Hyperloop

When I first heard about the Hyperloop idea, I was sure it would just be a vactrain. They have been talked about for ages, but just haven't quite been cost effective enough for anyone to try.

I was right. After reading through their blog it seems to actually be something quite a bit more brilliant though. An idea to reduce the cost of a vactrain by operating at fairly high pressures compared to other vactrain designs. Like all great ideas, it is dead simple. Put a fan on the front of your train to push air behind you.

The problem is that a train will push most the air in the tube up to the front of the tube as the train goes along. By the time the train is at the end of the tube air friction will be tremendous because most of the five hundred miles of air in the vactrain tube will be in the last few miles. This can be solved by making the vacuum really good. Most vactrains proposed had really good vacuum pumps to overcome this problem. A fan is much cheaper than a vacuum pump though.

Unfortunately my fluid mechanics is not good enough to spot a flaw in this design if there is one. Still though, this sounds really plausible. We build long pipelines and linear motors all the time too so I bet that even their cost estimate is fairly good.