Originally Posted by
B744IRE
Cylindrical tanks on the upper deck and above the main deck ceiling...and maybe in the centre wing tanks?
Center wing tank is a non-starter - the beauty of Jet-A is that it doesn't care if you have big pieces of structure in the middle of the tank - you can't even think of doing that with cryogenics. At best you could put a large number of small tanks stuck between the primary structural elements - but integrating a large number of small tanks is a nightmare (especially when refueling). It's also very expensive.
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.