wasn't tt brown, was NASA.
the skeptical claim is there's no way to create a pure vacuum and lower pressure air is much easier to ionize. requires much lower voltage to create the ion wind in that situation. NASA in the last 20yrs showed there was still a thrust and wasn't related to the ion wind, still though was significantly weaker. Was a lifter mounted on a horizontal pivot. Turned a little bit.
I agree it exists. Trick is how did TT brown get significantly greater results in his specific experiment of a stack of glass and metal plates. It weighed 300lbs, flew up into the air when energized with high voltage, high frequency AC. Then he never discussed it again but of course he was under a Naval research contract. From then on he only researched his simple asymmetric capacitor plate experiments.
Tesla himself said the 'space' between two capacitor plates becomes 'rigid' when the capacitor is charged-discharged with high frequency oscillation.
Makes ya go hmm

(of course, simple voltage is required to make ormus, but i'm sure that's not related, hehe)
Einstein would be of help here. He would know the answer with his Tesla coil.