GSX Incorrectly fueling default 747-800

[Awemeter]

The 748 has an interesting fuel tank setup. A real-life 747 pilot told me that main 1&4 must be full prior to adding fuel to reserve 1&4. Mains 1&4 can only be full if mains 2&3 have equal to or more than full tanks 1&4 + reserve. Only after Mains 1&4, 2&3, and both res tanks are fuel can the center and stab tanks be fueled. GSX attempts to load main 2&3 to its maximum capacity before loading 1&4 first which is incorrect. Also the res tanks should only be filled when the total of main tanks 2&3 is higher than the maximum capacity of 1&4. The res tanks would be filled in order to make main tanks 1&4 + res tanks = main tanks 2&3. Would it be possible for GSX to correct the fueling error or is this a simulator limitation?

[Captain Kevin]

The problem with default airplanes is I don't think they ever got the fueling process correct.

[Awemeter]

It uses the default fuel panel so the process of how to load fuel is entirely up to the user and maybe gsx.

[virtuali]

Do you happen to know if this order is specific to the 747 ?

Right now, GSX uses this priority to fill up tanks (on default airplanes only, where it controls the fueling process):

1 - Left and Right Main (2&3)
2 - Left and Right AUX (1&4)
3 - Left and Right Tip (Res 1&4)
4 - Center
5 - External

So, if I understood correctly, you wanted to change this sequence to be like this ?

1 - Left and Right AUX (1&4)
2 - Left and Right Tip (Res 1&4)
3 - Left and Right Main (2&3)
4 - Center
5 - External

Note that, the default 747-800 doesn't have any tanks for the stabilizer defined, it has 3 center tanks all in the center, with center3 defined but with 0 capacity, and 2 external tanks, also defined at 0 capacity so, it doesn't seem to match the real airplane configuration exactly.

My question would be if this sequence would be ok for every airplane, or we might need to think adding airplane-specific sequences, something that might be overridden in the airplane profile.

[Captain Kevin]

I'm afraid the refueling sequence gets a little more complex than that for the 747-8, and really, the 747 in general. Just throwing some random values here for the 747-8 using PMDG as a reference.

40,000 pounds:

Main 1 and 4: 10,000 each, 20,000 total.
Res 1 and 4: 0 each, 0 total.
Main 2 and 3: 10,000 each, 20,000 total.
Center: 0.
Stabilizer: 0.

80,000 pounds:

Main 1 and 4: 13,400 each, 26,800 total.
Res 1 and 4: 6,600 each, 13,200 total.
Main 2 and 3: 20,000 each, 40,000 total.
Center: 0.
Stabilizer: 0.

120,000 pounds:

Main 1 and 4: 19,700 each, 39,400 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 30,000 each, 60,000 total.
Center: 0.
Stabilizer: 0.

160,000 pounds:

Main 1 and 4: 29,700 each, 59,400 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 40,000 each, 80,000 total.
Center: 0.
Stabilizer: 0.

200,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 54,100 each, 108,200 total.
Center: 0.
Stabilizer: 0.

240,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 74,100 each, 148,200 total.
Center: 0.
Stabilizer: 0.

280,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 94,100 each, 188,200 total.
Center: 0.
Stabilizer: 0.

320,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 96,700 each, 193,400 total.
Center: 34,800.
Stabilizer: 0.

360,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 96,700 each, 193,400 total.
Center: 66,100.
Stabilizer: 8,700.

400,000 pounds:

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 96,700 each, 193,400 total.
Center: 97,300.
Stabilizer: 17,500.

421,142 pounds (max):

Main 1 and 4: 35,600 each, 71,200 total.
Res 1 and 4: 10,300 each, 20,600 total.
Main 2 and 3: 96,700 each, 193,400 total.
Center: 113,900.
Stabilizer: 22,100.

From what I can tell, main 1, 2, 3, and 4 will remain equal initially until main 1 and 4 reach 13,400 pounds, then reserve 1 and 4 will start to fill up until reaching maximum capacity. The sum of main and res 1 and 4 would then be equal to main 2 and 3 up until main 1 and 4 reach capacity, at which point main 2 and 3 are filled to capacity, followed by the center. Somewhere down the line, the stabilizer tank starts to get filled, but it's not clear when that is or at what rate it gets filled relative to the center tank, though I guess this point wouldn't be relevant if the default 747-8 doesn't have a center tank anyway. This is specific to this airplane, as with most twin-engine airplanes only have the main wing tanks and the center tank, so you would fill up the wing tanks first before filling up the center tank. The 747-400, on the other hand, has the reserve tanks tied to 2 and 3 rather than 1 and 4, so here are values for that, again, from PMDG as reference.

40,000 pounds

Main 1 and 4: 10,000 each, 20,000 total.
Main 2 and 3: 10,000 each, 20,000 total.
Res 2 and 3: 0 each, 0 total.
Center: 0.
Stabilizer: 0.

80,000 pounds

Main 1 and 4: 20,000 each, 40,000 total.
Main 2 and 3: 20,000 each, 40,000 total.
Res 2 and 3: 0 each, 0 total.
Center: 0.
Stabilizer: 0.

