According to the Environmental Protection Agency, airplanes account for approximately 12% of U.S. transportation emissions and about 3% of the nation’s total greenhouse gas production. In 2018, aviation contributed 2.4% of human-generated CO2 emissions worldwide. In the interest of reversing climate change, then, what can be done to reduce air pollution by replacing jet-fuel burning aircraft with low- or zero-emission electric airplanes? What new technologies will be needed to effect this change and how long might it take?
Getting Off the Ground
The idea of electric airplanes is not new.
In October 1973, a 23-year-old Austrian aircraft manufacturer, Heino Brditschka, became the first person to fly an electric plane, a modified version of an HB-2 power glider. The Swiss-built, solar and electric-powered Solar Impulse II aircraft circumnavigated the globe over the course of 16 months in 2015-16. And since 2010, aircraft manufacturer Airbus has developed and flown a series of all-electric demonstrator aircraft.
But the laws of physics remain a daunting challenge to all who take on this new, cleaner, quieter form of aviation.
“For an electric airplane, the top three priorities are weight, weight and weight,” said Cory Combs, co-founder and chief technology officer of Los Angeles-based Ampaire, Inc. “It has to spend a lot of its energy just keeping itself in the air.”
The fundamental challenge, he explained, is that an electric plane has to carry enough battery power to allow it to take off carrying a nominal payload of passengers or cargo, fly at a reasonable speed, then travel a sufficient distance, notionally 100 miles, to make it commercially viable. If its battery packs become too large or too heavy, the aircraft will have a limited ability to carry passengers and cargo.
This energy requirement is exacerbated, Combs added, by the Federal Aviation Administration (FAA)’s requirement that all aircraft must carry at least 45 minutes of reserve fuel, enough to divert to another airport or go around for another landing attempt.
Making Contact With Reality
“Lithium (Li) ion batteries are the current state-of-the-art stored energy technology for aviation,” said Dr. Ajay Misra, deputy director, Research and Engineering Directorate, NASA’s Glenn Research Center, “the same type of technology used in cells phones and electric cars.”
For aviation, Misra added, the relevant measure of battery suitability is called pack specific energy, also referred to as pack gravimetric energy density. A pack contains thousands of battery cells. The units of pack specific energy are watt-hours per kilogram (Wh/kg).
According to Misra, the pack specific energy of the most commonly used Li-ion batteries today is about 150 to 170 Wh/kg. By contrast, the specific energy of jet fuel is nearly 12,000 Wh/kg, or about 70 to 80 times more energy dense than Li-ion batteries.
Putting Propulsion First
According to Roei Ganzarski, CEO of magniX, a Redmond, Washington producer of electric motors, however, electric aviation is facing a chicken/egg situation.
“You’re not going to get batteries for aviation unless there’s an electric airplane that needs them,” he explained. “And no one is going to design and build an electric plane unless there’s an electric propulsion system that can power the plane.”
That’s why Ganzarski believes that electric propulsion will drive the so-called third revolution in aviation, just as the automotive-derived piston engine used by the Wright Flyer launched the first revolution, and the advent of the jet engine ushered in the second.
To support this idea, magniX is working with Vancouver, B.C.- based Harbour Air, a regional airline, to retrofit several types of seaplanes with electric propulsion systems. In Dec. 2019, the two companies conducted first flight of the world’s first fully-electric commercial aircraft, a five-passenger de Havilland Canada DHC-2 Beaver propelled by magniX’s Magni500 560kW system.
Navigating the Certification Process
In coming months, magniX will be seeking FAA certification of its Magni500 motor while Harbour Air hopes to obtain certification for the DHC-2 Beaver. Eventually, the air charter company hopes to electrify its entire fleet of approximately 40 seaplanes.
Current FAA regulations, adopted in 2017, allow certification of electric airplanes weighing 19,000 pounds or less, with 19 or fewer passenger seats.
As Ganzarski sees it, retrofitting existing, previously-certified aircraft with new electric propulsion systems is a faster, less expensive way to reduce air pollution through electric aviation than building electric airplanes from scratch.
“The FAA already knows the de Havilland Beaver,” he said. “There’s nothing ‘new’ about this aircraft except now it will be electrically powered.”
The downside of electrifying older seaplanes, Ganzarski admits, is that they won’t have the range of the original aircraft, which were designed with large, heavy engines on the front. Traditional seaplanes can also carry high-energy-density fuel in their wings and don’t need to make room for lots of heavy batteries.
magniX’s second pathway into the electric airplane market, explained Ganzarski, is to provide electric motors to aircraft OEMs such as Israel-based Eviation Aircraft. Eviation is developing a new, all-electric commuter jet called Alice from scratch. The aerodynamic, nine-passenger jet, which was designed to take full advantage of its magni250 electric motors, has an advertised range of 540 nautical miles, or about 620 statute miles.
