A Jetsons future? Assessing the role of flying cars in sustainable mobility

A Jetsons future? Assessing the role of flying cars in sustainable mobility
Artistic rendering of an electric vertical takeoff and landing taxi cruising through an urban center. Credit: Dave Brenner/University of Michigan School for Environment and Sustainability

In the 1960s animated sitcom The Jetsons, George Jetson commutes to work in his family-size flying car, which miraculously transforms into a briefcase at the end of the trip.

A new study of the environmental sustainability impacts of flying cars, formally known as electric vertical takeoff and landing aircraft, or VTOLs, finds that they wouldn't be suitable for a Jetsons-style short commute.

However, VTOLs—which combine the convenience of vertical takeoff and landing like a helicopter with the efficient aerodynamic flight of an airplane—could play a niche role in sustainable mobility for longer trips, according to the study, scheduled for publication April 9 in Nature Communications. Several companies around the world are developing VTOL prototypes.

Flying cars would be especially valuable in congested cities, or in places where there are geographical constraints, as part of a ride-share taxi service, according to study authors from the University of Michigan's Center for Sustainable Systems and from Ford Motor Co.

"To me, it was very surprising to see that VTOLs were competitive with regard to and greenhouse gas emissions in certain scenarios," said Gregory Keoleian, senior author of the study and director of the Center for Sustainable Systems at U-M'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," he said.

The U-M-Ford study, the first comprehensive sustainability assessment of VTOLs, looked at the energy use, greenhouse gas emissions and time savings of VTOLs compared to ground-based passenger cars. Although VTOLs produce zero emissions during flight, their batteries require electricity generated at power plants.

The researchers found that for trips of 100 kilometers (62 miles), a fully loaded VTOL carrying a pilot and three passengers had lower greenhouse gas emissions than ground-based cars with an average vehicle occupancy of 1.54. Emissions tied to the VTOL were 52 percent lower than gasoline vehicles and 6 percent lower than battery-electric vehicles.

Akshat Kasliwal, first author of the study and a graduate student at the U-M School for Environment and Sustainability, said the findings can help guide the sustainable deployment of an emerging mobility system prior to its commercialization.

"With these VTOLs, there is an opportunity to mutually align the sustainability and business cases," Kasliwal said. "Not only is high passenger occupancy better for emissions, it also favors the economics of flying cars. Further, consumers could be incentivized to share trips, given the significant time savings from flying versus driving."

In the coming decades, the global transportation sector faces the challenge of meeting the growing demand for convenient passenger mobility while reducing congestion, improving safety and mitigating climate change.

Electric vehicles and automated driving may contribute to some of those goals but are limited by congestion on existing roadways. VTOLs could potentially overcome some of those limitations by enabling piloted taxi services or other urban and regional aerial travel services.

Several aerospace corporations and startup companies—Airbus, Boeing, Joby Aviation and Lilium, for example—and agencies such as NASA have developed VTOL prototypes. One critical efficiency enabler for these aircraft is distributed electric propulsion, or DEP, which involves the use of several small, electrically driven propulsors.

The U-M and Ford researchers used publicly available information from these sources and others to create a physics-based model that computes energy use and greenhouse gas emissions for electric VTOLs.

"Our model represents general trends in the VTOL space and uses parameters from multiple studies and aircraft designs to specify weight, lift-to-drag ratio and battery-specific energy," said Noah Furbush, study co-author and a master's student at the U-M College of Engineering.

"In addition, we conducted sensitivity analyses to explore the bounds of these parameters, alongside other factors such as grid carbon intensity and wind speed," said Furbush, who is also a member of the U-M football team.

The study began while Kasliwal and Furbush were summer interns at Ford. The work continued when the students returned to Ann Arbor, with the help of a Ford-University of Michigan Alliance grant.

The researchers analyzed primary energy use and greenhouse gas emissions during the five phases of VTOL flight: takeoff hover, climb, cruise, descent and landing hover. These aircraft use a lot of energy during takeoff and climb but are relatively efficient during cruise phase, traveling at 150 mph. As a result, VTOLs are most energy efficient on long trips, when the cruise phase dominates the total flight miles.

But for shorter trips—anything less than 35 kilometers (22 miles)—single-occupant internal-combustion-engine vehicles used less energy and produced fewer than single-occupant VTOLs. That's an important consideration because the average ground-based vehicle commute is only about 17 kilometers (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 traveled on the ground," said study co-author Jim Gawron, a graduate student at the U-M 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."

Not surprisingly, the VTOL completed the base-case trip of 100 kilometers much faster than ground-based vehicles. A point-to-point VTOL flight path, coupled with higher speeds, resulted in time savings of about 80 percent relative to ground-based vehicles.

"Electrification of aircraft, in general, is expected to fundamentally change the aerospace industry in the near future," Furbush said.

The study's authors note that many other questions need to be addressed to assess the viability of VTOLs, including cost, noise and societal and consumer acceptance.

Explore further

Why aren't there electric airplanes yet?

