Originally Posted by
SplineDrive
Tip speed is the most important parameter in noise generation..
Its my understanding variable tip speed capability, the number of lifting/thrust units used, and electric propulsion were all required to get the low noise levels required for UAM ops. And what those blades are called is still up for debate considering the FAA calls them props, EASA lift/thrust devices, and NASA prop-rotors.
All the eVTOL aircraft I've ever examined have serious weight challenges and the drive for low tip speeds is a contributor (electric motor sizing, like transmissions, are mostly sized by torque)
From what I've seen its the same reason for any new aircraft concept when they are first fielded: the technology needs to mature. For example, as new hybrid power units are released by most turbine OEMs for the e-aviation market, I think some of those performance limits will be reduced as the eVTOL concept matures.