BB wrote:
Errors in measurement can be made up for with lots and lots of data, so
long as the errors are not biased one way or another. Thus, you should
be able to get an accurate polar even in thermally air, without
spending a fortune on tow fees. Turn on data recording, then fly
absolutely straight and same speed, through thermals as well as sink,
while taking data. Turn off data recording before thermaling back up to
altitude.

The key is to fly so that on average you're not biased toward flying in
lift vs. sink. You should randomize heading (if you always go
up/downwind you'll be in streets), randomize time of turning on/off the
data recording (if you turn on after leaving a thermal and off when you
find a new one, you'll be biased toward sink). If you do this for a
season, for example getting 20 minutes of data in the 1-2 hours of
prestart fooling around at contests, you might have a really good polar
at the end of it.

You could also do the opposite: A good pilot should be flying faster
through sink and slower through lift, and should spend more time in
lift than in sink. The difference between the "polar" measured in
thermal conditions and the factory polar can be a basis of a measure of
pilot skill. A good pilot should give a polar with a worse high speed
end -- because he always flies fast through sink -- a much better low
speed end -- becasue he always flies slow through lift -- and a
positive bias -- the whole polar shifted up.

In principle, all pretty easy to add to a glide computer. Of course we
all have a long list of more important features.

John Cochrane (BB)

Wouldn't it be simpler and much more scientific to arrange to do a
series of test runs over a LIDAR site, and simply post process the radar
and glider data recorder data ?