Graham Warwick Bye Aerospace doubles down on its lead in certifying electric aircraft to directly target the turboprop-twin business aircraft market.
Graham Warwick
Bye’s eFlyer 800 is advanced yet conventional in aerodynamic and structural design. Credit: Bye Aerospace
Electric aircraft are establishing themselves by targeting market niches dictated by their performance limitations, such as light training aircraft, short-hop air taxis and short-range regional transports. But it is only a matter of time before electric aircraft challenge conventional aviation head on.
Bye Aerospace believes that time has come. The electric aircraft pioneer has unveiled the eFlyer 800, an all-electric eight-seater designed to compete directly with Textron Aviation’s storied Beechcraft King Air, the bestselling turboprop twin in business aviation.
With a projected cruise speed of 320 kt., a 35,000-ft. ceiling and 500-nm range with 45-min. instrument flight rules reserves at 280 kt., the eFlyer 800 is designed to compete head-to-head with the nine-seat King Air 260-— but at one-fifth the operating costs.
Bye is targeting FAA Part 23 certification in 2025 and expects the eFlyer 800 to be one of the first electric aircraft to be approved for Part 135 charter operations. Launch customers are fractional-ownership sister companies Jet It in the U.S. and JetClub in Europe. L3Harris will develop a multimission version for the global intelligence, surveillance and reconnaissance market.
Denver-based Bye Aerospace was founded in 2007 by CEO George Bye, who first tested an electric-powered Cessna 172 and developed the Silent Falcon solar-powered unmanned aircraft before launching the eFlyer program to develop FAA-certified electric aircraft.
The eFlyer 800 is the third member of a family that includes the eFlyer 2 two-seat trainer, now in development, and the follow-on eFlyer 4 four-seat air taxi. Bye is aiming for FAA certification of the eFlyer 2 by the end of 2022. But is all-electric-propulsion technology ready to be scaled from a single-engine trainer into the twin-turboprop class?
“It turns out the underlying technology is scaling appropriately to create the possibility,” Bye says. “The battery modules are repeatable. The battery management system, the communication system, how that’s presented on the displays—all are modular and repeatable. And the electric motor and controller likewise scale.”
Building on the eFlyer 2, Bye has assembled an experienced Tier 1 supplier team to develop the eFlyer 800: Safran for the electric motors, Moog for the battery system, Garmin for the cockpit avionics and Toray for the composite materials. “Collectively, the team is legacy aerospace, with great depth of experience,” Bye says. “We know how to develop, certify and produce airplanes.”
The scaling up builds on flight testing of electric aircraft that goes back to the modified Cessna 172 in 2012, the experimental Sun Flyer in 2015 and the proof-of-concept eFlyer 2 in 2018. “This is tangible,” Bye says. “There is a foundation of research and development and flight test, real prototypes flying for years, building data, going though updates—a systematic test program to get to where we are today, the first and only Level 1 Part 23 normal-category certification program with the eFlyer 2 starting back in April 2018.”
Additionally, Bye has focused on bringing propulsion innovation to classic aircraft configurations. “The aerodynamics and structure we’ve been doing for decades: a conventional aircraft, a tractor-propulsion twin with proper weight, balance and trim—all that is well known and understood,” Bye says.
“So we are scaling the electric-propulsion system with our partners who’ve indicated their readiness to do that, together with a traditional tractor twin design that customers are comfortable with-—that King Air type of configuration we’ve embraced for 50-60 years,” he says, noting this is critical to the market.
“We understand it; we like the redundancy; we like the safety,” Bye says. “It’s just comfortable, and the market needs some comfort when we’re going to a new-generation propulsion system. Let’s not create an environment that has resistance—let’s create an environment that has acceptance.”