The tradeoff for customers hoping to obtain a newer, higher performance electric airplane, Ganzarksi advised, is that such planes will come with longer FAA certification times and higher price tags than retrofits.
Giving Wings to Hybrid Electric
Ampaire’s solution to the weight/range dilemma of electric airplanes is what they call a parallel hybrid-electric propulsion system. It includes both a conventional internal combustion engine and an electric motor with a scalable battery pack.
Compared to conventional, jet-fuel burning aircraft, explains Combs, this approach promises to reduce fuel consumption (50 to 70%), maintenance costs (about 25%), air pollution and takeoff noise.
“We believe that the dramatic drop in operating costs and noise levels associated with hybrid-electric propulsion could also lead to the revitalization of regional air travel,” he said. Using hybrid-electric aircraft, he calculates, airlines could provide less expensive and more frequent passenger and cargo services between smaller, regional airports.
As an example, Combs points to Ampaire’s first commercial product, the Electric EEL, a six-seat Cessna 337 Skymaster retrofitted with the company’s hybrid-electric system. The Electric Eel flew for the first time in May 2019. In 2020, Ampaire plans to conduct flight demonstrations of the EEL in Hawaii in collaboration with Mokulele Airlines by tracing a 31-mile commercial route currently flown on Maui by the regional carrier. Ampaire hopes to get FAA certification for the EEL in 2021.
Meeting Safety, Environmental Goals
Hybrid-electric airplanes, emphasized Combs, will meet the performance, safety and environmental expectations of commercial air travelers.
“Typically, we use battery power for taxi, a combination of engine power and battery power for takeoff (to match takeoff performance of current aircraft), and then when we’ve reached sufficient altitude, we can idle the fuel engine and fly electric,” he said. “So for short hop routes, we can essentially fly all electric.”
For longer routes, Combs added, hybrid-electric aircraft share power between the engine and the electric motor; longer routes require more engine power and less electric power but the battery size remains the same.
“The goal is to always use the battery because that’s the cheapest, most efficient, and most environmentally friendly form of power,” he said. “The fuel engine serves as your emergency reserve or provides power for that extra go-around.”
In addition to its work on the Electric EEL, Ampaire is also retrofitting nine- and 19-seat passenger aircraft with hybrid-electric propulsion systems
Facing the Anode Ahead
For the foreseeable future, explains NASA’s Misra, Li-ion batteries will remain the go-to stored energy technology for electric airplanes.
“With incremental increases in the chemistry of the Li-ion battery, its pack specific energy could rise another 20 to 30 percent, reaching perhaps 200-220 Wh/kg,” he said. “More advanced battery chemistries, such as those using silicon or lithium metal anodes (vs the graphite anode used by most Li-ion batteries today) may be able to reach 300, even 400 Wh/kg, if we are lucky.”
These specific energy levels, he believes, could enable introduction of all-electric regional jets capable of carrying 10 to 20 passengers, or slightly larger (50 to 70 passenger) jets powered by hybrid-electric propulsion systems.
Training the Future
Centennial, Colorado-based Bye Aerospace has taken a different approach to matching the maturity of battery technology to the needs of the general aviation markets. The company is developing a two-seat, Li-ion-powered training aircraft called the eFlyer 2.
“Over the next 20 years, the airline industry expects a five-fold increase in the demand for commercial pilots from the 155,000 such pilots flying today,” explained Bye Aerospace founder and CEO George E. Bye. “We’re meeting this need by developing a trainer aircraft that’s five times less expensive to operate than two-seat trainers in service today. And it produces no air pollution and no noise using modern technology.”
The eFlyer 2’s lower operating cost is particularly important for aspiring pilots, he added, because the cost of becoming a pilot today rivals that of becoming a doctor or lawyer.
The flight qualities and endurance of the eFlyer 2 (about 3 hours), Bye claimed, also line up well with the flight training syllabus and the learning capabilities of most people.
“New pilots mostly do takeoffs, landings and perhaps a few maneuvers recommended by their instructor,” he said. “Research has shown that after about an hour, maybe a little bit more, their ability to learn is greatly diminished. We believe that the eFlyer 2 and its electric propulsion technology are a great match for that learning curve.”
Bye Aerospace is also developing several four-seat versions of the eFlyer, known as the eFlyer 4 and the eFlyer X respectively, added Bye.
So how soon can we expect electric airplanes to become a ubiquitous part of our lives, and to begin turning the tide on climate change?
“Within 10 years, we will likely see hybrid-electric regional jets capable of flying 500 miles,” projected Misra. “Larger, all-electric passenger jets like the 737, however, are not likely before 2040 as significant advances in battery technology will be required.”
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