Google-backed Kittyhawk is shutting down as questions, hurdles remain

The dream of flying cars zipping around in the air has suffered a major reality check.

Last week, the secretive air-taxi start-up Kittyhawk, run by Google veteran Sebastian Thrun, announced on Twitter that it was going to “wind down.” It was one of a handful of companies working to bring a “Jetsons” like reality to the world, where electric-powered cars, planes and helicopters become commonplace and offer clean-burning modes of transportation to a world of clogged and polluted…