Comparative helicopter noise analysis in static and in‐flight conditions

Rotary wing aircraft, i.e. helicopter, is a source of intense noise, external and internal alike, in conclusion becoming serious environmental and health issue. The generated noise is in some aspects similar to propeller noise in fixed wing aircraft (airplane), while differing in main noise source alignment in respect to the relative airflow: in helicopters, both rotors, i.e. main and tail, that produce forces necessary for flight, are inline with the direction of flight, while in airplanes rotor(s) are perpendicular to it. Another distinctive noise in helicopters, well known as "slapping", comes from the rotor cutting its own wake/vortex air inflow, especially while descending. In this article main helicopter noise sources will be discussed and most significant results of various static and in‐flight noise measurements on two different types of helicopters will be presented and analyzed.