Stability of the Sikorsky S-76 Bearingless Main Rotor

The stability results of an extensive wind tunnel test of the Sikorsky proof-of-concept 5-bladed full-scaled bearingless main rotor are presented. The test was conducted in 1992 at the NASA Ames 40×80 wind tunnel. All five blade flexbeams were instrumented with edgewise and flapwise strain gauges. This provided a rare opportunity to compare BMR stability in both rotating and fixed reference frame, and to check for blade-to-blade dissimilarities. Analytical predictions are also included to demonstrate that stability can be predicted reasonably well. The effect of nonlinear damping characteristics are also shown. Furthermore, this paper reveals an experimental study of how the lag mode stability differs among the different lag modes (i.e. regressing, progressing, and collective).