Mark Zivley wrote:

We all know what the manufacturer's polars look like, but what about
our individual planes. Has anyone done any work to develop a program
that would look at some flight logs and determine what a particular
glider's actual polar is? At one point Ball was making a vario
system that would determine the aircraft's polar over time just by
flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be
able to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of
cruise flight at varios airspeeds it should be do-able. Question is,
has it been done.

I haven't heard of it being done, and I can't imagine how one would
compensate for air motion, both vertical and horizontal, just using the
GPS info. Both motions change with location, altitude, and time. Perhaps
if the flight record included the airspeed, like some varios can supply,
there would be some hope of doing it. I don't think you could count on
the vertical motion averaging to zero during the cruises, since we
typically adjust our path to include as much up air as possible.

You can get some good info using a flight recorder, but you have to do
it when the air is calm. If you are really interested, invest in a few
high tows and make the measurements. Take a look at this test done on a
DG 800:

http://groups.yahoo.com/group/ASA-NewsGroup/message/59

You don't have to be a group member to read the message.


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Eric Greenwell
Washington State
USA