My money would be combat ships being most likely to go rogue. Many years ago at the SIG contest, Dad and I watched a combat flyer, whose thong broke, let go of the handle. Handle acted as a counterweight and model climbed out, and thermaled OOS. Saw it gliding back down about 30 minutes later east of the field. Wildest thing I ever saw.
I posted this here somewhere in 2007. My favorite combat flyaways:
1. In Alton, Illinois, about 1968, I was flying against Jim Flynn, one of my KC pals. I went at him head on and decided I'd better stick my arm out so I'd get a cut and he wouldn't. We passed a little too close, and my plane was gone. It came down on the concrete median strip of the nearby road. It was interesting to see how many pieces a G.21 could break into.
2. At the 1972 Nats, I was flying Richard Stubblefield. I got cut loose, and my plane vanished in the direction of the base golf course. It ran out of fuel and landed without breaking the prop. A gang of kids went after it and returned it. That's when I decided that combat is better than free flight. In free flight, you have to retrieve your own plane.
3. At the Golden State Cuts & Kills a few years ago in Vacaville, CA, I got a kill just after the start of the match. Immediately thereafter, my lines were cut, and the airplane headed up. It went out of sight overhead. We saw the little puff of fuel at the end of the engine run, but the plane didn't reappear for a minute or so. It drifted in different directions and landed in the circle as my match timer was beeping five minutes, so it must have been flying for 4:40 or so. I ran toward the plane as it landed, but didn't quite get to it to catch it. That would have really been cool. I patched the kill mark in the LE and flew it in the next round. I ended the day winning $1,000 and a case of microwave popcorn.
4. At a Bladder Grabber in Marymoor Park in Redmond, WA, my airplane took off toward McDonalds. I followed through blackberry bushes. I ran through the briars and I ran through the brambles, and I ran through the bushes where a rabbit wouldn't go. There was no plane at McDonalds, but a witness said that it almost hit a car, and the driver picked up the plane and took it away. I walked back to the contest by a less direct route. When I arrived, my airplane was there. The guy who picked it up had noticed that there was a contest in the park and returned the plane.
5. Bill Maywald had a flyaway at a Bladder Grabber in Shohomish, WA. I gave chase by automobile, having been eliminated several rounds earlier and having not much to do. His airplane selected the softest spot in Snohomish county to land: a sod farm about two miles from the contest. The airplane was unscathed and much cleaner than it would have been had it landed as planned.
6. I was flying FAI at the Northwest Regionals in Eugene back in the days before a flyaway gave you the choice to continue the match or call a rematch. My plane got cut loose and flew into a parking lot with Bob Carver, my pit crew, in hot pursuit. I had to chase down Bob. He had the spare streamer in his pocket, so I had to fetch either him or the flyaway to get a streamer for the second plane.
7. My last flyaway at the Northwest Regionals passed through the stunt circle at about four feet altitude. It was amusing to see my now-fellow stunt flyers hit the deck. The airplane landed at full speed in the field beyond. The funny part was how the streamer bunched up in a wad behind the wreckage, like in a Road Runner cartoon. I think that was the flyaway that got us banished from Eugene.
8. At the first Duke Fox Memorial, I watched with amusement Pete Athans's plane fly into a cornfield, never to be seen again. In the next match on that circle, my airplane got cut away in the same place and on the same heading as Pete's. I had a shutoff, though, and my plane glided down nearby and unbroken. That's when I decided shutoffs are OK.