Dynamics and Performance of Corotating and Counterrotating Coaxial Rotors on a Support Arm

The present study investigates the dynamics and aerodynamic performance of coaxial counterrotating (CCR) rotors and corotating coaxial (stacked) rotors on a flexible support arm. The coupled rotor and supporting arm systems have been analyzed, and the rotor hub vibrations were examined using rotor RPM sweeps for any potential resonance problems. The rotor hub vibrations were examined for both the CCR and the stacked rotor systems. Parametric studies of upper and lower rotor separations and rotor phase angles were conducted to evaluate their effects on rotor hub vibratory loads and rotor performance. The study found that arm frequency placements had a significant impact on the dynamics of the rotor-arm systems. While CCR rotors had less hub vibration with 0° phase between the upper and lower rotors, the stacked rotors experienced much less vibration with 90° rotor phase, The vibration reduction could be up to 50% when compared to 0° phase. The study also found that the rotor separation had significant impact on both CCR and stacked rotor systems, the narrow rotor separation resulted in up to 10% reduction in terms of rotor L/De for certain flight conditions.