A340 trim tank transfer

[WelshRoots]

just a bit of a rookie question here guys and gals but would appreciate any help.

During the cruise how does fuel burn affect CoG position? Now: is there a generalisation that can be made for widebodies or is it very type specific? Just figuring out the reason behind the fwd transfer of fuel from the trim tank on the A340. I'm guessing its the change in CoG due to fuel burn which means less loading is required on the THS. Could someone please explain the actual changes in CoG and aerodynamic loading etc. .

Cheers people..

WR

[Swedish Steve]

The A330/340 fuel trim system is designed to put the CG as far aft as possible in the cruise.
The aft CG limit is stored in the FCMC, and during the climb fuel is transferred aft to reach this limit.
Now as fuel is used in the cruise, the CG moves aft. As the aft CG limit is reached, the system transfers fuel fwd to the centre or wing tanks to reach another limit stored in the computor. This will happen regularly through the flight, because as fuel is used from the wing tanks the CG moves aft.