ORIGINAL: meaden
Your lucky it flew off to 3 o'clock and not 9 o'clock. I'd add to a lock nut that you make a practice of moving behind the plane before you run the engine up or even take the glow starter off.
I'm a bit paranoid of this situation and spend as little time as needed in front or in the arch of the prop.
Agreed, very lucky, and my father-in-law was there, and happened to comment that he never stands in front of a running engine.