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From Past to Future: Going Hybrid

A round up of airplane modification projects in hybrid-electric aviation.

Ampaire has three aircraft in its fleet to advance hybrid-electric propulsion technologies. (Photo: Ampaire)

Traditional aerospace engine makers are known to modify existing aircraft to test future propulsion technologies. The start-ups follow the giant’s steps to prove their designs on various platforms. Here’s a look at what technology demonstrators are flying and the potential technologies that’ll come to an airplane near you.

Battery-electric powered the first wave of emission-free aviation innovations. However, the industry has agreed that battery-electric airplanes will not carry enough volume nor fly far enough to make a significant impact soon. Therefore, more and more players are entering the hybrid-electric arena.

There are two types of hybrid technologies. The most popular one is parallel-hybrid, which uses combustion and electricity as energy sources. It’s more efficient as it allows different modes of operation during different phases to optimize energy usage. The plug-in hybrid is also a parallel hybrid architecture, which utilizes two types of energy to power two independent propulsion systems. Then there’s the series hybrid architecture, which runs a small combustion engine as a generator to power an electric motor. 

Not only is hybrid electric technology the most hotly contested technology, but it is also the most promising, with many more miles and hours flown by the demonstrators compared to the other types of novel propulsion technologies.

Ampaire Electric EEL and Eco Caravan

Ampaire is one of the earliest companies to work on hybrid electric conversions. The Californian company has converted two types of aircraft so far: the Electric EEL based on a Cessna 337 Skymaster and the Eco Caravan converted from a Cessna 208 Caravan.

Electric EEL

Ampaire’s Electric EEL, a modified Cessna 337, flying over Hawaii. (Photo: Ampaire)

Its first Electric EEL aircraft had an electric propulsion system at the rear of the aircraft and maintained its combustion engine on the nose. It first took flight in June 2019 and has conducted route-proofing tests in Hawaii, Scotland, and, most recently, Alaska. The second prototype flipped the configuration to allow a more streamlined design and placing of battery packs in the cargo hold. The duo also set impressive records, such as the longest non-stop hybrid-electric flight at 1,135 miles in 2022. In July, the company announced that it had surpassed 20,000 hours running hybrid.

The EEL was used to develop high-power electronics under Advanced Research Projects Agency–Energy (ARPA-E) funding, which designated the flying test beds ARPA-E Bird. The startup received funding in 2022 to further study its AMP-H270 drivetrain. The company hopes to put it on the nose of the ARPA-E Bird test bed along with a fully electric powertrain in the back. 

Eco Caravan

Ampere’s Eco Caravan taking off on its first flight. (Photo: Ampaire)

ARPA-E also provided $9 million in funding to further develop the propulsion developer’s drivetrain for the Caravan. Surf Air Mobility was the original suiter for this project before it abandoned plans to acquire Ampaire in 2022. The Hawthorne, Calif.-based company managed to power through the difficulty and conducted its first flight of the Eco Caravan seven months after losing its investor. The program also found its customer shortly after in January 2023, with Azul Connecta signing a Letter of Intent for up to six upgrade conversions.

VoltAero Cassio 1

VoltAero’s Cassio 1 testbed aircraft is the world’s first parallel hybrid aircraft. It is validating the company’s electric-hybrid propulsion unit at the full 600-kW power rating. (Photo: VoltAero/Jean-Marie Urlacher)

VoltAero’s Cassio 1 is another test platform modified from the SkyMaster. It first flew in March 2020 with its original combustion engine in the aft fuselage and two Safran ENGINeUS 45 electric motors mounted on the wing. The demonstrator received its hybrid power train later that year and took to flight in October, becoming the world’s first true parallel-hybrid aircraft. The French company announced surpassing 10,000km in flight testing in 2022 and plans to use the hybrid technology for its upcoming Cassio 330 aircraft.

European Union H3PS

Tecnam P2010 H3PS flying. (Photo: Tecnam)

The European Union funded the High Power High Scalability Aircraft Hybrid Powertrain (H3PS) project to study the feasibility of a parallel hybrid powertrain for general aviation and the scalability of the technology for aircraft up to 11 seats. The three-year project included airframer Tecnam, engine maker Rotax, and electric motor maker Rolls-Royce Electric. It produced a Tecnam P2010 flying test bed and performed its first flight in December 2021. The research concluded that hybrid-electric powertrains are beneficial and scalable for future demonstrator projects.

Airbus EcoPulse and E-fan X

Europe’s largest commercial aircraft maker, Airbus, has shown its interest in hybrid-electric propulsions. It worked on two projects, the EcoPulse, which is based on a Daher-Socata TBM 900, and the E-fan X, a modified British Aerospace 146, which was the largest demonstrator if it had not been canceled.

