Extensive testing on the Lockheed AH-56A Cheyenne after a fatal crash showed the pilot's arm was just the right mass to excite an oscillation in the collective control system, leading to the rotor cutting thru the cockpit, and slicing the tail off the airplane.
A man of a different physical construction would not have encountered this.
A Cheyenne mounted in the full-scale tunnel at NASA Ames also cut itself in half during an unmanned test following the accident.
The airplane although extremely advanced in other areas, some of which are just being equalled today was deemed unsafe to continue with and the program (and all the other rigid-rotor programs at Lockheed) abandoned.