Electric Planes Are Coming: Short-Hop Regional Flights Could Be Running on Batteries in a Few Years

Q: How does hybrid aviation work to cut emissions?
Cınar: Hybrid electric aircraft are similar to hybrid electric cars in that they use a combination of batteries and aviation fuels. The problem is that no other industry has the weight limitations that we do in the aerospace industry.

That’s why we have to be very smart about how and how much we are hybridizing the propulsion system.

Using batteries as a power assist during takeoff and climb are very promising options. Taxiing to the runway using just electric power could also save a significant amount of fuel and reduce the local emissions at airports. There is a sweet spot between the added weight of the battery and how much electricity you can use to get net fuel benefits. This optimization problem is at the center of my research.

Hybrids would still burn fuel during flight, but it could be considerably less than just relying entirely on jet fuel.

I see hybridization as a mid-term option for larger jets, but a near-term solution for regional aircraft.

For 2030 to 2035, we’re focused on hybrid turboprops, typically regional aircraft with 50-80 passengers or used for freight. These hybrids could cut fuel use by about 10%.

With electric hybrids, airlines could also make more use of regional airports, reducing congestion and time larger planes spend idling on the runway.

Q: What do you expect to see in the near term from sustainable aviation?
Çınar: Shorter term we’ll see more use of sustainable aviation fuels, or SAF. With today’s engines, you can dump sustainable aviation fuel into the same fuel tank and burn it. Fuels made from corn, oilseeds, algae and other fats are already being used.

Sustainable aviation fuels can reduce an aircraft’s net carbon dioxide emissions by around 80%, but supply is limited, and using more biomass for fuel could compete with food production and lead to deforestation.

A second option is using synthetic sustainable aviation fuels, which involves capturing carbon from the air or other industrial processes and synthesizing it with hydrogen. But that’s a complex and costly process and does not have a high production scale yet.

Airlines can also optimize their operations in the short term, such as route planning to avoid flying nearly empty planes. That can also reduce emissions.

Q: Is hydrogen an option for aviation?
Çınar: Hydrogen fuel has been around a very long time, and when it’s green hydrogen – produced with water and electrolysis powered by renewable energy – it doesn’t produce carbon dioxide. It can also hold more energy per unit of mass than batteries.

There are two ways to use hydrogen in an airplane: either in place of regular jet fuel in an engine, or combined with oxygen to power hydrogen fuel cells, which then generate electricity to power the aircraft.

The problem is volume – hydrogen gas takes up a lot of space. That’s why engineers are looking at methods like keeping it very cool so it can be stored as liquid until it’s burned as a gas. It still takes up more space than jet fuel, and the storage tanks are heavy, so how to store, handle or distribute it on aircraft is still being worked out.

Airbus is doing a lot of research on hydrogen combustion using modified gas turbine engines with an A380 platform, and aiming to have mature technology by 2025. Australia’s Rex airline expects to start testing a 34-seat, hydrogen-electric airplane for short hops in the next few years.

Due to the variety of options, I see hydrogen as one of the key technologies for sustainable aviation.

Q: Will these technologies be able to meet the aviation industry’s goals for reducing emissions?
Çınar: The problem with aviation emissions isn’t their current levels – it’s the fear that their emissions will increase rapidly as demand increases. By 2050, we could see three to five times more carbon dioxide emissions from aviation than before the pandemic.

The International Civil Aviation Organization, a United Nations agency, generally defines the industry’s goals, looking at what’s feasible and how aviation can push the boundaries.

Its long-term goal is to cut net carbon dioxide emissions 50% by 2050 compared with 2005 levels. Getting there will require a mix of different technologies and optimization. I don’t know if we’re going to be able to reach it by 2050, but I believe we must do everything we can to make future aviation environmentally sustainable.

Gökçin Çınar is Assistant Professor of Aerospace Engineering, University of Michigan. This article is published courtesy of The Conversation.