There are plenty of companies working on emission-free eVTOL aircraft. Nearly all of them rely on batteries. Piasecki has pivoted away from this technology to a hydrogen fuel cell system for its PA-890 helicopter. This compound aircraft has wings that rotate to vertical during takeoff and horizontal during flight, and will use a compact fuel cell from HyPoint that the company claims has four times the energy density of lithium-ion batteries, twice the power of existing fuel cell systems, and offers a 50 percent lower operating cost. The two companies hope to have a prototype in the air for certification by 2024 with commercial deliveries of what would be the first manned hydrogen-powered helicopter beginning in 2025.