The acoustics of a small-scale helicopter rotor in hover

perforated steel decking. Pulse reflection measurements (ref. 6) indicate that with no flow through the test section and at incidence angles less than 45' (this is the case of interest for this test geometry) absorption coefficientsgreater than 0.8 are obtained a t frequenciesabove approximately 200 H z , decreasing to a value of approximately 0 . 7 at 125 Hz (fig. 4). Absorption coefficients greater than 0.9 were measured abve 1 lcHz at all directivity angles.

The lining perfomxd well in absorbing mid- and high-frequency wall reflections, as determined by a series of impulsive source measurements made before rotor testing began. This measurement procedure consisted of firing a starter pistol and recording the impulsive transient waveform. The pistol was fired h m several positions corresponding to different source locations. For most microphones and source positions, only a single pulse corresponding to the incident wave was observed, there were no significant secondary pulses. For a few of the microphones, a secondary pulse having a relatively high amplitude was also observed, indicating the presence of a reflective surface. From the measured delay times, the proba- ble reflection points were identified as localized f l a t areas such as the bases of some of the microphone stands and the RTR mount. After those areas were covered with 7.5-cm-thick absorptive foam, these reflections were eliminated. Figure 5 shows typical t i m e traces before and after local treatment with final test setup to be acousticaUy quite good. No attempt was made to absorptive foam. We judged the measure the reverberation characteristics of the tunnel test section using steady sources.

TEST MATRIX

The primary variables during the hover test were tip Mach number and collective pitch. Operating con- ditions were chosen to cover a wide range of perfomance parameters. Table 3 is a compilation of test conditions for each data run point.

RESULTS After completion of the test, the acoustic data recorded on tape were reduced using a GenRad GR 1995 1/3-OctaveBand Analyzer. The analyzer was calibrated for each microphone and each run by making use I of the calibrated piston-phone signal of known amplitude recorded during testing. The integration time was set to 60 sec for a majority of the data points to make use of as much of the recorded data as possible (however, care was taken to avoid tape start/stop transients). A relatively long averaging time was chosen because a preliminary review of the data indicated the presence of non-stationary characteristics,a com- mon feature of hover acoustic data. Averaging the data over a long time m r d was deemed the best method for characterizingthe signal without resorting to much more sophisticated statistical techniques.

Such techniques are presently under evaluation. As indicated on each plot in appendix A, some data points required shorter integration times because of shorter availablerecord lengths.

The nonstationarity is related primarily to the recirculation patterns existing in the confined environ- ment of the test section, even though its dimensions are large compared to model size. Piziali and Felker (ref. 7) have shown the sensitivity of rotor aerodynamics to flow circulation patterns in a hover chamber and Amiet et al. (refs. 8 and 9) have demonstrated the sensitivity of rotor acoustics to inflow unsteadiness in hover. The postulated mechanism is the stretchingof turbulent eddies leading to a blade/eddy encounter, highly correlated blade-t*bkt.de in hover. The resulting acoustic radiation is phase additive (coherent), producing high amplitudes.

Table 4 lists the operating conditions, rotor performance parameters, and corresponding OASPL and dBA values for microphones in the main array (Le., not including the sideline microphones) for the two data runs for which data have been reduced.

.

Appendix A contains a representative set of 1/3-octaveband plots (as well as integrated unweighted OASPL and A-weighted dBA values) for the test parameters covered during runs 16 and 19, for micro- phones 5,7,8, and 9 (figs. Al-A4). These cover the range of distances and directivity angles studied during the test.

Appendix B contains plots of OASPL and dBA trends as functions of test parameters. The thrust and figure-of-merittrend plots include polynomial curve fits of second- and third-order, respectively B 1-B12). The order of the polynomials were chosen by trial and error on the basis of the maximum (figs.

correlation coefficient at minimum order. Curve fits are not included for the tip Mach number trend plots because data were obtained at only two values.

Appendix C contains plots of acoustic levels at several frequency bands as functions of distance and directivity angle for various operating conditions (figs. Cl-C4). Each of these plots also includes a curve, proportional t o (r/D)-l, which indicates free-field decay. The SPL level of this curve is arbitrary and was chosen for convenient comparison with the data.

DISCUSSION The trend plots indicate a smaU increase in acoustic levels with tip Mach number. This is as expected since the tip Mach numbers during the test were relatively low, below the drag divergence Mach number of 0.76. On the other hand, because a wide range of thrust conditions were set during the test, more variation in acoustic levels is seen with thrust changes, especially for CT/O > 0.05.

The acoustic radiation pattern is frequency dependent, as expected. At the blade passage frequency (1 12 -128 H z depending on rpm, which is within the 125-Hz 1D-octaveband) the acoustic directivity is quite broad at the lower tip speed but becomes noticeably more directional near the plane of the rotor at the higher tip speed. As thrust is increased, however, this directionality is somewhat moderated. At higher frequencies,on the other hand, acoustic radiation is distinctly greater at an angle 45’ to the rotor plane.

This is most pronounced at the low-tip-speed, low-thrust condition.

From these trends one can infer that thickness noise even at these low tip Mach numbers contributes significantly to the overall acoustic radiation. Loading noise, as expected, increases in amplitude away from the rotor plane and is more directional at 8 = 45’. The directivity lobe of loading noise grows “fatter” at higher thrust levels (i.e., there is less difference in acoustic levels with directivity change). T h i s can be attributed to the increase in the induced drag dipole noise-component at higher thrust conditions, which is confirmed by the high sensitivity of acoustic levels to variations in rotor figure of merit for FM > 0.5.

The plots in appendix C show the behavior of the acoustic field near the rotor plane as a function of distance. The 5-kHz data exhibit a noticeable reverberation effect (they have a shallower slope than (r/D)-l) a t the lower tip Mach number. This is absent at the higher tip Mach number. The two lowest frequencies, approximately the first two blade passage harmonics, have considerably steeper slopes than free-field behavior, indicating that the measurement of these low frequencieswere not made far enough from the source.

