Gene Whitt wrote:
Y'all,
Been many years on rec.aviation.student but even more years since
gliding. Unable to explain the 'why' of water ballast to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt

For the long answer, see
http://home.comcast.net/%7Everhulst/...t/ballast.html

The real short answer is - see the polar at the end of the above
article. One curve is with ballast, the other without.

The slightly longer answer is that a glider's best glide, for instance,
occurs at one speed. Increase the weight and that same best glide (more
or less) now occurs at a higher speed. You can go faster and maintain a
better L/D than you would without ballast.

Tony V.