Researchers from the University of Cambridge, in association with Boeing, 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. The demonstrator aircraft uses up to 30% less fuel than a comparable plane with a gas-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 Boeing funding support. 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 takeoff and climb, when maximum power is required, the engine and motor work together to power the plane, but once cruising altitude 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 – the same principle at work in a hybrid car.
The hybrid power system in the Cambridge demonstrator is based on a Honda engine, in parallel with a custom lightweight motor. A power electronics module controls the electrical current to and from the batteries. The gas engine is optimally sized to provide the cruise power at its most efficient operating point, resulting in an improved fuel efficiency overall.