Further discussion of the data, including comparison to some full-scale data, can be found in reference 10.

CONCLUSIONS Acoustic 1/3-octave band spectra W R presented, followed by acoustic levels in terms of OASPL and dBA as functions of rotor operating conditions, and acoustic levels at several 1/3-octave band frequencies as functions of distance and directivity angle.

The data displayed nonstationary characteristicsrelated to wake recirculation effects. The acoustic levels were m o r e sensitive to thrust variations than to tip speed variations because the data were obtained at below the drag divergence Mach number. Some of the data displayed reverberant effects. Also, there were indications that the lower frequencieswere not measured under far-field conditions even though several microphones were placed at distances of two rotor diameters from the hub.

.

REFERENCES 1. Schmitz, F.H.; Boxwell, D.A.; L e v , S . ; and Dahan, C.: A Note on the General Scaling of Heli- copter Blade-Vortex Interaction Noise. Prcsented at the 38th Annual National Forum of the American Helicopter Society, Anaheim, CA, May 1982.

2. Boxwell, D.A.; Schmitz, F.H.; Splettstoesser,W.R.; and Schultz, K.J.: Helicopter Model Rotor Blade Vortex Interaction Impulsive Noise: Scalability and Parametric Variations. Presented at the 10th European Rotorcraft Forum, the Hague, Netherlands, Aug. 1984.

3. Schmitz, F.H.; Boxwell, D.A.; Splettstoesser,W.R.; and Schultz, K.J.: Model-Rotor High Speed Impulsive Noise: Full-scale Comparisons and Parametric Variations. Vertica, vol. 8, no. 4, 1984, pp. 395-422.

4. Shenoy, R.K.; Kohlhepp, F.W.; and Leighton, K.P.: Acoustic Characteristicsof 1DO-ScaleModel Helicopter Rotors. NASA CR- 177355,Aug. 1986.

5. Sternfeld, H.; and Schaeffer, E.G.: An Investigation of Rotor Harmonic Noise by the Use of Small Scale W i n d Tunnel Models. NASA CR-166337, Jan. 1982.

6. Soderman, P . T . : Oblique Incidence Sound Absorption of Porous Materials Covered by Perforated Metal and Exposed to Tangential Airflow. Internoise 82 Proceedings, San Francisco, 1982, pp. 401-404.

7. Piziali, R.A.; and Fellcer, F.F.: Reduction of Unsteady Circulation in Hovering Model Helicopter Rotor Testing, J. American Helicopter Society, Jan. 1987.

8. Paterson R.W.; and Amiet, R.K.: Noise of a Model Helicopter Rotor Due t o Ingestion of Turbulence.

NASA CR-3213, NOV. 1979.

9. Simonich, J.; Schlinker, R . ; and Amiet, R.: ExperimentalAssessment of a Turbulence Ingestion Noise Theory. hsented at the 44th Annual Forum of the American Helicopter Society, Washington, DC, June 1988.

10. Kitaplioglu, C.; and Shinoda, P.: Hover and Forward Flight Acoustics and Perfoxmance of a Small- Scale Helicopter Rotor System. NASA TM-86786, Dec. 1985.

TABLE 1.- MODEL ROTOR CHARACTEXISTICS

Radius, R ................................. 1 . 0 7 m

Chord, c .................................. 6.3 cm

M o i l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S C l 0 9 5

Number of blades, B .......................... .4

t

Twist.. ............................... .-lo0 linear

Solidity, o ................................. 0.075

TABLE 2.- MICROPHONE ARRAY

Microphone No. e

w

1 .o 135' 4 5 '

1 .o 210' -10'

1 .o 150' -10'

1 .o 180' -10'

+lo'

1 .o 180'

180' +lo' 1.5

+lo'

2.0 180' 2.0 180' +30' 2.0 180' +45'

TABLE 3.- TEST MATRIX

Run No.

Point Mtip 16 1 - 4 Zero and calibration points 0.55

1 .o

0.55 3 .O 0.55 5.0 , 0.55 7.0 0.55 9.0 0.55 11.0 0.55 12.9 0.55 10.9 0.55 9.0 0.55 6.9 0.55 5.1 0.55 2.9 0.55 1.1 Zero point

-

18 1 4 Zero and calibration points 0.63 1.6 0.63 3.1 0.63 5 .O 0.63 7.0 0.63 9.0 0.63 11.0 0.63 12.0 0.63 11.0 0.63 9.0 0.63 7.0 0.63 5 .O 0.63 3.1 0.63 1.5 Zero point

-

19 1 - 4 Zero and calibration points 0.63 1.5 0.63 3.1 0.63 5.0 0.63 7.0 0.63 9.0 0.63 11.0 0.63 12.0 0.63 11.0 0.63 9.0 0.63 7.0 0.63 5 .O 0.63 3.1 0.63 1.5 Zero point

-

TABLE 4.- RTR/40 x 80 HOVER TEST DATA

Microphone No. 4

Rotor test conditions r/D = 1.0, e = -10.0

-

Run Point RPM Coli (&a CT/S

OASPL

- ~~ ~ ~~ ~ ~ ~~ ~

-

16 5 0.55 188.8 1W 1 . o 0.00 0.001 0.02 91.1 94.1 0.55 188.8 0.01 0.002 16 6 1690 3.0 0.18 93.0 95.7 7 0.55 188.2 5 .O 0.03 0.002 0.42 16 1685 90.5 95.8 8 0.55 1885 1687 7.0 0.05 0.004 89.5 96.5 16 0.59 1 6 9 0.55 1885 1687 9.0 0.07 0.006 0.68 93.4 98.3 16 10 0.55 188 .O 1683 11.0 0.10 0.008 0.73 95.5 100.1 16 1 1 0.55 188.1 1684 12.9 0.12 0.01 1 0.71 104.0 107.6 16 12 0.55 188.8 1690 10.9 0.10 0.008 0.72 95.0 99.7 1 6 13 0.55 188.4 1686 9.0 0.07 0.006 0.68 91.8 97.8 1 6 14 0.55 188.6 1688 6.9 0.05 0.004 0.60 91.5 97.0 16 15 0.55 188.4 1686 5.1 0 . 0 3 0.002 0.41 90.1 95.9 16 16 0.55 188.6 1688 2.9 0.01 0.002 0.16 93.6 96.0 0.001 0.01 16 17 0.55 188.7 1689 1.1 0.00 90.8 93.8

