Examination of the Air Resonance Stability Characteristics of a Bearingless Main Rotor

A compatible pair of computer analyses have been developed by RASA Division for predicting the performance, dynamic loads and the aeroelastic stability behavior of rigid to fully articulated, flex-strap, gimballed, teetering, or torque tube controlled bearingless rotors attached to an elastic support structure in hover or forward flight. These analyses were used to obtain a basic understanding of the air resonance characteristics and to ascertain the relative importance of various system parameters on these characteristics for a bearingless main rotor system. The nominal full scale rotor/support system model studied was based on a Boeing Vertol preliminary design configuration designated I-9A with design modifications in precone, predroop, retention beam pitch orientation, and blade root pitch stiffness. For an analytical model configured to be compatible with the wind tunnel model tested by Boeing Vertol, the predicted results compare favorably with test results. This paper will first briefly describe the characteristics of the analysis methods that were utilized and then extensively discuss some of the more interesting results that were obtained during the investigation.