In 26 years of flying, Brig. Gen. Darryl L. Roberson has had the chance to ride four different Air Force steel horses. Until Dec. 7, it had been more than 20 years since Roberson had been in the cockpit of an F-4 Phantom. In 1989, as a captain, Roberson left the F-4 for the F-15 Eagle, a jet he