747 stabilizer fuel

[tornadoflyer]

Hi,

I would very much appreciate it, if another forum member could explain to me why the 747 has fuel in the stabilizer, where exactly it is located and how and by what means it is trasferred within the overall flow of the 747 fuel system. Any additional information in this context would also be nice.

Thanks in advance for any replies.

[TopBunk]

Why does it have it?

To increase range.

How does it work?

It gets transferred into the centre wing tank after an amount is burnt off. The transfer is by a pair of AC moto driven transfer/jettison pumps.

[gas path]

Consists of the centre torque box and inner third of the stab, there is also a small eleven gallon vent surge tank on the r/h side.
total qty. is 12492 ltrs.
Transfer (into the CWT) takes place when the CWT fuel load drops below a set figure, it is controlled by the fuel management system through 2 pumps and a transfer hose.

[BlueEagle]

Last time I looked the transfer starts when the centre wing tank has reduced to 36,470kgs.
If the transfer fails to take place then if your gross weight is less than 378,000kgs you have, as usable fuel remaining, wing tanks 1 and 4 and main tanks 2 and 3 down to 7,700kgs in each, by which time you must have landed to maintain c of g limits.
If your gross weight is more than 378,000kgs at the time the transfer fails then you have, as usable fuel remaining, everything in wing tanks 1,2,3 & 4. Land before main tank 2 & 3 are empty to maintain c of g within limits.

[barit1]

Why does it have it?

Yes, it increases range; but even if you aren't on a very long segment it is of use, because it optimizes CG for lowest cruise drag, thus lower fuel burn.

(Funny how every decade or so someone new discovers this bit of aeronautical enlightenment. I recall a UAL F/E getting a nice bonus 40 years ago for suggesting a standardized loading routine toward the aft end of the CG envelope!)

[tornadoflyer]

Thanks a lot for all the detailed replies. In this context, I have one more question. Is there any way to reverse the flow of fuel, so that it flows back from the CWT to the stabilizer or is it a one way flow always from the stabilizer?

Thanks again for any comments.

[gas path]

One way only . . . . . unless it's on the ground being refuelled:p