The Main Rotor Bifilar Absorber and Its Effect on Helicopter Reliability/Maintainability

The requirements of higher aircraft availability, lower maintenance costs, and a more comfortable passenger/crew environment demand low vibration in helicopters. To meet this objective, Sikorsky Aircraft has developed and reduced to practice the main rotor head bifilar absorber. The bifilar absorber reduces vibration directly at the source-the main rotor. It cancels the rotor system exciting forces before they are transmitted into the airframe, and thus effectively controls vibration throughout the helicopter. Reduced vibration levels translate directly into improved reliability and maintainability.

The principle of the bifilar absorber and the vibration reductions achieved in production installations are described. The quantitative improvement in reliability and reduction in maintenance resulting from the reduction in vibration are presented. The field data were collected from 15 aircraft without the bifilar absorber and from 15 aircraft with the bifilar absorber. The data show a 40% reduction in maintenance resulting from a 55% average vibration reduction.