Adios, Queen of the Sky!
Hydrogen needs too much volume to be stored. Therefore it's not the future aviation fuel for commercial aviation. However it might still be better/ more promising than today's batteries to store energy onboard.
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Jet A = 43 MJ/Kg
Lithium battery = 1 MJ/Kg (43 times the weight of Jet A)
Hydrogen = 130 MJ/Kg (one third the weight of Jet A) assuming LIQUID hydrogen.
Natural hydrogen is lighter than air so the effective weight of and aircraft would be reduced at take-off and would increase as the hydrogen is used...now where did I put that G & T?
The B747 or the A380 are ideal candidates to carry large volumes of hydrogen by using the upper decks and even the large area above the lower deck ceiling...maybe less G and more T next time
True, but on the other hand...
Jet A = 43 MJ/Kg
Lithium battery = 1 MJ/Kg (43 times the weight of Jet A)
Hydrogen = 130 MJ/Kg (one third the weight of Jet A) assuming LIQUID hydrogen.
Natural hydrogen is lighter than air so the effective weight of and aircraft would be reduced at take-off and would increase as the hydrogen is used...now where did I put that G & T?
The B747 or the A380 are ideal candidates to carry large volumes of hydrogen by using the upper decks and even the large area above the lower deck ceiling...maybe less G and more T next time
Jet A = 43 MJ/Kg
Lithium battery = 1 MJ/Kg (43 times the weight of Jet A)
Hydrogen = 130 MJ/Kg (one third the weight of Jet A) assuming LIQUID hydrogen.
Natural hydrogen is lighter than air so the effective weight of and aircraft would be reduced at take-off and would increase as the hydrogen is used...now where did I put that G & T?
The B747 or the A380 are ideal candidates to carry large volumes of hydrogen by using the upper decks and even the large area above the lower deck ceiling...maybe less G and more T next time
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Cylindrical tanks on the upper deck and above the main deck ceiling...and maybe in the centre wing tanks?
You need total isolation between H2 tanks and any passengers - a leak would displace so much O2 it would rapidly asphyxiate anyone in the same pressure vessel so you can't have the H2 tanks in the pressurized part of the aircraft. About the only semi-practical method of carrying H2 is to have a dedicated section of the fuselage - but if you don't put it over the wing you start running into CG problems was the fuel is used - so you end up with passengers front and rear, and a big H2 tank in the middle. Hardly ideal.
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Sadly, passenger B747s are no longer economical so I am talking about adapting freighters. The C of G problem has already been addressed by systems used by aircraft spraying oil slicks...a simple computer programme to sequence the tanks, starting front and rear and working to the middle. The tanks containing the chemicals are double skinned and vented in case of leaks. A B747 on a 12 hour flight will use 120,000 Kg of Jet A. The same aircraft would use 40,000 Kg of hydrogen so there is an 80,000 Kg saving for the weight of the tanks.
It all depends on your objective to reach with your H2 driven 747.
If your objective is to enlarge your payload (if tanks could be made lighter than 80 tons then go ahead.
If you want to reduce carbon foot print:
As long as we do not have a global surplus of green produced electricity, we do not have to bother to produce H2 by grey or black produced Electricity.
Electrolysis , cooling, pressurization, and (road) transport to the airfield costs about 5 times the amount of hydro carbons to produce of same amount of electricity for land use.
So unless the H2 would produce trust 5 times more efficient than a hydro carbon (jet) engine your carbon foot print only increases.
Only the argument that could change this is that a jet engine delivers the CO2 directly high in the atmosphere and an electrical power plant low at the ground could extract the CO2 and inject into empty gas fields.
If your objective is to enlarge your payload (if tanks could be made lighter than 80 tons then go ahead.
If you want to reduce carbon foot print:
As long as we do not have a global surplus of green produced electricity, we do not have to bother to produce H2 by grey or black produced Electricity.
Electrolysis , cooling, pressurization, and (road) transport to the airfield costs about 5 times the amount of hydro carbons to produce of same amount of electricity for land use.
So unless the H2 would produce trust 5 times more efficient than a hydro carbon (jet) engine your carbon foot print only increases.
Only the argument that could change this is that a jet engine delivers the CO2 directly high in the atmosphere and an electrical power plant low at the ground could extract the CO2 and inject into empty gas fields.
The last two British Airways 747s left Heathrown this morning.
Sad day. Such a shame to see the back of an iconic BA type leaving LHR for the last time. My last flight on Victor Sierra to BOS in December 2019...I had no clue it would be my last ever.
Back when I spent several months wandering around TBA I couldn't be bothered to take a photo of a 747, as they were everywhere. Now, all of a sudden, they're gone... 
A sad day indeed for UK enthusiasts and those who flew on them, both SLF and FD. I do wonder why BA were fixed on today, as I'm sure in the big scheme of things it wouldn't have hurt to wait for good weather, so as to be able to do the parallel take-off and a much better optic to catch this moment in aviation history.
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The BBC showed it live during the Breakfast News. Sad to see. Pity they referred (twice) to the "engines cranking up".... Must have had early 747 engines? 