Andy Blackburn wrote:
At 23:30 27 March 2005, Bruce Hoult wrote:

Could headwind account for the 100% example? And tailwind

for the 75%?

In other words, your airspeed was not the same as your
ground speed?


I did a quick check at the time and in most cases there
was a light crosswind of 5-8 knots, so I ignored it.
Obviously a few knots at the high end makes a big difference
in energy (10 knots below redline costs 130 feet).
Maybe I'll do a more rigorous analysis.

9B



Wind gradient?

If you have a speed differential of a couple of knots between the 50' low and
the top of the pull up you are effectively getting "free" energy and will get a
higher apogee.
Since the finish line is generally set up downwind the pull up is into slower
moving air relative to the glider - Faster relative to the ground.
Look at it arithmetically - 100kt 50' up into a 15kt wind.
Pull up into headwind of 35kt - you got to slow an extra 20kt relative to the
ground. Pulling up harder allows you to convert the kinetic energy into
potential, (height)while retaining airspeed.

I know the argument that a glider flies and maintains energy relative to the
body of air it is flying in - but this only holds true if you simplify the model
to assume that the airmass is behaving homogeneously. A rapid transition between
air at different speeds is the technique used by albatrosses etc to soar the
oceans.

The greater the wind speed, and wind gradient the higher you are likely to be
able to pull up. I am not sure but at a guess I would say this would also work
to some degree for coss wind, as the relative wind speed would also tend to
increase (with increased track angle) to maintain ground track.