The future contains flying taxis


Modelling finds airborne vehicles are economic for long journeys and multiple passengers. Neil Dowling reports.


VTOL vehicles work best on a for-hire multi-passenger basis, modelling finds.

cenkerdem/Getty Images

Flying cars have the potential to replace many road journeys after independent research in the US today found they could be more economical, have lower emissions and be more efficient over long distances.

The research, by Gregory Keoleian of the US University of Michigan’s centre for sustainable systems, and colleagues, was based on modelling vertical take-off and landing (VTOL) craft that need minimal ground area for operation and can be placed close to cargo points.

The results are published in the journal Nature Communications.

The paper shows the theoretical ability of an electrically-powered VTOL craft to confirm century-old dreams of beating road traffic and, in many cases, doing it more safely, more economically, and all while producing fewer greenhouse-gas emissions.

“In principle, VTOLs can travel the shortest distance between two points, and their relatively modest sizes would enable near point-to-point service,” the researchers write.

“Conversely, road networks are much less direct and consequently have an associated circuity factor, defined as the ratio of the shortest network route to the Euclidian distance between two points.

“This benefit of VTOL aerial systems could favour energy and travel-time performance, particularly in locations with congested and circuitous routing.

“High VTOL cruise speeds could reduce travel time further. Significant time savings and associated productivity gains could be a key factor in consumer adoption of VTOL transportation.”

But the main factor chased by commuters – at least since George Jetson first went airborne in his cartoon world of 1962 – is saving time.

The researchers found that a point-to-point VTOL flight path resulted in a 100 kilometre trip time of about 27 minutes, with a cruise speed of 241 kilometres per hour.

“For a highly congested commute of a similar distance, approximately the span of a major city, time savings of point-to-point travel can be significant,” Keoleian and colleagues note.

Indeed, the modelling showed that on average 100 kilometre trips by VTOL took 83% less time than equivalent car journeys. The time-saving, the researchers suggest, could act as a catalyst for consumer adoption.

“From the viewpoint of energy use and hence greenhouse-gas emissions, it appears that VTOLs could have a niche role in sustainable mobility, particularly in regions with circuitous routes and/or high congestion,” they write.

Despite numerous stalled attempts to bring a flying car to the market, none have volume production.

Historically, only a handful of examples of the 1950s Taylor Aerocar and Waterman Aerobile were made, though Chinese company Geely is currently ramping up development of its Terrafugia car-plane.

Though optimistic on the future of a limited role for flying cars, the researchers caution that there are further issues that need investigation, including safety, cost, noise, consumer and community acceptance, and legal, insurance and operator concerns.

The modelling completed by Keoleian and his team found that for trips of less than 35 kilometres – the majority of road journeys – VTOLs would use more energy and produce more emissions than cars.

However, comparing VTOLs with battery-electric vehicles (BEVs) and conventional internal-combustion engine vehicles (ICEVs), the research found that over a 100 kilometre journey, VTOLs produce 30% fewer emissions than ICEVs but 40% more than BEVs.

But VTOLs become more efficient when carrying four occupants – operating, perhaps, as an aerial taxi. Using a passenger-kilometre metric, the research found that VTOLs had 52% lower emissions per passenger than ICEVs and 6% loweerr than BEVs.

“Service providers would target near-full occupancy from a utilisation-maximisation standpoint, similar to current commercial airlines,” the researchers write.

“Passengers could be incentivised to share VTOL rides given the significant expected time savings from flying. Thus, it seems likely that the average occupancy of VTOLs will be greater than conventional passenger cars.”

The research found that VTOLs escaped much of the traffic congestion of ground-bound vehicles, but had their own issues, including the impacts of wind, that could affect emission levels.

“Weather remains an important consideration that can affect VTOL energy use for a given trip,” the authors write.

“We estimate a 16% reduction in base-case emissions with a favourable 30-knot (56 kilometres per hour) tailwind. Conversely, a 30-knot headwind increases these emissions by nearly 26%.”

Keoleian and team found that electric VTOLs had several benefits, but would only ever make up a small fraction of total annual vehicle-miles compared to those traveled by ground-based vehicles.

“Subsequently,” the researchers conclude, “VTOLs will be limited in their contribution (and role) in a sustainable mobility system.”

  1. https://www.nature.com/articles/s41467-019-09426-0
  2. https://www.eaa.org/en/eaa-museum/museum-collection/aircraft-collection-folder/1949-taylor-aerocar---n4994p
  3. https://cosmosmagazine.com/technology/a-bird-a-plane-car-actually
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