On Saturday, December 14, 2019 at 8:57:57 PM UTC-8, Duster wrote:
A friend has installed a system in his home-built glider that enables shifting the CG position forward during higher cruise speeds (e.g., between lift, final glide, etc.). It uses two water reservoirs whose content can be transferred using a 12v pump. This is done, ostensibly, to reduce elevator-induced drag. Does anyone know of other gliders outfitted similarly and is there a demonstrated utility?

There was one prototype Schweizer with a trolley that could be cranked forward/aft.
Dick Brandt's Nimbus 3 had a Mercury weight shift ststem for a while. Believe George Moffatt wrote about it in Winning 2.
Jim