VIBRATION ATTENUATION THROUGH THE USE OF ACTIVE FRAHMS

Active vibration control for helicopters is attractive because it provides good performance with lower weight compared to passive alternatives. Their superior performance is attributed to their ability to be adaptive to an ever-changing vibration environment. This paper provides an overview of the active vibration control system (AVCS), also known as active frahm system, developed by Lord Corporation for the Advanced Light Helicopter (ALH) of the Hindustan Aeronautics Limited (HAL). The three stages of the development process used by Lord Corporation are identified and discussed. In the first stage, helicopter transfer functions are obtained and fuselage vibrations at various flight conditions are measured. In the second stage, this data is used to optimize the system by defining the location and force capacity of the actuators (active frahms) and, location of the accelerometer. In the third stage, the AVCS is installed on the helicopter and performance is demonstrated through flight test. This paper also provides the overview of the main components of Lord Corporation’s active vibration control technology. Performance of various system configurations developed for the ALH is presented. Accuracy of Lord Corporations analytical capability is demonstrated by comparing the flight test data with the numerical predictions.