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.