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Is that Richard Brown, I also know him if so!
Surely higher disc loadings compared to helicopter (higher induced velocities by the rotor) is only going to help prevent vortex ring state since higher gust velocities/descent rates will be needed to reach vortex ring state? Not saying it won't need to be something carefully monitored. Seems that a lot of eVTOL's will have advanced flight control systems which will help control things such as descent rate.
wjrh-
I knew him when he was plain old Doc Brown - he'd undertaken some highly experimental stuff with flux capacitators but had moved onto working on recycled fuel sources. Sounds like he's being a bit more measured and responsible about the risks involved in experimental modes of travel these days, but he was more fun back in time.
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Yes it is; small world! I can't recall the details (and it's decades since I took his rotorcraft course), but IIRC his work on the V-22's vortex ring state led him to believe that a lot of the eVTOL designs might encounter problems in a wider area of the flight envelope than might be expected.
kl
Thrustvector
I am suspicious of a lot of the claims for these on general hype grounds; there's a heck of a lot of regulatory hurdles to overcome before you can even think about passengers. FWIW, my pal Prof. Brown the rotorcraft aerodynamicist is suspicious about the flow regime that most of these designs are operating in (disc loadings etc.); he reckons a lot of them will be susceptible to vortex ring problems once they get into real-world testing.