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06 February 2015

The Hybrid Airplane Takes Off

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A couple of litres of fuel and 33 cents in electricity – that’s the price to travel 80 kilometers, soaring through the sky with an airplane designed by the University of Cambridge. Its secret is a hybrid engine developed thanks to funding from Boeing. It’s the first hybrid aircraft capable of recharging its batteries while airborne, providing hope for greener air traffic, capable of reducing CO2 emissions.

This modified Czech-built SONG plane reduces fuel consumption by 30%. But that’s only the first step. “Yes, we can improve efficiency by optimizing the mixture of air and fuel and the helix angle,” says Dr. Paul Robertson from the Department of Engineering at Cambridge and leader of this project. The airfares of the plane do not rise dramatically and “they would cost more or less the same as a conventional one, perhaps between 5 and 10% more,” told Robertson to OpenMind.

The key to this system is found in the electronic belly of the plane. The wings house 16 lithium cells, which are monitored by a computer system. In the engine area, two motors are combined: a Honda GX combustion motor and a Joby JM1 electric motor rotating at 7,000 rpm, and the whole system records its flight data on an SD card to help improve performance. As well, an unprecedented milestone has been reached according to the researchers since “the engine can also act as a generator and charge the batteries from the flight. And this is the first time this has been achieved,” says Robertson. The system also has other advantages: “The engine is much quieter and, with careful design, there could be safety improvements by having a system of dual power, so the plane could continue flying using only fuel or only electricity.” In other words, in case of failure, the aircraft would have another engine available to avoid an accident.


That airplanes have become hybrids is a response to a growing environmental problem. The International Civil Aviation Organization (ICAO), the UN agency responsible for regulating this sector worldwide, estimates that air traffic is responsible for at least 2% of total emissions of CO2 and consumes 13% of fuels fossil annually. And it also predicts that this number could multiply by four to six times by 2050.

This investigation at the University of Cambridge marks a path to drastically reduce this source of pollution. Although Robertson recognizes that there is still work to be done in this area because the use of lithium batteries also has an environmental impact: “We have not yet studied in detail this aspect because we are still at the prototype stage. But the ecological problems of the aircraft involve the scarce magnetic materials and the lithium used in the batteries. But as they are building more and more electric vehicles of all kinds, they will have to be produced in a sustainable manner, including recycling [of the batteries]. Moreover, the fact of burning of less fuel is already a benefit.” Researchers at the University of California have already analyzed the polluting effect that lithium batteries can have, concluding that they pose a risk because they contain elements such as cobalt, nickel, copper or lead.

OpenMind-avion-hibrido-Hybrid SONG3

2050 goals

2050 is a key date for the reduction of CO2 emissions worldwide. In 2010 the United Nations set the target of reducing CO2 emissions so as not to exceed 450 parts per million in the atmosphere. For many leading countries this means travelling back in time to pollution levels from over two decades ago. At the meeting on September 24, 2014 of the United Nations on the ecological state of our planet, the ICAO set targets to reduce aviation CO2 emissions. The first point of its plan: “New and more efficient aircraft technologies and sustainable alternative fuels.”

The research led by Robertson in Cambridge could be the cornerstone for achieving a hybrid aircraft, which would help to meet these environmental goals. At the moment, the airplane in the project, as shown in this video, has nowhere near the size or capabilities of a commercial airliner –it weighs about 120 kilos and flies to a height of some 460 meters– but in the medium term this could change. “For a large aircraft, the energy density of the batteries is the main technological limitation. But this is improving at the rate of 5% per annum. With what will be available in 10 or 20 years, it would be feasible to use hybrid propulsion in a much larger aircraft, and in 30 years time, for an airline.” If these projections are met, it would arrive in time to help meet the 2050 targets.


Angel Luis Sucasas

for Ventana al Conocimiento (Knowledge Window)


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