Two sorts of questions for those who support this idea 1) If is is so workable, then why don't we have hydrogen test planes flying today? Are there any techno

Two sorts of questions for those who support this idea 1) If is is so workable, then why don't we have hydrogen test planes flying today? Are there any technological problems that remain to be solved? 2) How is hydrogen supposed to be better than synfuel kerosene produced with renewable energy? And note than any argument must include the cost of replacing every current airliner with an all new hydrogen one, as opposed to keeping the present airliners.