How sustainable are electric air taxis?

Air taxis only bring environmental benefits for flights over 35 kilometers

Can electric plane taxis make transport more environmentally friendly? Researchers have now determined that. © Dave Brenner / University of Michigan
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Limited niche: Electric air taxi taxis could make traffic more environmentally friendly - but only under very specific conditions, as a comparative study reveals. Because when it comes to energy requirements and CO2 emissions, electric vehicles only fare better than normal cars for distances of at least 35 kilometers. However, if the air taxis carry at least three passengers, they could even be more sustainable than electric cars on 100-kilometer routes.

They are regarded as the traffic trend of the future: electrically operated air taxis and manned drones could soon relieve traffic in our cities. Already, companies have developed prototypes of multicopters or vertical starters, which are supposed to transport passengers from airports to city centers as air taxis, for example. The big advantage: Such air taxis generate no traffic jams and reduce the pollution of the city air.

Vertical starters as shuttles and air taxis

But how environmentally friendly are such taxis really? That's exactly what Akshat Kasliwal from the University of Michigan and his colleagues have investigated. For their study, they compared the energy and carbon footprint of a typical whiz-star flight taxi with electric cars and classic automobiles. Vertical starters have rotatable rotors that allow them to take off and land like a helicopter. In cruising, however, they fly like a winged airplane - and are therefore more efficient than pure multicopters.

"Several companies are already developing such aircraft for four to five passengers, " explain the researchers. The aircraft manufacturer Boeing has just completed its maiden flight with its passenger aircraft (PAV). Already in early 2018, the electric whiz Vahana of Airbus had its maiden flight. Both have a range of 80 to 100 kilometers.

While electric vehicles such as these taxicabs do not emit emissions while on the move, they do produce when charging their batteries when parts of the electricity are generated from fossil fuels. For their study, the researchers assumed the US power mix, which is based on more than 60 percent coal and natural gas. display

Vertical Star air taxi in comparison test. University of Michigan

On the track it depends

The comparison showed that whether an electric taxi is more sustainable than a car or electric car, depends heavily on the route and the number of passengers traveling. Because the whiz-starter consumes the most energy during take-off and landing, its energy efficiency increases with increasing flight distance. For example, the flight taxi on short distances of five kilometers generates 0.59 kilograms of CO2 equivalent per kilometer flown, at 100 kilometers it is only 0.15.

These figures show: "At distances of up to 35 kilometers, cars with combustion engines perform better than electric taxis, " the researchers report. But for longer distances, the air taxi is ahead: "For our base distance of 100 kilometers, the air taxi has 35 percent lower greenhouse gas emissions than the car, " said Kasliwal and his team.

However: with the electric car, neither of the two means of transport came along: this was another 28 percent lower than the whiz.

From three passengers, the air taxi is in front

But how does it look if you include the number of passengers? "It is likely that the passenger utilization of electric whiz-starters will be higher than the conventional passenger cars, " say the researchers. After all, such air taxis are economically rewarding for operators, especially if as many paying passengers as possible are flying along. In the car, on the other hand, 1.54 people per vehicle are the guideline.

Passenger-related CO2 emissions for Air Taxi, Combustion Car (ICEV) and Electric Car (BEV) Kasliwal et al./ Nature Communications, CC-by-sa 4.0

The result of the passenger-related comparison for 100 kilometers of flight route: "For two or more passengers, the electric whiz-starter in front of the car with internal combustion engine, " report Kasliwal and his team. "With three passengers, the air taxi is also in front of the electric car." Specifically, in this case, the CO2 emissions generated are 52 percent below the normal car and six percent below the electric car.

Only a small niche

"It was very surprising to me that the whiz-starters were quite competitive in terms of energy and greenhouse gases - at least in certain scenarios, " says Kasliwals colleague Gregory Keoleian. Thus, the electric air taxis would be rather unsustainable when used in inner cities, depending on the energy mix in the power grid, but on flights between the city and the surrounding area or between two neighboring cities.

According to the researchers, air taxis could well play a positive role in the traffic revolution - but only in very specific niches. "The routes on which air taxis are more sustainable than cars with internal combustion engines account for only a small proportion of vehicle kilometers driven per year, " says co-author Jim Gawron of the University of Michigan. "Therefore, taxis of this type will only play a limited role in sustainable mobility." (Nature Communications, 2019; doi: 10.1038 / s41467-019-09426-0)

Source: University of Michigan

- Nadja Podbregar