Optimum Hover Conditions for Reduced Noise From a Notional eVTOL Rotor

The trade-space between hover performance and acoustics for different blade loading conditions of a 35% scale notional eVTOL rotor is characterized. The database comprises systematic changes to rotor collective, Mach tip speed, and rotor solidity using identically shaped blades. Thrust and torque levels are shown to follow a log-linear relationship over the range of Mach tip speeds tested while blade loading coefficient and rotor figure of merit appear unaffected by Reynolds numbers at this scale. The sound field is evaluated separately for changes to rotor solidity and Mach tip speed with an emphasis on observers located below the rotor disk plane. The trends demonstrate that higher rotor solidity configurations may be capable of generating less total noise than lower solidity configu- rations for the same thrust setting. Human perception effects are then considered using the D-weighting function while non-linear metrics like skewness and kurtosis are used as annoyance indicators. The D-weighted trends provide evidence that, above a certain thrust threshold, the rotor collective and Mach tip speed required to achieve a desired thrust will generate the same perceived noise regardless of rotor solidity. However the higher-order metrics reveal how, for the same rotor figure of merit at high disk loading conditions, significant reductions in both metrics are achieved by increasing rotor solidity.