The exciting development of electric aircraft (EA) has been referred to as “the Third Revolution in Aviation.”1 The first revolution was the Wright brothers’ first successful powered flight, the second one, the invention of jet propulsion which allowed us to fly faster and farther. The growth of aviation that followed introduced the big carbon emission problem. The advent of EA propelled by clean electricity marks the dramatic transformation to zero carbon emission for aviation, and the “third revolution.”
EA hold tremendous potential to improve emission, noise, and operating economics across a range of different applications in support of the aviation industry’s goal of achieving net-zero carbon emissions by 2050. There are, however, technology challenges that must be overcome for achieving this goal.
These revolutionary EA have already demonstrated significant cost savings. For example, the energy cost of the two-seat Pipistrel aircraft per hour is at 0.9 € while a conventional Cessna two-seat aircraft C152 commonly used for training is approximately $34 (pre-Ukraine war estimate), which is equivalent to 34× that of the Pipistrel Alpha Electro.2 An estimate of the per hour total operating cost for the C152 vs. the Alpha Electro is approximately 3.6:1; i.e., the conventional two-seat fossil fuel-propelled aircraft is almost fourfold more expensive to operate than the equivalent two-seat EA.
In March 2022, the aviation industrial conglomerate Textron, parent company of Cessna, decided to underwrite the expansion and success of electric aviation for commercial use with its acquisition of Pipistrel. By April 18, 2022, Textron completed acquisition of Pipistrel for a cash purchase price of €218 million. This deal will dramatically accelerate the development, deployment, and adoption of EA.
In the span from 2016 to 2022, there have been over 300 EA projects and up to 200 EA startups around the world, similar to the renaissance of aviation period in the early 1900s. The overall EA service domain is loosely referred to as “Advanced Air Mobility” (AAM), which covers the “Urban Air Mobility” (UAM) and part of “Regional Air Mobility” (RAM). EAs for UAM are primarily equipped with vertical lift capability, also referred to as eVTOL (electric Vertical Take-Off and Landing), while the RAM EAs take advantage of the runway to gain momentum (hence less energy demand) for take-off and landing and are referred to as eCTOL (C for Conventional) or eSTOL (S for Short).
The eVTOLs operate similar to rotorcraft and require heliports (or “vertiports”) in urban environment. Examples of eVTOLs include projects from Joby, Volocopter, Lilium, Archer, EHang, Wisk, and many more. In contrast, eCTOLs and eSTOLs are fixed-wing aircraft that can use the massive number of existing airports, transforming the regional travel due to the unprecedented economic and environmental benefits. These EAs are developed by a number of startups and OEMs, including Airbus, Ampaire, Electra.Aero, Heart Aerospace, MagniX (with Eviation), Rolls Royce Electric, VoltAero, ZeroAvia, and others. NASA’s white paper on RAM3 outlined how the application of EA will dramatically increase the accessibility and affordability of regional travel while building on the extensive and underutilized US local airports.
Shift Toward Electric
Aviation has witnessed the shift toward “more electric aircraft” (MEA) since the introduction of Boeing’s 787 in 2011. For the traditional airplane, power is extracted from the engines in two ways to power other airplane systems. First, the generators are driven by engines to create electricity (e.g., to power avionics system). Second, a pneumatic system “bleeds” air off the engines to power other systems (e.g., hydraulics). The B787’s MEA approach uses electric instead of the pneumatic system and provides much more efficient power generation and distribution for use and reduces systems weight, including the adoption of a higher capacity electric energy storage system (ESS).
The evolutionary change toward MEA for large transport aircraft, such as the B787, is a very slow process. However, the significant technology development and adoption of ground electric vehicles (EV) in the last decade has made the EA more feasible. In addition to the relevant technological advances, the economy of scale and new supply base growth have driven down the component systems cost tremendously. These potentially common component systems include, e.g., electric motors and inverters, which when operating together in an EA are defined as the “electric engine”4 (e-engine) and ESS (battery or fuel cell) instead of the conventional “fuel system.”
Key Challenges and Opportunities
Today’s state-of-the-art commercial lithium batteries are ~50X heavier than aviation fuel. Even accounting for the much lower losses through an e-engine leaves a ~25X net energy weight disadvantage. However, an e-engine weighs a lot less than a combustion engine. ARPA-e’s ASCEND project seeks to extend this advantage leading to 12 kW/kg for an e-engine compared to a MW-class gas turbine at ~3 kW/kg,5 or 4X the power-to-weight performance. In addition, there is a rapid development in solid-state batteries (SSB), which will reach 4X higher energy density and power density, substantially surpassing the performance, safety, and processing limitations of Li-ion batteries.
