![Dornier 228](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-1_zeroavia-promo_1.jpg?itok=eP8vvozF)
ZeroAvia ZA600
After replacing one of the turboprops on a 19-seat Dornier 228 with a prototype of its 600-kW ZA600 hydrogen-electric powertrain, startup ZeroAvia conducted the first flight from Kemble, England, on Jan. 19, the testbed becoming the largest aircraft to date to fly with hydrogen fuel-cell propulsion.
![De Havilland Canada Dash 8-300](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-2_universal_hydrogen.jpg?itok=KiekDy7I)
Universal Hydrogen
Startup Universal Hydrogen seized the crown of the largest aircraft to fly on hydrogen fuel-cell propulsion on March 2 when it flew a 40-passenger De Havilland Canada Dash 8-300 modified with one of its turboprops replaced by a 1-megawatt-class hybrid-electric powertrain demonstrator system.
![UltraFan demonstrator engine](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-3_rolls-royce.jpg?itok=ASDFvTxp)
Rolls-Royce UltraFan
Rolls-Royce ran its UltraFan demonstrator engine, the world’s largest geared turbofan, for the first time on April 24 using 100% sustainable aviation fuel on that run. With a 140-in.-dia. fan—6 in. wider than the largest turbofan now in commercial service—the UltraFan reached 85,000 lb. thrust in early November.
![X-57 Maxwell](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-4_nasa.jpg?itok=ap5Jl4p8)
NASA X-57
After struggling for years with a variety of technical problems and setbacks, NASA decided in June to conclude its X-57 Maxwell distributed electric propulsion demonstrator program at the end of September without attempting an electric-powered flight.
![Diamond Aircraft](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-5_diamond_aircraft.jpg?itok=9orIyhWb)
Electric flight
Austria’s Diamond Aircraft flew its eDA40 electric two-seat trainer on July 20, but Italy’s Tecnam Aircraft suspended plans to develop the P-Volt all-electric version of the 11-seat regional aircraft after concluding near-term battery technology is not sufficiently mature.
![Arcus-J glider](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-6_airbus.jpg?itok=JoL5jsBN)
Project Condor
Airbus UpNext launched flight tests of a modified glider powered by a hydrogen-fueled turbojet on Nov. 8 under its Blue Condor project to research the impact of hydrogen on contrail formation. The modified Arcus-J glider made its initial self-propelled takeoff from Minden, Nevada.
![HY4 demonstrator](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-7_h2fly.jpg?itok=Zco6o8eD)
H2Fly LH2
Germany’s H2Fly in September completed the first flights of a hydrogen-electric aircraft using cryogenic liquid-hydrogen storage. The startup’s piloted HY4 demonstrator performed four flights from Maribor, Slovenia, under Europe’s Heaven research project, including one lasting more than 3 hr.
![Chaparral uncrewed cargo aircraft](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-8_elroy_air.jpg?itok=NlQJpZiD)
Elroy Air Chaparral
Startup Elroy Air conducted the first hover flight of its Chaparral uncrewed cargo aircraft on Nov. 12, the 300-lb.-payload, 300-mi.-range uncrewed cargo aircraft becoming the first turbogenerator-based hybrid-electric vertical-takeoff-and-landing (eVTOL) vehicle to fly.
![EL-2 Goldfinch](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-9_taylor_mickal-electra.jpg?itok=E6W-AvPi)
Electra EL-2
Startup Electra.aero completed the first pair of piloted test flights with its hybrid-electric short-takeoff-and-landing (eSTOL) full-scale technology demonstrator in November, the two-seat EL-2 Goldfinch flying in both all-electric and hybrid-electric configurations.
![Cessna 337 Skymaster l](/sites/default/files/styles/crop_freeform/public/2023-12/ad24-propulsion-gallery-10_ampaire.jpg?itok=7-GFoyXL)
Ampaire Electric EEL
Ampaire claimed a world record for hybrid-electric aircraft endurance after completing a nonstop 12-hr. flight with its Electric EEL propulsion testbed on Dec. 10. The modified Cessna 337 Skymaster landed with 2 hr. of fuel and battery reserves remaining, the U.S. startup says.
Alternative propulsion technologies made the headlines in 2023, from first flights of hydrogen-electric and hybrid-electric to both advances and setbacks for all-electric aviation. The year also saw the first tests for the world’s largest-diameter turbofan engine.