Quote:
Originally Posted by Brickfire
Wonder if an a380 freighter would be viable with the upper deck refitted as a giant fuel tank
For the freighter, Google says 17 pallets up top, and 28 on main deck. Total cargo volume 1134 m^3.
Rough swag: 17/(17+28) = .38 upper deck volume ratio.
.38 x 1134 = 428 m^3
Assume you could use 80% of upper deck volume for fuel volume after accounting for for fuel tanks, MX access, and associated hardware: .8 x 428 m^3 = 343 m^3
Liquid H2 specific density = 71kg/m^3.
71 * 343 = 24,000kg H2
Liquid H2 energy density = approx 36,000 W*h/kg
24000 * 36000 = 864M W*h worth of energy on our upper deck.
A380 carries 320,000 L of Jet A (energy density 9,800 W*h/L):
320,000 * 9,800 = 3.136 Billion W*h
864M W*h H2 / 3.136B W*h Jet A = 27%.
So not quite 1/3 of the Jet A range. So the math says it's suitable for domestic ops, but not much long haul. Maybe barely transatlantic?
Yes you save some weight since Jet A is a lot heavier than H2 but you're going to use up a lot of that weight savings on the fuel tanks for liquid H2 since (unlike Jet A) it cannot be stored in the aircraft structure directly. You don't save much structural weight by ditching Jet A, since that lives in the wings and fuselage... both of which you still need. You might even need to add ballast to the wings since a heavy fuselage with light wings will result in additional cantilever stress on the wings (that's why we burn center/aft tanks first).
*** Disclaimer: Feel free to check my math, I did not bother.