A 747 guru once told me that the theoretical range limit of a 747 was 29 hours (close to the 33 hours quoted above for 3%/hr). If you had unlimited fuel capacity, the longest you could fly for was 29 hours. Any fuel added above that would be burned by the time you reached 29 hours. (For G&D's son's benefit, flying 29 hours in a 747 would require "infinity fuel")...
It would be interesting if someone could post the kg cost of carriage for a 787-9 or A350 at max range (full tanks) and MTOW. I'm guessing it would be at least 500 kg per tonne but these aircraft are obviously more efficient than the 747.
I recall once reading the cost of carriage for a Saturn V rocket. I don't recall the figure but it was so close to 100% the fact that it could actually escape the planet is staggering. If Earth was a few percent larger than it is we would never have made it to the moon. It would have become theoretically impossible from a single launch. Of course an orbital re-fuelling stop enroute would still have been a possibility.
Which begs an amusing question. If Qantas wanted to fly Sydney to London direct (probably around 21-22 hours), what would be the cost of launching an airborne refuelling tanker out of Singapore en-route (Air Force 1 style)?
I'm sure someone's suggested it before, just prior to being laughed out of the bar...
