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Royce to compete in the electric air race

Time:2018-03-13 13:54Turbochargers information Click:

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Energy Digital takes a look at the race to deliver the first commercial electric aircraft. Mark Cousin, SVP Flight Demonstrators CTO at Airbus, talks about the company’s collaboration with Rolls-Royce and Siemens.

The great electric air race is underway. European aviation heavyweight Airbus is collaborating with Rolls-Royce and Siemens, while budget airline easyJet has teamed up with California’s Wright Electric, with both partnerships targeting the introduction of electric energy storage.

Analysts agree the probability of purely electric shorthaul airliners in the next decade is realistic, but these will be relatively small aircraft carrying 15-20 passengers. Energy storage capacity will be too low to fly a full journey on a 100% electric flight, so we won’t see 100-passenger aircraft flying from London to Amsterdam in 10 years’ time. The airlines involved in this endeavour are starting to ask whether their future fleet will still consist of large 100-plus seat aircraft, or if they’ll have a fleet of smaller aircraft flying shorter routes on full electric.

“We could see a proliferation of smaller aircraft flying out of the less congested airports on relatively short one-hour routes,” suggest Mark Cousin, SVP Flight Demonstrators CTO at Airbus. “This would change the dynamics of air transport and pave the way for autonomous aircraft with no pilot on board, resulting in aviation costs falling dramatically, while maintenance for an electric aircraft will be much cheaper than for one powered by gas turbines.”

Cousin is at the forefront of the Airbus Demonstrators initiative. The programme’s goal is to set an objective not achievable with today’s technologies to force the development of innovations – in this case, the future of hybrid electric propulsion. “In the next couple of years, we’ll see three major demonstrators,” reveals Cousin. “The first is being developed by our colleagues in Silicon Valley – Vahana is a tilt wing single person urban air mobility vehicle. By the end of 2018 we expect the first flight of the City Airbus, a proof of concept of a four-seater air taxi. And we’re also due to announce the successor to our E-Fan, the E-Fan X. The only way we can learn what the issues will be, and how we can overcome them to improve our product, is by flying and testing.”

Cousin identifies four key challenges Airbus has chosen to focus on…

Energy Storage Density

“Improvement in the power-to-weight ratio, or energy storage density, of batteries is required. Even when we take into account the favourable efficiency difference of electric motors versus gas turbines, the conversion of energy from kerosene to thrust is 50 times as high as the conversion we see with energy storage systems. That is going to limit how much energy you can carry and how far you can fly.”

Weight

“The weight of hardware with new electric propulsion systems will be greater than traditional aircraft with electric motors and power electronics in the system adding to the payload. A hybrid electric aircraft will be heavier so improvements will be needed to boost overall efficiency when compared with today’s traditional aircraft.”

Power transmission

“We’re running a 2MW motor directly powering a turbo fan which will generate thrust, so in order to achieve efficiency in the megawatt class, you need to transmit the power at a very high voltage. We’ll be transmitting power around the E-Fan X at 3,000 volts DC, yet the highest voltage on aircrafts flying today is 230 volts – it’s a big step. The challenge at 3,000 volts is what we call partial discharge. You get a corona effect. Unless you put massive amounts of insulation around the cables, there is currant leakage from the transmission line to any conducting elements. At sea level in trains and boats it’s not a big issue because air can be a good insulator, but at altitude the air is much thinner and that effect is less powerful. We need to establish the right levels of insulation on the wiring and the separations between cables and structure to control this difficult phenomenon.”

Efficiency

“Today, high-powered electric motors are around 96% efficient, which means the other 4% is coming out as heat. We need to get those losses down to less than 1% in the motor and transmission systems. All of these elements need to be addressed or the hybrid system will be less attractive compared to a traditional gas turbine because you can’t waste the energy you store and transmit.”

Tesla CEO Elon Musk states that once batteries are capable of producing 400 Watt-hours per kilogram, the potential for energy density to beat the weight problem and deliver pure electric transcontinental flight becomes ‘compelling’. Currently, it would be impossible to fly from London to Singapore with pure electric power because an aircraft would have to carry too much weight in battery to have any room for passengers. Until that goal is reached, Cousin believes larger, longer range aircraft will follow a hybrid model. “Initially we’ll see a large generator (2MW) installed between the thrust-producing fan and the gas turbine, and that motor/generator will be used throughout flight to either inject or extract power depending on the phase of flight you’re in,” he predicts.

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