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  • 1
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    Acoustic Load Considerations for Spacecraft Structures (1986)
    In:  CASI
    Details
    Publication Date: 2012-08-15
    Description: An analytical model to predict the space averaged sound pressure levels in the payload bay of the Space Shuttle orbiter vehicle at lift-off was developed. A modified form of the model can also be used to predict vibration levels of the orbiter mid fuselage and to evaluate noise control concepts for the interior of the proposed Aft Cargo Carrier (ACC). The analytical model is presented and predicted payload bay sound pressure levels are compared with launch data for an empty bay. Estimated and measured sound pressure levels for regions above large diameter payloads are found to be significantly higher than those for the empty bay. The use of helium as a purge gas to reduce sound pressure levels in the ACC is proposed.
    Keywords: SPACE TRANSPORTATION
    Type: ESA Proceedings of an International Conference on Spacecraft Structures; p 133-143
    Format: text
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  • 2
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    Measurements of propeller noise in a light turboprop airplane (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 26; 40-47
    Format: text
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  • 3
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    Helicopter cabin noise: Methods of source and path identification and characterization (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Internal noise sources in a helicopter are considered. These include propulsion machinery, comprising engine and transmission, and turbulent boundary layer effects. It is shown that by using relatively simple concepts together with careful experimental work it is possible to generate reliable data on which to base the design of high performance noise control treatments.
    Keywords: ACOUSTICS
    Type: NASA. Langley Res. Center Helicopter Acoustics, Pt. 2; p 583-594
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    In-flight acoustic measurements on a light twin-engined turboprop airplane (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Four series of flight tests were conducted to measure sound pressure levels inside and outside the cabin of a twin-engined turboprop airplane. Particular emphasis was placed on harmonics of the propeller blade passage frequency. The cabin was unfurnished for the first three flights, when the main objective was to investigate the repeatability of the data. For the fourth flight, the cabin was treated with fiberglass batts. Typically, the exterior sound pressure levels were found to vary 3 to 5 dB for a given harmonic, but variations as high as 8 dB were observed. The variability of harmonic levels within the cabin was slightly higher but depended on control of the relative phase between the propellers; when phase was not controlled the average variability was about 10 dB. Noise reductions provided by the fuselage structure were in the range of 20 to 40 dB, when an exterior microphone in the plane of rotation of the propeller was used as reference.
    Keywords: ACOUSTICS
    Type: NASA-CR-178004 , NAS 1.26:178004
    Format: application/pdf
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  • 5
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    Measurements of propeller noise in a light turboprop airplane (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In-flight acoustic measurements have been made on the exterior and interior of a twin-engined turboprop airplane under controlled conditions to study data repeatability. It is found that the variability of the harmonic sound pressure levels in the cabin is greater than that for the exterior sound pressure levels, typical values for the standard deviation being +2.0 dB and -4.2 dB for the interior, versus +1.4 dB and -2.3 dB for the exterior. When insertion losses are determined for acoustic treatments in the cabin, the standard deviations of the data are typically + or - 6.5 dB. It is concluded that additional factors, such as accurate and repeatable selection of relative phase between propellers, controlled cabin-air-temperatures, installation of baseline acoustic absorption, and measurement of aircraft attitude, should be considered in order to reduce uncertainty in the measured data.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 87-2737
    Format: text
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  • 6
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    Flight investigation of cabin noise control treatments for a light turboprop aircraft (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The in-flight evaluation of noise control treatments for a light, twin-engined turboprop aircraft presents several problems associated with data analysis and interpretation. These problems include data repeatability, propeller synchronization, spatial distributions of the exterior pressure field and acoustic treatment, and the presence of flanking paths. They are discussed here with regard to a specific aeroplane configuration. Measurements were made in an untreated cabin and in a cabin fitted with an experimental sidewall treatment. Results are presented in terms of the insertion loss provided by the treatment and comparison made with predictions based on laboratory measurements.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: SAE PAPER 850876
    Format: text
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  • 7
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    Propeller aircraft interior noise model (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analytical model was developed to predict the interior noise of propeller-driven aircraft. The fuselage model is that of a cylinder with a structurally-integral floor. The cabin sidewall is stiffened by stringers and ring frames, and the floor by longitudinal beams. The cabin interior is covered with a sidewall treatments consisting of layers of porous material and an impervious trim septum. Representation of the propeller pressure field is utilized as input data in the form of the propeller noise signature at a series of locations on a grid over the fuselage structure. Results obtained from the analytical model are compared with test data measured by NASA in a scale model cylindrical fuselage excited by a model propeller.
    Keywords: ACOUSTICS
    Type: NASA-CR-3813 , NAS 1.26:3813 , BBN-5058
    Format: application/pdf
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  • 8
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    Evaluation of Aero Commander sidewall vibration and interior acoustic data: Static operations (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Results for the vibration measured at five locations on the fuselage structure during static operations are presented. The analysis was concerned with the magnitude of the vibration and the relative phase between different locations, the frequency response (inertance) functions between the exterior pressure field and the vibration, and the coherent output power functions at interior microphone locations based on sidewall vibration. Fuselage skin panels near the plane of rotation of the propeller accept propeller noise excitation more efficiently than they do exhaust noise.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-159290 , BBN-4016
    Format: application/pdf
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  • 9
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    Interior noise control prediction study for high-speed propeller-driven aircraft (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An analytical model was developed to predict the noise levels inside propeller-driven aircraft during cruise at M = 0.8. The model was applied to three study aircraft with fuselages of different size (wide body, narrow body and small diameter) in order to determine the noise reductions required to achieve the goal of an A-weighted sound level which does not exceed 80 dB. The model was then used to determine noise control methods which could achieve the required noise reductions. Two classes of noise control treatments were investigated: add-on treatments which can be added to existing structures, and advanced concepts which would require changes to the fuselage primary structure. Only one treatment, a double wall with limp panel, provided the required noise reductions. Weight penalties associated with the treatment were estimated for the three study aircraft.
    Keywords: ACOUSTICS
    Type: NASA-CR-159200 , BBN-4026
    Format: application/pdf
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  • 10
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    Application of stiffened cylinder analysis to ATP interior noise studies (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analytical model developed to predict the interior noise of propeller driven aircraft was applied to experimental configurations for a Fairchild Swearingen Metro II fuselage exposed to simulated propeller excitation. The floor structure of the test fuselage was of unusual construction - mounted on air springs. As a consequence, the analytical model was extended to include a floor treatment transmission coefficient which could be used to describe vibration attenuation through the mounts. Good agreement was obtained between measured and predicted noise reductions when the foor treatment transmission loss was about 20 dB - a value which is consistent with the vibration attenuation provided by the mounts. The analytical model was also adapted to allow the prediction of noise reductions associated with boundary layer excitation as well as propeller and reverberant noise.
    Keywords: ACOUSTICS
    Type: NASA-CR-172384 , L-5552 , NAS 1.26:172384
    Format: application/pdf
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