Dynamic Characteristics of Advanced Bearingless Rotors at McDonnell Douglas Helicopter Company

The McDonnell Douglas Helicopter Company designed, fabricated, and tested two bearingless main rotor systems consisting of advanced composite blades and composite flexbeams. These rotor systems eliminate the bearings and hinges associated with conventional rotors producing a more structurally efficient design with improved life cycle costs. Comprehensive flight testing with the bearingless rotor hub mounted on a modified MD 500E aircraft and subsequent scale model wind tunnel testing verified the design and analysis of the first rotor system. Scale model testing in the Duits-Netherlands Wind Tunnel confirmed the design and analysis of the second rotor. This paper addresses dynamic and aeroelastic stability issues affecting the design of both rotor systems. First, the paper presents analytical results on the effects of dynamic requirements on damper sizing, pitch-flap-lag stability, blade frequency placement, whirl mode stability, and vibration. Next, the document confirms the assumptions made in the design and analysis of the rotor system using test results. Finally, the paper compares the dynamic characteristics of the two flexbeam designs.