Control Redundancy for Power and Vibration Reduction on Lift-Offset Coaxial Rotor Helicopters

Lift- offset coaxial helicopters are a promising concept for high speed flight up to 230-250 kt and of great interest to the US Army’s Future Vertical Lift program. In addition to collective, longitudinal and lateral cyclic pitch available on conventional helicopters, as well as differential collective pitch (used in lieu of pedal for yaw control), several additional controls are available on coaxial rotor helicopters including differential lateral cyclic pitch, propulsor thrust, and main rotor RPM. The presence of this control redundancy allows for aircraft trim to be achieved corresponding to a multitude of possible operating states.  This project examines the states (and controls) that minimize power requirement and main rotor vibration, and focuses on understanding the aerodynamic operating conditions at the rotor and the rotor loads corresponding to these reductions. The study is conducted using the comprehensive analysis RCAS, and the effects of various aerodynamic models (dynamic inflow, free-wake, and computational fluid dynamics using Helios) on the predictions are also examined.