Performance Advantages and Resonance Analysis of a Variable Speed Rotor Using Geometrically Exact Beam Formulations

Abstract

The efficiency and operating envelope of a rotorcraft is constrained by the speed of the rotor. Most helicopters operate with a constant rotor speed. Varying the speed of the rotor based on the operating condition could significantly improve the rotor’s performance. In this study, a hingeless rotor model with elastic blades is built in Dymore to study various aspects of Variable Speed Rotor (VSR) technology. The rotor blades are modeled as one-dimensional beams using state of the art beam theory known as the geometrically exact beam theory (GEBT). An unsteady aerodynamics model with dynamic stall and finite-state dynamic inflow is used to obtain the aerodynamic loads acting on the rotor. The power savings that can be achieved at various advance ratios by varying the speed of the rotor is evaluated. Maximum power savings of 41:47% was achieved at mN = 0:2. However, changing the rotor speed leads to vibration issues when a rotor passes through a resonance point. A methodology to identify the important resonance points for a given flight condition and rotor speed transition is also provided. The forces acting on the rotor blade during resonance crossings at different advance ratios is evaluated.