Evaluation of the Effect of Elastomeric Damping Material on the Stability of a Bearingless Main Rotor System

The Army/Boeing Vertol Bearingless Main Rotor (BMR) has demonstrated through flight test and wind tunnel research programs that it is an important advance in the evolution of helicopter rotor systems. It has the potential for significantly reducing maintenance costs while increasing hardware reliability. An important factor in the design of soft in-plane hingeless rotor systems is aeroelastic stability. The BMR demonstrated positive aeroelastic stability in both flight and wind tunnel testing. The next generation bearingless rotor design will attempt to simplify or eliminate structural and manufacturing complexities inherent in th present configuration. This paper will discuss model and full scale wind tunnel test results which included a simple method to increase structural damping through the use of bonded elastomeric damping material, resulting in improved aeroelastic stability characteristics. A full scale test of the BMR in the 40-by-80 Wind Tunnel at NASA-Ames demonstrated that this simple design change could increase fixed system modal damping with the potential benefit of reduced design complexities. Earlier model scale testing at Boeing Vertol provided the initial data showing that the elastomeric damper strips would prove beneficial.