Researchers from the UK’s University of Cambridge have successfully tested the first aircraft to be powered by a parallel hybrid-electric propulsion system, where an electric motor and gas engine work together to drive the propeller. Test flights consisted of a series of ‘hops’ along the runway, followed by longer evaluation flights at a height of over 1,500 feet. The demonstrator aircraft uses up to 30% less fuel than a comparable plane with a gasoline-only engine. The aircraft is also able to recharge its batteries in flight, the first time this has been achieved. The demonstrator is based on a commercially-available single-seat aircraft, and its hybrid engine was designed and built by engineers at Cambridge with funding support from Boeing. The aircraft uses a combination of a 4-stroke piston engine and an electric motor/ generator, coupled through the same drive pulley to spin the propeller. During take-off and climb, when maximum power is required, the engine and motor work together to power the plane, but once cruising height is reached, the electric motor can be switched into generator mode to recharge the batteries or used in motor assist mode to minimize fuel consumption.