I have quite a few problems / questions about the fuel system in the default Boeing 747-8i. (Unmodded, Xbox)
(The Reserve and STAB tanks are completely unusable, let’s even forget them, I have no direct problem with that.)
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A big problem: If there’s no fuel in the inner main tanks (Main 2 and 3), the APU simply doesn’t turn on. This is a problem, because on shorter flights you set a lower amount of fuel, and MSFS’s slider empties the Center and Main 2 and Main 3 tanks first. The only way to start up the plane is to allocate at least 1 “slider unit” of fuel in Main 2 and 3.
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An even bigger problem: As soon as the fuel depletes from Main 2 and 3, engines 2 and 3 lose power respectively. Even with all fuel pumps open, there is no crossfeed from Main 1 to engine 2 and Main 4 to engine 3. The diagram shows that the XFEED valves are open but the fuel doesn’t reach the inner engines. The only way to restart them is to manually put fuel in the inner tanks via the toolbar, and/or use quick stop and quick start shortcuts. The only way to “safely” fly is to load enough fuel into Main 2 and 3 so that they feed engines 2 and 3 during the whole flight, because crossfeed doesn’t work most of the time. Annoyingly enough, it does work sometimes, even though I’m doing everything the same every time.
Am I doing something wrong or is this system so glitched? What is the “proper” (e.g. reliable) way to load fuel in the 747?
Caveats: i use salty modded 747 and haven’t read IRL procedures for this.
Stability tanks have, irl, stopped being used. They are nonfunctional in game. Do not load anything into them. (EDIT: this may be incorrect!)
When I load fuel, i use the in game fuel loader. I use simbrief to calculate my fuel load, then I drag the total fuel weight as close as I can get to that number then top it off with 1-2 “units” into the center tank.
What this does is put the majority of fuel into tanks 2&3 which are your main storage tanks. I would guess about 2/3 of fuel (lol) goes into these 2 tanks with the remaining fuel going to 1&4 tanks.
Most fuel should be in 2&3 with OVRD 2&3 pumps on from takeoff throughout the flight until the tanks 2&3 are equal to 1&4 and center tanks empty. At that point, you are supposed to shut off OVRD and xfeed to both sides.
To be clear:
Takeoff= all pumps on
Center tanks= off when empty
OVRD pumps and xfeed = off when 1&4=3&4
You are now direct to engine feeding and should be okay for the rest of the flight.
However, if tanks 2&3 ovrd pumps have been on too long (happens to me most flights) and you now have more fuel in the wings (1&4) you SHOULD be able to turn off pumps 2&3 (and ovrd pumps) and have the 1&4 pumps feeding all 4 engines to re-balance the plane through the xfeed. When they’re equal again, turn 2&3 pumps back on, verify flow, then shut the xfeed.
If that’s not possible then something is wrong with Asobo fuel system because 1&4 pumps can definitely fuel all 4 engines on their own (edit, this is not true if 2&3 run to empty). But again, APU draws from tank 2 i believe so make sure you fill with about 2/3 into 2&3, then 1/3 into 1&4, then center for whatever else you need topped up.
Wingtip tanks only get filled on ultra long flights i believe
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The problem is that MSFS’s fuel logic works the opposite way. The fuel slider fills the wingtip tanks first, and only starts filling 2&3 after 1&4 are full. I don’t use Simbrief, I only watch the range on the world map, and try to adjust fuel percentage accordingly.
What I will try is after figuring out the percentage, I’ll switch tanks. Manually fill 2&3 until the overall percentage reaches what I need. Or even better (but even more cumbersome), fill up all Mains evenly, but only so much as to reach the overall percentage needed. This way XFEED should not even play a part.
Quite annoying, though, to be honest. Thank you for the detailed information!
OK, so I ended up with this setup. On shorter flights I empty all tanks and fill only Main 2 and 3 as needed. This feeds all engines for the whole flight.
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BTW I was wrong. I had my center engines (2&3) go out on a long flight last night as all fuel collected in wings while I let the sim run to test.
Here’s what happened to my fuel setup:
Here’s what I got from the Salty discord on fuel management
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Thanks. The default system is different in a way that there’s no usable STAB tank (and reserve tanks either), but the rest is the same.
Yes, it looks as though Main 1 & 4 are unable to feed engines 2 & 3 respectively, though this behaviour is not consistent. Amazingly I have flown many hours with empty Main 2 & 3, only putting 1 “unit” of fuel in them so that the APU could be turned on. By the time I finished taxiing, they would about to run out, I switched off all their valves (including OVRD) and Mains 1 & 4 kept feeding all engines without problems. Other times, engines 2 & 3 would just stop, just like on your photo. I don’t know which is the correct behaviour but I won’t fly like that again.
I still haven’t tested the Center tank, never needed it yet.
Overall it’s not an overly complex system once you learn it. But the default system’s behaviour is not consistent. We just have to make sure to never let Mains 2 & 3 deplete.
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I wonder if you simply turn OVRD off before 2&3 run out if the other tanks can keep 2&3 running or if they’ll still go out? I will try that next time I do a long 747 flight and post here - might be a while haha
