I calculated again. I first got the per minute / per second thing mixed up. :-) Yes, for a 14 inch prop's tips to travel at the speed of sound, it would have to spin at around 18000 rpm. Which is not gonna happen. Even to approach that speed (not considering the fact that the prop would disintegrate), there is no motor and no ESC that would fit any model plane that would take the amps that the motor would pull at those rpms.