- - - - - -

0.001 0.07 19 5 0.63 215.3 1927 1.5 0.01 95.5 100.0 19 6 0.63 2153 1927 3.1 0.02 0.002 0.25 95.2 101.0 19 7 0.63 215.3 1927 5.0 0.04 0.003 0.48 96.0 102.0 19 8 0.63 2153 1927 7 . O 0.06 0.004 0.64 96.0 102.9 19 0.63 215.3 1927 0.08 0.007 0.70 99.1 104.0 9 9.0 19 10 0.63 215.2 1926 11.0 0.11 0.009 0.71 104.2 107.8 19 1 1 0.63 214.9 1924 12.0 0.12 0.01 1 0.70 108.0 110.2 1 9 12 0.63 215.4 1928 11.0 0.1 1 0.010 0.72 104.3 107.6 19 13 0.63 215.2 1926 9.0 0.08 0.006 0.69 99.8 104.9 19 14 0.63 2153 1927 7 .O 0.06 0.004 0.66 96.7 102.3 1 9 15 0.63 215.2 1926 5 .O 0.03 0.003 0.48 94.0 101.7 19 16 0.63 215.3 1927 3.1 0.02 0.002 0.26 95.0 100.6 19 17 0.63 215.1 1925 1.5 0.01 0.001 0.07 95.9 99.8

- - - -

I .

TABLE 4.- CONCLUDED Microphone No. 9 Microphone No. 5 Microphone No. 6 Microphone No. 7 Microphone No. 8 r/D = 1.0.8 = 10.0 r/D = 1.5.8 = 10.0 r/D = 2.0.8 = 10.0 r/D = 2.0.0 = 45.0 r/D = 2.0.8 = 3 0 . 0 ~ ~~

OASPL &A I OASPL OASPL

91.0 94.2 86.6 89.3 84.1 87.8 86.5 88.5 90.6 91.0 94.0 95.5 89.3 90.6 86.8 90.0 87.8 90,O 93.0 92.4 91.9 94.9 87.3 90.0 85.1 87.8 87.5 89.0 90.8 91.1 91.0 96.0 86.3 91.0 84.0 86.1 87.8 88.5 89.0 90.1 96.0 100.8 91.6 96.0 88.8 90.5 92.1 93.0 92.8 94.0 98.0 104.0 93 .O 98.2 90.0 91.0 94.0 94.7 93.0 96.0 104.0 107.6 111.9 103.2 107.6 100.0 100.8 105.1 101.7 106.0 93.5 98.1 103.8 98.3 90.5 91.8 94.7 94.9 94.0 96.0 90.0 94.9 87.2 89.0 91.2 92.4 94.5 99.6 91.2 93.1 96.8 89.0 92.6 87.0 89.0 89.8 91.0 92.0 93.1 92.9 91.0 93.8 87.0 90.0 85.1 88.0 87.1 89.0 91.7 92.0 95.1 96.1 90.2 91.2 88.0 91.5 88.8 91.5 94.5 94.1 90.4 95.3 86.0 88.7 84.0 87.4 86.3 88.1 90.8 91.0

-

97.6 100.3 93.0 95.5 90.7 93.7 93.5 94.0 96.0 96.2 96.8 99.4 92.0 95.4 89.1 91.1 93.2 91.8 94.2 94.2 97.2 100.0 92.0 95.9 89.2 91.9 93.6 93.0 96.4 96.4 96.7 103.0 92.8 98.8 90.4 92.0 96.0 96.0 94.0 96.3 100.9 107.0 96.3 102.0 94.0 94.9 99.0 98.9 96.1 98.3 106.2 110.9 101.8 105.8 99.0 99.7 102.3 102.3 100.5 102.3 110.6 114.0 106.0 109.1 103.0 104.0 106.2 106.5 104.6 107.0 106.3 111.3 101.6 106.3 98.9 99.6 103.0 102.5 100.7 102.4 101.0 106.9 97.0 102.0 94.3 95.2 98.6 99.1 96.4 98.7 98.0 103.0 93.6 98.6 91.1 92.8 95.2 96.0 94.3 95.6 95.0 99.2 89.7 95.0 87.6 89.7 92.9 91.7 93.5 94.0 96.0 99.0 91.0 94.7 89.0 91.0 93.0 91.6 94.0 94.0 98.0 100.5 93.0 95.7 91.0 94.0 93.7 94.2 96.3 96.5 Figure 1.- Rotor test rig (RTR) in Ames 40- by 80-Foot Wind Tunnel test section.

c PORT TOP VIEW

e = 45"\

"BELOW" ROTOR

+ ROTORHUB

THRUST

\

-

1 ROTOR DIAMETER TUNNEL FLOOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SIDE VIEW Figure 2.- Micmphone array for hover test.

POWER SUPPLY IN-

Q9 OUT-

CATHODE FOLLOWER

I

1/3-OCT PLOTTER ANALYZER

4 3 SPEAKER

Figure 3.- Acoustic data acquisition and reduction system.

1 .o

.8 a .6 I - .

z

w

-

.4 w

z

2 1.0

k

K .8 .6 .4 5k 100 200 500 l k 2k FREQUENCY, Hz characteristics at incidence angle Wind Tunnel wall acoustic absorption Figure 4.- Ames 40- by 80-Foot 8 in zero wind (from ref. 6).

