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A higher harmonic control test in the DNW to reduce impulsive BVI noiseA 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.
Document ID
19950052056
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Splettstoesser, Wolf R.
(DLR Research Center Braunschweig, Germany)
Schultz, KLAUS-J.
(DLR Research Center Braunschweig, Germany)
Kube, Roland
(DLR Research Center Braunschweig, Germany)
Brooks, Thomas F.
(NASA Langley Research Center Hampton, VA, United States)
Booth, Earl R., Jr.
(NASA Langley Research Center Hampton, VA, United States)
Niesl, Georg
(ECD Ottobrunn Germany)
Streby, Olivier
(ECF Marignane France)
Date Acquired
August 16, 2013
Publication Date
October 1, 1994
Publication Information
Publication: American Helicopter Society, Journal
Volume: 39
Issue: 4
ISSN: 0002-8711
Subject Category
Aircraft Design, Testing And Performance
Accession Number
95A83655
Distribution Limits
Public
Copyright
Other

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