Engineering news
However, the research into the environmental effect of VTOLs (vertical take-off and landing aircraft) by the University of Michigan and Ford suggested that they could have a role to play for longer trips, particularly between congested urban areas or areas with geographical constraints.
"To me, it was very surprising to see that VTOLs were competitive with regard to energy use and greenhouse gas emissions in certain scenarios," said Gregory Keoleian, senior author of the study and director of the Center for Sustainable Systems at the university's School for Environment and Sustainability. “VTOLs with full occupancy could outperform ground-based cars for trips from San Francisco to San Jose or from Detroit to Cleveland, for example.”
The study looked at the energy use, greenhouse emissions and time savings of VTOLs compared to ground-based passenger cars. Researchers found that for trips of 62 miles, a fully loaded VTOL with a pilot and three passengers had lower emissions than ground-based cars with an average occupancy of 1.54. The journeys were also 80% quicker.
“With these VTOLs, there is an opportunity to mutually align the sustainability and business cases," said Akshat Kasliwal, first author of the study. "Not only is high passenger occupancy better for emissions, it also favours the economics of flying cars. Further, consumers could be incentivised to share trips, given the significant time savings from flying versus driving.”
However, for journeys shorter than 22 miles, single-occupant vehicles with an internal combustion engine used less energy and produced fewer emissions than single-occupant VTOLs. The average ground-based commute is currently only 11 miles.
"As a result, the trips where VTOLs are more sustainable than gasoline cars only make up a small fraction of total annual vehicle-miles travelled on the ground," said study co-author Jim Gawron, a graduate student at the University of Michigan's School for Environment and Sustainability and the Ross School of Business. "Consequently, VTOLs will be limited in their contribution and role in a sustainable mobility system."
Obviously, given the close connection with Ford, the results of the study should be taken with a pinch of salt. Although a number of companies, including Airbus, Boeing and Lilium, are developing VTOL concepts, there are serious doubts over their energy efficiency and regulation.
Steve Wright, an aerospace expert at the University of the West of England, has pointed out that the safety hurdles required to have cars flying over densely populated areas could prove insurmountable. Energy density is another issue – batteries currently aren’t good enough to lift vehicles into the air for more than about 30 minutes.
The research was published in the journal Nature Communications.