Up, up and ‘oh no’: The trouble with air taxi startups | The Seattle Times

"This is harder than people generally understand," said John Hansman, a professor at the Massachusetts Institute of Technology who co-authored a paper on the challenges facing the new electric-powered, vertical-takeoff vehicles. "You're pushing the state of the art in multiple dimensions at the same time." 

https://www.seattletimes.com/business/up-up-and-oh-no-the-trouble-with-air-taxi-startups/