A STUDY OF THE ORIGIN AND MEANS OF REDUCING HELICOPTER NOISE. PDF Download
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Author:
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Category :
Languages : en
Pages : 120
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Book Description
Results are presented of an experimental and analytical study of the origin and possible means of reducing helicopter noise. Acoustical and performance data are presented for a single rotor turbine powered helicopter (HU-1A) with several main rotor configurations. Also, simultaneously recorded rotor blade pressure and acoustical test data are given. Noise criteria are reviewed and established on the basis of over-all sound pressure and loudness level. The latter pertains to the auditory sensation as perceived by an observer and is preferable as a measure of the relative importance of the various noise sources. Based on the loudness level criterion, the most prominent noise components of the test helicopter are identified. For the far field case these are, in their order of prominence: main rotor blade slap (when it occurs), tail rotor rotational noise, main rotor vortex and rotational noise, and drive system and power plant noise. Blade slap is characterized by high intensity sound pressures of all frequencies and occurs at the blade passage frequency. This noise is shown to be dependent upon flight condition and configuration. It is noted that single rotor helicopters are less susceptible to blade slap than tandem machines.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 120
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Book Description
Results are presented of an experimental and analytical study of the origin and possible means of reducing helicopter noise. Acoustical and performance data are presented for a single rotor turbine powered helicopter (HU-1A) with several main rotor configurations. Also, simultaneously recorded rotor blade pressure and acoustical test data are given. Noise criteria are reviewed and established on the basis of over-all sound pressure and loudness level. The latter pertains to the auditory sensation as perceived by an observer and is preferable as a measure of the relative importance of the various noise sources. Based on the loudness level criterion, the most prominent noise components of the test helicopter are identified. For the far field case these are, in their order of prominence: main rotor blade slap (when it occurs), tail rotor rotational noise, main rotor vortex and rotational noise, and drive system and power plant noise. Blade slap is characterized by high intensity sound pressures of all frequencies and occurs at the blade passage frequency. This noise is shown to be dependent upon flight condition and configuration. It is noted that single rotor helicopters are less susceptible to blade slap than tandem machines.
Author: Bryan Edwards
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 94
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Book Description
Author: Bryan Edwards
Publisher:
ISBN:
Category : Helicopters
Languages : en
Pages :
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Book Description
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.
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781723974304
Category : Science
Languages : en
Pages : 90
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Book Description
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.Edwards, Bryan and Cox, Charles and Booth, Earl R., Jr. (Technical Monitor)Langley Research CenterAIRCRAFT NOISE; NOISE REDUCTION; NASA PROGRAMS; ROTARY WING AIRCRAFT; AEROACOUSTICS; SOUND WAVES; WAVEFORMS; VORTICES; WIND TUNNELS; AIRFOILS; BLADE-VORTEX INTERACTION
Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 176
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Author:
Publisher:
ISBN:
Category : Astronautics
Languages : en
Pages : 628
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Author: Michael A. Bowes
Publisher:
ISBN:
Category : Helicopters
Languages : en
Pages : 256
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Book Description
A study was performed to determine the noise reduction benefits and economic costs associated with applying state-of-the-art noise reduction methods to future design civil helicopters. As part of this study, a survey of the make-up of the civil fleet was performed, and this fleet make-up was projected to the 1980 time frame. Analytical methods were developed and/or adopted for calculating helicopter component noise, and these methods were incorporated into a unified total vehicle noise calculation model. Analytical methods were also developed for calculating the effects of noise reduction methodology on helicopter design, performance and cost. The analytical methods were used to calculate baseline noise and cost characteristics of several existing civil helicopters. These methods were also used to calculate changes in noise, design, performance and cost due to the incorporation of engine and main rotor noise reduction methods. All noise reduction techniques were evaluated in the context of an established mission performance criterion which included consideration of hover ceiling, forward flight range/speed/payload and rotor stall margin.
Author:
Publisher:
ISBN:
Category : Space medicine
Languages : en
Pages : 28
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Author: Harvey H. Hubbard
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 620
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 524
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Book Description
