History of ROSA™ technology has its roots in the evolution of Slow Rotor Compound (SRC) developed by Jay Carter.
Jay Carter had an idea for an aircraft that began by looking at the initial performance calculations of a rotorcraft by adding wings like an airplane. Jay realized the enormous performance improvements that could be achieved by slowing the rotor in flight.
To actually slow the rotor in operation and keep it stable, Jay identified the issues that had to be solved. To test his solutions, he fabricated a 6' foot diameter rotor, mounted it on an 8' foot boom in front of a pickup truck, and then drove the whole setup down the highway at up to 80 mph. With this scaled rotor, Jay demonstrated an advance ratio of 8 (pickup truck traveling eight times faster than the tip speed of the rotor). The rotor was so stable that he could pass semi-trucks on the opposite side of a 2-lane road. With this early success, the initial testing let to the development of the first prototype of a slow rotor aircraft.
Carter's first prototype was the CarterCopter Technology Demonstrator (CCDT). While flying this aircraft, Carter learned many valuable lessons about the technologies and methods needed for flight at high speed with a slowed rotor. The CCTD became the first aircraft to reach μ-1, where the rotor was slowed down so slow that the retreating blade was entirely in reverse flow.