Another problem is power supply. A giant heli-craft would need lots of power. Nuclear power plants actually don’t have that good of a ratio of power to weight, especially given the shielding problem. And there wouldn’t be much point in building a giant rotary craft that had to land and refuel every couple of hours.
All I’m really claiming is that Londoners (and lots of folks all over the globe) are using satellite-based communication services today. So if a cheaper way to provide those services comes along, it may well be of interest.
As N9IWP mentioned, satellite communication has very high latency. In voice communication, it causes the noticable lag in transcontinental phone calls that you don’t get when the call is routed over an undersea cable. For data services, latency is not much of a problem for web browsing, email, or large file transfer, but it’s a huge problem for interactive applications such as video conferencing and gaming.
So, how are you going to provide bandwidth to these floating platforms? Are they going to use satellites themselves for their external connection? If so, they’re basically just an extra hop with extra latency and the main benefit to the end user is that they don’t have to carefully align a satellite dish. If the floating platform is going to use radio to a ground station for it’s link, then it’s basically just a really high antenna and the only benefit to the user is a somewhat expanded service area. In this case, you might be better served by balloon antennas tethered to ground stations.
I’ve seen proposals that used one or more fixed-wing aircraft circling over an area to provide wireless bandwidth services (radio frequency, but longer range than wi-fi). However, it’s tough to make the economics work. If you do this over a city, then you have a large number of potential customers but those customers have many other high-speed options including DSL and wireless hotspots. If you do this over a less-populated area, you might provide services that no ground-based provider competes with, but you have much fewer customers. I think the main consumer of something like this would be military and emergency services units that needed to provide temporary bandwidth to an area like a battlefield or disaster site.
Fair point. But existing technology (high speed mobile phone connections etc.) is surely capable of providing what is necessary, at an acceptable cost?
Can’t find any images, but helicopter airships were also used in the anime feature Laputa: Castle in the Sky – Laputa: The Castle in the Sky // Nausicaa.net. (The flying island itself was not held up by rotors but but by some black box antigravity technology never even mentioned, let alone described.)
It is. But “acceptable cost” tends to be a moving target, strongly influenced by new technology. If long-duration aircraft become practical, they may perhaps make us view the current cost of satellite comms in the same way that we now look at the first transatlantic cable charges. Or the way we look at mobile telephone costs in the “pre-cellular” era.
Come on! Nobody takes Freud seriously any more! 
Yep, that’s it.