isplayed at Amsterdam's 43rd International Motor Show in 1961, Ford Motor Co.'s air-powered Levacar promised drivers a future of wheel-less wonders. The single-seat, Fiberglas-bodied Levacar could theoretically accelerate to 500 miles per hour, nearly 80 percent of the top speed of a Boeing 747. For the show, however, the concept car traveled around a circular glass track propelled by blasts of compressed air that flowed out of its underside. Once considered impractical flights of fancy, airborne autos are slated to appear on roadways and airways this year at a sky-high cost of $280,000.