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Comment by tgb | Hacker News Reader

Why are maglevs so much slower than airplanes? We're looking at a factor of 2 difference and airports don't take over 30 years to install. Isn't the point of a maglev to reduce the friction against the ground, so aren't both planes and maglevs fighting primarily against air resistance? Or is it not that they can't go faster, just that it's too loud or they need to turn too much or something?

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Plotting (can't be all straight), air density (as mentioned by jessridel). Current high speed trains go at 180-200 mph due to sharply increased consumption above those speeds, even though they could go a lot faster in current setups.

In 30 years we'll probably have more efficient airplanes, and less fuel, so higher prices. Maybe it's more expensive in the short term, but it's much more sustainable to have ground-based transportation for trips under 400 or 500 miles.

In Spain, we have the Madrid-Barcelona route. It's 50 minutes by plane and 2h30 by train (620 km, 385 miles). Airports are outside cities, stations are in the center of them and very well connected by road and commuter trains from everywhere. It's gone from being one of the busiest air routes to losing more than half of its traffic to high speed train. Why? Much more comfortable and, in the end, takes the same time.

I think g-forces from turning is a real concern, but so is the fact that there's a lot more air at sea level than 30k feet. Planes land and take off at less than 200 mph.

Air density on the ground. Air is a lot soupier close to the surface in the troposphere vs way up high in the stratosphere.

Most commercial flights are actually in the troposphere, which is about 17km deep in the temperate zone. Your point is still right: air density at 36000ft is ~0.37 kg/m^3, as opposed to 1.23 kg/m^3 at sea level.

To build on this, the drag force varies linearly with fluid density and quadraticly with velocity, so the four-fold increase in fluid density from airplane altitude to sea level corresponds to a doubling in velocity. Which is actually the difference we see! Cool!

I don't think it has much to do with air density as it does with guideway inductivity issues - which would limit it's top speed (aside from the obvious things like how curved the path is, if and where it has to make more gradual stops and turns, etc).

Jet propulsion and magnetic propulsion are fundamentally different. There are limits to what those magnets can push/pull, how much energy can be put into the system, and the stresses involved coming from the fields.

http://en.wikipedia.org/wiki/Electromagnetic_propulsion

Thanks for the answers everyone. One more question:

Can maglevs use jet propulsion to go faster?

Might as well just graduate and use warp-drive.

That would mean they have to carry fuel for the engines which they do not at the moment.

So yes, but you wouldn't want to

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