In addition to semi-announced long term initiatives like the Tesla pickup truck, Elon Musk has also floated the idea of making a Tesla plane. And while it sounds far fetched now, once it finishes developing its range of electric vehicles, bringing renewable energy to commercial aviation seems like a pretty logical next step.

“The exciting thing to do would be a vertical takeoff and landing supersonic jet of some kind,” Tesla CEO Elon Musk said during a September appearance on Joe Rogan Experience, noting that he’d discussed the idea with “friends and girlfriends.”

It sounds like pie-in-the-sky thinking, but Tesla has built a reputation as a firm that can take existing vehicles and electrify them with great success. The company first released the Roadster in 2008, the first all-electric production car with a lithium-ion battery, back when electric cars were a rare oddity. It then launched the Model S sedan in 2012, the Model X sports utility vehicle in 2015, and the Model 3 entry-level car in 2017. It’s now planning the entry-level Model Y, a Semi electric truck and second-generation Roadster, all while producing around 7,000 cars per week.

Tesla also has a lot of experience with building bigger and bigger batteries technology. It built the world’s largest lithium-ion battery in South Australia with 100 megawatts of storage, using the Powerpack commercial product to store wind and solar energy. It also sells the Powerwall for home users, while the company’s Solar Roof can blend into an existing property to harvest energy. If anyone knows how to make a huge battery fly through the air with passengers and cargo, it could be Tesla.

Tesla Electric Plane: What’s Elon Musk Said About It?

Musk has discussed his plane idea several times over the years, going back to 2009 when he mentioned the idea to George Zachary at the Charles River Ventures CEO Summit, stating that “an electric plane gets more feasible as battery energy improves,” but “I try not to think about because I have too much to think about.” His comments were captured on (somewhat grainy) video which was published by TechCrunch at the time.

There have also been some pop cultural references. In the 2010 film Iron Man 2, Musk makes a brief cameo appearance by telling Robert Downey Jr.’s character Tony Stark that he’s “got an idea for an electric jet.” Stark, whose character Downey Jr. is said to be modeled on Musk in the first place, tells him that “we’ll make it work.”:

The idea continued gaining steam. In 2012, he mentioned in a Jalopnik discussion that he had “this airplane design that I’ve had in mind for about four years.” In 2013, he said during a YouTube video chat that “maybe at some point in the future” he would complete the plane if nobody else would. In 2014, Musk said at an MIT Aeronautics and Astronautics Centennial Symposium that he was “toying” with designs:

By 2015, then, Musk was saying pretty consistently that he had “a design in mind.” The following year, he told Tesla investors he was “dying to do that.” But his most recent remarks seemed like a hedge, when in 2017 he said he had “no plans right now” to begin pursuing the project in earnest.

Tesla Electric Plane: When Will It Take Off?

The key holdup with Musk’s idea, in his words, is that he’s waiting for battery technology to improve. A plane would require a high energy density, 400 watt-hours of energy per kilogram of plane. The battery found in a Tesla car ranks at around 250 watt-hours per kilogram. However, 400 is the bare minimum for making such a plane work, and Musk claims 500 is more ideal.

As for when we might reach that point? Subhash Dhar, CEO of XALT Energy, predicted in August 2017 that density is likely to reach that point by 2022. This would bring big benefits for electric cars, reaching a range of 400 miles per change from a 50 kilowatt-hour battery pack. Dhar was speaking in an industry-wide sense, though, and it’s possible that Tesla’s internal developments envision a different timetable. Musk suggested during a chat with Tesla investors in 2017 that the company was “maybe four years or five years away from having 500 watt-hours per kilogram…maybe half a decade in volume production.”

While Tesla waits for the technology to catch up, Musk told Joe Rogan in September that the plane “isn’t necessary right now…electric cars are important. Solar energy is important. Stationary storage of energy is important. These things are much more important than creating an electric supersonic VTOL.”

Tesla Electric Plane: How Would It Work?

The energy density is critical to the way the plane works. Musk told Joe Rogan in September that with an electric plane, “you want to go as high as possible, so you need a certain energy density in the battery pack, because you have to overcome gravitational potential energy.” While it requires a lot of energy to rise, the energy used in cruising “is very low, and then you can recapture a large amount of your gravitational potential energy on the way down.” That means “you really don’t need any kind of reserve fuel if you will, because you have…the energy of height.”

Musk’s plane would probably focus on using electric motors to move a fan, as he explained to Stephen Colbert in 2014, which would also reduce the need for giant runways as seen with traditional jet engines. The main issue is reaching those higher altitudes.

“The higher you go, the faster you’ll go with the same amount of energy,” he told Joe Rogan in September. “At a certain altitude, you can go supersonic with quite a lot less energy per mile than an aircraft at 35,000 feet. Because it’s just a force balance.”

Tesla Electric Plane: Why Not a Flying Car?

Musk has actually spoken out against flying cars. In an April 2017 TED talk, he described the anxiety about the concept of over-head vehicles, saying “did they service their hubcap? Or is it going to come off and guillotine me as they’re flying past?”

In February 2017, he told Bloomberg that he was focusing on digging tunnels with The Boring Company as a means of increasing capacity in cities instead of taking to the skies, explaining that “if somebody doesn’t maintain their flying car, it could drop a hubcap and guillotine you. Your anxiety level will not decrease as a result of things that weigh a lot buzzing around your head.”

Musk has also dismissed Uber’s plan for a city-focused vertical takeoff and landing jet:

While Musk may be considering an electric jet, he’s notably cool on the idea of using them to solve traffic woes.

Tesla Electric Plane: What’s the Competition?

A number of competitors are already trying to beat Musk to the punch. Boeing-backed Zunum Aero aims to release a 12-seat hybrid electric plane by 2022, while a consortium of Airbus, Siemens and Rolls-Royce plans to release the E-Fan X hybrid plane in 2020. Like hybrid cars, these machines would depend on more than one fuel source to complete the trip.

Similar to Uber’s VTOL concept, Audi has worked with Airbus and Italdesign on a modular concept vehicle, capable of running for 31 miles across a city:

The PopUp.Next concept. Audi

While these are cool, their short ranges leave the playing field open for a design that can handle international voyages. In June 2016, designers from the Technical University of Munich unveiled a design for the “Lilium Jet,” a two-passenger plane that could travel 300 miles on one charge with speeds of up to 250 mph. Another competitor on this front is budget airline Easyjet, which is working with Wright Electric to build a nine-seater plane set to fly next year with a long-term goal of electrifying its short-haul flights:

Easyjet's electric plane. Easyjet

The race is on to electrify the skies.

Related video: Siemens’ World Record Electric Plane Makes First Flight