Hover Performance and Acoustics of a 35% Scale Notional eVTOL Rotor.
Charles E. Tinney, John Valdez
Abstract
A first principles understanding of the hover performance and acoustics of a 35% scale notional eVTOL rotor is presented. Measurements are acquired in a large acoustically treated enclosure with rotor speeds corresponding to blade tip Mach numbers and Reynolds numbers around 0.3 and 500,000, respectively. Rotor thrust and torque are measured alongside a line array of microphones traversed between 1.0 and 3.5 rotor diameters from the rotor hub; this captures a two-dimensional map of the pressure field generated by this rotor. Blade collectives are varied from 0 deg to 15 deg in 3 deg increments. Different blade number combinations are studied and comprise a 5-blade, 4-blade, and 3-blade setup. Hover performance measurements at different rotor speeds demonstrate Reynolds number independence with a peak figure of merit of 0.75 at 15 deg collective. Acoustic data are projected to a common distance using spherical decay and a hub centered source. The projection demonstrates that the measurements are, for the most part, being captured in the acoustic regions and that the enclosure and sound treatment are adequate for studying rotors of this scale.