Fuel Savings From Cg

[FE Hoppy]

doesn't make it any less safe, just restricts max weight. The rules are set by those who's job it is to oversee safety. Our job is to maximise profit within those rules. This is a business not a sport.

[Angels 60]

Can't argue with that...if the numbers don't add up right, no one flies, it has to make sense financialy to fly a plane.....

Not being familiar with moving fuel forward and aft...do you try to move the fuel center of CG for take off, then aft once at cruise?

[exeng]

Have a natter with ex Concorde F/E's

They were fairly slick at moving fuel about.

For the rest of us on slower aircraft such as the 747 the fuel management was predicated on wing bending moment. So you got rid of the fuel in the centre tank as soon as you could (which also had the effect of moving the C/G aft) then burnt from the inners and then from all four mains.

Happy days they were


Regards
Exeng

[Angels 60]

That makes sense..thanks Exeng.

[OutOfRunWay]

Big Busses

I always thought the bigger busses, from the A310 onward used an automatic pumping system to keep CG aft (within limits) pumping fuel into the horizontal stabiliser?

Isnt that why the stab tanks are called trim tanks? Any big bus drivers out there who can correct me..

Im only a little bus man...

regards

OORW

[groundfloor]

This is what the Airbus 34-6 book says:


The trim tank transfer system controls the aircraft's Center of Gravity (CG).
The system either transfers fuel to the trim tank (aft transfer), or from the trim tank (forward transfer).
This movement of fuel changes the aircraft's CG.
When the aircraft is in cruise, the system optimizes the CG position to increase fuel economy by reducing drag.
Normal operation is automatic, but the crew can manually select a forward fuel transfer.
The Fuel Control and Monitoring Computer (FCMC) calculates the aircraft's CG and compares it to a target value. (This target depends on the aircraft's actual weight. See AFT CG Target Graph below).
Based on this calculation, the FCMC determines the quantity of fuel to be moved aft or forward in flight.

It does it very effectively.

[Admiral346]

All the A330/340 family do that kind of transfer, usually after takeoff - there might be fuel in the stabilizer tank (trim tank) during takeoff, but that depends on the overall quantity taken.

If this particular system is inoP (the aft transfer), there is a fuel penalty according MEL of something like 1.5 - 2% (I forgot, it's been a while now).
So this percentage should be what is saved by having an aft CG.

Nic