Dbamax value of the group c was higher than that of

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dBAmax value of the group C was higher than that of group D at all the three mic locations. The average dBAmax of the center mic for group C was 2.2 dB higher than that of group D. An analysis of the group-to-group dBAmax variation of the three multi-segment noise abatement approach profiles presented in figure 20 was determined to be relatively small, amounting to less than 2.3 dB. It is interesting to note that the in-group variation was relatively large, how- ever, for the HAI-Medium profile (group G) and the HAI- Light profile (group H). The average dBAmax at the center mic #2 and the starboard mic for the HAI-Light profiles was the lowest of the three groups, both being 2.2dB less than the highest group of the Quiet profile. (For the center microphone, this also amounts to a 2.4 dB reduction from the standard 6 deg decelerating approach profile of the group D.) Interestingly, the directivity effect was strong, particularly for the Quiet profile. For this profile, the average dBA max at the starboard mic
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9 location was more than 7 dB higher than that at the port side mic. As a result, the Quiet profile registered, at the port microphone location, the lowest average dBAmax of all the profiles tested. This can be seen from figure 20. In addition to dBAmax, other instantaneous sound-level metrics, such as OASPL and PNLTmax (ref. 18) were also calculated from the measured acoustic data and com- pared for each run tested. The general trends of the PNLTmax values are very similar to those of the dBAmax shown in figure 20. However, for the OASPL, the quiet- to-noisy ranking for the groups changed significantly. At the center mic, the average OASPL value was the lowest for the group of 9 deg decelerating approach profile (group E), followed by 6 deg at 80 knots, 6 deg decelerat- ing, HAI-Medium, Quiet, and HAI-Light. The lowest group E was approximately 6.8 dB of the OASPL below the noisiest group H. For this instantaneous sound-level metric, the directivity effect became less pronounced when compared to dBAmax discussed earlier. Run-to-run SEL comparison– It is important to also assess the noise characteristics using duration corrected single-event metrics to account for added annoyance due to duration. Two metrics, SEL and EPNL, were calculated for all the runs at each mic location. Figure 21 shows a run-to-run comparison for those runs in the groups C through H. The EPNL plots follow the same trend as the SELgraphs in figure 21, but the EPNL dB values are 3 to 4.5 dB higher than the SEL dB values. The difference in SEL dB values between the 6 deg con- stant approaches and the 6 deg decelerating approaches was very slight, less than 1 dB for all the mic locations. In this case the improvement with deceleration was very lit- tle for this helicopter. With the level of deceleration flown for the 6 deg decelerating approaches, the TPP angle-of- attack increased on the order of about 3deg (see fig. 13), which would, as seen from the rotor, appear to be flying on a 9 deg glideslope over the centerline mics. At the scheduled flyover airspeed of 66knots (see table 1), it could not be expected to improve the noise impact over
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