Bell Helicopter Coaxial Rotor
A little-known fourth research helicopter was constructed, and used to evaluate the coaxial configuration employed successfully by Breguet in France and Hiller in California. A single-seat prototype with two counterrotating rotors on a common shaft briefly took flight. "With a torque corrected by a torque, it was much more precise in hover than a tail-rotor machine," said Arthur Young, the only one to fly it. "It was just like standing on the floor; you could move it an inch or a half inch or whatever you wanted".
The coaxial helicopter was set aside a couple of days into testing when the transmission gears were found to be badly gouged. Although he had learned what he needed from this unusual prototype, Young was later distressed to find that it had been unceremoniously taken away and junked.