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

I'm starting to think that the textbook circular thermal is primarily a flatland phenomena.

On 07/29/2013 12:00 PM, son_of_flubber wrote:
I'm starting to think that the textbook circular thermal is primarily a flatland phenomena.

Not even in the flat lands - the textbook circular thermal is an
approximation!

Cheers,
Luke

On 7/29/2013 10:03 AM, Luke Szczepaniak wrote:
On 07/29/2013 12:00 PM, son_of_flubber wrote:
I'm starting to think that the textbook circular thermal is primarily a
flatland phenomena.

Not even in the flat lands - the textbook circular thermal is an approximation!

Cheers,
Luke

People like Son of Flubber tick me off. He seems to have learned "circular
thermal" closely approximates an oxymoron far more quickly than I ever did. In
any event, "What Luke said!"

"Circular thermal" is a great place to start in book-learnin' terms. Reality,
on the other hand...

Bob - :-) - W.

The thermal helper in XCSoar gives a pretty good depiction of the relative
strengths around a thermal. It's definitely not circular!

I learned a long time ago to tighten up when lift falls off and ease up a
bit on the bank when the lift goes up. With practice, you'll get it and
won't need a graphical depiction of a thermal.


"BobW" wrote in message
...
On 7/29/2013 10:03 AM, Luke Szczepaniak wrote:
On 07/29/2013 12:00 PM, son_of_flubber wrote:
I'm starting to think that the textbook circular thermal is primarily a
flatland phenomena.

Not even in the flat lands - the textbook circular thermal is an
approximation!

Cheers,
Luke

People like Son of Flubber tick me off. He seems to have learned "circular
thermal" closely approximates an oxymoron far more quickly than I ever
did. In any event, "What Luke said!"

"Circular thermal" is a great place to start in book-learnin' terms.
Reality, on the other hand...

Bob - :-) - W.

On Monday, July 29, 2013 4:45:35 PM UTC-7, Dan Marotta wrote:
....

I learned a long time ago to tighten up when lift falls off and ease up a

bit on the bank when the lift goes up. With practice, you'll get it and

won't need a graphical depiction of a thermal.

Isn't it the other way around? (fly tight circles when the lift is good, widen out when not (so you can run into it again?)

No. You got that backwards....

No, as the lift peters out, you want to move away from that area. You do
that by tightening your turn. When I feel a spike in the lift, I let up for
a couple of seconds to drift into the area of strong lift and then tighten
up to try to stay there. More often, as stated elsewhere, the thermal is
not circular and you have to do what you have to do. A depiction of the
areas of stronger and weaker lift can be helpful on weaker days, but we
don't have too many of those here.

Maybe I didn't describe it correctly.


"Bill Palmer" wrote in message
...
On Monday, July 29, 2013 4:45:35 PM UTC-7, Dan Marotta wrote:
...

I learned a long time ago to tighten up when lift falls off and ease up a

bit on the bank when the lift goes up. With practice, you'll get it and

won't need a graphical depiction of a thermal.

Isn't it the other way around? (fly tight circles when the lift is good,
widen out when not (so you can run into it again?)

On Monday, July 29, 2013 10:00:11 AM UTC-6, son_of_flubber wrote:
I'm starting to think that the textbook circular thermal is primarily a flatland phenomena.

Most of the "Thermal Assistants" will assume circular but give a reasonable idea of the varied strength all the way around. WinPilot is the best I have used, SeeYou Mobile is about the worst. You can choose to adjust position from the values but in general seat feel will tell you more most of the time. I have not seen a nice circular and even strength thermal all the way around in months. Last Friday every thermal had multiple cores and strong centers about 50 feet across. They would also increase right until they dropped off a cliff. Level out into the stronger lift and it would increase through about 10 knots and then drop to sink instantly. I felt like a needed to go back to basic flight training again.

On Monday, July 29, 2013 5:14:01 PM UTC-7, Tim Taylor wrote:
On Monday, July 29, 2013 10:00:11 AM UTC-6, son_of_flubber wrote:

I'm starting to think that the textbook circular thermal is primarily a flatland phenomena.



Most of the "Thermal Assistants" will assume circular but give a reasonable idea of the varied strength all the way around. WinPilot is the best I have used, SeeYou Mobile is about the worst. You can choose to adjust position from the values but in general seat feel will tell you more most of the time. I have not seen a nice circular and even strength thermal all the way around in months. Last Friday every thermal had multiple cores and strong centers about 50 feet across. They would also increase right until they dropped off a cliff. Level out into the stronger lift and it would increase through about 10 knots and then drop to sink instantly. I felt like a needed to go back to basic flight training again.

+1 on Winpilot's thermal assistant being markedly better than the others. SYM useless, XCSoar marginal on its best days.

Thermals may not be circular, but your glider flies in a pretty good approximation of a circle. So the cylindrical graph depicted in Winpilot is all the information you can really use. XCSoar's polar graph might fool you into thinking that is the shape of the lift - but it is a polar graph of strength around a fixed radius circle, not a map of the thermal. Oh yeah they are different!

Tim were you flying the Tahoe/Minden/Truckee area? Last weekend the thermals were diabolical.

I think you've hit it jfitch. I didn't consider the polar graph.


"jfitch" wrote in message
...
On Monday, July 29, 2013 5:14:01 PM UTC-7, Tim Taylor wrote:
On Monday, July 29, 2013 10:00:11 AM UTC-6, son_of_flubber wrote:

I'm starting to think that the textbook circular thermal is primarily a
flatland phenomena.



Most of the "Thermal Assistants" will assume circular but give a
reasonable idea of the varied strength all the way around. WinPilot is the
best I have used, SeeYou Mobile is about the worst. You can choose to
adjust position from the values but in general seat feel will tell you
more most of the time. I have not seen a nice circular and even strength
thermal all the way around in months. Last Friday every thermal had
multiple cores and strong centers about 50 feet across. They would also
increase right until they dropped off a cliff. Level out into the
stronger lift and it would increase through about 10 knots and then drop
to sink instantly. I felt like a needed to go back to basic flight
training again.

+1 on Winpilot's thermal assistant being markedly better than the others.
SYM useless, XCSoar marginal on its best days.

Thermals may not be circular, but your glider flies in a pretty good
approximation of a circle. So the cylindrical graph depicted in Winpilot is
all the information you can really use. XCSoar's polar graph might fool you
into thinking that is the shape of the lift - but it is a polar graph of
strength around a fixed radius circle, not a map of the thermal. Oh yeah
they are different!

Tim were you flying the Tahoe/Minden/Truckee area? Last weekend the thermals
were diabolical.