Operational Noise Data for CH-47D and AH-64 Army Helicopters
CONSTRUCTION ENGINEERING RESEARCH LAB (ARMY) CHAMPAIGN IL
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The objectives of this study were to develop sound exposure level SEL versus distance curves for flight operations and time-average sound level LEQ contours versus distance for static operations for two new Army aircraft. Sound levels produced by the helicopters were measured for the aircraft both hovering and traveling at various speeds. The CH-47D was operated in both a heavily and a lightly loaded configuration the heavy load was achieved by sling-loading a 10-ton Army truck. The data show that the aircraft are quieter than the types they are replacing the CH-47C and the AH-1G. Except at the highest speeds, sound variation with speed is not a large factor. In terms of sound variation with load, the CH-47D actually made less sound during level flight at full load than it did lightly loaded, although the sound did increase with load during takeoff and landing. As with other aircraft, the CH-47D makes more sound during landing than it does during level flight or takeoff, but the sound levels for the AH-64 are virtually independent of operation. Only two of each aircraft were supplied. Both types of aircraft exhibited sound levels which were a little higher than expected, and more aircraft would have enhanced the statistical reliability of the data. In the future, a minimum of four aircraft of any type should be supplied. They should be measured in two groups of two, separated by at least 1 month in time to better insure the statistical reliability of the data.