Piasecki Spells Out How it Will Bring a Hydrogen-Powered Aircraft Into Commercial Service | FutureFlight

https://www.futureflight.aero/news-article/2022-04-05/piasecki-prepares-step-testing-regime-hydrogen-powered-helicopter 

https://piasecki.com/projects/pa-890-evtol-slowed-rotor-winged-compound/2719/

https://newatlas.com/aircraft/piasecki-world-first-hydrogen-helicopter/