The world altitude record for nonrocket-powered aircraft, formerly held by the Air Force’s mighty SR-71 Blackbird, was shattered this summer by a flying wing. The unmanned Helios aircraft, made up of 14 propellers and 65,000 solar cells, averaged 25 miles an hour as it climbed 96,500 feet over the Hawaiian islands, three times the cruising altitude of a commercial airliner and 10,000 feet past the previous record. Next, engineers are planning to equip it with a fuel cell, allowing for multiday flights above 50,000 feet.