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  • 1
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    A higher harmonic control test in the DNW to reduce impulsive BVI noise (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A model rotor acoustic test was performed to examine the benefit of higher control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) impulse noise. A 40-percent dynamically scaled, four-bladed model of a BO-105 main rotor was tested in the German-Dutch Wind Tunnel (DNW). Acoustic measurements were made in a large plane underneath the rotor employing a traversing in-flow microphone array in the anechoic environment of the open test section. Noise characteristics and noise directivity patterns as well as vibratory loads were measured and used to demonstrate the changes when different HHC schedules (different modes, amplitudes, phases) were applied. Dramatic changes of the acoustic signatures and the noise radiation directivity with HHC phase variations are found. Compared to the baseline conditions (without HHD), significant mid-frequency noise reductions of as much as 6 dB are obtained for low speed descent conditions where BVI is most intensive. For other rotor operating conditions with less intense BVI there is less or no benefit from the use of HHC. Low frequency loading noise and vibratory loads, especially at optimum noise reduction control settings, are found to increase.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 39; 4; p. 3-13
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Forward sweep, low noise rotor blade (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-16
    Description: A forward-swept, low-noise rotor blade includes an inboard section, an aft-swept section, and a forward-swept outboard section. The rotor blade reduces the noise of rotorcraft, including both standard helicopters and advanced systems such as tiltrotors. The primary noise reduction feature is the forward sweep of the planform over a large portion of the outer blade radius. The rotor blade also includes an aft-swept section. The purpose of the aft-swept region is to provide a partial balance to pitching moments produced by the outboard forward-swept portion of the blade. The noise source showing maximum noise reduction is blade-vortex interaction (BVI) noise. Also reduced are thickness, noise, high speed impulsive noise, cabin vibration, and loading noise.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NAS 1.71:LAR-14569-1
    Format: application/pdf
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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