We're all familiar with hybrid cars, but hybrid planes are virtually unheard of. Now though, researchers from the University of Cambridge, UK, have partnered with Boeing to test what they say is the first hybrid-electric aircraft. It is said to use 30 percent less fuel than a gas-only equivalent.

"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," says project lead from Cambridge's Department of Engineering Dr Paul Robertson. "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."

Gizmag is no stranger to hybrid aircraft. Volta Volaré promised its hybrid four-seater GT4 back in 2012, while just last month we featured the Faradair BEHA concept that will theoretically be powered by electric motors and a bio-diesel engine. The Cambridge/Boeing test plane is a much simpler design than both of those, however.

The single-seat aircraft, which is based on a commercially-available model, is powered by a Honda 4-stroke piston engine and a custom-made electric motor/generator. The two power sources are coupled so that either can drive the propeller. At times when a lot of power is required, such as during take-off, the plane uses both the engine and the motor to drive the propeller.

Once it is at cruising height, however, the motor can continue to assist the engine to help save fuel or be switched into "generator mode" and for it to recharge the batteries while the plane is in flight. According to the University of Cambridge, this is the first time that this has been achieved. A module designed by the engineering department at Cambridge is used to control electrical current to and from the lithium-polymer cell batteries, 16 of which are housed in compartments in the wings.

The hybrid aircraft was tested at the Sywell Aerodrome, near Northampton, UK. Initial tests comprised a series of "hops" along the runway. These were then followed by longer flights at an altitude of over 1,500 ft (457 m). Ongoing tests are aimed at optimizing performance and fuel economy.

The video below provides an introduction to the hybrid plane project.

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