Analytically, uneven (modulated) spacing of main rotor blades was found to reduce helicopter noise. A study was performed to see if these reductions transferred to improvements in subjective response. Using a predictive computer code, sounds produced by six main rotor configurations: 4 blades evenly spaced, 5 blades evenly spaced and four configurations with 5 blades with modulated spacing of varying amounts, were predicted. These predictions were converted to audible sounds corresponding to the level flyover, takeoff and approach flight conditions. Subjects who heard the simulations were asked to assess the overflight sounds in terms of noisiness on a scale of 0 to 10. In general the evenly spaced configurations were found less noisy than the modulated spacings, possibly because the uneven spacings produced a perceptible pulsating sound due to the very low fundamental frequency.
Subjective Test of Modulated Blade Spacing for Helicopter Main Rotors
2002
8 pages
Report
No indication
English
A SUBJECTIVE TEST OF MODULATED BLADE SPACING FOR HELICOPTER MAIN ROTORS
British Library Conference Proceedings | 2002
|A subjective test of modulated blade spacing for helicopter main rotors
Tema Archive | 2005
|A Subjective Test of Modulated Blade Spacing for Helicopter Main Rotors
Online Contents | 2005
|Predicted noise for a main rotor with modulated blade spacing
Tema Archive | 2005
|