The location of fuel pump of 744

[kuobin]

Hello,any body got ideal why no.1 and no.4 fuel pumps of 744 are actually located inside of n0.2 and n0.3 tamks,Is that for better cooling or .....

[belowMDA]

I don't know for sure because I don't fly the 747, however the same thing is done in the 737 where the centre tank pumps are actually located in the main wing tanks. It isn't written in the vol 2 so you don't need to know it, but I suspect it is as you say for cooling. The centre tank fuel is used first and then the main wing tanks, so the centre pumps should always be cooled by surrounding fuel even when the centre tank is empty. The theory also being that the wing tanks should never get that empty

[gas path]

It's not for cooling as the 'turtle shells' that the pumps sit in are completely uncovered by the time the inb'd mains are down to about 28500kgs.
More than likely it is to ensure that that maximum amount of fuel is available for use from the outbd mains as the fuel pick ups are just outbd of the (inbd) tank wall, and space is at a bit of a premium. Not that you'd see it (hopefully!) but the aft boost pumps will run dry first.

[coded_messages]

????????

So how is fuel pumped out of Mains 1 and 4 then?

[Silverado]

The pumps are enclosed in a housing ("turle shell") which is supplied fuel through gravity via plumbing from #1 or 4, which is then pumped into the fuel feed manifold. So the #1 and 4 pump housings may be uncovered when #2 or 3 tanks deplete however they will still be primed and able to supply fuel until #1 or 4 tanks empty.