Leeham News and Analysis
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The state of alternative propulsion aircraft? Part 2.
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By Bjorn Fehrm
November 20, 2025, © Leeham News: In our series about alternative propulsion aircraft, we started last week by discussing what happened after the trigger by the Airbus E-fan flight in 2014 and the introduction of the Tesla Model S car two years before. The alternative propulsion aircraft projects that followed had a rocky path. They followed the Gartner Hype-curve, Figure 1.
There were hundreds of projects announced, more or less serious. A few of these came to producing hardware, and flew test flights, then stopped. Most stayed as PowerPoint presentations and fancy renderings, promising capabilities that were not possible to realize. The result was that we passed the Peak of Inflated Expectations and entered the Trough of Disillusionment. Investors fled to AI, and projects froze or stopped.
Figure 1. The Gartner Hype-curve. Source: Gartner Inc.
By 2025, we are in the Disillusionment phase. As there are signs we can now enter a phase of real, sustainable progress, it’s timely to take stock of where we are and what progress we can expect over the next decade.
To understand why progress has been so difficult, after explaining that learnings from Cars are not transferable last week, we start by focusing on two components that we find in every alternative propulsion concept, the Electric Motor and the Battery system. Of the two components, the motor is the most straightforward to develop and certify for an aircraft. Still, we have only limited progress so far, and we detail why in today’s article.
The Battery System is the most challenging component for alternative propulsion aircraft, both in development and in use. We will spend next week’s article detailing why and how it has slowed down progress so far, and how this can change going forward.
What’s the status of the alternative propulsion projects for air transport?
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By Bjorn Fehrm
November 13, 2025, © Leeham News: The interest for new and more environmentally friendly aircraft got underway in 2014, when Airbus flew the battery-electric E-fan demonstrator at the Farnborough Air Show in July, Figure 1.
The car revolution to battery-electric cars had taken off two years earlier, when Tesla introduced the Model S sedan with elegant styling and very good performance and economy for a family car (Figure 1).
Figure 1. The battery-electric aircraft demonstrator and the car that started it all. Credit: Airbus and Tesla Inc.
Tesla cars had proven that electric cars could match and even outpace combustion-engine cars in performance and operational costs, though not in driving range. But range was a matter of battery capacity development, and hopes were high for a similar situation and development for aircraft.
As is the case with almost every technological leap, the progression of alternative propulsion aircraft projects followed the Gartner Technology Hype curve (Figure 2).
Figure 2. The Gartner Hype Curve for alternative propulsion aircraft. Credit: Gartner and Leeham Co.
The start was around 2015, passing the Peak of Inflated Expectations around 2020. In the 11 years since 2014, we’ve had hundreds of entrepreneur-driven projects declare they will make environmentally friendly aircraft and airliners a reality.
Nothing useful has come out of these projects, so today, we are passing the Trough of Disillusionment. Investors have stopped funding alternative propulsion startups as these have not produced useful air transport. The result is a mass death of projects, most silently, some more openly.
The core of the remaining projects are run by experienced teams with solid aeronautical knowledge. These are now passing into the Slope of Enlightenment and will make real progress. Given that we are now entering a more productive phase, we take stock of these developments and their programs.
To help the analysis, we use our Aircraft Performance and Cost Model, APCM, to show what the challenges are and how alternative propulsion can address these challenges.
What’s the next new aircraft, Part 5
By Scott Hamilton and Bjorn Fehrm
July 31, 2025, © Leeham News: We wrap up our five-part series today on What’s the Next New Airplane in the coming decades. We now look at Airplanes 9-13 in Figure 1 below.
Figure 1. The 13 airliners we look at in the series. Source: Leeham Co.
These are the (9) COMAC 929, (10) Eco-version of New Light Twin, (11) CFM Open Fan single aisle, (12) the Boeing 787 re-engine, and (13) the Airbus A350 re-engine.
Bjorn’s Corner: Air Transport’s route to 2050. Part 32. Epilogue.
By Bjorn Fehrm
July 25, 2025, ©. Leeham News: In October last year, we began a series on how air transport is performing against the emission goals for the year 2050.
The ambition to reduce and eventually eliminate greenhouse gas emissions began in earnest 11 years ago, when Airbus flew the Airbus E-Fan at the 2014 Farnborough Air Show (Figure 1).
Figure 1. The Airbus E-fan flying at the 2014 Farnborough Air Show. Source: Wikipedia.
The result of this inspiring flight, which utilized technology that emitted no CO2 or other greenhouse gases (if the batteries were charged with green electricity), was an avalanche of projects from established players as well as upstarts. The optimistic view was that there was a solution to the emissions from airliners.
