For a few seconds, Raymond Kohn was airborne. “It’s a cool feeling being in the air like that,” the stuntman from Ohio said, about an hour after he drove his 1969 Dodge Charger at 55 m.p.h. off a 5-foot ramp just behind the Cobo Center and landed, grill first, with a crash into the pavement. “It’s like a roller coaster ride. But in the end, it’s like the roller coaster derails.” He landed with a metal-twisting crash. A few seconds later, one of his crew waved a green flag, and the crowd cheered.