On 2014-10-24 10:34:02 +0000, Karl Striedieck said:

On Thursday, October 23, 2014 9:09:20 PM UTC-4, Nick Kennedy wrote:
https://www.youtube.com/watch?v=srNTtuTqUBE

Surfing Aircraft Vortices for Energy

Interesting piece from Boeing Aircraft

Next summer when KS goes past me in his Duo Discus I think I am going
to try this technique to keep up.

Hey Nick, John Seymour and I have done such many years ago in our
ASW-20's. One would position his glider behind lead about 100 feet,
level in altitude and with the wing tip behind leads spoiler. Sure
enough, the guy behind slowly moves forward and has enough energy to
pass under or over. Lead is now number two and can repeat the same
thing in a sort of grown ups leap frog.

Grown ups leap frog is something else entirely!