Failed attempt 1, 11 years old, Spring 1956: KeilKraft 'Champ' with a clapped-out second-hand 1cc. ED Bee diesel. Wouldn't start. I over-choked it, got a hydraulic lock that ripped the engine and its plywood mount clean out of the model when I flicked the prop.
Failed attempt 2, Christmas 1956: KeilKraft Phantom Mite with brand new DC Merlin .76cc. diesel. I don't remember why I was trying to fly it on lines only 20 ft. long, but it must have been doing 2 sec. laps - two or three of them before I got dizzy, lost control and crashed it. Plane wrecked, engine OK.
Success (sort of), April 1957: another KK Champ, better built than the last one, with the Merlin engine. Flew OK on 25 ft. lines but, like all Champs, had almost zero control response and a glide like a sack of bricks.
(Later that year, I put the Merlin in a crude own-design with a tissue-covered, symmetrical-section wing. Amazingly, it flew and I did my first loops with it. I still have that engine, which runs as well as it ever did.)