BY GARETH WILLMER
As the aviation industry emerged from the impact of the COVID-19 pandemic, when the number of passengers decreased, the number of flights increased again. The industry is recovering to pre-pandemic levels of air passenger travel, with some estimates predicting more than 40% growth by 2050.
Overall, barring crises, air passenger travel is likely to double every 15 years, with the aviation sector also proving to be one of the fastest growing sources of greenhouse gas emissions (GHG ). It currently accounts for 2% of global GHG emissions, but it is estimated to triple by 2050 from 2015 levels on the current trajectory.
Given that the European Green Deal calls for climate neutrality by 2050, a green reset is called for to promote the sustainability of aviation. Follow the link to find out more about the measures the EU is promoting to reduce aviation emissions.
Aviation has become more efficient with engine improvements, but decarbonisaton calls for alternatives to today’s fossil fuel-hungry aircraft.
Hybrid-electric and full-electric propulsion systems offer one answer. Such powertrains are already gaining traction on the ground, with global sales of electric cars doubling last year to 6.6 million.
Many projects have been started to follow aviation, but they face many challenges, especially the heavy weight of the batteries. Follow the link to read more about sustainable aircraft design in Horizon Magazine.
Yet finding environmentally friendly alternatives that are simultaneously high-performance and profitable is ‘of the utmost importance’, says Fabio Russo, head of research and development at aircraft manufacturer Tecnam in Capua, Italy.
Scalability
Russo leads the H3PS (High Power High Scalability Aircraft Hybrid Powertrain) project, which explores the potential of hybrid-electric systems in so-called ‘general aviation’ (GA) aircraft.
Containing more than 400 000 civilian aircraft worldwide, this category includes private planes, business jets, helicopters and more, but not commercial planes.
As aircraft are relatively small, the H3PS initiative sees them as a first step towards the development of electric propulsion systems for wider flights.
‘We need environmental solutions today, and the H3PS project was created to prove an efficient, low-weight and scalable solution,’ said Russo.
‘Scalable means you can move this concept from a four-seater plane to an 11-seater or, eventually, more-seater plane.’
Hybrid powertrain
The project also involved Rolls-Royce and engine manufacturer Rotax. One of its goals is to fly a four-seater aircraft powered by a so-called ‘parallel hybrid powertrain’ – which combines a traditional internal combustion engine and an electric motor.
The hybrid propulsion system can provide a power ‘boost’ to the aircraft during flight phases such as take-off and climb, said Russo. With a hybrid, you can, for example, use a gasoline engine with less power than normal and fill the gap so that the plane takes off and climbs with an electric motor.
‘So you can have access to a low fuel consumption engine,’ said Russo.
This method enables a reduction in the size and weight of the machine, which allows the battery for the electric motor to be included without adding weight to the system.
Late last year, the project succeeded in taking to the skies with the Tecnam P2010 H3PS aircraft. As the first four-seater to do so using a parallel hybrid system, the H3PS highlights the achievement as ‘a major milestone in the aviation industry’s journey towards decarbonisation and R&D of alternative powertrains.’
Battery economy
However, Russo emphasized that the project is about demonstrating the feasibility of such an aircraft rather than creating a product for the market. There are some ways to make this a reality on a large scale, he said.
‘There are still many limitations in terms of economics behind the development of this type of engine and aircraft,’ said Russo.
A major limiting factor is how the batteries degrade as they cycle through recharges. This means that there will be high costs to continue to replace them on timescales that, currently, Russo estimates can be as little as a few months.
He believes that the developments are in a real drive, supported by the support from the battery manufacturing industry, to improve the battery technology, while reducing the costs of shipping and decommissioning, and improving the circular economy.
‘A local economy for battery manufacturing is important,’ said Russo. ‘This also means that CO2 is not only saved during operation, but well before and after battery use in an aircraft.’
He added that for aircraft components in general, it is necessary to focus on the entire end-to-end lifecycle and impact of the products.
Viable hybrids
Russo believes that such a hybrid aircraft could become more economically viable in the 2030s, with the potential to significantly save emissions during certain phases of flight.
A test carried out by his team showed a potential 50% reduction in carbon emissions during take-off and initial ascent, and 20% throughout the three-hour flight, which is suggested by low amount of fuel used.
‘At the end of the flight, when we measured the fuel we used, the difference was amazing,’ Russo said.
Other projects are investigating how to optimize various components for future electric flight systems to make them as light as possible, as well as safe and efficient.
Electromagnetic interference
For example, the EASIER project is designing systems to limit electromagnetic interference (EMI) between components that can affect the operation of an aircraft.
The team is also investigating thermal methods to better dissipate heat generated by electrical components. That’s all while trying to make sure the aircraft remains light, considering the size and weight of current batteries.
Dr Ignacio Castro, a senior principal engineer at Collins Aerospace, based in Cork, Ireland, is the coordinator for EASIER. He said the project looked at EMI filtering and wiring options with lower volume and weight for the aircraft’s electrical powertrains, plus ‘two-phase’ cooling systems and methods to improve the rate. of heat transfer to the outside of the plane.
He explained that there is a need to prepare now for the long-term future of power systems. ‘Any change we make to an aircraft to make it green can increase the weight of the aircraft,’ said Dr Castro.
‘ That also increases the amount of fuel consumed, so that we don’t have an airplane that is fully ready for flight. We have to make things smaller.’
Some of EASIER’s future work involves further investigation of trade-offs between methods. “The idea is that we can see how thermal systems affect EMI and vice versa, to see what the implications are,” said Dr Castro.
Trade-offs
There are all kinds of other trade-offs to understand when it comes to building electric aircraft. For example, while making things smaller reduces weight, it can also cause things to heat up faster – just like a smaller house heats up faster. ‘That’s kind of the trade-off with weight, size and efficiency, and it’s not simple,’ said Dr Castro.
He added that integrating all the individual technologies into a well-functioning overall aircraft system will be the key to future research.
“It’s about understanding what architectures look like to be as efficient as possible,” Dr Castro said.
Comparing it to construction, he emphasized that you cannot put bricks together in any way to make a building. ‘You have to put things in a way that is smart in the context of delivering power,’ he said.
Correct direction
Although there are many complex issues to be solved in electric aviation, Dr Castro believes that things are starting to move in the right direction. ‘I think we’re taking the right paths towards hybrid-electric aviation, and there’s a lot of interest and a lot of programs,’ he said. ‘That’s the first step to start reducing carbon emissions.’
Ensuring these new systems run smoothly and securely is also important. Safety is paramount and one crash is enough to generate big headlines and a lot of fear.
That means being careful with developments. ‘There is a risk that things will be good, especially if things should be more reliable for the aircraft,’ pointed out Dr Castro. ‘This is a paradigm shift in technology.’
There is also a lot of investment needed and a lot of questions to be answered in the coming decades, he said. ‘The challenge of net-zero emissions in the EU by 2050 is a big challenge, and I don’t think anyone has a definitive answer,’ said Dr Castro. ‘This is the million dollar question.’
The research in this article was funded by the EU and was originally published in horizonthe EU Research and Innovation Magazine.
