Flywheels put a new spin on electric vehicles.

Advances in high-strength composite materials, frictionless magnetic bearnings, high-efficiency motor/generators, and lower-cost miniaturized power conditioning and control electronics have resurrected the possibility that the venerable flywheel could be used to power pollution-free electric

ENGINEERS WORKING TO develop "zero-emissions" cars and trucks for the future are facing an extremely tough task in trying to supplant the long-dominant internal combustion engine, which environmentalists tell us wastes energy and pollutes the air. Not only must any replacement drivetrain produce pollution-free power with high efficiency, reliability, safety, and affordability, it must also meet the expectations of drivers accustomed to the high torques and accelerations provided by gasoline- and diesel-fueled internal combustion (IC) engines. Researchers developing altenative vehicular power sources are finding it hard to match the extensive energy content of cheap and readily available hydrocarbon fuels.

Carmakers are acutely aware that the first company to offer an affordable, resonably performing, and environmentally friendly automobile will have a significant advantage over competitors, especially if government environmental regulations continue to be tightened. The state of California, in particular, has provided automakers with a powerful incentive to develop practical alternatives by requiring companies to ensure that 2 percent of their vehicles have zero emissions by 1998.

As has been widely reported, the current focus is on electrochemical batteries. Although chemical bettery-powered electric vehicles (EV) use energy more efficiently than their IC engine--powered counterparts, the limited range and performance of current EVs are caused by the modest energy and power densities of today's batteries, particularly in cold weather. In addition, chemical batteries typically contain hazardous materials that pose disposal and recycling questions. Battery researchers have worked long and hard to overcome these drawbacks in numerous industry- and government-funded programs, but, barring a breakthrough, the realities of electrochemistry make the prospects for major improvements in chamical battery technology unclear.

There is another alternative, however, that has been around since ancient times--the flywheel, a balanced mass spinning around a constant axis that stores energy as rotational kinetic energy. One of humankind's earliest inventions, the flywheel served as the bases of the potter's wheel and the grindstone. Today, flywheels are widely used in IC engines to convert the pulsing bursts of combustion energy produced in the cylinders into smooth continuous power for the drivertrain. Less well known are aerospace flywheel systems that act gyroscopes to help orient orbiting satellites and store energy collected by photovoltaic arrays in their rotation. Flywheel technology is familiar to readers of this magazine, which published articles on the topic in February 1978, June 1988, and December 1990.