Recently, an aircraft with a parallel hybrid engine – the first ever to be able to recharge its batteries in flight – has been successfully tested in the United Kingdom. This could be an important early step towards cleaner, low-carbon air travel.
The aircraft is based on a commercially-available single-seat aircraft. Its hybrid engine was designed and built by engineers at Cambridge with funding from Boeing.

The result is an airplane that uses 30% less fuel than a comparable 100% gasoline powered plane.

The aircraft uses a combination of a 4-stroke piston engine and electric motor/generator, while a drive pulley spins the propeller. During take-off and altitude climbing, when maximum power is required, the engine and motor work together to power the plane. Once cruising height is reached, the electric motor can be switched into generator mode to recharge the batteries or used as a motor assist to minimize fuel consumption. The same principle is at work in a hybrid car.

The hybrid power system in the Cambridge airplane is based on a Honda engine, in parallel with a custom lightweight motor. A power electronics module designed and built in the Engineering Department at Cambridge controls the electrical current to and from the batteries – a set of 16 large lithium-polymer cells located in special compartments built into the wings. The petrol engine is sized to provide the cruise power at its most efficient operating point, resulting in an improved fuel efficiency overall.

“Although hybrid cars have been available for more than a decade, what’s been holding back the development of hybrid or fully-electric aircraft until now is battery technology,” said Dr. Paul Robertson of Cambridge’s Department of Engineering, who led the project. “Until recently, they have been too heavy and didn’t have enough energy capacity. But with the advent of improved lithium-polymer batteries, similar to what you’d find in a laptop computer, hybrid aircraft – albeit at a small scale – are now starting to become viable.”

“Our mission is to keep our sights on finding innovative solutions and technologies that solve our industry’s toughest challenges and continually improve environmental performance,” said Marty Bradley, Boeing’s principal investigator for the program. “Hybrid electric is one of several important elements of our research efforts, and we are learning more every day about the feasibility of these technologies and how they could be used in the future.”




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