We recently published an article stating that some scientists and entrepreneurs favor the idea of urban air mobility (UAM) since it could have less environmental impact than our current road-going vehicles. But data and statistics can be applied in many ways, and how we see given phenomena determines how we use them, and often how popular they become.
This time it’s the University of Michigan and Ford — mild surprise regarding the latter — that tested the idea of cleaner eVTOL aircraft. Two University of Michigan students who were doing internships at Ford brought their curiosity back to the campus for the study.
eVTOL & the Environment — Good or Bad?
Will UAM and their electric vertical take-off & landing (eVTOL) aircraft have less of an environmental impact than road cars? Some think so, while others are on the fence. The answer may simply be, “it depends.”
Ultimately, the University of Michigan and Ford point out that an electric air taxi traveling less than 35 km (22 miles) wouldn’t be as environmentally sustainable as the equivalent car ride.
“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 greenhouse gas emissions than single-occupant VTOLs. That’s an important consideration because the average ground-based vehicle commute is only about 17 kilometers (11 miles).”
Gregory Keoleian, senior author of the study and director of the Center for Sustainable Systems at U-M’s School for Environment and Sustainability said:
“To me, it was very surprising to see that VTOLs were competitive with regard to energy use and greenhouse gas emissions in certain scenarios.
“VTOLs with full occupancy could outperform ground-based cars for trips from San Francisco to San Jose or from Detroit to Cleveland, for example.”
Importantly, the U-M + Ford team found that the energy use, greenhouse gas (GHG) emissions, and time savings of VTOL aircraft didn’t just beat ground-based transport in gasoline cars, but also in electric cars, for trips of 100 kilometers (62 miles), assuming a fully loaded VTOL aircraft carrying a pilot and three passengers, and assuming average vehicle occupancy of 1.54 on the ground.
“Emissions tied to the VTOL were 52 percent lower than gasoline vehicles and 6 percent lower than battery-electric vehicles.” But as a reminder, a key assumption was that the eVTOL aircraft would be fully loaded (3 passengers and a pilot) while only 1.54 people would be in the electric car.
“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.”
As far as time, eVTOL aircraft won again for the case tested. “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.”
eVTOL UAM — Are We There Yet?
We haven’t heard the end of pros and cons when it comes to eVTOL UAM, but as various designs and configurations vie for top efficiency, a new industry is being born.