BEFORE LOCAL TREATMENT I 10.75 msec

-

MIC 7 AFTER LOCAL TREATMENT MIC 7 Figure 5.- Example of time delay measurements before and after local foam treatment to eliminate local acoustic reflections.

APPENDIX A ONE-THIRD-OCTAVE BAND ACOUSTIC SPECTRA RUN 16 POINT 5 m U MIC #5 4- 60 sec AVG.

w dBA

2 100

.OASPL w K

z

W

I

K

z

* 70

P-

~~~ ~~~ 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 6 m 110 '0 MIC #5 Ji 42 sec AVG.

W dBA

> 100

W

/ ,OASPL

J W K W ac

E 80

z

*

1 I 1 I 1 I 1 I * * 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- 1/3-octave band acoustic spectra-Microphone No. 5: r/D = 1 .O, yf = 1 80", 8 = + 10".

-

RUN 16 POINT 7

m 110

MIC #5 dBA J i 57 sec AVG.

w

. 2; 100 OASPL

Mtip = 0.55 / J CT/U = 0.03 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 8 MIC #5 dBA J i 41 sec AVG.

W OASPL

- I

2 100

Mtip = 0.55 / J CT/U = 0.05 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

-

RUN 16 POINT 9 dBA m 110 'El MIC #5 OASP L i I 49 sec AV G .

I W

W ' 100

J

r

.

W r

a

? 4

W a n

z

v) I I I 1 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 RUN 16 POINT 10 POINT 10 m 'El MIC #5 MIC #5 J i W 48 sec AVG. 48 sec AVG.

>

w MtiD = 0.55 Mtip = 0.55 J w 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 16 m 130 POINT 11 U MIC #5 W 60 sec AVG.

dBA

2 120

Mtip = 0.55

I nncnt

W

I /"-L CT/U = 0.12

/ a V Y W a VY 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 12 MIC #5

J i ' "'1 dBA

35 sec AVG.

Mtip = 0.55 CT/U = 0.10 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

Q RUN 16 POINT 13 m 110 dBA MIC #5 U OASPL 4- 42 sec AVG.

-- w / Mtip = 0.55

z

J CT/U = 0.07 W a v) v) w a n n 80

z

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 14 m 1 1 0 1 U MIC #5 dBA 42 sec AVG.

, I OASPL

Mtip = 0.55 I CT/U = 0.05

r

1 I I > 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 16

POINT 15 -

rn 110 U MIC #5 OASP L Mtip = 0.55 / CT/U = 0.03 w a n 8 0 -

z

v)

-

1 I I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 16 MIC #5 dBA 55 sec AVG.

OASPL

w A l o o t I

/ ' Mtip = 0.55 CT/U = 0.01 W a

2 9 0 -

v) u a n n 8 0 -

z

-

U

-

1 1 1 I

-

RUN 16 POINT 17 0 m 1 1 0 1 MIC #5 dBA 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 19 POINT 5 dBA m 110 '0 MIC #5

/ OASPL

60 sec AVG.

I

2 100

J w a

; t

-

v) v) w a n

-

n

I

z

r

v) n I

-

n I U

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ 12c RUN 19 POINT 6 m 11C dBA '0 MIC #5 Ji OASPL 53 sec AVG.

I

w S! loa

M,ip = 0.63 CT/U = 0.02 W K

i

w K n n

z

1 1 25 100 1 oc3 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A1 .- Continued.

120 1

RUN 19 POINT 7 a l l o t '0 dBA MIC #5 60 sec AVG.

OASP L /

=' I /

Mtip = 0.63

2 100

r

CT/U = 0.04

J

-

-

1 nn RUN 19 POINT 8

-

a 110 OASPL MIC #5

'0 I

i 60 sec AVG.

w Mtip = 0.63

2 100-

r

J CT/U = 0.06 w K 3 9 0 - w K n

r

n 8 0 -

z 1

a

-

I

1 I

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A1.- Continued.

RUN 19 POINT 9 m 120 0 MIC $5 d BA 4- 60 sec AVG.

w OASPL /

2 110

w CT

= 100

cn cn w CT n n 90

I

v) II.

-

I I I d 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 RUN 19 130 POINT 10 POINT 10 m '0 MIC #5 MIC #5 60 sec AVG. 60 sec AVG.

W

> 120

w Mtip = 0.63 W K 3 110 cfa cfa W K a .

0 100

z

El 90

c 1 I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 19 l 4 O 8 POINT 11 MIC #t5 60 sec AVG.

' w A- 13't dBA

1/3-OCTAVE BAND FREQUENCY, HZ R U N 19 dBA POINT 12

m 120 1

MIC st5 U OASP L 60 sec AVG.

/ $110

d l J

I

I c d F 1 1 1 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 19 POINT 13 m 120 U MIC n5 dBA A- 60 sec AVG.

OASPL

w 9 110 /

Mtip = 0.63 A CT/U = 0.08 w CT

= 100

w CT

: 90

z

v) L- I I I 1 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 14 MIC #5 60 sec AVG.

OASPL Mtip = 0.63 / w CT/U = 0.06 a

2 100

v) w LT n n 90

-

1 1 1 I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 19 POINT 15 MIC #5 4- OASPL 57 sec AVG.

w /

2 100 -

Mtip = 0.63 w K

-

ii

w K a .

-

n

z

v1

-

1, I I I 1 1 I

-

RUN 19 POINT 16 MIC #5 OASPL / 60 sec AVG.

w

I

> 100-

W

-

-

I

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A 1 .- Continued.

RUN 19 POINT 17 MIC #5 OASP L J i 60 see AVG.

W /

I

-

2 100

I

.J w K

2 9 0 -

w K Q n 8 0 - 3 c v) 1

-

P M I 1 I 1 1

-

RUN 16 POINT 5 m 110 MIC #7 U 60 sec AVG.

