The CarterCopter is an experimental compound autogyro developed by Carter Aviation Technologies to demonstrate slowed rotor technology. On 17 June 2005, the CarterCopter became the first rotorcraft to achieve mu-1 (μ=1), an equal ratio of airspeed to rotor tip speed, but crashed on the next flight and has been inoperable since.
Read more about CarterCopter: Design and Development, Specifications