Despite his disappointment over the loss, Carter said he was "ecstatic" over the success of Friday morning's flight. "We exceeded a Mu of 1 for the first time in history. This has been our goal ever since we started flight-testing in 1998. ... History will prove out the significance of this." The "Mu-1 barrier" is an aerodynamic limit defined by a forward speed and rotor rpm combination that results in advancing (moving into the relative wind) blade tips reaching speeds of twice that of the aircraft. At the same time, the retreating blade tips experience zero airspeed (as they rotate away from the relative wind) on the opposite side -- the entire inboard portion of the blade sees "reverse" air flow. The predicament prevents rotorcraft from achieving high forward speeds (CarterCopter sports small wings). According to the company, the barrier was breached during normal flight-testing Friday morning, while collecting data on a newly developed speed controller for the rotor. Initial data from Friday's flight shows that the airspeed was 170 mph and the rotor was slowed to 107 rpm, for a Mu value of 1.02. A Mu of 1 would enable a gyrocopter to fly up to 300 mph, Carter said.
The milestone attempt wasn't planned but evolved as the rotor proved to be stable as the rpm was decreased. Carter said he believes the breakthrough paves the way for rotorcraft to reach up to Mu-5 and fly up to 500 mph. With vertical takeoff and landing capabilities and the safety of a lifting rotor that acts as "built-in parachute" -- "That's pretty darn good. We hope we'll get the opportunity to build another one," he said. It was a combination of patented technologies that led to the breakthrough. "It's about eight things combined, but the key things that made this possible are the rotor-blade design and the computer-automated controls," Carter said. The data and video from the morning's breakthrough flight are being analyzed. As an element of a current U.S. Army contract the Army is scheduled to verify the calibration and accuracy of the data in the next few weeks.