It is estimated that these SSBs will become commercially available in 2030s in the EV and aircraft market respectively.6 Some eVTOLs, (hybrid) eCTOLs, and eSTOLs, such as Ampaire’s 9-seat Eco Caravan and Outlander with compelling emission reduction and meaningful range performance of up to 500+ miles, are already on the horizon to enter into service by 2025.
The hydrogen fuel cell is another ESS. It is an electrochemical device that converts hydrogen directly into electricity supply for the e-engine while releasing heat and water. Boeing’s hybrid-electric and fuel-cell demonstrator flew in 2007 for approximately 20 minutes on energy from the fuel cell ESS. However, Boeing “does not envision that fuel cells will ever provide primary power for large commercial airplanes.”7
The second key challenge is unique to the aerospace industry, as it is a highly regulated industry for an important reason, safety. All of the new (and retrofit) EAs must be type certified for air worthiness by regulatory bodies, including FAA and EASA. With over 200 projects of new EAs going to the regulatory bodies for certification, the regulators will have not only a resource issue but also knowledge and experience issue, which is necessary to address the gaps of existing standards and rules.
The Pipistrel two-seat “Velis Electro” is the world’s first EA to receive a Type Certificate from EASA in June 2020, approved for pilot training in Day Visual Flight Rule operations. The knowledge and experience gained from the Pipistrel’s certification activities have been used to develop the Special Condition SC E-19 “Electric/Hybrid Propulsion System” to further enable EA certification projects. In the U.S., the FAA also released Special Conditions for engines from MagniX, based on a new American Society for Testing and Materials standard, for electric engine Airworthiness in October 2021.
The third challenge area is in the eco-system readiness for enabling the EAs operation, e.g., clean energy availability and distribution to the plug-in EAs for charging. This eco-system includes stakeholders, such as airports from an infrastructure and operations perspective, airlines who may need to modify their existing process on ground and flight routing to take advantage of the EAs capabilities, and the energy industry which could be the supplier, on-site storage, or distributors for the energy management.
Electrifying aviation at airports to date includes plugging planes into gate power for Auxiliary Power Unit, electric taxi to the runway, as well as electric tugs and ground equipment. Moving forward, this means investing in development and scaleup, from adoption of electric trainer aircraft to integrating the plug-in (hybrid) EAs. This is where the demonstration projects such as 2ZERO (Towards Zero Emission Regional Aircraft Operations) and SATE (Sustainable Aviation Test Environment), sponsored by the Future Flight Challenge program of Innovate UK, are extremely valuable as the public and the private sectors come together to solve the systems problem collaboratively.
Ampaire’s participation in these projects allowed us to work with Highlands and Islands Airports Limited (HIAL), Exeter, and Newquay airports and chart the course of aviation electrification roadmap. In August 2021, the hybrid demonstrator “Electric EEL” was able to achieve the longest nonstop flight of 418 nautical miles in UK, at a 38 percent reduction to fuel emission. A mobile charger was used for the demonstration flights, which incorporates the standard plug-in interfaces both on aircraft and to the airport energy outlet with advanced coordination.
This EEL demonstrator is a hybrid of independent parallel architecture, which is not optimized. We estimate that for an optimized parallel hybrid EA using SAF (at 50 percent blend) for the combustion engine, it can achieve up to 90 percent emission reduction with today’s technology. As batteries and electronics improve, smaller planes can move to all-electric and larger planes can convert to hybrids over time, using a combination of SAF and clean electricity.
If we want to reduce climate change, decarbonizing aviation is a must — electric aviation needs to be an important part of the solution. But launching the EA operations widely will require the combined vision and focus of both the public and the private sectors. The time to act is now. By building a strong foundation to support the EA development, including the regulations and standards for airworthiness certification of these new aircraft and systems, and infrastructure for enabling the EA, we can achieve something truly revolutionary in our industry.
This article is written by Dr. Susan X. Ying, SVP Global Operations, Ampaire. Dr. Ying is also a member of the SAE International Board of Directors. For more information, visit here .
- “Could electric airplanes propel a third revolution in aviation?” Miles O’Brien, PBS News Hour, May 26, 2021.
- “Alpha Electro, the first serially produced electric trainer”, Tine Tomažič, AIAA-IEEE Conference, Aug, 2020.
- “Regional Air Mobility: Leveraging Our National Investments to Energize the American Travel Experience”, Kevin Antcliff et. al., April 2021.
- “Taxonomy, Architecture, Safety, Endurance Testing”, SAE E-40 Electrified Propulsion standard publication, ARP8689, Q1, 2023.
- “Solid-State Batteries: The Technology of the 2030s but the Research Challenge of the 2020s”, Faraday Insights, Issue 5: Feb 2020.
- “Boeing makes history with flights of Fuel Cell Demonstrator Airplane”, Tom Koehler, Boeing Frontiers, May 2008.