These prototypes are electric and don’t give off any planet-warming greenhouse gases during flight, but mining and producing the electricity to charge their batteries is still an environmental cost. But the flying air taxis of the near future, which can both hover like helicopters and glide like airplanes, might be more energy efficient than you’d think—provided you carpool and only use them for long-distance travel.
That’s according to scientists at the University of Michigan, who recently considered the energy costs of these vehicles compared to ground-based cars.
“I was surprised by how competitive [the flying cars] were in these scenarios that we explored because of the energy intensity to lift the vehicle,” says Gregory Keoleian, an author of the study and director of the university’s Center for Sustainable Systems. Flying cars rely on distributed electric propulsion, which is basically a series of small propellers along the vehicle’s wings. With this system, they can avoid runways and move about much like a drone, with vertical take-off and landing.
To understand what energy these flying vehicles would require, the scientists used available data from other scientific and industry reports. The model vehicle they considered had one pilot and four passenger seats, flew at an altitude of 1,000 feet, and could zoom around at up to 150 miles per hour. They compared this example to two cars: one, gasoline-powered, driving 34.1 miles per gallon, and another, electric-powered, which drove the equivalent of 108.5 miles per gallon based on its energy use. The scientists compared efficiency between the three vehicles at distances from three to 155 miles.
For short trips of less than 22 miles, both gasoline and electric cars beat out the airborne vehicles in efficiency, according to the study, published Tuesday in Nature Communications. Short trips make up most of Americans’ driving—the average commute distance is 11 miles. Over short distances, air taxis would mostly hover, using up a lot of energy in the process.
But over long distances, air taxi efficiency improved. For a 62-mile, nonstop trip, air taxi use led to 35 percent fewer greenhouse gas emissions compared to the gas-burning car. But compared to an electric car travelling the same distance, the air taxi had 28 percent more emissions. This scenario ignores passengers, however. If you load up the air taxi with four people and compare it to the other cars with average occupancy—1.54 people—it looks even greener. On the basis of emissions produced per passenger across these 62 miles, the full-capacity air taxi has 52 percent fewer emissions per trip than the gas car, and 6 percent less than the electric car.