Clarence R. "Butch" Thorne, a free-lance graphic specialist from Washington, D.C. created this month's cover design to symbolize the long history of the Parachtue Club of America and its successor, today's United States Parachute Association.  PCA's emblem—the "triangle" so familiar to old-time jumpers—was based on a sketch found in the notebook of Leonardo da Vinci (1452-1519), who visualized a way to get man down out of the sky before man had learned to get up.  Da Vinci neither built nor tested his design.  Surrounded by a freefall formation is today's familiar USPA wings emblem.  Artist Thorne, 36, also designed the very popular 1980 and 1981 National Championships emblems—all without ever making a jump himself.  "And I have no plans, either," he says.