Technically speaking, lighter-than-air airships that have the ability to rise vertically just by dropping ballast are VTOLs. But a lot has struck me about how these heavier-than-air contraptions should be, but mostly aren’t, a staple of alternate history the way airships are. Oh, in science fiction they appear in force (see the Orcas from Command and Conquer and Vertibirds from Fallout), but in regular AH, not so much.
VTOL craft run a gamut from simple (conventional helicopters) to ultra-complex. After normal rotorcraft you have so-called “compound helicopters” like the cancelled Cheyenne that have additional horizontal engines to make them go faster. Then you have tilt-rotors/wings like the V-22. After those there are airplanes with dedicated lift engines. Then you have Harrier-style thrust vectored craft. Perhaps the most complex proposal was a giant Beriev seaplane with literally dozens of lift engines.
VTOLs have been technically possible as long as aircraft themselves, but they’ve run into issues. Trading complexity and the problems that come with it, as well as other performance issues, for small advantages (mostly speed for helicopters and takeoff distance) is one problem. Another is stability, with computerized controls being almost necessary. Of course, another design with tradeoffs that has been underused despite being technically possible is…. lighter-than-air airships!
Yet while the presence of airships has become a cliche in alternate history circles, VTOLs have not been. Alternate history is full of Victorian zeppelins, not Vietnamese tilt-wings and jet-copters. If I had to give one reason why, I’d say it’s because of brand appearances. Zeppelins look like something from the past, therefore it’ll be “historic but with zeppelins”, aka alternate history, while VTOLs look futuristic, and therefore writers are more likely to just make a story with them pure science fiction (or sold as such).
Or it could just be genre inertia. But it’s a fascinating subject about fascinating vehicles all the same.