Hybrid aircraft takes to the skies

Aircraft able to charge its own batteries consumes 30% less fuel

Engineers from the University of Cambridge have developed the first electric aircraft able to recharge its own batteries during flight.

The parallel hybrid-electric aircraft was successfully flown at Sywell Aerodrome, near Northampton in late September.

The demonstrator single-seat plane, which is said to consume 30% less fuel than a comparable petrol-only 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 minimise fuel consumption.

The aircraft's hybrid engine was designed and built by engineers at Cambridge with funding from US aircraft-maker Boeing. The hybrid power system is based on a Honda engine. A bespoke power electronics module 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 optimally sized to provide the cruise power at its most efficient operating point, resulting in an improved fuel efficiency overall.

Dr Paul Robertson, from the University pf Cambridge’s Department of Engineering, said: “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. 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.”

The 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 development team, which includes PhD students Christian Friedrich and Andre Thunot and MEng student Tom Corker, is now conducting ongoing test flights to characterise and optimise the system for best performance and fuel economy while extending flight times.