Today, we ride a fast train. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
Perhaps you've seen a
magnetic desktop toy, built in two parts. One's an
axle with two circular magnets that look like
wheels, and a needle-like point on one end. The
other's a holder with a small mirror on the same
end. Position the point against the mirror and
start the axle spinning. It floats above the holder
on a magnetic field and keeps spinning for a long
time. However, it's tricky, because any wobble can
amplify; it's not stable.
That has much in common with the so-called
Maglev train -- an idea whose time seems
to've come. Maglev is short for magnetic
levitation. It's a train supported by magnetic
fields, which are stabilized by feedback control
systems. The floating train does not touch the
track, at least when it's moving at full speed.
And full speed is fast. The Japanese are
building a forty-mile line that will run reach 340
miles an hour. In another episode I argue that
practical land speeds are redlined at about 150
miles an hour. But this is not land transport; it's
constrained flight. These trains do, quite
literally, fly.
Maglev comes in different forms. It can use either
magnetic attraction or magnetic repulsion to hold
the train in the air. In either case, the linear
motor that drives it is not part of the train, but
built into the track. As with any new technology,
this next generation of rail has its critics. They
worry about noise, safety, and usefulness. As for
noise, it appears to be less than that of
conventional rail. And it's aerodynamic, not
mechanical.
One feature augurs in favor of safety: since the
motor is in the track, head-on collisions are
physically impossible. The motor cannot run two
ways at once. The track, however, has to be built
far more solidly and accurately than conventional
rail is.
Usefulness can also be hard to predict, because
it's something that only users can decide -- and
then only once a system is in place. Critics of
urban light-rail systems argue that they're
practical only in very high-density environments.
But this is not light rail -- even though most
lines presently under construction are fairly short
and are wed to such urban problems as connecting
with distant air terminals. Maglev is ultimately
intended for longer inter-city systems.
I once heard a friend predict that air travel would
one day strangle on one limitation: airplane flight
paths can spread out in the sky, but they're
constrained to converge at the place where they
take off or land. Rail, on the other hand, runs
between cities on one or two tracks, then spreads
out where it begins or ends.
The many forms of clogging that occur at air
terminals are now so severe that the actual flight
takes the lesser part of the time we spend on most
trips. Watch now, as rail reaches a significant
fraction of airplane speeds. I usually avoid trying
to make predictions -- but this technology really
does have my attention.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
P. Sharke, Ticket to Ride. Mechanical
Engineering, October 2002, pp. 46-50.
For more on Maglev trains, see, e.g.,
http://www.calpoly.edu/~cm/studpage/clottich/fund.html
http://faculty.washington.edu/jbs/itrans/maglevq.htm
For more on fast trains, see Episode 449.
A magnetically levitated spindle
(Photo by John Lienhard)
The Engines of Our Ingenuity is
Copyright © 1988-2002 by John H.
Lienhard.