Bjorn’s Corner: Air Transport’s route to 2050. Part 31, Conclusions.
By Bjorn Fehrm
July 18, 2025, ©. Leeham News: We have done a Corner series on the state of actions to mitigate the global warming impact from Air Transport. Now, we start to summarize what we’ve learned.
During the series, we compiled tables describing the warming effect of air transport in 2024 and a calculation of the effect during 2050. We made two tables, one with the most probable effects, Figure 1, and one where we downplayed the non-CO2 effects to the maximum given in the Lee et al. 2021 study, to a 5% probability, Figure 2.
Figure 1. The effects of Actions 1 to 4 on CO2 and NOx, represented as CO2e emissions during 2050. Source: Leeham Co. Click to enlarge.
Before we summarize by examining the tables, we will discuss the additive effects of CO2 and non-CO2 warming over a given time period, as the different components don’t have the same decay time of their warming effects.
Bjorn’s Corner: Air Transport’s route to 2050. Part 30.
By Bjorn Fehrm
July 11, 2025, ©. Leeham News: We feature a Corner series on the state of actions to mitigate the global warming impact from Air Transport. We try to understand why different developments have been slow.
In the last Corner, we correlated the growth of airliners between 2024 and 2050 and the growth in Greenhouse gas emissions of CO2 and NOx that would result. We also calculated the increase in warming from contrails based on the traffic increase by 2050. The results are in Figure 1.
We also discussed that the warming effects of CO2 are undisputed, whereas the impact of NOx and contrails is less mature in its complicated effects research. The performed research has a lowest and a highest warming probability. We will now do an “acid test” and see what their impact is when we apply their lowest probable effect on global warming.
Figure 1. The effects of Actions 1 to 4 on CO2 and NOx, represented as CO2e emissions by 2050. Source: Leeham Co. Click to enlarge.
Bjorn’s Corner: Air Transport’s route to 2050. Part 29.
By Bjorn Fehrm
July 4, 2025, ©. Leeham News: We feature a Corner series on the state of actions to mitigate the global warming impact from Air Transport. We try to understand why different developments have been slow.
In the last Corner, we wanted to understand the relationship between Greenhouse gas emissions of CO2 and NOx and the effect of global warming from contrails. After some iterations, we arrived at the comparison shown in Figure 1, where we compare different warming effects using CO2 and CO2e (CO2 equivalents, i.e. the same warming effect as CO2).
Figure 1. The Global waring effect of CO2, NOx and warming contrails by 2050 as CO2 and CO2e. Source: Leeham Co. Click to enlarge.
Bjorn’s Corner: Air Transport’s route to 2050. Part 28.
By Bjorn Fehrm
June 27, 2025, ©. Leeham News: We do a Corner series about the state of developments to improve the emission situation for Air Transport. We try to understand why development has been slow.
We have explored various methods to mitigate global warming throughout the series. Over the last few weeks, we have summarized the practical results we can expect from the different alternatives available to reduce global warming in air transport. We looked at the following:
- Alternative, lower-emission propulsion technologies.
- The industry’s typical improvement in fuel consumption over time.
- The improvements that SAF can offer by 2050.
- The different Emission Trading Schemes (ETS) that exist globally.
- And finally, what warming contrail reductions can achieve.
We have summarized what the first four actions can achieve by 2050 and presented the results in a table, Figure 1. Now we add what global warming contrail avoidance can do.
Figure 1. The effects of Actions 1 to 4 on CO2 and NOx counted as CO2e emissions by 2050. Source: Leeham Co.
Bjorn’s Corner: Air Transport’s route to 2050. Part 27.
By Bjorn Fehrm
June 20, 2025, ©. Leeham News: We do a Corner series about the state of developments to improve the emission situation for Air Transport. We try to understand why development has been slow.
We have examined different ways to lower global warming over the course of the series. Over the last weeks, we have summarized what practical results we can expect from the different alternatives we have to reduce global warming from Air Transport. We looked at the following:
- Alternative, lower-emission propulsion technologies.
- The industry’s typical improvement in fuel consumption over time.
- The improvements that SAF can offer by 2050.
- The different Emission Trading Schemes (ETS) that exist globally.
- Finally, what warming contrail reductions can achieve.
Bjorn’s Corner: Air Transport’s route to 2050. Part 26.
By Bjorn Fehrm
June 13, 2025, ©. Leeham News: We do a Corner series about the state of developments to improve the emission situation for Air Transport. We try to understand why development has been slow.
We have examined different ways to lower global warming over the course of the series. Over the last weeks, we have summarized what practical results we can expect from the different alternatives we have to reduce global warming from Air Transport. We looked at the following alternatives:
