From: tpalm@nada.kth.se (Thomas Palm)
Newsgroups: sci.environment
Subject: Re: Steering a New Course -- some misinformation
Date: 14 Dec 92 10:08:43 GMT
Organization: Royal Institute of Technology, Stockholm, Sweden

In article <Bz2oxD.9BF@cgl.ucsf.edu>, jdavis@socrates.ucsf.edu (Jonathan H. Davis%James) writes:
| >> Some arguments form Mike Vandeman about cost of Maglev
|> 
|> OK, now you have given away the clue, that your oft-touted PhD is
|> not in a physical science.  WHY should it take more energy to hold
|> a train up than to pull it along rails?  Although your assertion may
|> seem like common sense to those who are ignorant of physics, it
|> is in fact incorrect.  Yes, it would
|> be much more difficult for _YOU_ to hold a train up in the air and
|> carry it than it would be to pull it on rails, but superconducting
|> magnets do not rely on muscle power and the conversion of ATP -- 
|> they can keep a train up effortlessly and without using any
|> substantial energy.  Then the train can be moved with only air friction
   ^^^^^^^^^^^
If we had room temperature superconductors yes. Until then cooling does require
energy. I have no exact figures whether it may be considered substantial.

|> and momentum to resist the motive force.  And a clever design can
|> recover the kinetic energy when you stop.

My impression is that air resistance is much more important than friction 
against the track for conventional trains. Thus no major advantage for 
maglev here.

|> 
|> Maglev is not commercially viable now, but to give up would be folly.
|> Technological advances in high-temp. superconductors and other
|> necessary technologies could easily change this state of affairs,
|> making maglev the overwhelmingly energy-efficient way to transport
|> people and goods.

It'll never be >overwhelmingly< more efficient than conventional trains. If seen 
as an alternative to aircraft on the other hand, I agree. Of course,
tele-commuting is an even better way of reducing much unnecessary movement for 
people. That's really high speed, and energy efficient.

|> BTW, 'Safely'?  What is so dangerous about being a few cm. off the ground?

Nothing if you stand still, but when moving at 300 mph touching the ground
is a problem. Ever tried jumping out of a car in 50 mph? You're just a few 
decimeters abouve the ground then. Supposedly it can be solved by having
reserve wheels able to hold the vehicle up while braking, but it's not trivial.

I see maglev as a niche market for some very dense corridors. The cost for the
track is so high that few areas motivate it. For the same price you can build
a much denser net of conventional rail. Then the somewhat lower speed can be
offset by more direct routes. You are little helped by a fast transit between
A and B if you live in C has to take a bus/slow train to A, zip along to B and
then another slow transit to your target.

|> However, I want you to know that I appreciate much of what you say
|> about our approaches to our environmental future.  Just be careful
|> of your physics.

You too. Probably me too, we all make mistakes and misunderstand each other.

|> -- Jonathan Davis, Almost PhD (next year?) in Biophysics

Unless talking about one's field of expertise, let's forget about titles, OK?

-- 
"Good planets are hard to find."     Thomas Palm
				     Department of Microwave Engineering
				     Royal Institute of Technology
				     S-100 44 Stockholm, Sweden
				     tpalm@mvt.kth.se