A- W Mtip = 0.55

2 100

A = 0 CT/'J dBA W a

I OASPL

2 90

W K n n 80

z

a

7a

i

I - + I 1

I .

6 C RUN 16 POINT 6 '0 MIC #7 A i 42 sec AVG.

W

2 100 Mtip = 0.55

dBA A CT/U = 0.01 W a 3ASPL

I

r

i i

W a n 0 80

z

a

1 I - 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- 1/3-octave band acoustic spectra-Microphone No. 7: r/D = 2.0, w = 180", 0 = +lo" RUN 16 POINT 7 m 110 '0 MIC #7 58 sec AVG.

W

w > 100

dBA w

/ OASPL

K

i

w K n n

z

v) I I 1 25 100 1000 10000 HZ 1/3-OCTAVE BAND FREQUENCY, RUN 16 POINT 8 m 110 '0 MIC #7

i

41 sec AVG.

W

w> 100

Mtip = 0.55 -I CT/U = 0.05 w K ASP.

i i

w K n n , I 1 1 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 16 POINT 9 MIC #7 49 sec AVG.

Mtip = 0.55 CT/U = 0.07 OASPL W a

; 90 J

W K

E 80

z

%

r

I I, I I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ

-

RUN 16 POINT 10 m 110 MIC #7 U 48 sec AVG.

4- dBA W Mtip = 0.55

> 100

IASPL w -I CT/U = 0.10

I

W K

I

2 90

v) W K L D 80

' 70

I I I 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, Hz.

Figure A2.- Continued.

-

RUN 1 6 POINT 1 1 m 120 TI MIC #7 i 60 sec AVG.

W

2 110 Mtip = 0.55

J CT/o = 0.12 W [I $100 w a n n c n

m 1 1

25 100 1000 10000 l/S-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 12 m 110 U MIC #7 35 sec AVG.

Mtip = 0.55 CT/U = 0.1

90 -

n

80 -

70 -

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 16 POINT 13 m 110 MIC #7 '0 42 sec AVG.

J- w

2 100

J W K w a

E 80

Z

a

RUN 16

I L U I

POINT 14 MIC #7 42 sec AVG.

Mtip = 0.55 CT/U = 0.05 K n

z

a 70

I 1 I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

- RUN 16 POINT 15 m 110 U MIC #7 i .

44 sec AVG.

W Mtip = 0.55 dBA CT/U = 0.03 W K

/ OASPL

ii

I/

W K n v)

n

I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 16 MIC #7 55 see AVG.

Mtip = 0.55 CT/U = 0.01 W )ASP L a 3 90 v) v) W a n n 80

z

I I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 16 POINT 17 MIC #7 45 sec AVG.

Mtip = 0.55 .J dBA CT/U = 0.0 w a OASPL

I

$ 9 0 -

w

r

a

E 8 0 -

z

-

G

I n- 60 L 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 19 POINT 5 m 110 U MIC #7 4- 60 sec AVG.

W

’ 100 Mtip = 0.63

iu J CT/U = 0.01 w K v) v) w a n n

z

v) 25 100 1000 10000 1/3-OCTAVE 6AND FREQUENCY, HZ RUN 19 POINT 6 U MIC #7 53 sec AVG.

OASPL

YBA

I

1 -

n 1 1 25 100 1000 10000 113-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 19 POINT 7 m 110 '0 MIC #7 J 60 sec AVG.

w

2 100 Mtip = 0.63

J CT/U = 0.04 w a

il

w a n n

a

r

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 8 m 110 MIC #7 60 sec AVG.

J W 3ASPL Mtip = 0.63

> 100

W J CT/U = 0.06 w a v) w

n

a I I n n n

z

v) d I 1 I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 19

I L U I

POINT 9 dBA MIC z7 / OASP L 60 sec AVG.

/ Mtip = 0.63

3 100

“ l 1 O I J CT/O = 0.08 w

; v) gob

w 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 10 m M I C ft7 ‘0 60 sec AVG.

2 110 1 dBA

Mtip = 0.63 W IASPL CT/U = 0.1 1 J l

5 100

v) v) w CT 90-

z

v, 8 0 -

I

I, 1 1

70 -

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 19 POINT 11 MIC #7 60 sec AVG.

Mtip = 0.63 J I CT/o = 0.12

i

v) W

L CT t

I 1 I

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 12 MIC #7 I 60 sec AVG.

OASPL A W

-

5 100

v) v) W K n n 9 0 -

I

a 8 0 -

L 1 1 I

-

RUN 19 POINT 13 m 110 MIC #7 U J 60 sec AVG.

w

g + 100

J w a

a

w a Q n

z

v)

U u -

I I I 1 I 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 14 m 110 U MIC #7 J dBA 60 sec AVG.

9 100

OASPL w

- I

r

I 1 1 1

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Continued.

RUN 19 m 110 U

I dBA

Mtip = 0.63 CT/U = 0.03

n

I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, H t RUN 19 POINT 16 m 110 U MIC #7 J . 60 sec AVG.

W dBA

> 100 Mtip 0.63

W OASPL CT/U = 0.02 W K

z

W K n P 80

z

' 70

c

25 100 1000 10000 1M-OCTAVE BAND FREQUENCY, H t Figure A2.- Continued.

RUN 19 CT/U = 0.01

E 80

z

%

In I I 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A2.- Concluded.

RUN 16 POINT 5 #8 MIC 60 sec AVG.

Mtip = 0.55 * dBA CT/o = 0.0 OASP L a0 25 100 1000 10000 l/S-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 6 m 110

MIC #a

U 43 sec AVG.

Mtip = 0.55 W

c*/u = 0.01

OASPL w LT

= 9 0 -

w a a n 8 0 -

z

-

1 1

-

