On Thursday, October 11, 2012 8:03:04 PM UTC-4, (unknown) wrote:
Weirdest thing today. On the grid, ready to takeoff. I had a highly experienced contest pilot hookup the small ring into my TOST hookup. When the towplane started rolling, after about 20 feet, it released uncommanded. I thought that it must have been the way it was hooked up, so we tried it again. Before the second attempt we did a very focused test and it seemed normal. Then on my second takeoff the same thing happened and I rolled to a stop again. We took the towrope and hooked up the ring just like we always do for a third time. Towplane engine shut off at this point. This time I pulled the rope with both hands as two guys were holding back on the sailplane and it disconnected just with my force. I now have the seat pan out, the instrument panel out and looking it over very thoroughly with a couple other pilots and see nothing. The cable looks normal, the sleeve looks normal, pulley system looks normal, the clamps at each end of the cable look fine. Essentially, everything associated with the release system looks brand new. The plan is to purchase a new TOST hook from Tim Mara and be done with it. I'm just writing this on here to inquire information regarding this from others. I am puzzled as to why this would have happened.

Saw exactly that a few years ago at the contest in Perry, SC in a '27. Turned out that the pilot, who was a bit on the 'portly' side, had bowed the seat-pan to the point that it was slightly pinching the release cable between it and bottom of the fuselage. That created enough resistance so the spring of the TOST release could not fully close the over-center mechanism. Replacing the cable and re-routing it solved the issue. There was nothing wrong with the release itself.
'GM'