Fractional operator Jet It is the U.S. launch customer for the eFlyer 800. Credit: Bye Aerospace
Like the eFlyer 2, the eFlyer 800 will use the latest in aerodynamic and structural design, with a high-aspect-ratio wing and all-composite airframe. It will also offer modern cabin and cockpit environments. “Going back into King Air legacy, the cabin is kind of small. It was built around a human that was a different size many years ago. We’ve gone to great lengths to make sure the cabin of the eFlyer 800 is comfortable for today’s people. So we have a 65-in.-wide cabin,” he says. “We want the customer experience for passengers to be wonderful and not feel cramped like a Caravan or King Air or TBM. It’s a traditional but advanced design with the twin arrangement for redundancy and safety and the perception that this is a classic airplane I’m going to be comfortable getting into.”
There is a price to pay for using motors instead of turboprops because of the much lower energy density of batteries compared with jet fuel. “We are giving up range,” Bye says. “This is a 500-nm-range airplane with 45- min. reserves. There are going to be some market segments and some customers that say they want 1,000 nm. I can’t offer them an all-electric airplane that has a 1,000-nm range today. But 90% of the mission profile is under 500 nm. The 90% passenger load factor is two or three people. So if I’m optimizing for the prime mission at the prime passenger load for business, I’ve hit the target—I’ve got the 90th-percentile solution with one-fifth the operating costs.”
The eFlyer 800 is an ambitious undertaking for a company that has yet to certify an aircraft. Assembly of the first conforming eFlyer 2 is underway. “We’ve gone through the G-2 issue paper, which is the road map to finish certification,” Bye says. “More than half the system-specific certification plans are complete. We’re well on track with the FAA to complete normal category Part 23 Amendment 64 certification.”
After the eFlyer 2 will come the larger eFlyer 4, a Level 2 aircraft under Part 23 rules, and then the Level 3/4 eFlyer 800. This will also entail moving up from Part 91 general aviation operating regulations to more stringent Part 135 commercial operations. “Part 135 isn’t magic—it’s well understood. You just build that into the system,” he says.
The eFlyer 2 and 4 have two redundant Moog battery packs powering a single Safran EngineUS electric motor. The eFlyer 800 will have four battery packs, two for each Safran motor, and each motor will have double windings. “In the collective, we have a quad-redundant electric-propulsion system, more than ever imagined with a classic twin turboprop,” Bye says.
“That gets everyone excited because it’s about safety. We want to hear: ‘Here comes the world’s first electric Part 135 aircraft,’” he says. The eFlyer 800 will also have a full-airframe parachute, the same used in the Cirrus Vision Jet, as well as Garmin’s Autoland autonomous emergency-landing system.
Battery cells used in the eFlyer 2 are above 300-Wh/kg energy density, but the eFlyer 800 needs a 500-Wh/kg level to work. The company had been working with Oxis Energy, a pioneer in developing high-energy-density lithium-sulfur battery cell technology, and appeared to suffer a setback in May when the UK company entered bankruptcy receivership. But Bye seems unconcerned.
L3Harris is leading development of eFlyer 800 special-mission variants. Credit: Bye Aerospace
“We are on solid ground,” he says. “There are at least 10 batteries that are highly competitive and fit well within our family of aircraft, both today and going into the future. Are we making that announcement now? No. But from Panasonic to LG, plenty [of companies have] solid-state lithium-ion and lithium-sulfur advances underway.”
Bye is not rushing to commit to a battery technology. “It’s highly advantageous to keep the industry competitive,” he says. “We don’t want to preselect items that are going to advance in technology and price point. The key thing is to keep the battery-cell competition alive. That gets us the best price.”
For Bye, the key is integrating the chosen cell technology into a safe battery system. “If I’m building an i-Phone, do I care about the battery? Of course I do. But there’s a million different batteries I could put in there. The key thing is to get the phone right,” he says.
“We want to make sure the battery pack is right, [as is] how we communicate from the pack to the battery management system for safety, charging, state of charge, recycle life. And how that is translated to the inverter/controller and into the motor. That’s the secret sauce.”