More information: "Role of flying cars in sustainable mobility" Nature Communications (2019). DOI: 10.1038/s41467-019-09426-0 , https://www.nature.com/articles/s41467-019-09426-0
Journal information: Nature Communications

Citation: A Jetsons future? Assessing the role of flying cars in sustainable mobility (2019, April 9) retrieved 21 October 2019 from https://techxplore.com/news/2019-04-jetsons-future-role-cars-sustainable.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Apr 09, 2019
"To me, it was very surprising to see that VTOLs were competitive with regard to energy use and greenhouse gas emissions in certain scenarios,"

Sure. To a limited extent. But if we're looking at a "Jetson's" scenario I wouldn't vouch for noise pollution levels being anything but deafening.

Think of the occasional helicopter in a city sky. You can often (faintly) hear it. Now scale this down to a one seater octacopter and then scale it back up a hundred (a thousand? ten thousand?) times to make an appreciable dent in traffic.

For comparison: 270000 cars cross the bay bridge in San Francisco every day. That's only one of four major bridges.

Apr 09, 2019
what gets really annoying about the energetic analysis of transport is that time and again people forget that the transport works in conjunction with the static set of 3d locations to which people would fly it to. you cannot assess a transport system independently of the set of locations and the time and frequency dynamics of necessary and discretionary trips that people would make. IT'S A NETWORK PEOPLE!!!!

Apr 09, 2019
Aesthetically, flying cars and the like will be a disaster. Night sky turned into a freeway. Noise raining down from above, unless someone finds a way to make quiet propellers.

Accidents will often be lethal to people who were no where near a street. Debris from a collision will crash through the roofs of unsuspecting individuals. I'd like a personal VTOL/flying car for myself, but it just does not scale.

Apr 09, 2019
Were they comparing these with best-available vehicles, such as EVs or even just 54 MPG Priuses? If they're looking at the average 25 MPG it isn't meaningful because that level of efficiency is already technologically obsolete.

Apr 09, 2019
Accidents will often be lethal to people who were no where near a street.

While I agree with the rest of your comments accidents is the one thing I wouldn't worry about because these things will be fully autonomous.
There's no way anyone will be allowed to fly these by hand and on any route they want to if there's any appreciable number of them in the sky.

Safe autonomy (or safe guided pathing from a central traffic control which you log into) in 3D space - with VTOL to boot - is incredibly easy.

Apr 10, 2019
accidents is the one thing I wouldn't worry about because these things will be fully autonomous.

I would worry about it even more in that case. Without pilots to take over from the automation, you can down tens of thousands of these vehicles with one electrical or software fault in the system, or just because your AI couldn't handle an edge case.

Safe autonomy (or safe guided pathing from a central traffic control which you log into) in 3D space - with VTOL to boot - is incredibly easy.

If you know absolutely nothing about the subject.

Airplanes run with such "safe autonomy" already, leaving kilometers of space between the corridors, and still they manage to crash into each other occasionally.

Apr 10, 2019
Though of course, when the automation has run the airplane into a corner where it can't back out,the resulting crash is always put down or at least partially blamed as "human error" and the people are blamed for issues largely caused by automation that is too dumb for the task.

That comes naturally, because the airplane manufacturers can't admit that their systems are fundamentally unsafe and simply waiting for the accident to happen; the bugs are fixed in silence and the rest is PR. The public gets the illusion that the computers can't err and Artificial Intelligence is already here.

Apr 12, 2019
Leaving aside the other questionable assumptions mentioned above the study compares apples to oranges: full occupancy VTOLs vs 1.54 person occupancy ICE vehicles. Assuming that humans will change their occupancy behavior for VTOLs is just silly. Since the VTOLs require a pilot that means 3 person VTOL occupancy at 48% of the emissions. Adjusting for occupancy to get apples to apples results in only a 4% difference in emissions - in essence a push.

Also, no city government is their right mind is going to allow hundreds of thousands of VTOLs (minimum required to make a dent in surface traffic), in their airspace. Surface vehicle failures can pull off to the roadside - VTOL vehicles will come crashing down. And with thousands of VTOLs there WILL be failures - not just in flight collisions.

Apr 12, 2019
Most of these comments are very cogent. As a private pilot, I shudder at the thought of remotely piloted electric vehicles (RPeVs) crowding the sky so that I cannot take off or land at a local airport, much less, travel on a 400 mile trip in congested skies.

But wait, you say, who said anything about remote pilots? I suggest this is the only way to use these contraptions because the weight of the pilot is a lost passenger, and that costs profit. Self driving machines. Boeing 737 MAX 8.

RPeV might make these things economically workable, but one next needs to know where the commute points are. Regular airports are already congested. Helipads? These mostly belong to hospitals and the police. Rooftops? Very windy up there, dangerous. Parking lots? Full of cars already, and will stay that way because these are not scale-able transport systems. (Did you eve notice that the take-off and landing zones are either airports or mock-up computer graphics of places that do not exist?)

Apr 16, 2019
Adjusting for occupancy to get apples to apples results in only a 4% difference in emissions - in essence a push

Most single-occupancy commutes are local. Longer trips are taken more often with company, or with cargo on-board such as deliveries.

Since these vehicles have to be operated point-to-point to avoid local noise issues and endangering the public by crashing over residential zones, they are likely to be used like inter-city busses rather than private single occupancy vehicles.

The reason why they will be operated like busses is because of the last mile problem: once you get there, you still have to drive to your destination, because you can't just land on someone's driveway. The riders need to catch a bus or taxi after they land, so they have to land near a public transportation hub.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more