Vibration control of a swashplateless coaxial rotor

A method of reducing vibration in a rotary wing aircraft airframe having a dual, counter-rotating, coaxial rotor system having an upper rotor system including an upper rotor shaft and a lower rotor system including a lower rotor shaft, the upper and lower rotor shafts being rotatable about a common axis of rotation comprising:

• providing a plurality of upper actuators, each of the plurality of upper actuators being coupled to a blade assembly of a plurality of blade assemblies of the upper rotor system such that each upper actuator is operable to control movement of the blade assembly coupled thereto about a pitch axis, the plurality of upper actuators being positioned exterior to the upper rotor shaft and to the plurality of blade assemblies, wherein a rotational axis of the plurality of upper actuators and the pitch axis of the plurality of blade assemblies of the upper rotor system are arranged within a plane;
• providing a plurality of lower actuators, each of the plurality of lower actuators being coupled to a blade assembly of a plurality of blade assemblies of the lower rotor system such that each lower actuator is operable to control movement of the blade assembly coupled thereto about a pitch axis, the plurality of lower actuators being positioned exterior to the lower rotor shaft and to the plurality of blade assemblies, wherein a rotational axis of the plurality of lower actuators and the pitch axis of the plurality of blade assemblies of the lower rotor system are arranged within a plane;
• actively controlling the plurality of upper actuators and the plurality of lower actuators separately;
• individually and actively controlling at least one actuator of the plurality of upper system to control the upper rotor system in an X-Y-Z axis and to reduce vibration within an airframe of the aircraft in accordance with a Higher Harmonic Control (HHC) algorithm in response to vibration in the airframe sensed by the sensor system;
• and
• individually and actively controlling at least one actuator of a plurality of lower actuators to control the lower rotor system in an X-Y-Z axis and to reduce vibration within an airframe of the aircraft in accordance with the HHC algorithm in response to vibration in the airframe sensed by the sensor system, wherein six unique vibration loads of the upper rotor system and six unique vibration loads of the lower rotor system combine in the coaxial rotor system to yield six net vibratory hub loads applied to the airframe at a location where the coaxial rotor system is mounted to the airframe, the plurality of upper actuators and the plurality of lower actuators are operated independently, such that the plurality of upper actuators and the plurality of lower actuators in combination suppress the six net vibration hub loads are suppressed to produce low fuselage vibration;
• and
• generating commands for a plurality of force generators positioned about the airframe, the plurality of force generators being configured to cooperate with the plurality of actuators to reduce vibration within the airframe.