Fabrication and Testing of High-Speed Single-Rotor and Compound-Rotor Systems

Acquiring the data needed to generate a comprehensive set of measurements of the blade surface pressures, pitch link loads, hub loads, rotor wakes and performance of high-speed single-rotor and compound-rotor systems necessary to support the development of next-generation rotorcraft, such as those envisioned in the Joint Multi-Role (JMR) rotorcraft program.

Army Research Office, Research Triangle Park, North Carolina

Slowed rotors - traditionally associated with autogyros and gyroplanes - have long been recognized as one potential solution for high-speed helicopters (200-300 knots). During the 1950s-70s, there were several significant programs that led to the development of high-speed helicopters with thrust and lift compounding. The key technology barriers common to all were extremely high fuel consumption due to high advancing side drag and large reverse flow, complexities associated with RPM reduction, large blade motions during RPM reduction, and unexplained but catastrophic aeroelastic instabilities of rigid rotors (Cheyenne). None of these helicopters entered regular production.

Today, the CarterCopter gyroplane is the only aircraft to have demonstrated a rotor advance ratio of 1.0 in flight in 2005. With the advancement of materials, controls, and propulsion/drivetrain technologies (15-20% direct variation in RPM possible with same nominal specific fuel consumption and more dramatic reduction promised with variable drivetrain), slowed rotors have once again begun to emerge as a viable solution to high-speed, high-efficiency helicopters of the future (along with tilt-rotors and lift-offset coaxial compounds). The intent is the fundamental understanding of such rotors, using both analysis and experiment at the very high-advance ratio reverse flow conditions they are envisioned to operate in (μ∼1.5-2.0 and beyond).