120,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 30,000 each, 60,000 total.
Res 2 and 3: 0 each, 0 total.
Center: 0.
Stabilizer: 0.

160,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 43,600 each, 43,600 total.
Res 2 and 3: 6,400 each, 12,800 total.
Center: 0.
Stabilizer: 0.

200,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 61,100 each, 122,200 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 0.
Stabilizer: 0.

240,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 81,100 each, 162,200 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 0.
Stabilizer: 0.

280,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 84,000 each, 168,000 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 34,100.
Stabilizer: 0.

320,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 84,000 each, 168,000 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 65,600.
Stabilizer: 8,500.

360,000 pounds

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 84,000 each, 168,000 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 97,000.
Stabilizer: 17,100.

382,928 pounds (max)

Main 1 and 4: 30,000 each, 60,000 total.
Main 2 and 3: 84,000 each, 168,000 total.
Res 2 and 3: 8,900 each, 17,800 total.
Center: 115,000.
Stabilizer: 22,100.

From what I can tell, main 1, 2, 3, and 4 will remain equal initially until main 1 and 4 reach capacity. Main 2 and 3 will then continue to be filled until reaching 43,600 pounds, at which point reserve 2 and 3 start to get filled until reaching capacity. Once that's done, main 2 and 3 will continue to fill to capacity, followed by the center tank. Stabilizer tank gets filled at some point, but again, it's not clear when or how it gets filled relative to the center tank.

[virtuali]

I'm afraid the refueling sequence gets a little more complex than that for the 747-8, and really, the 747 in general. Just throwing some random values here for the 747-8 using PMDG as a reference.

Doesn't make much sense trying to replicate that on a default airplane. Users interested in such detail will use a realistic 3rd party add-on, and those won't be fueled by GSX anyway.

[airifr]

The stab tanks get filled after center tank is full, then during flight when center tank fuel decreases from about 64,000 pounds to 3,350 pounds stab tank fuel transfers to center tank intermittently. Only the 747-8i has stab tank, the freighter -8f is not equipped with stab tank.
The default MSFS 747-8 is the intercontinental not the freighter, so it does have the stab tank, and filled all tank to max on a flight from Sydney to LAX and the fuel logic was accurate enough.

Not sure why GSX won't fix the fueling for the 747, one fix for the 747-8 and one for the 747-400, just need to program the sequence in fueling, just different than the one implemented already?
So we can't use GSX fully with the 747, only with twin engines??

Especially with the nice feature with Simbrief fuel automatically populated in the fueling choices..

All my MSFS 747-8 flights I have to fly with Mains 1 4 empty and x/feed engines 1 and 4 from 2 and 3 when using GSX, that's normal?

[Awemeter]

Do you happen to know if this order is specific to the 747 ?

Right now, GSX uses this priority to fill up tanks (on default airplanes only, where it controls the fueling process):

1 - Left and Right Main (2&3)
2 - Left and Right AUX (1&4)
3 - Left and Right Tip (Res 1&4)
4 - Center
5 - External

So, if I understood correctly, you wanted to change this sequence to be like this ?

1 - Left and Right AUX (1&4)
2 - Left and Right Tip (Res 1&4)
3 - Left and Right Main (2&3)
4 - Center
5 - External

Note that, the default 747-800 doesn't have any tanks for the stabilizer defined, it has 3 center tanks all in the center, with center3 defined but with 0 capacity, and 2 external tanks, also defined at 0 capacity so, it doesn't seem to match the real airplane configuration exactly.

My question would be if this sequence would be ok for every airplane, or we might need to think adding airplane-specific sequences, something that might be overridden in the airplane profile.

It would definitely be aircraft specific but unfortunately, it's not as simple as stated. Res 1 and Res 4 should only be filled if main 2+3 is higher than the max capacity of main 1+2. Res 1 and 4 are used to give main 1 & 4 the extra boost in capacity. I don't know the actual sim names for the tanks so I am just using the names that are displayed on the fuel page of the 747.

[airifr]

 "I don't know the actual sim names for the tanks so I am just using the names that are displayed on the fuel page of the 747."

What you mean sim names for the tanks?


Maybe Asobo could correct the tanks filling priorities so that when moving the main fuel slider at the top in %, the corresponding tanks below should fill in quantity not in %, so that the fueling logic could be respected, then GSX could read MSFS fuel logic. Example, when in the fuel loading menu, say we move the main slider to 20%, which is 80,000lbs (we're assuming 400,000lbs capacity rather than 421,000lbs for simplicity for the example calculations), main 1 2 3 4 sliders should move together as quantity not percentage, ie 20,000lbs each, then for higher % on the main fuel slider, they continue moving equally as quantity then when main 1 4 max res 1 4 start filling equally as quantity, together with main 2 3, then when res 1 4 max ( this where tank to eng config stops for the -8, ovrd 2 3 come on anytime after res 1 4 max) main 2 3 continue equally alone until max then center etc..