Where is the next thermal?

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 |

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

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....img/img026.jpg

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

Mike

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...htId=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

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 |

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."

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

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.

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

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 he

http://www.gregorie.org/freeflight/t..._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 |