The Design and Evaluation of a Supercritical-Speed Helicopter Power-Transmission Shaft

Abstract

A series of research programs with small-diameter, supercritical-speed power-transmission shafting has led to the development of design techniques for the application of one or two viscous dampers to control shaft vibrations through as many as 20 critical speeds. These techniques have been used to design a large, 338.5-in-long helicopter rotor synchronizing shaft using aluminum tubing with an outside diameter of 4.50 in. and a wall thickness of 0.12 in. A single viscous damper located 30.0 in. from one end of the shaft has been used to successfully operate the shaft through its first five critical speeds. The design parameters and experimental results for this shaft are discussed, along with a description of the application of modal balancing at the third, fourth, and fifth critical speeds.