EcoPulse

Airbus EcoPulse on display at the Paris Air Show.(Photo: Airbus)

The EcoPulse is the only series hybrid demonstrator in the cohort. Despite a report by Aviation Week that the demonstrator was close to its first flight by the end of October, it had yet to take to the skies at the time of writing. The main goal of the demonstrator is to test a distributed electric propulsion, much like that of the canceled NASA X-57 Maxwell. It has six electric motors, four of which are powered by battery packs, while the other two are powered by an “e-Auxiliary power Unit” (e-APU) provided by Safran. 

E-Fan X

Airbus and Rolls-Royce was working on flight testing hybrid-electric propulsion on a British Aerospace 146 before the program was canceled in 2020. (Photo: Airbus)

E-Fan X was supposed to be the largest technology demonstrator for novel propulsion methods. Rolls-Royce and Airbus collaborated on the project and planned to put two of the Power Generation System 1 (PSG1) onboard the BAE146 airplane. The PSG1 uses a modified Rolls-Royce AE2100 combustor as a generator to power the electric motors. This plane would have been another series-hybrid demonstrator. Unfortunately, the manufacturers canceled the program in April 2020.

Flightlab Helo

Airbus is testing a hybris-propulsion system on it’s H130 Flightlab helicopter. Its engine backup system (EBS) uses a 100-Kw motor to provide electric power for up to 30 seconds in the event of main turbine engine failure. (Photo: Airbus Helicopters)

The Flightlab Helo is an Airbus demonstrator based on its popular H130 helicopter. While a 100-Kw motor connects to the main driveshaft, it only provides emergency backup power for 30 seconds in case of emergency power failures. The first revision of the system connects a battery pack to the backup motor to give pilots extra time to react to a possible failure. However, the planemaker is looking into developing a fully parallel hybrid propulsion system mixing thermal and electrical energy together with the aim of optimizing fuel consumption and enabling hybrid single-engine flights over urban areas.

NASA Electrified Powertrain Flight Demonstration

Across the pond, the U.S. government is also growing its industry base in novel propulsions through NASA’s Electrified Powertrain Flight Demonstration (EPFD) Project. 

GE Aerospace and magniX have revealed the paint schemes of the hybrid electric aircraft they will fly as part of NASA’s Electrified Powertrain Flight Demonstration (EFPD) project. (Photo: NASA / GE Aerospace / magniX)

GE Aerospace EPFD

GE partnered with Boeing to modify Saab 340B powered by GE CT7-9B turboprop engines. The CT7-9B engine includes a traditional CT7 gas turbine running in parallel with an electric motor/generator. While not much has been shared on the progress of the modification, the engine maker announced that it had conducted tests at NEAT, the NASA Electric Aircraft Testbed facility near Sandusky, Ohio, simulating altitudes of over 45,000 feet. 

MagniX EPFD

MagniX partnered with Air Tindi and AeroTEC to demonstrate electric propulsion technology on a hybrid De Havilland Canada Dash 7 aircraft. The group will replace the two outboard engines on the Dash 7 with MagniX magni650 engines. Air Tindi delivered the airplane to AeroTEC on October 27. In the meantime, the engine maker also delivered its first power unit to NEAT for testing in November 2023.

Both projects target flight demonstrations between 2025 and 2026.

Pratt & Whitney Canada Hybrid Electric Demonstrator

Pratt & Whitney Canada will build a Hybrid Electric Demonstrator using a Dehavilland Canada Dash8-100. (Photo: Pratt & Whitney Canada)

P&WC is working with De Havilland Aircraft of Canada Limited (De Havilland Canada) to integrate this hybrid-electric technology into a De Havilland Canada Dash 8-100 flight demonstrator. This demonstrator will include an advanced electric motor and controller from Collins Aerospace, also a Raytheon Technologies business. The company is replacing one of the engines on the airplane with a parallel-hybrid engine.

During the 2023 Paris Air Show, the group announced it had achieved a critical milestone in its hybrid-electric flight demonstrator program. It completed a rated power test of the demonstrator’s 1 megawatt (MW) electric motor, developed by Collins Aerospace. The 1MW motor will be combined with a highly efficient thermal engine developed by Pratt & Whitney as part of a hybrid-electric propulsion system. The project targets its maiden flight in 2024.

Conclusion

Hybrid electric is likely the most popular and realistic technology for conventional aircraft. Eight active programs are trying to demonstrate the viability of the technology. The most popular architecture is a parallel one; while it has to carry additional weight due to the more complex drive system, its efficiency could outweigh the additional emission. Manufacturers should gain more insight into the optimization strategy by gathering real-world data from the flight tests.

Next week, we’ll examine another popular low-emission propulsion source, hydrogen-electric.

Fangzhong Guo
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Author

  • Fangzhong Guo

    Fangzhong grew up near an OEM airport in northeastern China, where he developed his enthusiasm for aviation. Taking upon his passion, he's now working as an aircraft interior design engineer. Besides working in the aerospace industry, Fangzhong enjoys trying out different types of airplanes and seeing how airplane interiors have evolved. So far, he's flown on over 80 types of aircraft. He also planespots in his spare time. His rarest catches included the 747 Shuttle Carrier Aircraft and AN-225.

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