10000 25 100 1000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- 1/3-octave band acoustic spectra-Microphone No. 8: r/D = 2.0, w = 1 80°, 8 = +30°.

RUN 16

-

POINT 7 rn '0 MIC =8 J .

57 see AVG.

W

>

Mtip = 0.55

W - dBA

-I / CTIU = 0.03 W I OASPL a

i

w a n n

z

v) 1 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ 12c I' RUN16 rn 110 POINT 8 MIC 18 i w 41 sec AVG.

w ' 100

Mtip = 0.55 dBA -I w CT/U = 0.05 OASPL a /

i

w a a .

n

z

v) I I 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 16 POINT 9 MIC #8 48 sec AVG.

, 90- w K

I

80-

z

-

6 0 L 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 RUN 16 POINT 11

-

m 120 U MIC #8 W a 9 0 -

z

v)

-

rk I 1 RUN 16

- POINT 12

U MIC #8 dBA

i

35 sec AVG.

W

W 'loo -boAspL

W Mtip = 0.55 A CT/o = 0.10

$ 9 0 -

w a L n 80-

z

v)

-

1 1 I Figure A3.- Continued.

RUN 16 POINT 13 MIC #8 43 sec AVG.

Mtip = 0.55 OASPL CT/U = 0.07 / 9a 7a 1 1 1 1 6a 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, Ht RUN 16 POINT 14 MIC #8 Ai 41 sec AVG.

W dBA

2 100

.J OASPL

I

W K

J-

? 3

W K

n

n P

z

60 - 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 16 POINT 15 MIC #8 44 sec AVG.

w

I OASPL

a

z

w a n n

z

$

~ 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, H t RUN 16 POINT 16 MIC #8 4- 54 sec AVG.

w

2 100 Mtip = 0.55

CT/U = 0.01 I , ,, I 1

L-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, H t Figure A3.- Continued.

RUN 16

- POINT 17

m 110 U MIC #8 Ai 45 sec AVG.

W

W ’ 100

Mtip = 0.55 A CT/o = 0.0 W a

a 90

W K n

-

n 80

z

v)

-

1 I Figure A3.- Continued.

RUN 19 POINT 5 m 110 MIC #8 -a 60 sec AVG.

A i dBA w

2 100

A W a

$ 90

W a n n 80

z

v) 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, Hz.

RUN 19 POINT 6 MIC #8 53 sec AVG.

Mtip = 0.63 CT/U = 0.02 IASPL ci n 80

z

v)

I - n rl I I

I n rl I I

25 . 100 1000 10000 25 . 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 19 POINT 7 MIC #8 60 sec AVG.

ilOOL qBA OASPL

Mtip 0.63 , I I CT/U = 0.04

r

L.

LI 1 - 1 1 1 10000 25 100 1000 1/3-OCTAVE BAND FREQUENCY, H t RUN 19

lZ" i

POINT 8 MIC #8 '0 dBA 60 sec AVG.

Mtip = 0.63 CT/U = 0.06 10000 25 100 1000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 19 POINT 9 MIC #8 I J- 60 sec AVG.

w Mtip = 0.63

21 100

-

-

-

1 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ m '0 J- W

> I,+ OASPL

w J W er 3 100 v) v) w CT n n v)

I

I 1 I 1 I

Figure A3.- Continued.

RUN 19 POINT 11 MIC -"8 dBA 60 sec AVG.

OASPL Mtip = 0.63 ,

- I

J CT/o = 0.12 w K $100 W K n n

z

v) n RUN 19 POINT 12 MIC =8 J 60 sec AVG.

W dBA . I

> 110

W

1 OASPL

J / w

r

5 100

v) v) w

r

10000 25 100 1000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

-

RUN 19 POINT 13 m 110 dBA U MIC #8 A i / OASPL 60 sec AVG.

W /

2 100

A W K

$ 90

w K n n 80

z

v) 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 m 110 POINT 14 U MIC #8 60 sec AVG.

W T/\OASPL

w > 100

Mtip = 0.63 c,/o = 0.06 I

Ih

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 19

- POINT 15

MIC #8 58 sec AVG.

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 16 m 1101 '0 MIC #8 4- 60 sec AVG.

dBA

w 5 100

Mtip = 0.63

/ OASPL

CT/o = 0.02 n 70[ 60 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Continued.

RUN 19 POINT 17 MIC #8 60 sec AVG.

CT/U = 0.01

90 -

80 -

70 -

60 I 1 I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A3.- Concluded.

RUN 16 POINT 5 m 110 MIC #9 60 sec AVG.

=’ 1 dBA

5 100 I

J

I i /OASPL

f

I 1 I I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ

-

RUN 16 POINT 6 m 110 MIC #9 dBA 43 sec AVG.

.J W

> 100

W OASPL

I

J / I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- 1/3-octave band acoustic spectra-Microphone No. 9: r/D = 2.0, w = 180°, 8 = + 4 5 O .

RUN 16 RUN 16 POINT 7 POINT 7 m 110 MIC #9 MIC #9 '0 57 sec AVG. 57 sec AVG.

Ji w Mtip = 0.55 - dBA Mtip = 0.55

2 100

J CT/U = 0.03 CT/U = 0.03 w K

; 90

w a v) c m I I 1 25 100 1 000 10000 25 100 1 000 10000 1/3-OCTAVE BAND FREQUENCY, HZ 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 8 m 110 '0 MIC #9 A- 41 sec AVG.

W > 100 Mtip = 0.55 w J CT/U = 0.05 I w

5 90

v) v) W K n .

n 80

L

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 16 Mtip = 0.55

w ' l o O c / OASPL

' I CT/U = 0.07

r

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 POINT 10 m 110 #9 0 MIC dBA 48 sec AVG.

/ ,OASPL

w A w K

ii

