Acoustics Analysis of a Quiet Helicopter for Air Taxi Operations

Abstract

This paper investigates tonal noise and broadband noise for rotor designs used on urban air mobility vehicles. The rotor aerodynamics in edge-wise forward flight is calculated using the blade element theory, coupled with a dynamic inflow model and the moment-balance trim analysis. Loading noise and thickness noise are obtained using the lifting-line loading distribution and the dual-compact thickness noise model in PSU-WOPWOP.With the forward flight capability developed in UCD-QuietFly, broadband noise is obtained, including trailing-edge noise, trailing-edge bluntness noise, and airfoil stall noise. The air taxi designs, with varied tip speeds and the same mission specifications, are studied for their tonal noise and broadband noise. First, it is found that broadband noise is the dominant noise source for the rotor designs with low tip speeds and fewer blades, while tonal noise is dominant for the high-tip-speed designs. Second, for human hearing, A-weighting maintains the importance of broadband noise while reduces tonal noise significantly. Third, broadband noise is the dominant noise source for the rotor out-of-plane observers, while tonal noise is dominant for the in-plane observers. Fourth, both tonal noise and broadband noise increase proportionally with increasing the forward speed. Finally, low tip speed and more blades are found to be the preferable design features in terms of psychoacoustic metrics.