Approaching Hybrid Aircraft

While electric aviation is still in its infancy, hybrid solutions promise to replace conventional aircraft for regional flights soon. As it turns out, they offer much more than a reduction in CO2 emissions. Will they deliver?

When it comes to hybrid engines as an alternative to traditional kerosene-powered combustion engines for aircraft, optimism seems to be strong. “Of course, we cannot expect a full transition from one day to the next,” says Dr Sigurd Øvrebø, Managing Director Rolls-Royce Electric Norway. ”Instead, we must look at different market segments. And in the market for smaller aircraft, there is a business opportunity even now.” The company is closely working with Widerøe, the largest regional airline in Norway, on developing concrete concepts to fulfil Widerøe’s goal to completely electrify its fleet by 2030.

© Dr Sigurd Øvrebø – Managing Director Rolls-Royce Electric Norway

Airbus, for its part, is in the late stages of development of the hybrid aeroplane E-Fan X, a collaboration between Airbus and Rolls-Royce. Peter Pirklbauer (see also our full interview), who is responsible for innovation at Airbus, agrees that we should look at different segments when talking about alternative propulsion. “We’re researching technologies for both alternative propulsion systems as well as energy sources – such as electric motors for unmanned aerial vehicles, hybrid propulsion systems and hydrogen for combustion or synthetic fuel use,” Pirklbauer explains.

In other words, many developments are going on behind the scenes, and they all point in one direction: hybrid engines will come.

Or will they? Some critics argue that the technology is too complex or not practical, at least as of now. But this is not how Pirklbauer sees it. “There is no single technology to address future requirements – it’s a mix and the example of Tesla shows us that we don’t need the ultimate system to get it off the ground from day one,” the innovation manager says. “All you need is an entry scenario reaching a certain mission in terms of range and payload, and suddenly the technology takes off.” Sigurd Øvrebø from Rolls-Royce agrees: “When we can prove that we can offer an aircraft with a 65% reduction of noise that is cost-effective, all of this can play out quicker than we can imagine.”

The E-Fan X is scheduled to embark on its first flight in 2021. This means we are approaching a stage where hybrid aircraft becomes a reality, at least technologically. The question, then, is: how will the market react?

© Airbus S.A.S. – At the moment, hybrid aircraft are best suited for shorter routes.

Low Noise: A Revolution in Aviation?

An essential goal in the development of hybrid technology is, of course, a significant reduction of CO2 emissions. No doubt another major selling point is the promise of more efficiency, reducing operating costs for the airlines. But these promises make it easy to overlook another potentially huge advantage of electric and hybrid propulsion: the significant reduction of noise.

Think of hybrid cars. The combustion engine only kicks in after some time, especially on longer trips. But in city traffic, specifically during acceleration, only the electric engine is working – running quietly and smoothly. So quietly, in fact, that regulators are demanding electric cars should produce artificial noise at low speeds to warn pedestrians and bicyclists of the vehicle’s approach.

It’s the same with hybrid aircraft. During take-off or landing, the system might use electric power from a battery exclusively.

“CO2 and noise reduction go hand in hand with electric and hybrid systems,” Øvrebø puts it, adding that “clearly, noise reduction is the second most important goal after the reduction of pollution.”
Granted, intercontinental flights probably won’t be possible with hybrid technology, much less purely electric planes, in the very near future. The first electric commercial route is planned to open in Norway between Bergen and Stavanger in 2023 – a very short route. Hybrid can do more, but the first step is still about small, regional aircraft and relatively short distances.

However, even regional low-noise flights might be a game-changer. “This could have a massive impact on how people travel from A to B,” Øvrebø is convinced. It’s not difficult to see how even regional flights that can take off from urban centres because they are so quiet and that are connected to hub airports could change how people use aircraft – and what airlines can offer.

© Airbus S.A.S. – The new aircraft are much quieter – will this lead to a new breed of city airports?

Unintended Consequences

It can be hard to predict how the change in aircraft engine technology will play out. Take electric shipping, for example. When Norway introduced electric cruise ships, Øvrebø recalls, he witnessed first-hand how the crew couldn’t believe how quiet electric engines are. “Electric ships could even have big implications for fishing,” he adds, emphasising that there might be many consequences of electrification that we don’t usually think of. What else might low-noise aviation change? Will there be new types of airports that can operate 24/7 and be built wherever they are needed? How will regulations have to change? What market opportunities will open up for the different players in the aviation industry?

Speaking of different players, Peter Pirklbauer from Airbus is convinced that when it comes to hybrid technology and electrification, we need more cooperation. “As the aircraft itself is only one part of the system, making it work needs empowerment from airport logistics, regulations, air traffic management and of course, energy supply,” he explains, “so we see, as usual, a strong need for cooperation.”
Hybrid technology offers too many advantages not to be taken seriously. What impact it will have on the industry remains to be seen – but it’s a question of how, not if.

What is a hybrid aircraft?

The term “hybrid” can be confusing. There are generally two different meanings:

  1. Hybrid electric powertrain: this refers to using two different propulsion systems, such as a turbine engine and an electric motor, to drive the aircraft.
  2. Serial hybrid propulsion: an electric motor is the only propulsion system. But it is powered by different types of energy sources such as batteries and a fuel-powered generator.In all cases, the idea is to combine different solutions to reduce emissions without compromising on range.

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