What is that whine sound of the motors in your video. Electric of some kind able to go that fast?
Electric, yes .......... and that is one of my slow ones
660 Magnum is mostly correct, except that the motor really makes no noise at all. It is basically a modified 3 phase motor run by a VFD
The noise is the propeller crossing the the airframe, actually grabbing no air when it is in line with the airframe, then grabbing air as it crosses the airframe and hits air again. it is in a pusher config, meaning the prop is at the rear of the airframe.
IIRC, that setup was spinning at 33,500 rpms ............ or Mach .78 at the tips, which is less than 80% the speed of sound. Once the tip actually get above 95%, they make a churning sound and start to fray. Also the props start to become inefficient at about 95% the speed of sound