INDIANAPOLIS, Indiana—Engineers in Norway have started ground tests of a compact 2.5-megawatt generator, marking a key milestone towards flight tests of the Airbus and Rolls-Royce E-Fan X hybrid-electric demonstrator in 2021. The generator, which will be part of the largest electrical power system yet to take flight, was run for the first time Aug. 19 at Rolls-Royce Electrical Norway’s Trondheim facility.