Present the noise contours for the airspeeds of 60 80

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present the noise contours for the airspeeds of 60, 80, and 100 knots at the constant glide slope of 9 deg. Acoustic data were not available for decelerating approach flights to enable an assessment of the effect of deceleration. A scale of 1 to 10 (from least to most noisy) was used to score subjectively the noise intensity in combination with the area of coverage. The result is shown in figure 4 for the various test conditions expressed in the plane of airspeed and rate of descent. To improve the consistency of scoring, several scorers were used. It can be seen that the noise-intensive region lies in the high speed-steep glide slope area with a rate of descent in excess of 1200fpm, which is considered to be outside of the maximum operationally desirable value of 900 fpm as indicated in the figure. Next, the RASCAL-specific noise-abatement approach profile, which was given the name “Quiet” for this flight experiment, was defined on the plane of airspeed and descent rate to avoid the BVI noise intensive region. In addition to the maximum acceptable rate of descent for assuring the comfort of the crew and passengers, other factors similar to those described above for defining the HAI-Light and HAI-Medium profiles (ref. 2), such as minimum IFR airspeeds and OEI operational require- ments, were simultaneously considered to judiciously define the Quiet approach profile shown in figure4. The Quiet approach profile devised from the full scale flight acoustic data was briefly assessed using some available wind tunnel data to see whether the acoustic data from the two sources were consistent. To this end, a set of pertinent accoustic data of the 1/6 scale model of a main rotor similar to that of the RASCAL, which were obtained in the NASA Langley 14- by 22-Foot Subsonic Wind Tunnel (ref.3), were assembled and plotted on the plane of descent rate vs. airspeed. Figure 5 shows the BVI noise contours from two strategically located microphones, namely a center stand microphone (azimuth angle=177deg; elevation angle = –23 deg; r/D = 1.505), and a starboard floor microphone (azimuth angle=133deg; elevation angle = –25 deg; r/D =1.4). There was no port side micro- phone comparable with the starboard one to assess the effect of directivity in this set of data. The airspeed and glide slope corresponding to this set of data are also somewhat limited; the data cover only the airspeed range of 50 to 80knots and glide slope of up to 10 deg. These data were taken at the test condition of CT/ σ =0.086. The maximum noise level at the starboard mic is somewhat higher than that at the center mic even after adjustment for the distance discrepancy (about 0.63dB). Within the range of airspeed and rate of descent, the noise contours at the starboard mic seem to be somewhat consistent with the flight acoustic data shown in figure4. When plotted on figure5 with the Quiet approach profile, consistency appears to be reasonable for the starboard microphone noise-contours, although less obvious based on the noise contours of the center microphone.
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