Just by the way, how about a super-lifting gas? Say for example very hot hydrogen. While the resulting zep would be a zippo; would a super-light gas make HTA flight desirable?
Arthur C Clarke came up with concept of the Hot Hydrogen balloon as a way of exploring Jupiter.
In Space: 1889, a steampunk science fiction RPG, they used “monatomic hydrogen”. Presumably they put an electrical charge on regular H2 so it separated, and like charges kept the atoms apart? [ETA: I’m pretty sure it wouldn’t work this way, but what the heck, we’re talking science fiction!]
Seriously, we have Zeppelins in development now for a variety of purposes. If high speed isn’t a requirement, there are lots of uses for aircraft that stay aloft without needing engines to keep them there. Some probable uses are for lifting heavy objects to somewhere that has no railroad or runway, high-altitude surveillance, atmospheric sampling that doesn’t rely upon weather baloons, etc. Under some circumstances they’d be superior to helicopters for tourism flights, and some day maybe someone will come up with a business model for passenger cruise ships that will turn a profit.
http://www.nagyairship.com/ This company claims a 200 mph airship. They could replace airplanes from Chicago to Detroit or Boston to New York. It could be done.
Two TV Tropes articles that may be of interest:
You would also need super powerful engines, to counteract strong winds, and possibly a super strong outer skin, so when your super strong engines are pushing along at max speed the skin doesn’t buckle or pop.
That’s another issue. They are not fast enough to run out of the path of bad weather, which means they have to land, and there aren’t a lot of zeppelin hangars dotting the landscape. So even if one lands and the crew escapes, there’s a pretty good likelihood of damage or destruction on the ground.