During a flight test on June 17, the innovative CarterCopter unofficially broke the Mu-1 barrier — a goal that eluded rotary wing builders until that day.
Mu is the ratio of the aircraft’s forward speed to its rotor tip speed. As forward speed increases, the effective airspeed over the retreating blade decreases. At Mu-1, the forward speed and retreating blade tip speed cancel one another out. As airflow over the blade reverses, it has been thought impossible to fly beyond Mu-1.
Jay Carter has thought otherwise for at least 12 years, believing that the key was to slow the blade rotation as forward speed increases. The prototype CarterCopter has been working toward proving that concept for three years.
Carter says that during the short — just 1.5 seconds — excursion beyond Mu-1, test pilot Larry Neal reached Mu-1.2 at an airspeed of 170 mph and rotor speed of 107 rpm. The flight was part of an Army contract and accuracy of the flight data will be verified “in the next few weeks” by the Army, according to Carter.
During later flight tests that day the CarterCopter suffered mechanical problems that led to a hard emergency landing. The flight crew was uninjured, a credit to Carter’s unique landing gear design, but Carter says damage to the airframe is not repairable.