The future of human flight arrived quietly, at a time when no one was clocking up air miles. It was June 2020 and the skies were unusually empty as the world reeled at the speed of the COVID-19 outbreak. But down on the ground, something pretty huge was happening with a very small aircraft.
EASA, the European Union Aviation Safety Agency, certified a two-seater plane made in Slovenia as safe to fly. Within a few years it was certified by equivalent bodies in the UK, the US and elsewhere. The Pipistrel Velis Electro became the first fully certified electric aircraft in the world. It’s still the only one.
“The achievement represents a growing interest and trust in the reliability of electric aircraft,” says Dr Tine Tomažič, director of engineering and programmes at Pipistrel. “We recently completed production of our 100th Velis Electro, marking a significant milestone for Pipistrel and the industry.”
The future is already here, says Tomažič, but to borrow a line from sci-fi author William Gibson, it’s far from evenly distributed. Despite a growing number of cleaner aircraft in development, there remains big questions about the alternative fuels required to fly them, and more still about the political will to make it all happen.
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After several abandoned take-offs, is this the moment that air travel finally goes green? Or is zero-carbon flight still the stuff of blue-sky thinking?
Climate impact
“Right now, aviation isn’t a major contributor to climate change,” says Dr Guy Gratton, somewhat unexpectedly. Gratton is associate professor of aviation and the environment at Cranfield University in the UK. An aeronautical engineer by trade, he’s also a test pilot who flies experimental electric aircraft – in other words, he knows what he’s talking about.
“Aviation is generating around two and a half per cent of global carbon, which is small, particularly when you consider its importance to the global economy,” Gratton says. “There is science which is suggesting that the contribution through contrails may be rather worse than that, so it’s perhaps up to around seven per cent.”
The industry is improving its emissions by roughly two per cent per passenger mile per year, Gratton says. But it’s also growing by five per cent a year.
The global demand for air transport is estimated to double by 2040, which means that while other industries are showing meaningful signs of decarbonising in the face of the climate crisis, aviation is on track to increase its total emissions and, in the process, become one of the world’s worst polluters.
“In order for us to continue to keep the massive social and economic benefits aviation brings the world, we need to fix that and stop aviation from becoming a majority polluter in the future,” Gratton says. “Now, how can we do that?”
Small steps
The Velis Electro is leading the way, but the first electric planes aren’t designed to replace large passenger aircraft. The majority don’t have the range to cross the English Channel, never mind the Atlantic. Instead, these pioneer aircraft are built for short flights.
The Velis Electro is designed specifically for flight training, offering 50 minutes of flight time with 20 minutes reserve and a range of 100 nautical miles (185km). It’s powered by a 58kW electric motor with two lightweight lithium batteries, which are game-changers.
The problem with traditional batteries is that they’re either too heavy or too hot (or both) to be safe or practical for an aircraft. Pipistrel’s system, however, makes the whole powertrain safe, light and efficient.
“The powertrain is entirely liquid-cooled,” says Tomažič. “It has demonstrated levels of safety equivalent to, or higher than, conventionally powered aircraft.” The battery weighs 70kg (154lbs) and the whole aircraft weighs just 425kg (936lbs) when empty. But if the underlying technology is revolutionary, the cockpit is familiar and the controls are similar to conventional aircraft of the same size.
Pilots don’t need an additional license to fly the Electro, but they will notice some differences, Tomažič says. For starters, there’s no engine warm-up and much less noise.
“The aircraft delivers power instantly and without hesitation,” he says. “It uses a simplified user interface in a cockpit that maintains the same look and feel of its conventionally powered siblings. The cockpit is also much quieter than with conventional aircraft, which spurs better communication possibilities.”
Pipistrel’s future plans include a four-seater Electro with a range of 200 miles (370km) and it’s also working with the EU on a project called the Unifier 19. “It’s an EU initiative to develop a community-friendly, low noise and carbon emissions ‘mini liner’ to connect remote areas within Europe,” says Tomažič.
The Velis Electro will soon be joined in the sky by other electric aircraft. The Alice, from Israeli company Eviation, is a nine-seater ‘commuter’ plane that took its first prototype test flight in 2022.
Meanwhile, the E9X concept aircraft from Dutch start-up Elysian Aircraft is scheduled to fly in 2033. With batteries integrated into the plane’s wings, it’s hoped to carry 90 passengers some 430 miles (800km).
And Wright Electric (yes, named after the Wright Brothers) is a US start-up developing an electric 180-seater airliner in partnership with EasyJet.
As someone who tests electric aircraft, Gratton is cautious about hailing battery-powered planes as the answer. They may cut the carbon emissions of celebrities jetting from penthouse to music festival.
They’ll also cover short-haul routes between cities, such as London to Edinburgh or Jeju to Seoul in South Korea – the busiest domestic flight route in the world. But short-haul flights account for less than 20 per cent of aviation’s overall carbon emissions.
If battery technology doesn’t scale up to cover medium- and long-haul flights, then battery-powered aircraft will fix a pretty small part of a big and growing problem.
“They’re probably a necessary step on the route to other solutions,” Gratton says. “But they’re not going to solve it for the simple reason that the batteries we have aren’t good enough and they’re not projected to be good enough.”
