Having owned my Q500+ for a few weeks now, and with a few hours flying time under my belt, I can't help but be a bit concerned about the cases of props coming off the motor shafts. Recommendations on the subject seem to go from finger tight to one and a half turns of tightening using the supplied "tongs". With the top of the engine, the shaft and the prop turning together, would it not be possible to have some sort of fail-safe clip to stop the prop spinning off the shaft? I am currently trying out a small but strong rubber band, going round the shaft, beneath the o-ring and passed over the prop hub. Balancing could be a problem, but with the band going over the center spinner. it might not affect the balance too much. I'll see how I get on.