Helicopter Transmission Vibration and Noise Reduction Program

Abstract : A combined analytical and test program has been performed to develop a method for analytically determining the vibration and noise characteristics of a helicopter transmission. This effort included formulation of the necessary analytical method, validation of this method through direct comparison with test data, and use of the method to predict the effects of various transmission design changes. The analytical method formulated in this program makes use of available techniques for predicting gear-mesh-induced excitations. These techniques have been expanded to include a more rigorous treatment of spiral bevel and helical gear induced mesh excitations. Response of the dynamic system is predicted using a coupled torsion and bending analysis of the gearshafts, and includes the effects of bearing and case dynamics. Predicted case surface response is used directly to calculate radiated sound power.