On Fri, 7 Jan 2011 18:29:27 -0800 (PST), n7ly
wrote:


Particularly static system and instrument errors. These can be a big
surprise.

Not as surprising as airmass movements.
THIS is the thing to know - anything else can be measured by GPS with
sufficient precision.


Dick Johnson did a phantastic job - but some of his results are far
off because of his limited ressources.

So far the German Idaflieg get the most accurate performance numbers -
they measure performance by flying the glider-to-be-tested next to a
glider (the "holy" DG-300/17) whose performance is precisely known
(calibrating this DG-300 takes about half a year!).

By flying through the same airmass thermal convection can be ruled
out.


I'm afraid but I'm pretty sure this is the only chance to get halfways
accurate performance measurements with today's technology, since at
the moment it is not possible to get information about thermal
convection of the airmass with sufficient precision (one inch/sec of
rising/sinking air is about two points of L/D).


Andreas