Active Vibration Control Using Fluidlastic® Pylon Struts

The connection between the helicopter rotor/mast/transmission assembly, often called the pylon, is a primary path for transmission of rotor vibration to the airframe. Passive Fluidlastic® tuned anti-resonant devices have been in production as helicopter pylon vibration isolators for over 10 years. They have demonstrated their effectiveness in reducing the transmission of N/rev vibration from the rotor to the airframe while maintaining high static stiffness to limit relative motion. In many helicopters, the flight loads are transferred from the pylon to the airframe through struts. We have found that performance of passive Fluidlastic® struts can be further improved by incorporating a force actuator to implement active vibration control. Dynamic analysis has shown that active control of Fluidlastic® pylon struts can further improve their performance by reducing the transmitted N/rev vibration to near zero. The fluid components in these devices provide an effective interface for external force actuators. The resonant interaction between the fluid and elastomeric elements can amplify the input from a relatively small actuator to generate large cancellation forces at N/rev. This reduces the size, weight, cost, and power consumption requirements relative to other means of active vibration control. Electromagnetic, hydraulic, piezoelectric, or other actuators are incorporated to generate the force. Active control of a Fluidlastic® pylon strut also accommodates changes in isolator performance due to time, temperature, and system non-linearity. Active adjustment of the tuned frequency to accommodate variable speed main rotors can also be incorporated. A Fluidlastic® strut incorporating a servo-hydraulic actuator to provide active vibration control has been designed and made. This strut is currently being tested in the laboratory to verify the mechanical aspects and dynamic performance of the design.