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Revolutionary Concepts for Helicopter Noise Reduction: SILENT Program
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Author and Affiliation:
Edwards, Bryan(Textron Bell Helicopter, Fort Worth, TX United States);
Cox, Charles(Textron Bell Helicopter, Fort Worth, TX United States);
Booth, Earl R., Jr. [Technical Monitor]
Abstract: As part of a NASA initiative to reduce helicopter main rotor noise, a Phase 1 study has been performed of candidate noise reduction concepts. Both conventional and novel design technologies have been analyzed that reduce the community impact of helicopter operations. In this study the noise reduction potential and design implications are assessed for conventional means of noise reduction, e.g., tip speed reduction, tip shapes and airfoil tailoring, and for two innovative design concepts: modulated blade spacing and x-force control. Main rotor designs that incorporate modulated blade spacing are shown to have reduced peak noise levels in most flight operations. X-force control alters the helicopter's force balance whereby the miss distance between main rotor blades and shed vortices can be controlled. This control provides a high potential to mitigate BVI noise radiation. Each concept is evaluated using best practice design and analysis methods, achieving the study's aim to significantly reduce noise with minimal performance degradation and no vibration increase. It is concluded that a SILENT main rotor design, incorporating the modulated blade spacing concept, offers significantly reduced noise levels and the potential of a breakthrough in how a helicopter's sound is perceived and judged. The SILENT rotor represents a definite advancement in the state-of-the-art and is selected as the design concept for demonstration in Phase 2. A Phase 2 Implementation Plan is developed for whirl cage and wind tunnel evaluations of a scaled model SILENT rotor.
Publication Date: May 01, 2002
Document ID:
20020051150
(Acquired Jun 28, 2002)
Subject Category: ACOUSTICS
Report/Patent Number: NASA/CR-2002-211650, NAS 1.26:211650, Rept-699-099-529
Document Type: Technical Report
Contract/Grant/Task Num: NAS1-99109; RTOP 727-03-15-10
Financial Sponsor: NASA Langley Research Center; Hampton, VA United States
Organization Source: Textron Bell Helicopter; Fort Worth, TX United States
Description: 88p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: AEROACOUSTICS; AIRCRAFT NOISE; AIRFOILS; BLADE-VORTEX INTERACTION; NASA PROGRAMS; NOISE REDUCTION; ROTARY WING AIRCRAFT; SOUND WAVES; VORTICES; WAVEFORMS; WIND TUNNELS
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