Leeham News and Analysis
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The state of alternative propulsion aircraft? Part 7.
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By Bjorn Fehrm
March 12, 2026, © Leeham News: In our series on the state of alternative propulsion projects, we are analysing where the electric hybrid projects are and how parallel hybrids work and perform.
Figure 1. The Pratt & Whitney Parallel Hybrid DH8-100 test aircraft, presently under preparation. Source: Pratt & Whitney
We summarized the status last week and compared it to the serial hybrids that we analyzed before Christmas. Serial hybrids are motivated in special cases, but in general, they make an aircraft more expensive to produce and operate.
For those who react, “But hybrid work very well for cars”?, let’s summarize: The car thermal engines are energy hogs, and you brake away all the acceleration energy at the next stoplight. Hybrids reduce this waste by recovering energy during braking. Aircraft and aircraft engines are wonders of efficiency by comparison, and there are no energy-recovery phases in an airliner mission.
We now use our Aircraft Performance and Cost Model (APCM) to go deeper into the parallel hybrid. Can it avoid the negative verdict of the serial hybrid?
The state of alternative propulsion aircraft? Part 6.
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By Bjorn Fehrm
March 5, 2026, © Leeham News: Before Christmas, we started a series examining the status of alternative propulsion projects. We finished on December 18 by looking at Series Hybrids, often as battery-electric aircraft with range extenders (Figure 1).
The range extender is the natural next step when a project realizes that a pure battery-electric aircraft won’t be able to fly the missions the market is asking for.
Figure 1. The Heart Aerospace Battery-Rlectric ES-30 with dual range extending turbo-generators in the back. Source: Heart Aerospace.
After a while, analysing the range extender, the drawbacks become increasingly obvious. Charging the battery system in flight or directly feeding the electric propulsion system from a turbogenerator is inefficient. The losses along the path from the gas turbine through a generator, an inverter, and then to a motor that drives a propeller or fan are much higher than when the gas turbine drives the propeller directly.
A series hybrid can’t compete on operational economics with the aircraft it shall replace (for example, the Cessna Caravan or the SAAB 340). Projects then turn to parallel hybrids, the subject of today’s article.
Bjorn’s Corner: Faster aircraft development. Part 28. Development times.
By Bjorn Fehrm and Henry Tam
February 20, 2026, ©. Leeham News: We have, since August 2025, gone through an FAA CFR 14 Part 25 development project of an airliner in the 200-seat class. The aim was to identify the activities required for such a project and the regulatory actions needed to achieve Type Certification (TC) and Production Certification (OC) for the aircraft.
The program followed the time plan in Figure 1, which indicated that it would take about seven years from the start of conceptual design to deliver the first aircraft and enter service (EIS). At each phase, we assessed whether modern support techniques, such as AI, could help with development and certification and whether they would accelerate the program plan.
Figure 1. A typical Program Plan for a smooth-running Part 25 airliner development. Source: Leeham Co.
We now summarize the findings and incorporate additional modern support, such as Digital Twin support, to assess the overall impact of today’s technologies on the program plan timeline in Figure 1. Read more
Outlook 2026: The state of the major eVTOL projects
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By Bjorn Fehrm
February 9, 2026, © Leeham News: The eVTOL market saw a sobering 2025 after two of its high flyers, Lilium and Volocopter, both ceased operations in 2024. The remains of Volocopter were bought by Diamond Aircraft, which now markets a stripped-down VoloCity as a Light Sports eVTOL.
Further players ceased in 2025, with Hyundai’s Supernal halting further development, as did Airbus with its CityAirbus. Textron halted Nexus development, then shuttered the division, and Overair ceased operations after Hanwa stopped investing.
We have one VTOL that received local Chinese Type Certification in 2023, and one in 2024. EHang got the Type Certificate in 2023, Production Certificate in 2024, and Air Operator Certificate (AOC) in 2025. The drone multicopter looking Ehang EH216-S (Figure 1) was cleared to operate tourist flights in China. The other Chinese project was AutoFlight’s Prosperity five-seater, which achieved Chinese Type Certification in 2024.
Figure 1. The only certified eVTOL, the EHang EH216-S. Source: EHang.
The almost euphoric enthusiasm over eVTOLs that existed before COVID, where car manufacturers got involved as this could be the thing that took over personal transport for crowded cities, has now calmed down, as the operational use of the current generation of eVTOLs is 10 to 15-minute missions in fair weather, replacing helicopter services from the airport to the city centre.
The original story was different as early developers like Joby Aviation painted with a broad brush. There were statements about 150nm trips, 200 kts speeds, and unbeatable economics, with batteries that lasted 10,000 flights. What investors and pundits didn’t understand was that these were unrelated statements about physical limits: there was no AND between them.
