When are thermals not circular and do thermal helpers assume thatthey are?

What are you trying to say. Seems to me that the airmass is carrying the
thermal along and the glider with it. With that premise, circling in calm
air or in a wind makes no difference. I've thermalled straight up and with
a 20+ kt drift down wind. I never had to hold heading into a wind to
maintain center in a thermal.

Or do I misunderstand what you're saying? If that's the case, please
elaborate.


"jfitch" wrote in message
...
On Saturday, August 10, 2013 8:43:05 AM UTC-7, Dan Marotta wrote:
Your glider is drifting with the wind, too...




Unfortunately, the earth, and the GPS system that tracks with it, is
not.....

On Sunday, August 11, 2013 1:19:40 PM UTC-4, Dan Marotta wrote:
I never had to hold heading into a wind to
maintain center in a thermal.

Does it work like this east of Ohio?

On Sunday, August 11, 2013 10:19:40 AM UTC-7, Dan Marotta wrote:
What are you trying to say. Seems to me that the airmass is carrying the

thermal along and the glider with it. With that premise, circling in calm

air or in a wind makes no difference. I've thermalled straight up and with

a 20+ kt drift down wind. I never had to hold heading into a wind to

maintain center in a thermal.



Or do I misunderstand what you're saying? If that's the case, please

elaborate.







...

On Saturday, August 10, 2013 8:43:05 AM UTC-7, Dan Marotta wrote:

Your glider is drifting with the wind, too...









Unfortunately, the earth, and the GPS system that tracks with it, is

not.....

It makes a difference if you are trying to relate your thermaling track to a track projected to the ground. Some thermal assistants (like SYM) draw a track on the ground color coded by climb rate. If you are drifting with the wind, this track quickly drifts upwind relative to you and the airmass (which are drifting downwind). Therefore the next time around your circle, the track will not have much relevance. The only thing that matters (as you have said) is the glider relative to the airmass, which the GPS cannot accurately track and plot. That relationship has to be inertially derived, or simple inferred to be static. The GPS plot is relative to the earth, which can be thought of as moving underneath you at the speed of the wind. Such a plot is of little value when thermaling though they can be useful for ridge and wave, which are effectively anchored to the earth.

There have been some attempts to guess the drift of the thermal from an assumed or calculated wind speed, but most thermals where I fly are not so well behaved.

Thanks - now I see what you mean. My confusion was because XCSoar does a
pretty good job of predicting the wind drift (due to getting good
information from my CAI302) and so the flight track (rather than ground
track) is displayed while circling. This makes it pretty easy to get back
to the lift if, due to inattention or poor decisions, you get out of it.

Slightly off topic, but IIRC I can set up the software so that it accounts
for wind drift while circling and not in straight flight. I say this
because I use the track to stay in the best lift while wave flying.


"jfitch" wrote in message
...
On Sunday, August 11, 2013 10:19:40 AM UTC-7, Dan Marotta wrote:
What are you trying to say. Seems to me that the airmass is carrying the

thermal along and the glider with it. With that premise, circling in calm

air or in a wind makes no difference. I've thermalled straight up and
with

a 20+ kt drift down wind. I never had to hold heading into a wind to

maintain center in a thermal.



Or do I misunderstand what you're saying? If that's the case, please

elaborate.







...

On Saturday, August 10, 2013 8:43:05 AM UTC-7, Dan Marotta wrote:

Your glider is drifting with the wind, too...









Unfortunately, the earth, and the GPS system that tracks with it, is

not.....

It makes a difference if you are trying to relate your thermaling track to a
track projected to the ground. Some thermal assistants (like SYM) draw a
track on the ground color coded by climb rate. If you are drifting with the
wind, this track quickly drifts upwind relative to you and the airmass
(which are drifting downwind). Therefore the next time around your circle,
the track will not have much relevance. The only thing that matters (as you
have said) is the glider relative to the airmass, which the GPS cannot
accurately track and plot. That relationship has to be inertially derived,
or simple inferred to be static. The GPS plot is relative to the earth,
which can be thought of as moving underneath you at the speed of the wind.
Such a plot is of little value when thermaling though they can be useful for
ridge and wave, which are effectively anchored to the earth.

There have been some attempts to guess the drift of the thermal from an
assumed or calculated wind speed, but most thermals where I fly are not so
well behaved.

On Monday, August 12, 2013 8:49:40 AM UTC-7, Dan Marotta wrote:
Thanks - now I see what you mean. My confusion was because XCSoar does a

pretty good job of predicting the wind drift (due to getting good

information from my CAI302) and so the flight track (rather than ground

track) is displayed while circling. This makes it pretty easy to get back

to the lift if, due to inattention or poor decisions, you get out of it.



