Load prediction of hingeless helicopter rotors including drivetrain dynamics

• Published in: CEAS aeronautical journal Vol. 12; no. 2; pp. 215 - 231
• Main Authors: Weiss, Felix, Kessler, Christoph
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.04.2021; Springer Nature B.V
• Subjects: Aerospace Technology and Astronautics; Automatic pilots; Configuration management; Coupled modes; Dynamic response; Engineering; Loads (forces); Original Paper; Powertrain; Resonant frequencies; Rotary wings; Sensitivity analysis; Simulation; Stiffness; Structural models; Wind tunnel testing; Wind tunnels; Eigenfrequency variation; Rotor-drivetrain coupling; Sensitivity analysis; Drivetrain inertia; Lead-lag loads; Drivetrain stiffness
• ISSN: 1869-5582; 1869-5590
• DOI: 10.1007/s13272-020-00483-6

In contrast to analyses with constrained hub speed, the present study includes the dynamic response of coupled rotor-drivetrain modes in the aeromechanic simulation of rotor blade loads. The structural model of the flexible Bo105 rotor-drivetrain system is coupled to aerodynamics modeled by an analytical formulation of unsteady blade element loads combined with a generalized dynamic wake or a free wake, respectively. For two flight states, i. e. cruise flight and large blade loading, a time-marching autopilot trim of the rotor-drivetrain system in wind tunnel configuration is performed. The simulation results are compared to those of a baseline case with constant rotor hub speed. The comparison reveals a major change in the blade passage frequency harmonics of the lead-lag loads. Beside the full drivetrain model, reduced models are shown to accurately represent the drivetrain influence on blade loads, if the eigenfrequency of the coupled second collective lead-lag/drivetrain mode is properly predicted. In a sensitivity analysis, this eigenfrequency is varied by stiffness modification of a reduced drivetrain model. The resulting changes in blade loads are correlated to this eigenfrequency, which serves as a simple though accurate classification of the drivetrain regarding its influence on vibratory blade loads. Finally, the potential to improve lead-lag load predictions by application of a drivetrain model is demonstrated through the comparison of simulated loads with measurements from a wind tunnel test.