From electric trucks to flying vehicles

We based our research on a very accurate description of the energy required to move the vehicle along with details of the underlying chemical processes involved in Li-ion batteries. We found that an electric semi-truck similar to today’s diesel-powered ones could be designed to travel up to 500 miles on a single charge while being able to carry the cargo of about 93 percent of all freight trips.

Batteries will need to get cheaper before it makes economic sense to begin the process of converting the U.S. trucking fleet to electric power. That seems likely to happen by the early 2020s.

Flying vehicles are a bit further away, because they have different power needs, especially during taking off and landing.

What is an e-VTOL?

Unlike passenger planes, small battery-powered drones that carry personal packages over short distances, while flying below 400 feet, are already coming into use. But carrying people and luggage requires 10 times as much energy – or more.

We looked at how much energy a small battery-powered aircraft capable of vertical takeoff and landing would need. These are typically designed to launch straight up like helicopters, shift to a more efficient airplane mode by rotating their propellers or entire wings during flight, then transition back to helicopter mode for landing. They could be an efficient and economic way to navigate busy urban areas, avoiding clogged roads.

Energy requirements of e-VTOL aircraft

Our research group has built a computer model that calculates the power needed for a single-passenger e-VTOL along the lines of designs that are already under development. One such example is an e-VTOL that weighs 1,000 kilograms, including the passenger.

The longest part of the trip, cruising in airplane mode, needs the least energy per mile. Our sample e-VTOL would need about 400 to 500 watt-hours per mile, around the same amount of energy an electric pickup truck would need – and about twice the energy consumption of an electric passenger sedan.

However, takeoff and landing require much more power. Regardless of how far an e-VTOL travels, our analysis predicts takeoff and landing combined will require between 8,000 and 10,000 watt-hours per trip. This is about half the energy available in most compact electric cars, like a Nissan Leaf.

For an entire flight, with the best batteries available today, we calculated that a single-passenger e-VTOL designed to carry a person 20 miles or less would require about 800 to 900 watt-hours per mile. That’s about half the amount of energy as a semi-truck, which is not very efficient: If you needed to make a quick visit to shop in a nearby town, you wouldn’t hop into the cab of a fully loaded tractor-trailer to get there.

As batteries improve over the next few years, they may be able to pack in about 50 percent more energy for the same battery weight. That would help make e-VTOLS more viable for short- and medium-range trips. But, there are a few more things needed before people can really start using e-VTOLS regularly.