Source: 2015 Q1 Beartracks, Mark Scott
I found my window started to flutter at 85 knots, which is a little slow for air-to air photography. I would think others have seen flutter if they tried flying with the window open at this speed. I made a bumper to support the aft end of the window. It is made from a rubber stopper cut to length and drilled out for a 2-56 flat head screw. The screw replaces one of the fuel tank cover screws. The key is to make it long enough to put a little pressure on the back window frame. Mine is long enough to contact the frame about 1/4 inch before the latch gets into position under the wing. We tested it up to 100 KIAS, which is fast enough for me. The bumper also keeps the window from pressing up on the fuel sump drain.