Where is the next thermal?

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.

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

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....

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

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

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

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