Helicopters can't fly faster than 250MPH

This is a fascinating video of not only how a helicopter works when it's in flight but also why helicopters -- all helicopters -- cannot exceed approximately 250MPH. One reason is the speed at which the rotors are spinning while producing lift. At some point, they just can't spin fast enough without creating a devastating sonic boom that would knock the helicopter out of the sky. Another reason is that the helicopter basically has two "sides", one that lifts and one that doesn't, and those two sides are constantly canceling each other out.