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We already have drones that can hover for hours using hydrogen in carbon fiber tanks... https://www.borntoengineer.com/hydrogen-powered-drone-sets-world-record

• ncmncm 5y ago
  Tiny aircraft have an enormous advantage over those big enough to move much. It is easy to make an RC plane that can fly straight up. Or, an ornithopter. A 747 flying straight up is impossible. A 747-sized ornithopter is impossible. Those "tictacs" swooping around navy ships are most likely liquid-fueled drones. If they haven't shot any down yet, that is a disgrace.