Which aircraft are you experiencing this issue in?
Boeing 747
Are you using Developer Mode or made changes in it?
no
Have you disabled/removed all your mods and addons?
yes
Brief description of the issue:
Much improvement, eg synoptics, all tanks working. However, the reserve tanks do not drain quickly enough to keep 1 and 4 fed. the reserves started at @10K lbs of fuel, and they started draining when tanks 1 and 4 reached about 13.5K. By the end of the flight, the reserve tanks still had more in them than tanks 1 and 4. I think the engines would have demonstrated fuel starvation were they dependent only on the reserve tanks replenishing 1 and 4
Provide Screenshot(s)/video(s) of the issue encountered:
Detailed steps to reproduce the issue encountered:
fly with the main tanks 1 and 4 having more than 13.5k lbs fuel in them and the reserve tanks with a noticeable quantity in them. Even at cruise, the main tanks will feed the engines more quickly than the reserve tanks can replenish them.
PC specs and/or peripheral set up if relevant:
Build Version # when you first started experiencing this issue:
AAU 2 Beta (1.33.7.0)
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Do you have the same issue if you follow the OP’s steps to reproduce it?
Provide extra information to complete the original description of the issue:
If relevant, provide additional screenshots/video:
We looked into that when the rework was ongoing.
Pilot feedback suggested that the drain from engine consumption is probably higher than the gravity based transfer of fuel from reserves.
At the moment we have no definitive data on this.
747 type-rated pilot here. I can confirm that reserve tanks 1 and 4 should transfer faster than the current implementation. I don’t have an exact number for the time, but from memory (and a rough estimate), the transfer would usually be complete within 20 to 30 min.
The reserve tanks transfer into the main tanks faster than the engine fuel flow. The idea is that after the fuel has transferred, Main Tanks 1, 2, 3, and 4 all have the same quantity of fuel.
The last time I flew the beta version of the 747, I remember noting that the transfer rate was significantly slower than in the real aircraft. In fact, some fuel remained in the reserve tanks by the end of the flight.
If the reserve tanks drained at the same rate as the stabilizer tanks, that would be a step in the right direction. Also, although I noticed that the fuel burn was pretty close to simbrief on even a 15 hour flight, the “fuel remain” in the Prog page is not accurate. Salty’s Prog page is much more accurate in predicting fuel burn at this point, but they use engine calculations that end up with too much fuel still in the tanks at completion of the flight.
The stab tank transfer is driven by two fuel pumps. I doubt that the gravity based fuel flow from the reserves would achieve the same rate.
Since you term the fuel system as “work in progress” and adjusting the gravity based fuel flow puts it “in the right direction”, I am curious as to what you feel like is not working for you otherwise. Feedback is always welcome.
Right now, I think is is significant enough that I still have reserve tanks partly full upon completion of a flight. The rated 747 pilot described a 20-30 time to drain the aux tanks. I would think that would be a good target. Since they are gravity drained, why did they stop draining when I reverted back to OVRD and stopped using tanks 1 and 4? I would understand more easily if they were pump fed. I purposely tested where early in the flight I got below the trigger point. While 1 and 4 were pumping the aux tanks drained. But when I stopped, immediately the aux tanks stopped draining and did not resume even hours later, until I turned back on 1 and 4. Is there some sort of check valve?
Thank you.
Yes. The reserve transfer rate is already being worked on based on all you guys’ feedback.
As to why it would have closed the transfer valves in your scenario is hard to tell from here.
It is solely based on tank quantity of main 1 & 4 (aprox. 6100kg) and not being on the ground.
Additionally there is a switch on the overhead panel to force the transfer.
If you can get us steps to reproduce what you are seeing or a video, that would certainly help.
Thank you.
Along these lines, anyone have a good document or YT video on the 747 Fuel System? I found an old Salty Sims video below which is a quick “what to do”, but looking for something more in-depth.
Been away for awhile. Since you have referred to Salty’s, they have a fuel system guide. It still is not as in depth as what you might want, but it may be helpful. I don’t have the link right at hand, but Salty’s discord has it.
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