W K n n

z

I I II I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

I RUN 16

POINT 11 m 120 MIC #9 -0 4- 36 sec AVG.

w -I w K $100 v) W a n n 90

z

v) m i I 1 I 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ w a

nt

n n 8 0 - 7 0 - I I 1 * Figure A4.- Continued.

RUN 16 POINT 13 MIC #9 43 sec AVG.

2 100

/ OASPL

I I II I I I

60 1

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 16 RUN 16 POINT 14 POINT 14 m 110 #9 MIC #9 MIC '0 J i dBA I dBA 42 sec AVG. 42 sec AVG.

I W

> 100 Mtip = 0.55

W J CTIU = 0.05 W

; 90

W a n n 80

z

' 70

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 16 POINT 15 m 110 m MIC #9 A i 44 sec AVG.

W

I dBA

2 100

.

t I nncDi

w tT

cn = 90

cn w K n n 80

z

1 I 1

I

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ

I RUN 16

POINT 16 MIC #9 A i w

> 100

w A w K

2 90

cn w LT n n 80

' 70

n r"

I 1 1 I I I I 25 100 1000 10000 I/S-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

r

RUN 16 POINT 17 m 110 MIC #9 '0 J 46 sec AVG.

w dBA M~~~ = 0.55

w ' 100

J

3ASPL c,io = 0.0

I

I

c

-

-

-

1 I I I

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19 POINT 5 m 110 MIC #9 i 60 sec AVG.

w OASPL

2 100

J w K

$ 90

w 0: n n 80

z

v) I

r

1 ' I 1 1 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 6

w ' 100

-I $ 1

-

CT/o = 0.02 w K

$ 9 0 -

w K n n 80-

z

-

I I 1 1 60 L

1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19

I

POINT 7 m 110 MIC #9 TI dBA A 60 sec AVG.

I W

2 100

-I W K

; 90

LI W a

z

- 3

a

I - -

I)

I 7 - 1 I 1

*

1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 8 -0 MIC #9 4- 60 sec AVG.

W

7 0 ASP L

2 100

-I W K

z

W K I n 0 80

z

a 70

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19 POINT 9 m 110 -0 MIC *9 4- 60 sec AVG.

W

2 100 Mtip = 0.63

CT/U = 0.08 W K

v) = 90

v) w K n

n 80

z

v) 10000 .1.1.. ..

Figure A4.- Continued.

RUN 19 POINT 11 MIC #9 60 sec AVG.

OASPL I

i

w K

i loo

w a

: 90-

z L

v)

-

r

I 1 1 1

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 12 m U 1 2 0 1 MIC #9 60 sec AVG.

w LlOt J jBI\

OASPL / w

-

5 100

w K 90- n

z

v, 80-

I

1 1 I 1

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19 POINT 13 m 110 rn MIC #9 4- 60 sec AVG.

w

5 100

Mtip = 0.63 CT/U = 0.08 W a

$ 90

W a n n 80 cn 25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 14 MIC #9 dBA 60 sec AVG.

/OASPL

9 100

w n W

5 9 0 -

cn cn W K 8 0 - n

I n m

‘ 1 , L

1 u -

7 0 -

I I

25 100 1000 10000 l/S-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19 POINT 15 MIC #9 dBA 4 - 57 sec AVG.

W

-

2 100

Mtip = 0.63

1 OASPL

CT/U = 0.03 W K

$ 9 0 -

W K 8 0 -

-

-

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ RUN 19 POINT 16 m 110

'0 c

MIC #9

J i I dBA

60 sec AVG.

W 5 100

tL?AspL

W

2 90

W K n P 80

z

25 100 1000 10000 1/3-OCTAVE BAND FREQUENCY, HZ Figure A4.- Continued.

RUN 19

- POINT 17

m 110 '0 #9 dBA MIC Ai 60 sec AVG.

w OASPL

2 4 100 - / , Mtip = 0.63

CT/o = 0.01 w er

; 9 0 -

w K L n 8 0 - v)

-

I I I Figure A4.- Concluded.

APPENDIX B

EFFECT OF ROTOR PERFORMANCE ON ACOUSTICS

PRECEDING PAGE BLAGVK NOT FILMED

120- CT/S=0.03 0 dBA

+ OASPL

-

-

% l o o

+

D :

B

90- I I I

- CT/S=0.12

+

D -

% l o o - 9 0 - 1 I I 8 0 - Figure B1.- Acoustic levels as a function of Mb,. Microphone No. 5: r/D = 1.0, w = 180°, 8 = +loo.

- 0 dBA CT/S=0.03

+ OASPL

-

-

g 1 0 0

+

-

* 0

I I I

-

CT/S=0.12

120 I

g 100

llO!

t

1 I 1

80 1

.50 .55 .60 .65 Mtip Figure B2.- Acoustic levels as a function of Mb,. Microphone No. 7: r/D = 2.0, yf = 180°, 8 = +loo.

0 dBA CT/S=O.OJ 4 OASPL

-

I3

@I

80' I I I I3 B I 1 I

80 '

.50 .55 . 6 0 .65 Mtip Figure B3.- Acoustic levels as a function of Mtip. Microphone No. 8: r/D = 2.0, y/ = 180°, 8 = +30°.

0 dBA CT/S=0.03

+ OASPL

CT/S=O. 12

-

-

-

.50 .55 .60 .65 Mtip Figure B4.- Acoustic levels as a function of Mti,. Microphone No. 9: r/D = 2.0, w = 180°, 8 = +45".

0 d0A Mtip=0.55

+ OASPL

1 1 I I I 1 Mtip=0.63 I I I 1 I I 0 .02 .04 .06 .08 .10 .12 CTIS Figure B5.- Acoustic levels as a function of CT/O at two values of MtiP Microphone No. 5: r/D = 1.0, w = 1800, e = +loo.

0 dBA Mtip=0.55 OASPL .

110 i

I I I I 1 I Mtip=0.63 I I I I I 1 .12 0 .02 .04 .06 .OS .10 CTIS Figure B6.- Acoustic levels as a function of CT/O at two values of Mtip Microphone No. 7: r/D = 2.0, w = 1800, e = +loo.

