What's informative, Xeno, is that the family aircar has been mechanically practical since 1950. There are already various models of street-legal machines with foldable wings (or bolting, etc.) The problem was not one of engineering. The problem is the skill needed to run it, the airspace and regulation thereof, and the actual NEED (why, for instance, the Concorde failed. Few people needed to shave their trip time so badly that it was worth it to pay the fare.) I also wasn't aware of a time machine story. Verne had some harsh words for writers like H.G. Wells -- "I make my space ship in a way that is practical. He invents something that doesn't exist to make it run." Of course, in hindsight of better physical modelling, Cavorite makes more engineering sense than giant cannon! In any case, I doubt he'd write a time machine story. Oh...smell'o'vision was available. No-one bought it.