Slightly off topic, but IIRC I can set up the software so that it accounts

for wind drift while circling and not in straight flight. I say this

because I use the track to stay in the best lift while wave flying.







...

On Sunday, August 11, 2013 10:19:40 AM UTC-7, Dan Marotta wrote:

What are you trying to say. Seems to me that the airmass is carrying the



thermal along and the glider with it. With that premise, circling in calm



air or in a wind makes no difference. I've thermalled straight up and

with



a 20+ kt drift down wind. I never had to hold heading into a wind to



maintain center in a thermal.







Or do I misunderstand what you're saying? If that's the case, please



elaborate.















...



On Saturday, August 10, 2013 8:43:05 AM UTC-7, Dan Marotta wrote:



Your glider is drifting with the wind, too...



















Unfortunately, the earth, and the GPS system that tracks with it, is



not.....



It makes a difference if you are trying to relate your thermaling track to a

track projected to the ground. Some thermal assistants (like SYM) draw a

track on the ground color coded by climb rate. If you are drifting with the

wind, this track quickly drifts upwind relative to you and the airmass

(which are drifting downwind). Therefore the next time around your circle,

the track will not have much relevance. The only thing that matters (as you

have said) is the glider relative to the airmass, which the GPS cannot

accurately track and plot. That relationship has to be inertially derived,

or simple inferred to be static. The GPS plot is relative to the earth,

which can be thought of as moving underneath you at the speed of the wind..

Such a plot is of little value when thermaling though they can be useful for

ridge and wave, which are effectively anchored to the earth.



There have been some attempts to guess the drift of the thermal from an

assumed or calculated wind speed, but most thermals where I fly are not so

well behaved.

XCSoar does have the option to drift your track at the assumed wind speed to account for this problem. I have found it not to be accurate enough to make it usable (may depend on where you fly). The XCSoar thermal assistant does about the same thing as Winpilot, but the presentation is not as good: the correction arrow is inusfficiently scaled, the polar graph very blocky (if it is really plotting every 10 deg), no other information presented such as average or graphed climb, flarm targets, etc.

jfitch wrote, On 8/11/2013 9:59 PM:
It makes a difference if you are trying to relate your thermaling
track to a track projected to the ground. Some thermal assistants
(like SYM) draw a track on the ground color coded by climb rate. If
you are drifting with the wind, this track quickly drifts upwind
relative to you and the airmass (which are drifting downwind).

The Thermal Assistant in my version of SYM does not draw a track on the
ground (of course, the map shows the ground track); instead, it opens
it's own window with no map info on it, and uses about 20 or so small
circles ("bubbles") arranged uniformly in a large circle to display the
thermal. Each bubble is sized and colored to depict the lift at that
point: bigger bubble, bigger lift; red is stronger, blue is weaker (the
actual colors can be selected)

In essence, your circles do overlay each other, no matter how much the
glider drifts with the wind. I never had trouble with wind drift when
using the Assistant. ClearNav, what I am now using, does use a ground
track, and it's hard for me to make sense of the the thermal is doing
from it's depiction. I'm nagging them about this, and I hope it will be
improved soon.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

On Tuesday, August 20, 2013 1:55:53 PM UTC-7, Eric Greenwell wrote:
jfitch wrote, On 8/11/2013 9:59 PM:

It makes a difference if you are trying to relate your thermaling

track to a track projected to the ground. Some thermal assistants

(like SYM) draw a track on the ground color coded by climb rate. If

you are drifting with the wind, this track quickly drifts upwind

relative to you and the airmass (which are drifting downwind).



The Thermal Assistant in my version of SYM does not draw a track on the

ground (of course, the map shows the ground track); instead, it opens

it's own window with no map info on it, and uses about 20 or so small

circles ("bubbles") arranged uniformly in a large circle to display the

thermal. Each bubble is sized and colored to depict the lift at that

point: bigger bubble, bigger lift; red is stronger, blue is weaker (the

actual colors can be selected)



In essence, your circles do overlay each other, no matter how much the

glider drifts with the wind. I never had trouble with wind drift when

using the Assistant. ClearNav, what I am now using, does use a ground

track, and it's hard for me to make sense of the the thermal is doing

from it's depiction. I'm nagging them about this, and I hope it will be

improved soon.



--

Eric Greenwell - Washington State, USA (change ".netto" to ".us" to

email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm

http://tinyurl.com/yb3xywl

The latest version of SYM draws a color coded ground track, as well as the bubbles. Still has quite a ways to go to catch up with what Winpilot had in 2005....