Mtip=0.55 OASPL .

I 1 I I I I Mtip=0.63

r

I I I I I I .02 .04 .06 .08 .10 .12 CTIS Figure B7.- Acoustic levels as a function of C T / ~ at two values of Mb,. Microphone No. 8: r/D = 2.0, w = 1800, e = +300.

0 dBA Mtip=0.55 OASPL

110 t

I I I 1 I I

-

Mtip=0.63

-

m ‘0

-

“V 0 .02 .04 .06 .08 .10 .12 CTIS Figure B8.- Acoustic levels as a function of CT/O at two values of Mhp. Microphone No. 9: r/D = 2.0, w = 1800, e = +450.

0 dBA Mtip=0.55 OASPL I 1 I I Mtip=0.63 I I I

90 ’

0 .200 .400 .600 .EO0 FMERIT Figure B9.- Acoustic levels as a function of W R I T at two values of Mbp. Microphone No. 5: r/D = 1.0, w = 180°, 8 = +IOo.

0 dBA Mtip=0.55

+ OASPL

I 1 I

80 '

Mtip=0.63

120 1

% 100

1 I I 80 I 0 .2 .4 .6 .8 FMERIT Figure B 10.- Acoustic levels as a function of FMERIT at two values of Mbp. Microphone No. 7: r/D = 2.0, y~ = 180°, 8 = +loo.

0 dBA Mtip=0.55 OASPL

* /

g 100

. / : ..

--

Q

I-

Mtip=0.63

120 r

I I 1 1 0 .2 .4 .6 .8 FMERIT Figure B 11 .- Acoustic levels as a function of FMERIT at two values of Mtip Microphone No. 8: r/D = 2.0, w = 180°, 8 = +30°.

0 d0A Mtip=0.55 OASPL 1 I I I Mtip=0.63 l r n 1

110 c

I I 1 1 .o .2 .4 .6 .8 FMERIT Figure B 12.- Acoustic levels as a function of FMERIT at two values of Mbp Microphone No. 9: r/D = 2.0, w = 180°, 8 = + 4 5 O .

APPENDIX C

a

ACOUSTIC TRENDS AS A FUNCTION OF DISTANCE AND DIRECTIVITY ANGLE

%

PRECEDING PAGE BLANK NOT FILMED

-

CT/S = 0.08 [)- 125Hz

-

+-- 250Hz

e*- 1.25kHZ

O-.-*-- 5 kHZ b-- l/(r/D) 1 10 r/D Figure C 1 . - Acoustic levels at four frequency bands as a function of microphone distance from the rotor hub: Mtip = 0.55,8 = +lo".

CTfS = 0.08

110 i

D- 125Hz

- e-- 250Hz

1.25 kHz w

>

a

! - *) \ c I I I I I I 1 , l 1 10 r/D Figure C2.- Acoustic levels at four frequency bands as a function of microphone distance from the rotor hub: Mtip = 0.63, 8 = +loo.

110 0 125Hz CTIS = 0.08 1.25 kHz 5 k H Z A n v) s90 w

P b o t c

I I 1 I 1 CTIS = 0.12 w

>

a

I- I I I I I 0 10 20 30 40 50 e. deg Figure C3.- Acoustic levels at four frequency bands as a function of elevation angle (directivity): Mtip = 0.55, r/D = 2.0.

0 125Hz CTIS = 0.08 1.25 kHz

e 5 kHz

J n c v)

g 90

s

w .

>

a

! -

8 8o

P

c CTIS = 0.12 10 20 30 40 50 0. deg Figure C4.- Acoustic levels at four frequency bands as a function of elevation angle (directivity): Mti, = 0.63, r/D = 2.0.

Report Documentation Page

1. Report No.

2. Government Accession No. 3. Recipient's Catalog No.

NASA TM-101058

5. Report Date

The Acoustics of a Small-scale Helicopter Rotor

April 1989

in Hover

6. Performing Organization Code 7. Authork) 8. Performing Organization Report No.

A-890 15

Cahit Kitaplioglu

10. Work Unit No.

505-61-5 1

9. Performing Organization Name and Address 11. Contract or Grant No.

Ames Research Center

Moffett Field, CA 94035

13. Type of Report and Period Covered 2 . Sponsoring Agency Name and Address

Technical Memorandum

14. Sponsoring Agency Code

National Aeronautics and Space Administration

Washington, DC 20546 0001

5. Supplementary Notes Point of Contact: Cahit Kitaplioglu, Ames Research Center, MS TR-03 1 , Moffett Field, CA 94035

(41 5) 694-6679 or FTS 464-6679

6. Abstract A 2.1-m diameter, 1/6-scale model helicopter main rotor was tested in hover in the test section of

the NASA Ames 40- by 80-Foot Wind Tunnel. The primary objective of the test was to obtain

performance and noise data on a small-scale rotor at various thrust coefficients and tip Mach numbers for comparison with existing data on similar full-scale helicopter rotors. These data form part of a data base to permit the estimation of scaling effects on various rotor noise mechanisms. A secondary objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing. Acoustic 1/3-octave-band spectra are presented, together with variation of overall acoustic levels with rotor performance, microphone distance, and directivity angle.

~~ 7. Key Words (Suggested by Authorfs)) 18. Distribution Statement

Rotor

Unclassified--Unlimited

Noise

Small--scale

Subject Category: 02

___- i 9. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages 22. Price

Unclassified Unclassified 95

A05 NASA FORM 1626 OCT 86 I.or salc by thc N;itional Technical Inl'orn1;ition Scrvicc. Sprinsficld. Viryinia 22 16 I