Where is the next thermal?

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

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 |

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 |

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 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 |

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