There are a few flying prototypes of various sizes, so clearly there's a big flaw in your argument. In principle you can burn hydrogen in a jet or even in an i

There are a few flying prototypes of various sizes, so clearly there's a big flaw in your argument. In principle you can burn hydrogen in a jet or even in an internal combustion engine. Both have already been shown to work. Fuel cells are another possibility of course. As far as I understand it, most plane manufacturers are already designing planes with hyrdogen as a power source. Particularly for big Jets, the consensus seems to be that that is happening. The main challenge in the market is similar with what we've seen with existing car manufacturers. Changing technology disrupts them and threatens their profitability. So, you see companies that are talking the talk but not really committing to much beyond that. E.g. Airbus and Boeing have lots of fancy concept planes but not much in the line of actual planes being designed and marketed yet. As for battery, there are several battery powered planes flying and certified (or in the process of being certified). Most of the companies behind those are following up with longer range versions that they've already announced. Maybe aviation fuel goes a bit further but it is very expensive. Especially for general aviation, the value proposition might look pretty good a few years down the line with better ranges and charging speeds and lower cost. That does not even require that much in terms of breakthroughs in energy density either. Anything certified today is using battery tech that is several years old and was probably picked conservatively to speed up the process. That's just the nature of the certification process. What's flying legally today was the state of the art about half a decade ago in terms of batteries. Probably not that impressive compared to the latest electrical cars.