Engineers at the University of Cambridge successfully test a hybrid aircraft that can recharge its batteries in flight.

Hybrid cars are a common sight on the road. But hybrid planes in the sky? Not so much. But engineers at the University of Cambridge are working to change that. 

The researchers, with funding from Boeing, successfully tested “the first aircraft to be powered by a parallel hybrid-electric propulsion system, where an electric motor and petrol engine work together to drive the propeller,” according to a University of Cambridge press release

The plane uses 30 percent less fuel compared to a similar fuel-only aircraft, and, according to the release, it was the first plane “to recharge its batteries in flight.”

While we’ve all gotten used to seeing hybrid cards like the Toyota Prius on highways, why has it taken so long for hybrid planes to take flight? Blame it on the batteries.

“Until recently, they have been too heavy and didn’t have enough energy capacity,” explained project leader Dr. Paul Robertson. “But with the advent of improved lithium-polymer batteries, similar to what you’d find in a laptop computer, hybrid aircraft — albeit at a small scale — are now starting to become viable.”

“Small scale” is the key phrase here. The plane that researchers tested is single-seat propeller aircraft, so you won’t be flying on a hybrid plane on a nonstop flight from Los Angeles to New York anytime soon. Still, it’s a start, and the university’s tests will have an important impact on research for alternative fuels for planes.

“In the longer term, beyond that, we can also start evaluating alternative fuel,” Dr. Robertson said in a YouTube video. “Because we have the petrol and the electric combination together, then if either one of those engines were to malfunction, for example, or not perform as expected, we have the backup of the other power source.”

Watch the hybrid plane in flight in the video below.