In 2050, flying commercial may still mean crammed overhead bins and crummy food, but the engine could be powered by liquefied natural gas or electricity, according to an ongoing study on the future of flight.
Such planes might also be constructed with lighter materials, sport high-span truss-based wings, and be routed with improved air-traffic control systems, according to Marty Bradley, a technical fellow with Boeing Research and Technology who is the leading the NASA-funded study.
“We’re not really betting on any one of those [technologies] in particular, but we are identifying some future possibilities and then trying to make sure that the technology is developed far enough along so that they can be ready if they make sense at the time,” he told me Wednesday.
An energy-efficient commercial jet powered by a hybrid-electric engine similar to those in cars such as the Toyota Prius, Chevy Volt, and Nissan Leaf is among the more compelling possibilities identified to date, Bradley noted.
Such a plane, dubbed the Sugar Volt, would plug in at the airport to recharge batteries, for example, in the same way Leaf owners recharge in their garages. Conventional fuel would likely help it get off the ground. Once airborne, electricity would supply at least some of the power to the engines.
Batteries – the source of the electricity – are “the biggest challenge in making this concept work,” Bradley said.
They are heavy compared to conventional fuel and likely will be for the foreseeable future. Weight – how much of it planes have to carry – directly impacts how much energy they need, of course. That’s part of the reason, for example, that you get charged extra for heavy baggage.
“There is a penalty for carrying heavy batteries,” Bradley said. “But if you have a really efficient airplane, that penalty is reduced. So, in the study, we make the propulsion system more efficient, we make the aerodynamics more efficient, we make the airplane lighter.”
This engineering work, in turn, could translate to a plane that requires 50 percent less energy to fly than today’s commercial jets. And that means the battery only needs to be about half as big.
A similarly designed plane could also be powered by liquefied natural gas, Bradley and his colleagues have found in the course of the SUGAR study, which stands for Subsonic Ultra-Green Aircraft Research.
Challenges for liquefied natural gas are primarily the fuel tanks on the airplane and re-fueling infrastructure at the airport, Bradley noted. “Once you inject it into a jet engine, it actually burns really well,” he said.
The advantages to using liquefied natural gas include what may be low cost due to abundance and its lower greenhouse gas emissions compared to conventional jet fuel.
Whether or when any of these technologies are in commercial jets in the future depends on what the future looks like – the availability of natural gas or biofuels, for example, or whether there are limits on greenhouse gas emissions to combat climate change.
“We’re not quite sure what future we’re going to have,” Bradley said. “So, we’re in the business of getting different technology opportunities for the future.”