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Psychoacoustic Testing of Modulated Blade Spacing for Main Rotors
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Author and Affiliation:
Edwards, Bryan(Bell Helicopter Co., Fort Worth, TX United States);
Booth, Earl R., Jr. [Technical Monitor]
Abstract: Psychoacoustic testing of simulated helicopter main rotor noise is described, and the subjective results are presented. The objective of these tests was to evaluate the potential acoustic benefits of main rotors with modulated (uneven) blade spacing. Sound simulations were prepared for six main rotor configurations. A baseline 4-blade main rotor with regular blade spacing was based on the Bell Model 427 helicopter. A 5-blade main rotor with regular spacing was designed to approximate the performance of the 427, but at reduced tipspeed. Four modulated rotors - one with "optimum" spacing and three alternate configurations - were derived from the 5 bladed regular spacing rotor. The sounds were played to 2 subjects at a time, with care being taken in the speaker selection and placement to ensure that the sounds were identical for each subject. A total of 40 subjects participated. For each rotor configuration, the listeners were asked to evaluate the sounds in terms of noisiness. The test results indicate little to no "annoyance" benefit for the modulated blade spacing. In general, the subjects preferred the sound of the 5-blade regular spaced rotor over any of the modulated ones. A conclusion is that modulated blade spacing is not a promising design feature to reduce the annoyance for helicopter main rotors.
Publication Date: May 01, 2002
Document ID:
20020048532
(Acquired Jun 21, 2002)
Subject Category: ACOUSTICS
Report/Patent Number: NASA/CR-2002-211651, Rept-699-099-536, NAS 1.26:211651
Document Type: Technical Report
Contract/Grant/Task Num: NAS1-00091; RTOP 727-03-15-10
Financial Sponsor: NASA Langley Research Center; Hampton, VA United States
Organization Source: Bell Helicopter Co.; Fort Worth, TX United States
Description: 50p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: ACOUSTIC SIMULATION; AEROACOUSTICS; NOISE MEASUREMENT; NOISE POLLUTION; PROPELLER NOISE; ROTARY WINGS; SPACING
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