Generation of noise exposure contours for eVTOL aircraft including transition

With the advent of the Urban Air Mobility (UAM) sector, a wide variety of concepts have emerged in academic studies and industry preliminary designs. The majority of these concepts sport Vertical Takeoff and Landing (VTOL) capabilities taking advantage of progress made in the electric power delivery and storage systems. Acoustically the vertical takeoff and landing operations vary significantly to conventional fixed wing aircraft as drastic changes in the dominating noise sources, the air vehicle speed, trajectory, power settings and observer distances occur. This paper initiates the study of generating noise exposure contour maps for eVTOL aircraft, their unique operations and importantly the transition between vertical and horizontal flight. The method involves the generation of three-dimensional noise exposure surfaces surrounding the flightpath. The flightpath itself is deconstructed into fundamental operations such as hover, vertical climb/decent and flyover, allowing data in the format of Noise-Power-Distance curves to provide inputs for the various power settings. The aircraft is modelled as a lumped noise source whose directivity may rotate independently of the motion of the aircraft. Results using simple acoustic sources (monopoles and dipoles) along with more complex directivity patterns (using a spherical harmonic expansion) are generated and discussed.