Two companies promoting hydrogen power for aircraft are upsizing their aspirations, with aircraft hauling four to up to 40 passengers. Both have ambitious timelines. ZeroAvia, operating in Hollister, California and Cirencester, England has been flying a Piper Malibu demonstrator, but anticipates flying a 10 to 20 passenger Dornier by 2024. It would expand that to a 50-passenger craft by 2026. H2Fly in Germany has been flying their Pipistrel-designed HY4 for several years and through six generations. The firm looks forward to taking incremental steps toward a 40-passenger regional airliner by 2030. ZeroAvia ZeroAvia reports on troubling trends in aviation’s contribution to greenhouse gases, but follows with a possible solution. According to their web site, aviation accounts for over 12 percent of total transportation emissions, and may double that by 2050. High altitude contrails mean aviation emissions have two to four times the effect of ground source emissions. Regulators want drastic changes. The European Union mandates a one quarter the CO2 …