyone have experience with using thermal detectors to increase
> > > the "get away rate" when auto or winch towing full size gliders?
>
> > > Bill
>
> > When driving the winch, I often advise whether to turn left or right
> > at the top of the launch. *Most don't listen.
>
> > Frank
>
> Radio exchange immediately after winch launch:-)
>
> Frank: "Why are you circling right? *I said turn left.
> Me: "I'm climbing at 8 knots."
> Frank: "Oh."
>
> Actually, a system which could reliably locate thermals in the
> vicinity of a winch would be extremely useful even though most pilots
> find a thermal and soar away on better than 50% of their launches in
> thermic conditions.
>
> AFAIK, there are three methods that show promise.
>
> The cheapest is anemometer/wind vanes on the four corners of the
> airfield which can show surface inflow to a thermal. *Connecting these
> with radio modems and plotting the wind vectors on a laptop screen
> should indicate the surface location of a thermal. *Wireless weather
> stations are off-the-shelf items.
>
> Both lasers (LIDAR) and microwave (RADAR) can directly detect vertical
> air motion by reflecting the beam off entrained dust, pollen and/or
> insects. *None of these are exactly cheap but that has to be weighed
> against the utility of reliably finding thermals from a cheap winch
> launch.

1 out of 8 maybe;^)

Frank

[nate_fl]

On Sep 25, 10:21*pm, Brad > wrote:
> > I regularly find that
> > the best thermals are found on my downwind leg right before i want to
> > turn on base. Perhaps that's what he meant by the "downwind corner of
> > the field" :)
>
> your field is like that too eh? hmmmmmmmm................
>
> Brad

I never worry about getting low in the pattern anymore, I always find
a boomer abeam my aimpoint! Curiously, I don't seem to be able to find
them anywhere else....

[Bob]

Frank

Checking my logbook I find that, excluding training flights, my sucess
rate on winch launch is about 60%. Sucess is rated by climbing to a
height that allows me to glide to the next thermal. Some of our pilots
have better percentages because they are more "discerning" about when
they will take a flight.

Bob

[Bob]

On Sep 27, 8:49*am, Bob > wrote:
> Frank
>
> Checking my logbook I find that, excluding training flights, my sucess
> rate on winch launch is about 60%. Sucess is rated by climbing to a
> height that allows me to glide to the next thermal. Some of our pilots
> have better percentages because they are more "discerning" about when
> they will take a flight.
>
> Bob

Wish I could spell success!

Bob

[Frank Whiteley]

On Sep 27, 12:49*am, Bob > wrote:
> Frank
>
> Checking my logbook I find that, excluding training flights, my sucess
> rate on winch launch is about 60%. Sucess is rated by climbing to a
> height that allows me to glide to the next thermal. Some of our pilots
> have better percentages because they are more "discerning" about when
> they will take a flight.
>
> Bob

Actually, on thermic days our club achieves about an 80 percent 'hook'
rate. Pilots often release from aero tow lower than nominal winch
release height in similar conditions. What winch pilots find is that
lift starts quite early many days. The aero tow queue piles up about
1pm.

Several days include two shears, surface flow to about 600-800ft, and
another about 1400-1600ft and may be impacted by the passage of one or
two convergence lines in the afternoon resulting in temporary or
permanent 180 degree wind shifts. We have a house thermal area near
the most common IP, but sometimes it's clear that the best lift is in
the opposite direction, or over the launch point rather than the
winch. Thanks when I give a nudge.

Frank

[Mike I Green]

Very often the turbulence generated by the winch tow breaks loose a
thermal. Turn left or right a couple of times. That's what I learned
flying with the Vultures in Michigan 45 years ago.

MG

wrote:
> On Sep 24, 5:02 pm, Martin Gregorie >
> wrote:
>> On Wed, 23 Sep 2009 17:53:24 -0700, snead1 wrote:
>>
>>> Shat is a thermal detector?
>> Typically an DC amplifier watching a tiny, naked fast response thermistor
>> on a 5m (15ft) pole. The thermistor should be sensitive to air temp, so
>> it is fitted with a sunshade to keep direct or reflected sunlight off it.
>> They are also typically high resistance units (20K is a sensible minimum)
>> so the sensing voltage doesn't warm them. If this happens the detector is
>> sensitive to wind speed - something we don't want.
>>
>> Output is normally an analogue dial or a chart recorder built from RC
>> servos though I have seen one with an audio output tone that rose and
>> fell with temperature.
>>
>> Thermal detectors can be quite sensitive. Full scale deflection with a
>> 0.8 C temperature change is not uncommon, so the better units are
>> designed to let the zero setting track average day temperature. All have
>> a gain control, needed because the temperature swing as a thermal blows
>> through rises during the day, peaking in mid-afternoon.
>>
>> Some people use digital thermometers, but there are problems - the
>> sampling rate is often far too slow (usually every 3 or 10 seconds) and
>> the sensitivity to small temperature variations is limited by the
>> display. I've seen none that can show changes of less than 0.1 degree.
>>
>> That's probably more than you wanted to know, but there you go.
>>
>> --
>> martin@ | Martin Gregorie
>> gregorie. | Essex, UK
>> org |
>
> Does anyone have experience with using thermal detectors to increase
> the "get away rate" when auto or winch towing full size gliders?
>
> Bill