I was "shot down" by a B-17! The B-17 was operating from ALB, about 20 miles away from our gliding home plate, Saratoga County Airport, NY (5B2). The B-17 was taking well heeled passengers, who were willing to shell out several hundred bucks, for a ride. I was recently licensed in gliders and was struggling in a weak thermal near 5B2 at 2200'. The B-17 came on the CTAF and and announced he was doing a pass over 5B2 at 2000'. Before I could respond on the radio, someone else replied and told the B-17 "gliders in the area". The B-17 replied "glider in sight, no factor". I thought I was safe, but apparently the B-17 had another glider in sight and passed directly below me. The roar of those four big radials was deafening, and I remember looking right into the eyes of the passenger riding in the top turret. The close encounter had me so shook that I lost my thermal and ended up having to land soon thereafter - thus the "shoot down". I now have a transponder in my newer glider.