A Laboratory Method for Assessing Audibility and Localization of Rotorcraft Fly-In Noise

The low frequency content of rotorcraft noise allows it to be heard over great distances. This factor contributes to the disruption of natural quiet in national parks and wilderness areas, and can lead to annoyance in populated areas. Further, it can result in the sound being heard at greater distances compared to higher altitude fixed wing aircraft operations. Human response studies conducted in the field are challenging since test conditions are difficult to control. This paper presents a means of quantitatively determining the audibility and localization of rotorcraft fly-in noise, under a specified ambient noise condition, within a controlled laboratory environment. It is demonstrated using synthetic fly-in noise of a light utility helicopter. The method is shown to resolve differences in audibility distances due to different ground impedances, propagation modeling methods, and directivity angles. Further, it demonstrates the efficacy of an accelerated test method.