A SIMPLE classroom experiment illustrates a principle that, both literally and figuratively, could guide a major new phase in train transportation. Place two toy bar magnets together. You can align the magnets either to attract or to repel each other.
Magnetic levitation - maglev for short - is the ability of a magnet to suspend another magnet against gravity either by attraction or repulsion.
Applied in train transportation, it can hold a vehicle clear of guide rails. Such a vehicle, free of wheel-against-rail friction, guided and propelled by electromagnetic forces, can carry passengers and freight at speeds of several hundred miles an hour.
Its boosters claim maglev could revolutionize some aspects of train transportation. Skeptics consider it a novel technology whose economic feasibility is unclear. But even the skeptics agree that it is an engineering concept whose testing time has come.
Germany and Japan have developed different versions of maglev to the point where they are ready for commercial applications.
Now the United States is ready to take up its development again, having dropped out of the field for 15 years. The transportation bill that became law last December provides for a $900-million National Maglev Initiative to develop a prototype system by 1999. The federal government will put up $725 million to stimulate additional funding from private sources.
This American initiative has come none too soon for Gordon Danby and James R. Powell of Brookhaven National Laboratory in Upton, N.Y. After the federal government cut support for maglev research in 1975, they had to stand by glumly and watch Japanese engineers carry out a major development of a technological concept they had invented.
Referring to this in a press conference at the annual meeting of the American Association for the Advancement of Science (AAAS) in Chicago last month, Dr. Danby observed wryly that the Japanese plan to operate a 300-mile-an-hour train between Tokyo and Osaka early in the next century using a "system based on our inventions."
Danby says that "by the year 2000, commercial maglev will arrive on the world stage, with or without US technical participation." However, he adds, "There's still time to develop US maglev."
Reduced to simplest terms, there are two basic types of maglev systems. Their essential difference lies in whether they use repulsive or attractive magnetic force to suspend vehicles.
The Japanese use the magnetic repulsion concept, or electrodynamic system to use the engineering term. In this system, magnets suspend a vehicle several inches above a track while other magnetic forces keep it stably centered in its guideway. A moving "wave" of magnetic force propels the vehicle or decelerates it when it needs to stop (see diagram at left).
Vehicles have to be moving fairly fast for this kind of suspension to work. Thus the Japanese maglev train rolls on wheels until it hits a speed of about 100 miles an hour.
Vehicles supported by magnetic attraction, on the other hand, remain suspended even at low speeds. This is what engineers call an electromagnetic system. German engineers have developed and tested this concept extensively.
In the German system, a vehicle's suspension frame wraps around and beneath a guide rail. Magnets then pull the frame up toward the bottom of the rail, leaving a clearance of a fraction of an inch (see diagram at left).
The guide rail and guideway, the vehicle frame, and other system components must be built to tighter tolerances than those required for the electrodynamic system that suspends a vehicle with clearances of several inches. In spite of this greater demand for precision construction, the German Transrapid system is likely to be the first to go into at least small-scale commercial operation.
Last June, Florida gave Maglev Transit Inc. of Orlando the certification to build and operate a 14-mile Transrapid maglev route between Orlando airport and a point near Walt Disney Company's Epcot Center. Vehicles would hit a top speed of 250 miles an hour during the 6.5-minute ride along the half-billion-dollar system's route. The system may be running by 1995.
William W. Dickhart, consultant to Transrapid International, which markets the technology, notes that the German government and the German Federal Railroad have, this year, declared "that the Transrapid Maglev System had reached technical readiness for revenue service."
But that doesn't mean that the financial success of the Orlando project - or any maglev project - can be clearly foreseen as yet.
The National Research Council of the US National Academy of Sciences released a study last November, which concluded that no high-speed rail system in the United States - including maglev - would break even through the financial support of farebox revenue alone. Public subsidy would be needed. However, economist Thomas A. Lynch of Florida State University at Tallahassee warns that concern about such a subsidy is misplaced. He notes that the public highway system subsidizes cars and trucks, and publicly f unded airports subsidize airlines. "All [transportation] modes are subsidized in all countries," he says.
Maglev designers like Henry H. Kolm also object to assessing maglev's potential by railroad standards. Dr. Kolm and Prof. Richard D. Thornton of the Massachusetts Institute of Technology in Cambridge, Mass., had to mothball a design they had developed using magnetic repulsion when federal funding dried up in 1975. Now Kolm is pursuing the concept again as president of Magneplane International Inc. of Bedford, Mass.
Kolm explains: "Maglev ... can operate individually targeted vehicles which are not hitched together mechanically ... and are two miles apart.... If you build a corridor from Boston to Washington, you could operate vehicles independently." He envisions a system in which maglev guideways run along existing highway or rail rights of way. Feeder guideways would allow individual vehicles to join and leave the main trunk line, picking up or discharging passengers at local shopping malls.
Brookhaven's Powell gives this example: "If you were on a maglev line waiting to go from New York to Trenton, you wouldn't have to stop at every stop in between. You can pick the vehicle that's going to your particular stop ... then make one or, at most, two stops to the direct destination."
`MAGLEV is destined to be the next thing that will reshape our society as significantly as the automobile has," says Kolm. He adds, "If you could catch 300-mile-an-hour transportation in your nearest shopping mall, you certainly wouldn't want to drive [any farther]."
That's the vision boosters of maglev systems have. They see it as a socially transforming type of transportation, not just another high-speed train. Moreover, Danby of Brookhaven Lab emphasizes that engineers and designers envision it as low-cost, energy-efficient transport.
"At 300 miles an hour, [primary] energy consumption is one half that of autos and one quarter that of airplanes," he says.
But the National Research Council cautions that more research is needed to determine the potential for that dream to become a reality. The council recommends a careful study of the potential market for maglev as well as results of the National Maglev Initiative. That's a challenge American maglev designers are eagerly taking up.