Outlook 2026: The airliner projects that promise new technology and lower emissions
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By Bjorn Fehrm
February 5, 2026, © Leeham News: We survey new entrants that deviate from the classical gas-turbine tube-and-wing airframe concept and offer airliners the promise of lower emissions and, hopefully, lower costs.
We will do this by starting with those closest to certification and delivery, then tapering off to those who currently fly on PowerPoint.
If we didn’t apply this filter to what we consider real projects, we would describe over 50 entries, with additional ones announced with airline orders every month over the last few years. Few of these have progressed beyond plans, which is why we focus on those that have.
Overall, it’s amazing that 11 years after the Airbus E-fan battery-electric aircraft flew at the Farnborough Air Show in 2014, we still do not have a single certified alternative-propulsion passenger aircraft. We have one light-sport two-seat trainer, the Pipistrel Electro Velis, but nothing else.
Figure 1. The Airbus E-Fan at the Paris Air Show in 2015. Source: Wikipedia.
Boeing, others up SAF plans in Washington State
Credit: Boeing.
Announced on Thursday at Boeing Future of Flight, the museum located adjacent to Boeing’s Everett production facility, the Cascadia Sustainable Aviation Accelerator (CSAA) aims to ramp the region’s SAF production capacity to one billion gallons per year by 2035.
The state of alternative propulsion aircraft? Part 5.
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By Bjorn Fehrm
December 18, 2025, © Leeham News: In our series about alternative propulsion aircraft, last week we looked at the energy consumption and range of a typical nine-seater battery-electric commuter aircraft using our Aircraft Performance and Cost Model (APCM).
We could see that the useful range for this aircraft was short, even when using the full 19,000lb Maximum TakeOff Weight (MTOW) to give the battery the maximum size and using VFR flight rules. Under IFR flight rules, the commuter was not usable with available batteries this side of 2030.
Figure 1. Our battery-electric commuter was similar in design to the Tecnam P2012 nine-seater commuter. Source: Tecnam.
When a project discovers these constraints (which often happen several years into the project, as upstarts don’t have competent aircraft performance models that handle energy consumption for different phases of flight), they start looking at Hybrid architectures.
We do the same. Once again, our model will help us to predict performance, range, operational economics, and also production costs (as a hybrid is a more complex aircraft than a battery electric one).
Avolon: Looking to long-term eco-aviation investment opportunities
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By Charlotte Bailey
Dec. 11, 2025, © Leeham News: With around 50% of the world’s operational commercial aircraft owned by lessors, companies such as Avolon are keeping
a weather eye on the technologies that could power the fleet of the future.
And as the aircraft purchased today are likely to be operating well into the 2050s, understanding the impact of upcoming sustainability incentives and technologies is already a relevant consideration.
The state of alternative propulsion aircraft? Part 4.
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By Bjorn Fehrm
December 4, 2025, © Leeham News: In our series about alternative propulsion aircraft, last week we looked at the aircraft batteries. These are heavy components with very low energy capacity per unit weight.
To illustrate the kind of aircraft-level challenges the batteries pose, we are using our Aircraft Performance and Cost Model (APCM) to design a typical alternative-propulsion battery-electric aircraft and then fly it on typical missions.
The aircraft is similar in size to a 9-seat Tecnam P2012 commuter (Figure 1) but optimised for Battery-Electric propulsion.
Figure 1. The Tecnam P2012 nine-seater commuter. Source: Tecnam.
The APCM will give us the airframe-level energy consumption for each phase of the flight. Subsequently, we can add the different losses in the propulsion system to determine the energy consumed from the battery and the endurance/range it offers, dependent on VFR or IFR mission reserves.
The state of alternative propulsion aircraft? Part 3.
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By Bjorn Fehrm
November 27, 2025, © Leeham News: In our series about alternative propulsion aircraft, last week we looked at the electric motor of an electric aircraft, which drives propellers or fans. It’s a component that is straightforward to develop, but the certification requirements for the aircraft and VTOL industry have slowed progress.
Now we look at the component that causes trouble for all alternative propulsion aircraft, except those that burn hydrogen in gas turbine engines: the batteries. Batteries work well in cars, where the requirement for energy capacity relative to weight is much lower and where energy recovery during braking reduces the energy required from the battery.
Figure 1. The battery-electric aircraft that flies operational trials as we speak, the Beta Technologies Alia CX300. Source: Leeham Co.
Aircraft batteries are a heavy component with very low energy storage capacity. Today’s aircraft battery system has about 60 times lower energy density per kg or lb than aircraft fuel.
The hope over the last decade has been that this relationship should improve. It has, it’s gone from about 70 times to 60 times in the last 10 years. This will improve further, the question is if it will continue at the slow pace of the last 10 years or not?