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  • 1
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    Structureborne noise control in advanced turboprop aircraft (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Structureborne noise is discussed as a contributor to propeller aircraft interior noise levels that are nonresponsive to the application of a generous amount of cabin sidewall acoustic treatment. High structureborne noise levels may jeopardize passenger acceptance of the fuel-efficient high-speed propeller transport aircraft designed for cruise at Mach 0.65 to 0.85. These single-rotation tractor and counter-rotation tractor and pusher propulsion systems will consume 15 to 30 percent less fuel than advanced turbofan systems. Structureborne noise detection methodologies and the importance of development of a structureborne noise sensor are discussed. A structureborne noise generation mechanism is described in which the periodic components or propeller swirl produce periodic torques and forces on downstream wings and airfoils that are propagated to the cabin interior as noise. Three concepts for controlling structureborne noise are presented: (1) a stator row swirl remover, (2) selection of a proper combination of blade numbers in the rotor/stator system of a single-rotation propeller, and the rotor/rotor system of a counter-rotation propeller, and (3) a tuned mechanical absorber.
    Keywords: ACOUSTICS
    Type: NASA-TM-88947 , E-3362 , NAS 1.15:88947 , AIAA PAPER 87-0530
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    In-flight near- and far-field acoustic data measured on the Propfan Test Assessment (PTA) testbed and with an adjacent aircraft (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Flight tests to define the far-field tone source at cruise conditions were completed on the full-scale SR-7L advanced turboprop that was installed on the left wing of a Gulfstream 2 aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined source levels for input into long-distance propagation models to predict en route noise. In-flight data were taken for seven test cases. Near-field acoustic data were taken on the Gulfstream fuselage and on a microphone boom that was mounted on the Gulfstream wing outboard of the propeller. Far-field acoustic data were taken by an acoustically instrumented Learjet that flew in formation with the Gulfstream. These flight tests were flown from El Paso, Texas, and from the NASA Lewis Research Center. A comprehensive listing of the aeroacoustic results from these flight tests which may be used for future analysis are presented.
    Keywords: ACOUSTICS
    Type: NASA-TM-103719 , E-6402 , NAS 1.15:103719
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Measured far-field flight noise of a counterrotation turboprop at cruise conditions (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Modern high speed propeller (advanced turboprop) aircraft are expected to operate on 50 to 60 percent less fuel than the 1980 vintage turbofan fleet while at the same time matching the flight speed and performance of those aircraft. Counterrotation turboprop engines offer additional fuel savings by means of upstream propeller swirl recovery. This paper presents acoustic sideline results for a full-scale counterrotation turboprop engine at cruise conditions. The engine was installed on a Boeing 727 aircraft in place of the right-side turbofan engine. Acoustic data were taken from an instrumented Learjet chase plane. Sideline acoustic results are presented for 0.50 and 0.72 Mach cruise conditions. A scale model of the engine propeller was tested in a wind tunnel at 0.72 Mach cruise conditions. The model data were adjusted to flight acquisition conditions and were in general agreement with the flight results.
    Keywords: ACOUSTICS
    Type: NASA-TM-101383 , E-4437 , NAS 1.15:101383
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Unknown
    Structureborne noise control in advanced turboprop aircraft (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Structureborne noise is discussed as a contributor to propeller aircraft interior noise levels that are nonresponsive to the application of a generous amount of cabin sidewall acoustic treatment. High structureborne noise levels may jeopardize passenger acceptance of the fuel-efficient high-speed propeller transport aircraft designed for cruise at Mach 0.65 to 0.85. These single-rotation tractor and counter-rotation tractor and pusher propulsion systems will consume 15 to 30 percent less fuel than advanced turbofan systems. Structureborne noise detection methodologies and the importance of development of a structureborne noise sensor are discussed. A structureborne noise generation mechanism is described in which the periodic components or propeller swirl produce periodic torques and forces on downstream wings and airfoils that are propagated to the cabin interior as noise. Three concepts for controlling structureborne noise are presented: (1) a stator row swirl remover, (2) selection of a proper combination of blade numbers in the rotor/stator system of a single-rotation propeller, and the rotor/rotor system of a counter-rotation propeller, and (3) a tuned mechanical absorber.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 87-0530
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Unknown
    Farfield inflight measurement of high-speed turboprop noise (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A flight program was carried out to determine the variation of noise level with distance from a model high speed propeller. Noise measurements were obtained at different distances from a SR-3 propeller mounted on a JetStar aircraft, with the test instrumentation mounted on a Lear jet flown in formation. The propeller was operated at 0.8 flight Mach number, 1.12 helical tip Mach number and at 0.7 flight Mach number, 1.0 helical tip Mach number. The instantaneous pressure from individual blades was observed to rise faster at the 0.8 M flight speed, than at the 0.7 M flight speed. The measured levels appeared to decrease in good agreement with a 6 dB/doubling of distance decay, over the measurement range of approximately 16 m to 100 m distance. Further extrapolation, to the distances represented by a community, would suggest that the propagated levels during cruise would not cause a serious community annoyance.
    Keywords: ACOUSTICS
    Type: NASA-TM-83327 , E-1574 , NAS 1.15:83327 , AIAA PAPER 83-9745 , AIAA 8th Aeroacoustics Conf.; Apr 11, 1983 - Apr 13, 1983; Atlanta
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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