I had several (pre 9/11) cockpit rides in various Airbus types over
Germany. Some of the crew members were active glider pilots and they
claimed an L/D in the mid 20's, if they make the engines 'disappear'
drag-wise by keeping them going a bit above idle speed.

Remember the 'Gimli Glider', the Air Canada B767, that ran out of fuel?
There is a nice write-up at http://www.wadenelson.com/gimli.html
The author states a 11:1 for this 132t glider with two wind-milling P&W
engines and a RAT hanging out of it's belly.

Just out of curiosity - does anyone have a number for the space
shuttle?

Uli Neumann
Libelle 'GM'