Had a piston fail in flight. Was using 25% nitro fuel with 22% oil, The Cox Medallion was on it's second run. The engine shut down, but could hear a "Whrrrrr" as it got closer to landing. I was thinking the prop screw had come loose, but the piston had split apart on top (copper) from the ring (steel)sleeve. The rod had a little play, but nothing abnormal. The sleeve pushed out of the cylinder by hand, was not frozen.

First one I ever broke in many years of flying Cox engines. I tore down and replaced the cylinder/piston, and cleaned/checked the engine. It was able to be run and reflown with the replaced parts.

Is that good luck or what? Like I said, never happened before. Your thoughts are welcome, thanks guys!