I recently noticed that the B747-400SF has a „minimum flight weight“, which means it has to carry a minimum of roughly 10 tonnes of fuel when there’s no cargo aboard.
Why is this?
The limiting factors that spring to my mind don’t work:
Can’t be about CG, as the ballast fuel is carried very close to the CG …
... Can’t be about wing bending moment, as the ballast fuel can be carried in the center fuel tank…
Well, why is this? (Oh, just in case: I’m trying to find out the engineering/flight mechanics background -- a simple “Because it says so in the handbook!” doesn’t cut it.)
