ferpe From France, joined Nov 2010, 2804 posts, RR: 59 Posted (10 months 3 weeks 2 days 3 hours ago) and read 3726 times:
Fuel carried in the wings causes less empty weight increase as it alleviates wing bending moment ( at least does not increase it as much as would more payload/fuel in the fuselage).
Given that modern airliners have outer and central wing tanks (A350 shown) what is the normal consumption strategy from an FCOM or SOP perspective? The 788 FCOM says central first, then wing tanks, any ones that differs?
Pihero From France, joined Jan 2005, 4460 posts, RR: 76
Reply 1, posted (10 months 3 weeks 2 days 2 hours ago) and read 3683 times:
Quoting ferpe (Thread starter): what is the normal consumption strategy from an FCOM or SOP perspective?
The systems are different but the basic philosophy is :
- Improve the wing bending moment, hence :
- Center tank first
- Wing inner tanks second
- Wing outer last.
It is to be noted that, apart from the fuselage center tank, we do not empty the remaining tanks before switching to the next.
For instance, the A330 / 340 engines are always fed from the wing inners
That means that fuel will be transferred from the center to the wing inners,
Then from the wing outers to the inners.
That basic philosophy stems from the A320 system.
On the 744, things are quite a bit more complicated as the engines are fed either from the center or from each engine tank... The 777 has a much simpler system, quite similar to the Airbus set-up, but engine feed can be - and is initially - from the fuselage tank.
That philosophy here is of course very simplistically described ( for instance, the *triggereing* levels of transfer are not included, nor is the influence of the tail trim tank for CoG control ... etc... )
SmittyOne From , joined Dec 1969, posts, RR:
Reply 2, posted (10 months 3 weeks 16 hours ago) and read 3340 times:
Quoting Pihero (Reply 1):
On the 744, things are quite a bit more complicated as the engines are fed either from the center or from each engine tank...
Note: Not a pilot, just a bit of a flight simulator nerd...
If the materials I have are accurate, the 744 feeds as follows:
1) On takeoff, the center tank feeds the outboard engines 1 and 4 while the inner wing tanks feed engines 2 and 3
2) Once airborne, all engines feed from the center/stabilizer tanks until they are empty
3) When all center tanks are empty, the engines feed from the larger, inner pair of wing tanks (corresponding to engines 2 and 3) until the fuel in each of the four wing tanks is equal...total fuel of ~120,000lb if I recall correctly.
4) Then feeds directly from each outer wing tank to its corresponding engine and engines 2 & 3 from their corresponding tanks with the crossfeed between them open.
All this happens automatically except that the pilot is required to manually close the crossfeeds to engines 1 & 4 and turn off override pumps that are no longer required for the final 'tank to engine' configuration in step 4.