Center Fuel Tanks on long hauls

[jstonge24 0]

Hey everybody,

 

I am looking to do some extremely long flights in the 777-200 and I had a question about the actions of the center fuel tanks. I have noticed that during flight, when I have fuel in the center tank, I end up having to turn the center pumps off about 4 or 5 hrs in. Normally, this isn't an issue, but since some of these flights that I want to try will run overnight, while I'm asleep, I was wondering if there is a way to either have it switch over automatically to the wing tanks or to have it take fuel from the wing tanks AND the center tanks at the same time.

 

Thanks,

 

Joel

[77west 139]

Hey everybody,

 

I am looking to do some extremely long flights in the 777-200 and I had a question about the actions of the center fuel tanks. I have noticed that during flight, when I have fuel in the center tank, I end up having to turn the center pumps off about 4 or 5 hrs in. Normally, this isn't an issue, but since some of these flights that I want to try will run overnight, while I'm asleep, I was wondering if there is a way to either have it switch over automatically to the wing tanks or to have it take fuel from the wing tanks AND the center tanks at the same time.

 

Thanks,

 

Joel

 

Hi Joel

 

The reason the system uses fuel from the center tank first is that the fuel in the wings helps to relieve the bending moment due to the airplanes weight. The system will always use fuel from the center tank first.

 

However - in your situation, I think that the center tank pumps automatically turn off at some point, even though you will still get an EICAS message and amber light on the overhead pump switch.

 

So whilst not entirely realistic, I don't think your flight will crash...

[jcalder 25]

Well, to be fair it's not entirely realistic to have the pilot sleeping with no one in the cockpit either.  If you don't tell anyone, nobody will know whether or not the amber light is on

[bjratchf 80]

Does the PMDG simulate the nitrogen precharge like in 767 aircraft? 

[GolfSierra 5]

However - in your situation, I think that the center tank pumps automatically turn off at some point, even though you will still get an EICAS message and amber light on the overhead pump switch.

 

Really? I always thought the center pumps will eventually overheat if you leave them on for too long, without enough fuel in their tanks. Or does that only happen in the 737?

 

@ Joel:

 

Why don't you use the Auto Cruise to speed things up until to you get to the point where you need to turn off the center fuel pumps - then go to sleep?

 

P.S.: I hope you won't oversleep. :wink:

[PMDG777 231]

 

 

Why don't you use the Auto Cruise to speed things up until to you get to the point where you need to turn off the center fuel pumps - then go to sleep?

 

Could be VA restrictions. In one of my VAs, increased simulation rate is banned and in the other, you only get the actual real world hours flown, not the sim hours.

[77west 139]

 

 

Really? I always thought the center pumps will eventually overheat if you leave them on for too long, without enough fuel in their tanks. Or does that only happen in the 737?

737 - pumps blow up. 777 - pumps forgive you and turn themselves off - I think. I am a bit hazy on that.

[Ralgh 43]

At least on American 737s, and I think all 737s will be converted to this, each center tank pump will automatically shut off, after a short delay, when that pump’s sensor detects low output pressure. If we have more than 1000 pounds of fuel in the center tank at departure we turn both pumps on. We leave them on until one pump indicates low pressure, then we turn that one off. We turn the other pump off when the pump indicates low pressure and the center tank is empty. 

[jstonge24 0]

Thanks everybody! I'm debating on whether or not to leave my system running overnight due to a fear of overheating. Will keep this stuff in mind though!

[77west 139]

At least on American 737s, and I think all 737s will be converted to this, each center tank pump will automatically shut off, after a short delay, when that pump’s sensor detects low output pressure. If we have more than 1000 pounds of fuel in the center tank at departure we turn both pumps on. We leave them on until one pump indicates low pressure, then we turn that one off. We turn the other pump off when the pump indicates low pressure and the center tank is empty. 

 

That makes sense. Seems like a simple mod to make.

[downscc 1,327]

 

 

Seems like a simple mod to make.

 

LOL relatively simple. No such thing as a "simple" modification to an aircraft. First of all you need 100 lbs of paper for every pound of new equipment, get it approved by governments, provide tests to ensure the pressure sensor doesn't work backwards, and etc....

[PMDG777 231]

LOL relatively simple. No such thing as a "simple" modification to an aircraft. First of all you need 100 lbs of paper for every pound of new equipment, get it approved by governments, provide tests to ensure the pressure sensor doesn't work backwards, and etc....

 

Not to mention the fuel system software modifications and the hundreds of thousands of dollars worth of R&D and testing.

[Alpha Floor 237]

Thanks everybody! I'm debating on whether or not to leave my system running overnight due to a fear of overheating. Will keep this stuff in mind though!

 

Joel, you can go to bed and relax. Even if those pumps overheated (which they won't, they'll turn themselves off), who cares? The aircraft won't explode anyway.

 

In the morning you can turn those switches off.

[pete_auau 1,152]

Joel, you can go to bed and relax. Even if those pumps overheated (which they won't, they'll turn themselves off), who cares? The aircraft won't explode anyway.

 

In the morning you can turn those switches off.

 

 

That's  depends  on a few  things  when Joel wakes  up,   did the power  go in the night,  aircraft hits  some  turbulence  and  autopilot  switches  off :smile:

[77west 139]

That's  depends  on a few  things  when Joel wakes  up,   did the power  go in the night,  aircraft hits  some  turbulence  and  autopilot  switches  off :smile:

 

My cat once went to sleep on the controls somewhere over the pacific. Woke up to find the 777 flopping about on the sea surface like some deranged dragonfly. (crash turned off)