Constrained Layer Treatments for Noise Control in a Helicopter
Final rept. Sep-Dec 1972
AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OH
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The report describes some of the results of an investigation to evaluate the effect of constrained layer damping treatments on cabin noise levels in an HH-53C helicopter. Vibration and noise levels were measured for various flight conditions, including hover, forward flight and banked, and in each case it was observed that the damping treatment reduced vibration and noise levels in certain frequency bands within which natural modes of vibration were strongly excited. Ground vibration tests under artificial excitation and laboratory vibration tests on simpler but related structures were also conducted to further understand the phenomena involved and to develop appropriate damping treatments for broad temperature range noise control applications.