Hybrid Airliners

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By 2018-01-03

By Michael Gregson

Hybrid cars are seen everywhere on the roads these days – and hybrid planes may soon be just as commonplace in the skies. A consortium made up of Airbus, Rolls-Royce, and Siemens is working on hybrid electric jet engines which should be ready to take to the air aboard a demonstration plane by 2020.

The project, codenamed the E-Fan X, uses a BAE 146 jet as a test aircraft. The jet, which seats up to 100 people, will at first have one of its four gas turbine engines replaced with a hybrid engine. This engine will be powered by batteries and an onboard generator using jet fuel. If successful, the team will then move to two electric engines.

Paul Stein, Chief Technology Officer at Rolls-Royce, told the Guardian Newspaper: "It is a two-tonne battery pack – the batteries are still fairly heavy. Beating gravity into submission is a huge challenge, so weight is a big issue."

Siemens is designing the 2MW electric motor, Rolls-Royce is building the generator that powers the engine, and Airbus will integrate the system into the plane and link it to flight controls.

The consortium decided to develop a hybrid motor as fully electric commercial flights are currently out of reach because of the sheer weight of batteries.

Pound for pound, fossil fuels contain around 100 times as much energy as a lithium-ion battery, though more powerful and lighter power sources are being developed around the world.

Cars have their wheels planted firmly on the ground and it is relatively easy for engineers to offset the extra weight. Running out of juice on the ground is inconvenient. In the air, it could be a disaster. So, for the time being, batteries are not an option.

"For us, safety is paramount. The burden of proof to ensure we maintain that safety margin is very high. We cannot have a battery chemistry that risks a fire," said Paul Stein.

But the hybrid is a vital stepping stone in developing fully electric aircraft.

"The E-Fan X is an important next step in our goal of making electric flight a reality in the foreseeable future," said Paul Eremenko, Airbus' Chief Technology Officer.

The E-Fan X flying test bed is designed to explore the challenges of high-power propulsion systems, such as thermal effects, electric thrust management, and electromagnetic compatibility issues. There is a possibility that the giant electric motor could interfere with the aircraft's navigation and communication systems – the same reason why passengers are told to switch off their mobile phones.

The programme also aims to establish the requirements for future certification of electrically powered aircraft, while training a new generation of designers and engineers to bring hybrid-electric commercial aircraft one step closer to reality.

"The E-Fan X enables us to build on our wealth of electrical expertise to revolutionize flight and welcome in the third generation of aviation. This is an exciting time for us as this technological advancement will result in Rolls-Royce creating the world's most powerful flying generator," said Stein.

Bjorn Fehrm, an Aeronautical Analyst at Aviation Leeham News and Comment, told the Guardian: "For the range of today's thousands of single aisle (Airbus A320, Boeing 737) planes, it will have to be hybrid for at least another 30 years. For long range, it's unrealistic. There would have to be a breakthrough in fuel cells, or similar."

That's not soon enough for some airlines. EasyJet wants electric planes to fly passengers on its short-haul routes within 10 to 20 years. It has signed a deal with Wright Electric, a US engineering company, to develop electric-powered aircraft that could reach Paris and Amsterdam from London.

The attractions for airlines are clear. Jet fuel accounted for up to 36% of their running cost in recent years. Rolls-Royce's Stein reckons the E-Fan X could produce fuel savings of 15%.

In addition to saving fuel, hybrid jets will also help airlines meet tough new regulations. The European Union aims to cut carbon dioxide emitted by aircraft by 75% and nitrous oxide by 90% by 2050. Noise levels will also have to be reduced by 65% to meet the new standards, which will apply to all commercial aircraft flying in and out of the EU, including those from Sri Lanka.

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