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An alternative
Another option is hydrogen fuel, which can work in a couple of ways. Hydrogen could be burned in a turbine engine to produce thrust, or hydrogen fuel cells could generate electricity to power an electric motor.
It’s widely considered one of the best options available to decarbonise aviation. The only in-flight emission is water and projections suggest hydrogen planes will account for a third of the industry’s energy demands by the middle of the century.
Some of aviation’s biggest players are heavily invested in the technology. Airbus intends to bring its hydrogen-powered ZEROe airliner concept to market by 2035. It’s also investing in smaller companies like ZeroAvia, based in the Cotswolds.
In 2023, ZeroAvia demonstrated the maiden flight of a 19-seater Dornier 228 that it retrofitted with a prototype hydrogen-electric powertrain. It only flew for 10 minutes, but it’s the biggest plane to have ever flown on hydrogen power.
After the test flight, the company’s CEO Val Miftakhov said, “This is a major moment, not just for ZeroAvia, but for the aviation industry as a whole, as it shows that true zero-emission commercial flight is only a few years away.”
No less ambitious is Sirius Jet by Sirius Aviation. The Swiss-based company is developing a hydrogen electric vertical take-off and landing (eVTOL) business jet that can carry three people. It features 28 ducted jet fans that stretch across the plane’s wings, each powered by an electric motor and tilting to switch between regular and vertical flight.
Sirius Aviation’s CEO Alexey Popov says the aircraft will have a range of over 1,000 miles (1,800km), travelling at 323mph (almost 520km/h), but it’s the efficiency of the hydrogen fuel stack that he’s most proud of. “In a traditional jet aircraft, you see efficiency of around 30 per cent. In our fuel cell stack, it’s 50 per cent,” he says.
One problem, multiple solutions
Gratton agrees that hydrogen likely has a significant role to play in decarbonising flight, but that’s not to say it’s going to be an easy switch. “Hydrogen looks really good weight-wise,” he says.
“It’s pretty equivalent to kerosene, which is what we run jet aircraft on now. But volume-wise, it takes up a lot more space. If we’re going to go down the hydrogen route, then we would basically need new aircraft. You would need to be designing new airliners, new engines, new fuel systems, new ways of distributing fuel to airports.”
And that’s true of any solution. In 2023, Gratton contributed to a sobering report by the Royal Society on the future of green air travel and what would be required to hit the UK’s net zero targets. It found that “there is no single, clear, sustainable alternative to jet fuel able to support flying on a scale equivalent to present-day use.”
Assessing costs, available resources and other factors, it laid out the scale of the challenge.
Let’s say the world opted for biofuels as the preferred alternative to jet fuel. This is preferable to some because it requires the least amount of adaptation from existing infrastructure and propulsion technology. But just meeting existing aviation demand would require around half of all the UK’s agricultural land to grow the crops.
Likewise, to produce enough clean hydrogen fuel, the Royal Society report says we’d have to find somewhere between 2.4 to 3.4 times the amount of renewable electricity generated in the UK by wind and solar in 2020.
So, what’s the answer? Well, all of it, Gratton says. He believes we should be pursuing all forms of alternative fuel because it’s likely we’ll need a mix. That includes so-called electrofuels, a synthetic type of fuel created from captured carbon dioxide and carbon monoxide.
So far, this solution only exists in tiny quantities at the laboratory scale, which is why Gratton thinks we should still be building experimental aircraft and different kinds of fuel cells. “It may well be that once they’re mature, these solutions will scale up to bigger aircraft. So doing it is worthwhile.” The age of zero emissions flight has arrived, but making it the norm is still a long-haul challenge.
Test-flying alternative fuels
How do we fuel the flight to net zero aircraft?
Biofuels - Derived from crops and other biomass, biofuels can be mixed with existing jet fuels, but at best will only offer a 40 per cent saving on emissions, says Dr Guy Gratton, and there are related concerns over the land and deforestation required to produce them.
Electrofuels - Made by scrubbing CO2 and carbon monoxide from the atmosphere and combining it with hydrogen. A promising solution, but still at an experimental stage and, if scaled up, would require a lot of renewable electricity for true net zero production
Electric fuel cells - Already in use on some (mostly prototype) aircraft, these batteries are comparable to those used for electric cars. While they don’t produce emissions in flight, creating the technology is power-intensive and the batteries themselves need to be replaced.
Hydrogen fuel cells - Heralded by some as the best medium-term option we have for decarbonising aviation, hydrogen fuel cells could be scaled up to work with larger aircraft. Those aircraft and the infrastructure supporting them would need to be radically redesigned around the new fuel, however.
About our experts
Dr Tine Tomažič is the director of engineering and programmes at Pipistrel and award-winning expert in electric flight. His work has been published by Journal of Aircraft.
Dr Guy Gratton is associate professor of aviation and the environment at Cranfield University in the UK and an aeronautical engineer by trade. He’s also a test pilot who flies experimental electric aircraft. His work has been published in Quarterly Journal of the Royal Meteorological Society, Climatic Change, and The Aeronautical Journal.
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