Bye expects the eFlyer 2 to be the first electric aircraft to be type-certified by the FAA. Part 23 normal-category certification will allow the aircraft to provide “100% utility” out of the box, he says, enabling it to be used for flight training in the U.S. This contrasts with Pipistrel’s Velis Electro trainer, which in 2020 became the first electric aircraft to be type-certified.
The Velis Electro is certified under the European Union Aviation Safety Agency’s CS-LSA category for light sport aircraft, which comes with restrictions requiring exemptions to national aviation regulations. The aircraft is flown by flight schools in Europe, but no training use is yet allowed in the U.S., where the FAA does not yet recognize electric light sport aircraft.
In service, eFlyer operators can expect drastic reductions in operating costs by using electric energy at cents per kWh versus jet fuel at dollars per gallon. But what about battery life and replacement cost? Packs can degrade to 80% energy capacity and need replacement in as little as 1,000 charge-discharge cycles, or fewer for some advanced cell chemistries.
Bye downplays the concern. “Cycle life is one of the most misunderstood terms. The engineering definition of a cycle is from zero state of charge to 100% state of charge and back to zero again. Does anybody operate an aircraft from zero fuel to 100% back to zero again? Nobody ever,” he says.
“We fly with a 30-min. [visual-flight rule] to a 45-min. [instrument-flight rule] reserve as a minimum. Generally speaking, we operate between 25% state of charge and 85-90% state of charge. We have a 3-hr. battery size, and we fly 1.1-1.3-hr. missions, so we use about a third of the charge available per sortie,” Bye says. “So if I have a 1,500-cycle-life battery pack, and I roughly multiply that by three, that’s about 4,500 flight hours. We’re looking at a 1,500-2,000-cycle life, which would be 4,500-6,000 flight hours.”
Similar mathematics will apply to the eFlyer 800. “The average mission is under 449 nm for air charter in the Northeast U.S. and Europe. The 500-nm range would rarely be used, but [the mission] would be less than 2 hr. at 280-300 kt. There are four Level 3 charging ports on the eFlyer 800. Each battery string is charged independently. So it’s a 25-min. quick turn, as fast or faster than a King Air,” he says.
“When we talk about a 1.3-hr. sortie, in reality, your time in the air is 0.9-1.1 hr. The rest of the time you are taxiing or waiting. And we don’t consume much energy when we are taxiing,” he says. “There is no mechanical friction for us to overcome with electric propulsion, unlike a piston engine, which has to idle inefficiently while you are sitting there doing your checklist or making your first radio calls. When we sit there, the propeller stops. When we move, it’s with just enough energy to taxi,” Bye says. Additionally, the eFlyer 800 will have the option for in-wheel electric motors for taxiing and for solar cells to provide supplemental power, further extending battery life.
Another advantage of electric propulsion, beyond low energy cost and zero emissions, is reduced noise, which could open markets that are closed to turboprops. “Here in the U.S., over half our airports are in high-density urban areas. They have quiet hours,” Bye says.
“Our measured reduction in noise is 1,000%—a 30-dB reduction,” he says. “I’m sure it will vary to some extent from aircraft to aircraft, with time of day, temperature, moisture, etc. But the bottom line is it’s a gigantic difference in noise signature. It literally is just the propeller. That opens the possibility of aircraft utility that is otherwise restricted or prohibited.”
Taking on the King Air with an electric aircraft is an ambitious undertaking for a small company, but Bye Aerospace is growing. “We have two facilities here in Denver, our headquarters and an engineering R&D center with assembly area. We’ll be opening a test center here later this summer,” he says.
Also later this summer, Bye plans to announce its production location and break ground on a manufacturing facility. “The preliminary agreements have been signed,” he says. The facility will assemble aircraft using aerostructures from suppliers that have yet be named, one providing the wing and the other the fuselage. The company is “perpetually” raising funding, Bye jokes. “There will be another increment ahead as we proceed with the eFlyer 4 and 800, but we are well-funded today.”
