An Analytical Investigation of the Effect of Varying Rotor Tip Speed to Reduce Helicopter Acoustic Detection
ARMY RESEARCH AND TECHNOLOGY LABS FORT EUSTIS VA APPLIED TECHNOLOGY LAB
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The purpose of this study was to analytically determine the effect of incrementally varying helicopter rotor tip speed to decrease noise levels and detection distance. The basis for this study was that primary mission performance PMP would be maintained at each incremental change of rotor tip speed. A baseline helicopter was designed that met the Advanced Scout Helicopter ASH PMP requirements. It used a 700-fps tip speed four-bladed rotor system. Four generic configurations of the baseline helicopter were also designed which met the PMP requirements. The design rotor tip speed of these configurations varied to 105, 95, 90, and 80 percent of the baseline tip speed. Overall sound pressure levels OASPL, 13 octave band spectra, and detection distances were predicted for all helicopter configurations for a range of operational speeds. Results showed that the 90-percent 630 fps tip speed configuration was optimum in terms of reduced OASPL. When all configurations were analytically displaced in distance to the point at which their noise signature could first be perceived, the 100-percent 700 fps tip speed configuration was least detectable. It was also found that OASPL was not a reliable indicator of detectability and that ambient noise conditions had the largest net effect on detectability.
- Acoustic Detection and Detectors