I find hot air balloons and zeppelins fascinating since they can carry significant weight. I watched a mythbuster episode in which they busted the myth that an inflatable boat filled with helium could hover, and carry the weight of a human. The rubber boat couldn't even carry its own weight so they kicked the experiment up a few hundred notches and filled a series of massive pontoons with helium: which was also a complete failure because they couldn't even connect the pontoons together properly because the connecting material would add too much weight. This gives me an idea. If you were to connect a huge series of helium balloons, in vertical tandem, you could generate a lot of lift power, enough to attach a hot air balloon type basket to carry the weight of humans. I googled tandem balloon aircrafts but could only find pictures of things like this: thats a horizontal tandem array containing only 2 balloons which can probably barely even carry its own weight. What I'm talking about is a vertical array of hundreds of large balloons. Theres not much of a limit to how many balloons you could use, the array of balloons could stretch kilometers into the sky. Unlike a hot air balloon, it wouldn't require a fuel source. To build it, you could simply anchor it to the ground with chains and attach balloons one by one, in a serial manner. Can any of you see any reasons why this wouldn't work? The first major problem that comes to mind is how to devise a mechanism for controlling altitude. Maybe the cord connecting the array of balloons could contain a thin aluminium conductor in the center, surrounded by an insulator, that way an electrical current could be sent to the balloons to deflate them one by one using some kind of electronic mechanism. They could be deflated by releasing the helium using some kind of electronic valve, that way you could gradually lower the rate at which the aircraft rises by deflating balloons one by one. Similarly, you could slowly bring the aircraft down by deflating enough balloons. I can't think of a method to reinflate the balloons though. Maybe the carrier basket could contain pressurised helium tanks which could be fed into channels in the cord and fed into the balloons, via the same electronically controlled valves used to release helium. Problem there is the metal required to contain highly pressurised helium would be heavy. On top of that, you'd need massive amounts of helium in these tanks so that method just wouldn't work.