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  • 1
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    A new version of the helicopter aural detection program, ICHIN (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA Langley Research Center personnel have conducted an evaluation of the helicopter aural detection program I Can Hear It Now (ICHIN version-5). This was accomplished using flight noise data of five helicopters, obtained from a joint NASA and U.S. Army acoustics measurement program. The evaluation consisted of presenting the noise data to a jury of 20 subjects and to the ICHIN-5 program. A comparative study was then made of the detection distances determined by the jury and predicted by ICHIN-5. This report presents the changes made in the ICHIN-5 program as a result of this comparative study. The changes represent current psychoacoustics and propagation knowledge.
    Keywords: ACOUSTICS
    Type: NASA-TM-87745 , NAS 1.15:87745
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Study of stator-vane fluctuating pressures in a turbofan engine for static and flight tests (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: As part of a program to study the fan noise generated from turbofan engines, fluctuating surface pressures induced by fan-rotor wakes were measured on core- and bypass-stator outlet guide vanes of a modified JT15D-1 engine. Tests were conducted with the engine operating on an outdoor test stand and in flight. The amplitudes of pressures measured at fan-rotor blade-passage fundamental frequencies were generally higher and appeared less stable for the static tests than for the flight tests. Fluctuating pressures measured at the blade-passage frequency of the high-speed core compressor were interpreted to be acoustic; however, disturbance trace velocities for either the convected rotor wakes or acoustic pressures were difficult to interpret because of the complex environment.
    Keywords: ACOUSTICS
    Type: NASA-TP-2217 , L-15657 , NAS 1.60:2217
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Flight test of a pure-tone acoustic source (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Static and flight testing of a pure-tone acoustic source were conducted in order to: (1) determine if a 4-KHz tone radiated by a source in flight and mixed with broadband aircraft flyover noise could be measured on the ground with a high degree of statistical confidence; (2) determine how well a comparison could be made of flight-to-static tone radiation pattern and a static radiation pattern; and (3) determine if there were any installation effects on the radiation pattern due to the flight vehicle. Narrow-band acoustic data were measured and averaged over eight microphones to obtain a high statistical confidence. The flight data were adjusted to an equivalent static condition by applying corrections for retarded time, spherical spreading, atmospheric absorption, ground impedance, instrumentation constraints, convective amplification, and the Doppler shift. The flight-to-static results are in excellent agreement with the measured static data. No installation effects were observed on the radiation pattern.
    Keywords: ACOUSTICS
    Type: NASA-TP-1898 , L-14600
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A comparison of the three methods used to obtain acoustic measurements for the NASA Flight Effects Program (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The NASA Flight Effects Program has a requirement to compare acoustic data obtained from flyover, static test stand, and wind tunnel tests. Results a laboratory study of the acoustic characteristics of the three technqiues used to measure noise during these tests are presented. Recommendations are made to allow for a comparison of data obtained with each technique.
    Keywords: ACOUSTICS
    Type: NASA-TM-81906
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Noise measurements for a twin-engine commercial jet aircraft during 3 deg approaches and level flyovers (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Noise measurements have been made with a twin-engine commercial jet aircraft making 3 deg approaches and level flyovers. The flight-test data showed that, in the standard 3 deg approach configuration with 40 deg flaps, effective perceived noise level (EPNL) had a value of 109.5 effective perceived noise decibels (EPNdB). This result was in agreement with unpublished data obtained with the same type of aircraft during noise certification tests; the 3 deg approaches made with 30 deg flaps and slightly reduced thrust reduced the EPNL value by 1 EPNdB. Extended center-line noise determined during the 3 deg approaches with 40 deg flaps showed that the maximum reference A-weighted sound pressure level (LA,max)ref varied from 100.0 A-weighted decibels 2.01 km (108 n. mi.) from the threshold to 87.4 db(A) at 6.12 km (3.30 n. mi.) from the threshold. These test values were about 3 db(A) higher than estimates used for comparison. The test data along the extended center line during approaches with 30 deg flaps were 1 db(A) lower than those for approaches with 40 deg flaps. Flight-test data correlating (LA,max)ref with thrust at altitudes of 122 m (400 ft) and 610 m (2000 ft) were in agreement with reference data used for comparison.
    Keywords: ACOUSTICS
    Type: NASA-TM-X-3387 , L-10780
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Statistical comparisons of aircraft flyover noise adjustment procedures for different weather conditions (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Aircraft flyover noise spectra and effective perceived noise level (EPNL) values obtained under widely different weather conditions were adjusted according to a proposed national standard. The results were statistically compared with the same measured spectra adjusted according to an alternate procedure and with reference spectra and EPNL values obtained under almost ideal weather conditions. Three different ways to represent the weather condition through which the sound propagated were also evaluated.
    Keywords: ACOUSTICS
    Type: NASA-TP-1430 , L-12626
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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