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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.