i may be wrong but I am of the understanding that planes are usually fuelled from the outer wings in towards the center tanks and that the center tanks are used up first, but on my last flight on the a380 tanks 1 and 4 were less than the tanks 2 and 3 even though i filled those up first. is the fuel system in the a380 accurate enough to do this? or am i fueling the plane wrong?
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Hey mate, a plane need to keep his center of gravity near his center of lift, meaning that outer tank like 1 and 4 will be emptied first as you can see in this picture.
It’s a common procedure for every aircraft, first outter tank, then the other one closer to the body.
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@Klxndo and @LaTrixtance You made me curious about how complex the A380 fuel system actually is, making automation essential to reduce pilot workload. I saw it described as being similar to Concorde.
In addition to CG and everything else they also manage wing bending during takeoff (which I didn’t expect):
The following from: The A380 Fuel System. – Captain Dave
"In flight the transfer of fuel between tanks is completely automatic (so long as the system is working properly!). Shortly after takeoff what is known as a Load Alleviation Transfer takes place. Here, fuel is transferred from the inner or mid tanks to the outer tanks in order to reduce the upward bending of the wing.
Anyone who has watched an A380 take off from a window seat may have noticed the wing tips lifting by up to 4 metres during takeoff due to the airflow. Transferring fuel to the outer tanks reduces this. You may ask why these tanks are not, therefore, filled before takeoff. That is because the weight of the engines makes the wings bend down and any extra fuel in the outer tanks would only increase this. Filling the outer tanks also has the effect of moving the C of G rearward to around 41% This is the approximate targeted C of G for the cruise.
As the flight progresses the fuel transfer system keeps the fuel level in the feed tanks at the same level, to within 1000kg. The sequence of fuel transfer is as follows:-
- Inner tanks to feed tanks
- Mid tanks to feed tanks when the inners are empty
- Trim tank to feed tanks when the mid tanks are empty
- Outer tanks to feed tanks when the trim tank is empty
The fuel transfer rate from inner or mid tanks to the feed tanks is around 10000 kg per hour per feed tank. Once trim tank transfers start they are performed in a way which maintains the optimum C of G for as long as possible, until eventually the trim tank is empty. From this point on the C of G will continue to move forward as fuel is used and transferred from the outer tanks…
…By now you have probably come to the conclusion that the A380 fuel system is reasonably complex. I’d agree!
Now consider that everything I have described above is what happens when it is all working correctly! With so many pumps, valves and sensors we also have to consider how we handle things when part of the system stops working. It is these considerations which make the A380 fuel system quite so challenging for us as pilots…"
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What an incredible excerpt that you provided! The sheer complexity of the system is incredible to me. After reading something like that I tend to also think of all the other complex systems that function simultaneously within the aircraft during flight and that alone blows my mind.
I apologize if I misunderstood, but could you expand upon what is meant by targeting a 41% C of G? Is that referring to keeping it at 41% of the length of the aircraft?
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Thanks!, and good question.
I found:
Mean Aerodynamic Chord (MAC) | SKYbrary Aviation Safety
"In large aircraft, centre of gravity limitations and the actual centre of gravity are often expressed in terms of percent MAC…
…percentage of the distance from the leading edge of MAC to CG with respect to MAC itself.
…Mean Aerodynamic Chord is the average chord length of a tapered, swept wing."
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Wow nice explanation, thank you mate, it’s more complexe than I thought cough, cough…
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I wouldn’t have gone there if you hadn’t pointed the direction. That image you gave was like, what?! Imagine the control panel for the manual override, and the training to manage that.
It’s amazing humans cooperate to make something so complex like that, that works so well.
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This is so complex ! It’s horribly beautiful and technic, thank you for the picture, now i learned something new fue to @adit explanation. Thanks guys
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Awesome, I appreciate the clarification! This was a good refresher on C of G and Center of Lift. As I do believe that C of L would be further along the MAC. In that case, would C of L also be measured as a percentage?
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Reminds me of the Concorde in this way. Now that was a convoluted system.
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