well if it is a air unit, it probly will need fuel, (unless it can manufacture fuel from the air, or it has its cool fusion units powering electric moters that drive propellers)
if it does need fuel, mabe that would be the limatation of the vtol's they can only be in the air for a certon amount of time, or go a certon distance before being forced to land, of corse when they land at air bases they would be refuled
mabe have a series of vetols as tecnoligy progresses, the first ones would be the fusion ones, they would not run out of fuel, but they would be slow, and not be able to transport many units,
than you would have the fuled ones, and mabe you could upgrade them so they can hold more fuel, they would be faster and able to transport more units, t
he third one would be one that would be able to manufacture fuel from the air (such as if the planet has a nitrogen/oxygen based atmosphere ie earth, it would take the N2/O2 mix and make nitros oxide, wich would then be burned to propell the craft)(its a game, it dosnt have to work in real life)
it would be the biggest, most expencive, and fastest VTOL, and mabe make it be able to carry things into space (because, if it manufactures its own fuel in the atmosphere, it has a very low mass ratio (it carries no propellent other than emergency tanks) and thus there would be no reason why it couldnt go into space)
of corse that would be one heck of a hassle for knux, but I just felt like putting in my 2 cents worth lol