Program for Helicopter Gearbox Noise Prediction and Reduction
Final technical rept.
MECHANICAL TECHNOLOGY INC LATHAM NY
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A method of computing helicopter gearbox noise from design and operating data is verified by a comparison of calculated and measured gearbox noise spectra. Measurements on CH-47 helicopters are used to provide experimental data. Positive indentification of the source and mechanism of gearbox noise energy has been made. The most objectional noise originates in the meshing action of the gear teeth. The gear tooth deflection, together with tooth profile variations due to manufacturing errors, excites torsional vibrations in the helicopter power train. Each gear mesh produces noise components at frequencies corresponding to the tooth meshing rates and their higher harmonics. This gear-induced vibration is transmitted to the gearbox casing and thence to the aircraft structure. Results indicate that the CH-47 gearbox mounts transmit a significantly higher level of vibration to the aircraft structure than do the UH-1D mounts. Calculations on the CH-47 gearbox indicate that spur gear tooth profile variations can be used to reduce gearbox levels, but manufacturing tolerances do not yet appear to be low enough for application of this principle. Studies further indicate that variations in planet carrier torsional compliance will result in only modest changes in noise level over the range of compliance studied.
- Machinery and Tools