"Picture a huge, heavy flywheel—a massive metal disk mounted horizontally on an axle, about 30 feet in diameter, 2 feet thick, and weighing about 5,000 pounds. Now imagine that your task is to get the ...

After years of being billed as the next great revolutionary means of propulsion, flywheels may finally be ready for prime time. Aside from a few modest successes, flywheels have not lived up to this ...