Measured Acoustic Characteristics of Low Tip Speed eVTOL Rotors in Hover

To document noise characteristics and provide validation data for acoustic modeling of rotor systems appropriate for eVTOL/UAM aircraft, the team of Techsburg, AVEC, and Virginia Tech peformed an outdoor static test of a subscale 5-blade rotor. The testing was carried out as part of a program to demonstrate feasibility and performance of a quiet rotor system in support of the eVTOL industry. Techsburg designed a low-tip speed rotor to approximate performance required by a 4-5 passenger UAM vehicle. A driving design feature was low-tip speed operation (Mtip ~0.27) at system disk loadings of 7 to 8 psf (~3.7 N/m2). The test article was designed as a ground adjustable pitch 5-blade rotor, and 2-blade and 3-blade versions of this rotor were also tested during this project. The test article size of 3 feet diameter (0.91 m) represented a scale factor of approximately 30% compared to a full size vehicles currently in operation or development today. The aerodynamic performance in hover was consistent with other rotor systems tested in the past at Techsburg (Figure of Merit ~0.70), and the effects of naturally occurring turbulence on rotor acoustics was measured using a 180-deg arc array of ground plane microphones at the Virginia Tech Drone Park test facility. The paper closes with a discussion of simulating the experiment with the PowerFLOW LBM solver with and without flow turbulence.