Are eVTOLs sustainable?
The University of Michigan and car manufacturer Ford have released a study suggesting that eVTOL vehicles will have a greater impact on the environment than electric cars.
The study notes that, whilst eVTOLs are very efficient in cruising, the take-off and climb modes can consume substantial amounts of power that can overcome the savings in horizontal light.
The study compares well-to-wing and well-to-wheel greenhouse gas (GHG) emissions to asses the environmental impact of the aircraft. The energy use of electric vehicles in megajoules and GHG emissions in kilograms of carbon dioxide equivalents on a 100-year global warming potential basis are used to compare electric and combustion vehicles.
While this might sound complicated, according to the study, eVTOLs give off 28% more equivalent green-house gas emissions than battery-electric road vehicles (BEVs) making the same 100km journey. However, they still give off 35% lower emissions than internal-combustion road vehicles.
However, when comparing a “fully loaded [e]VTOL” (estimated at three passengers) to an average car occupancy of 1.54, VTOL GHG emissions are 52% lower than internal-combustion vehicles and 6% lower than battery-powered cars.
Overall, the study concludes that a VTOL travelling distances of less than 35km has a greater impact on the environment than an equivalent journey in a battery-powered car but outperform at longer ranges at full capacity. This makes up approximately 15% of vehicle trips.
Additionally, eVTOLs will be able to take more direct routes to destinations than cars, and with higher travel speed (approx. 150mph) their travel time to destinations will be substantially quicker than by road vehicle.
To round off the article, the paper concludes: “eVTOLs will be limited in their contribution (and role) in a sustainable mobility system. For shorter distances, energy-intensive hover dominates the flight profile, thereby preventing the eVTOL from leveraging efficient aerodynamic performance in cruise.
“[e]VTOL sustainability performance is more advantageous when competing with ground-based vehicles traveling congested routes or indirect routes with higher circuity factors.”
Additionally, passengers may be more inclined to take a VTOL due to the time savings, making it easier to fill eVTOL air-taxi flights. Ride sharing in cars will generally result in further travel time, as seen in car-hailing services such as Uber Pool – adding both the vehicle’s GHG emissions and the distance travelled.
“While ridesharing in ground-based cars, passengers often have to trade off cost for travel time. This is not expected to be the case with VTOLs, with time-saving benefits being potentially important for their adoption.”
All in all, direct comparisons between the different transport modes are neither simple nor straightforward. But that’s unlikely to slow the advance in the use of VTOLs and, perhaps, declining motor-vehicle use in developed economies. Watch this space for new developments.