Scientists believe if we’re going to combat climate change, we need to electrify all forms of transport. In fact, according to the International Civil Aviation Organization, the demand for air travel by 2050 could increase aviation sector greenhouse gases by 700 per cent compared to emissions in 2005.
As it stands, aviation is responsible for two percent of the world’s carbon emissions. While at cruising altitude, conventional aircraft release nitrogen oxides into the atmosphere, which also have a harmful effect on the environment.
Therefore, it’s critical for engineers to find a way to decarbonize aircraft.
Professor of energy and transport at University College London Andreas Schäfer said, “If you look at the opportunities for reducing aviation CO2 that have been looked at for a long time, then you’re running out of options. The potential for reducing CO2 emissions is not sufficiently strong in comparison to the growth rate of air transport.”
So what are the options? Well, some airlines are experimenting with biofuels, which are theorized to be carbon neutral. However, the cost of using biofuels is high. The other option is electrification.
Last year Norway declared they’re aiming for all domestic travel to be electric by 2040.
In March, Canadian seaplane airline Harbour Air announced they were working with an electric drivetrain manufacturer to retrofit existing aircraft with a battery-electric propulsion system. Harbour Air has a fleet of 42 seaplanes that travel 12 routes. This collaboration with magniX means they expect the first electric flight to take to the skies in 2022.
One of the biggest issues with battery-electric propulsion is the battery life. Currently, the best lithium-ion batteries have a specific energy of 250 watt-hours per kilogram. For aircraft the size of a Boeing 737 or Airbus A320 to travel up to 1100 kilometers, the battery would need a specific energy of 800 watt-hours per kilogram. In comparison, jet fuel has a specific energy of 11,890 watt-hours per kilogram.
One of the reasons Harbour Air is confident they can pull this off is because all of their flights are less than 30 minutes in duration, which means the battery-life limitations aren’t a concern. In fact, the company will significantly cut their costs by making the switch. A regular motor costs between US $300 and $450 per operating hour. The electric motor will cost only US $12.
However, Schäfer estimated that long haul flights won’t be electrified until the middle of the century, given that battery energy densities have been increasing by three to four percent each year.
“It is certainly a long way, but because the time scales of aviation are so long, [airliners] tend to live for 20 to 30 years, we need to start looking at these technologies now so they’re available in 2050,” he said.
Schäfer also said that while hybrid-electric aircraft are a potential stepping stone to fully electric aircraft, they still produce greenhouse gases and rely on cheap, yet powerful batteries.
NASA is building the X-57 Maxwell, the first all-electric X-plane. It features a slightly different design to most propeller-driven planes.
Principle investigator for the X-57 at NASA explains Sean Clarke, “For this scale aircraft, one of the driving design considerations is the landing and takeoff performance. Our wing has the cruise propellers at the wingtip, and that reduces the drag of the wingtip. We also have 12 small propellers that are distributed across the leading edge of the wing. That increases the lift at low speed.”
Since take-off and climbing to cruising altitude require a lot of energy and lift, conventional aircraft feature a large wingspan. However, that extra surface area adds drag and makes cruising less efficient. Electric motors are much cheaper and are less mechanically complicated since they don’t require fuel lines, valves and exhaust systems.
The 12 small propellers are switched on allowing the wing to be much smaller than it is on a conventional aircraft. This saves energy during the flight, by reducing drag.
Clarke said electric aircraft could change airline business operations, as the electric motors can allow for almost vertical takeoff and landing, rendering long runways unnecessary.
“There’s a lot of urban air mobility targets where different air framers and operators are advertising a future where you can take an air taxi from somewhere in a metropolitan area to somewhere 10 miles away and fly over all the rush hour traffic,” he said.
“It is really exciting because it’s starting to grow pretty quickly around the technologies that we’re already working with.”