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A high reduction ratio split torque gear train has been proposed as an alternative to a planetary configuration for the final stage of a helicopter transmission. A split torque design allows a high ratio of power-to-weight for the transmission. The design studied in this work includes a pivoting beam that acts to balance thrust loads produced by the helical gear meshes in each of two parallel power paths. When the thrust loads are balanced, the torque is split evenly. A mathematical model was developed to study the dynamics of the system. The effects of time varying gear mesh stiffness, static transmission errors, and flexible bearing supports are included in the model. The model was demonstrated with a test case. Results show that although the gearbox has a symmetric configuration, the simulated dynamic behavior of the first and second compound gears are not the same. Also, results show that shaft location and mesh stiffness tuning are significant design parameters that influence the motions of the system.

Publication Date



National Aeronautics and Space Administration and U.S. Army Aviation Systems Command


Washington, D.C.


split torque gearbox, gear dynamics, load sharing, transmission error


Aerodynamics and Fluid Mechanics | Aerospace Engineering


NASA TM--105681

AVSCOM TR--91--C--043

Prepared for the Sixth International Power Transmission and Gearing Conference sponsored by the American Society of Mechanical Engineers, Scottsdale, AZ, September 13-16,1992.

Dynamics of a Split Torque Helicopter Transmission