Dial Fellows

How to build an electric airplane

By retrofitting existing aircraft with a hybrid-electric system, mechanical engineer Cory Combs is building the biggest plane ever to fly with electric propulsion.

Cory Combs has always been obsessed with airplanes. Growing up near an airport in Temecula, CA, he would constantly watch planes fly overhead and dream up his own designs for new ones. “I was always excited about aviation because it pushes the boundaries of what’s possible.” Combs says. “We've been traveling on wheels for thousands of years, but in the scheme of things, aviation is still really new.”

But Combs, a mechanical engineer and Emerson Collective Dial Fellow, also knows the ugly truth about aviation: air travel is the biggest personal environmental impact of most regular fliers. “I take the metro to work instead of driving. I try to eat sustainably. I even do small things like reusing Ziploc bags by washing them,” he says. “But all of that is completely outweighed by my impact from flying.”

Combs at the 2019 Dial Fellows Summit. Credit: Barbara Kinney

Yes, planes are becoming more fuel-efficient. But the pace of improvement has stalled in recent years. What’s more, the number of people flying on airplanes has more than doubled since 2003 and isn’t slowing down. By 2050, if air travel continues to grow, related greenhouse gas emissions could increase from 2005 levels by 300 to 700 percent. The mounting awareness of the environmental impact of flying has even led to a new Swedish word – flygskam, or “flight shame.”

But Combs knows that shame isn’t going to keep the billions of people who will soon be able to afford to fly from flying, or provide essential connectivity across the globe. So Combs set out to build a cheaper, greener alternative himself: the world’s first commercial electric aircraft.

Ampaire’s first commercial product, the Electric EEL, at their flight test facility in Camarillo, CA.

In 2010, just after Combs had finished his masters degree in mechanical engineering at Stanford University, he saw Iron Man 2. In the movie, Elon Musk, CEO of Tesla and SpaceX, makes a short 15-second cameo. “I’ve got an idea for an electric jet,” Musk tells Iron Man Tony Stark. “You do?” Stark replies. “Then we’ll make it work.”

“It was just an offhand comment, but it really got me thinking,” Combs remembers. “I put pen to paper and realized, ‘Wow, with the right assumptions, an electric jet is actually something doable.’”

Electric aviation has long held great promise, but viable designs have been elusive. The biggest reason? Battery weight. Because so much energy is required to get an airplane off the ground and keep it in the air, a really big battery is needed – big enough that with current technology, it would be too heavy to make the plane usable.

“You can't just stick your Tesla battery and motor in a plane and expect it to work.” Combs says.

Over the last decade, a number of start-ups have made significant progress in the quest for all-electric air travel. Most are still years away from a commercial product. But Combs had a vision for getting electric aircraft into the sky more quickly.

You can't just stick your Tesla battery and motor in a plane and expect it to work.

Cory Combs, Electric Airplane Entrepreneur

In 2016, Combs co-founded Ampaire, an electric aviation company. Ampaire’s big idea is to start small. Their key innovation is to take existing small-haul airplanes – 19 seats or less – and retrofit them with an electric motor running in parallel to a fuel engine. With this hybrid approach – and because small planes require less energy to fly – the battery weight on Ampaire planes doesn’t prevent them from taking off.

“We're not just modeling some futuristic plane design and waiting ten years for a billion dollars to build a factory and produce it,” Combs says. “We can take these existing fleets out there and start converting them to a greener solution today.”

Ampaire’s first commercial product, the Electric EEL, is a six-seat Cessna 337 Skymaster retrofitted with an electric motor spinning a propeller in the front of the plane that works in parallel with a fuel engine driving a propeller in the back. The plane has been performing test flights in California since June 2019, and a second plane will soon take to the skies in partnership with Mokulele Airlines. It is the largest aircraft using electric propulsion ever to fly.

The Electric EEL is a six-seat Cessna 337 Skymaster retrofitted with an electric motor that spins the propeller in the front of the plane, working in parallel with a fuel engine that drives the propeller in the back.

Ampaire’s Electric EEL is able to reduce emissions by about 50-75%. But electric planes have a number of additional benefits beyond fuel efficiency. For example, electric motors are lower-maintenance than a typical engine; electric planes are much quieter, which benefits communities, often lower-income, living near airports; and Ampaire’s retrofit approach also dramatically reduces the waste created when planes are retired, while reducing the emissions that result from manufacturing new planes.

Electric planes are also cheaper. Right now, the cost of building an Ampaire plane is roughly equivalent to the cost of building a standard aircraft, but Ampaire’s planes cost 25-50% less to maintain because an electric motor has drastically fewer moving parts than a fuel engine.

“It's great that it's green, and we definitely think that that is going to be part of the reason people adopt it,” Combs says. “But it also makes financial sense for airlines.”

Starting small also means Ampaire is well-positioned to serve less connected rural areas and island nations. In fact, Combs believes that some of Ampaire’s early customers could be humanitarian operations delivering medical support and critical supplies to remote areas.

Ampaire’s first commercial product, the Electric EEL, at their flight test facility in Camarillo, CA.

Ampaire’s approach is already catching on. In June, just two weeks after the plane’s first demonstration flight, the start-up Personal Aviation Exchange purchased 50 Electric EELs. In October, Ampaire received support from NASA to test whether the 19-seat Twin Otter aircraft could fly using a hybrid-electric propulsion system.

The next 24 months will be critical for Ampaire – and quite possibly historic. Ampaire will soon complete its internal Electric EEL test flights. Then, early this year, an Electric EEL will head to Hawaii where it will be flown on island-hopping commercial routes operated by Mokulele Airlines. Combs says that Ampaire is on track to fly paying customers on Mokulele routes on their planes by 2021.

Five or 10 years ago, no one would have thought an electric plane like ours was possible.

Cory Combs, Electric Airplane Entrepreneur

Meanwhile, Combs waits his turn for a ride on his own electric aircraft, which will come this spring when a second test aircraft heads to Camarillo, CA for test flights. The first Electric EEL has been carrying so much test equipment that the only humans it has been able to fit are a pilot and co-pilot. So Combs has stayed on the ground, watching his invention cut quietly through the sky, just like he watched the planes over Temecula as a boy, dreaming of this day.

“I see the emergency we have right now as a country and as a world,” Combs says. “But it's just such a great feeling to see that this dream has become a reality and to prove that it is really possible. Five or 10 years ago, no one would have thought an electric plane like ours was possible.”