kimon
Posts: 252
Joined: Mon Nov 23, 2009 2:37 pm

741 Fuel Balance

Fri Jan 29, 2010 11:23 am

What is fuel balancing?
Is it now controlled by FADEC?

1641 -C- NO FUEL FLOW NOW FUEL FLOW ON NUMBER AH FOUR ENGINE
1644 -F- HOW AND OLD: Guangzhou - Baiyun (CAN / ZGGG) (closed), China">CAN WE HAVE NO FUEL FLOW IF WE GOT N1 AND EGT
1648 -C- WE MUST BE AH LOSIN' FUEL LIKE MAD OUTTA THAT -
1650 -F- *
1652 -C- NUMBER FOUR ENGINE YOU GOT THE THING BALANCED ON THE FUEL.
1657 -E- AH YES FUEL'S BALANCED.
Dum Romae consulitur, Saguntum expugnatur
 
lowrider
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RE: 741 Fuel Balance

Fri Jan 29, 2010 2:47 pm

You are making sure the fuel is distributed evenly between the wings. Since there are variations among the engines, you will get slight variations in fuel burns while. On either version 74, you vary the fuel use and pump configurations to correct fuel imbalances.

FADEC only deals with engine power settings.
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ex52tech
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RE: 741 Fuel Balance

Fri Jan 29, 2010 3:37 pm

On a 741 those engines were not FADEC equipped. Hard to believe that there are many 741s still flying. How old is this report.

On the larger airliners that I was in contact with, the method of fuel scheduling or balance, was to burn fuel out of the corresponding fuel tank to it's respective engine, #1 tank to #1 engine and on down the line. Then maintain the fuel level in those tanks by pumping fuel out of auxiliary or center fuel tanks, if they were being used, to the main tanks to maintain a high level of fuel in the tanks that the engines could suction feed out of in the event of power loss. Once the auxiliary or center tanks were empty the fuel in the inboard larger capacity mains was burned down to a level where all the main tanks were at the same level. Then each engine would burn off of its corresponding fuel tank, isolated to that tank.

In some cases there are internal leaks in the plumbing or manifolds, and the fuel level will grow in a tank when it should not, so one would have to either transfer fuel out of that tank, or cross feed it to another engine or engines to burn it off until a balance situation was reached.
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747classic
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RE: 741 Fuel Balance

Fri Jan 29, 2010 4:12 pm

Balancing the fuel on the classic 747's was accomplished by boost pump action from the tank with the higher. qty to the engine corresponding to the tank with the lower qty. This was done by feeding two engines on one tank via opening of the relevant X-feed valves.

In normal circumstances the maximum allowable X-ship fuel unbalance is 500kgs. In non normal circumstances (engine failure, internal fuel leak. etc) the limit is 2000kgs.

In extreme cases (large internal fuel leaks),it was also possible to operate the No 2 or 3 jettison pumps via the dump/refuelling manifold (dump valves closed !!!)and using the refuel vlv's to activ pump the fuel from from the main tanks 2 or 3 to the other tanks.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
B747FE
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RE: 741 Fuel Balance

Sat Jan 30, 2010 2:42 am



Quoting 747classic (Reply 3):
In extreme cases (large internal fuel leaks),it was also possible to operate the No 2 or 3 jettison pumps via the dump/refuelling manifold (dump valves closed !!!)and using the refuel vlv's to activ pump the fuel from from the main tanks 2 or 3 to the other tanks.

That is correct. However, since a tank-to-tank transfer requires the refuel valve in the tank selected to receive the fuel to be open, it can be done on the ground only. (Even though an optional fueling control module is installed on the P4 in some airframes)
Any tank (main's or CWT) to any tank = Ground
Any tank (main's or CWT) to any engine = Air

Regards,
B747FE.
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747classic
Posts: 1945
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RE: 741 Fuel Balance

Sat Jan 30, 2010 9:12 am

Quoting B747FE (Reply 4):
That is correct. However, since a tank-to-tank transfer requires the refuel valve in the tank selected to receive the fuel to be open, it can be done on the ground only. (Even though an optional fueling control module is installed on the P4 in some airframes)
Any tank (main's or CWT) to any tank = Ground
Any tank (main's or CWT) to any engine = Air



It was possible in all 747's I have flown with the old analogue fuel system and the cockpit fuel control module installed to bypass the groudsensing by operation of the override and battery switch on the F/E refuelling panel during flight. Opening of the refuelling vlv's was then possible in FLT.
Actually I had to use "this trick", when dealing with a heavy internal leak, transferring fuel from main tank 1 to 2 during crz.
However, after installing the new digital fuel indicating system it was not possible any more.

[Edited 2010-01-30 01:15:18]
Operating a twin over the ocean, you're always one engine failure from a total emergency.

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