[2.9.21.16552] Cells 5 and 6 do not feed while internal wing tanks are feeding

[Stickler]

As seen in the attached track, cells 5 and 6 currently do not feed into cells 1 and 2 after the internal wing tanks have gone through their first cycle of replenishing cell 3. This behaviour persists while the internal wing tanks are not empty and the internal wing transfer switch is in NORMAL. Cells 5 and 6 will feed if the internal wing transfer switch is in STOP TRANS.

I first hinted at this behaviour in this post but I feel the issue is specific enough to warrant a separate report.

The first of two specific pieces of evidence I found is this chart which is also contained (with fewer annotations) in all other RL flight manuals floating around:

It essentially describes a marked forward CG shift after all external tanks have fed and are empty, which is presumably caused by cells 5 and 6 depleting faster than 3 and 4 since the internal wing tanks constantly replenish cell 3 (and thereby 4) but not 5 (and thereby 6).

This behaviour is reflected in the below schematic as well, which indicates that cells 5 and 6 will be empty before cells 3 and 4.

In the game, since cells 5 and 6 do not transfer until internal wing fuel is empty, cells 3 through 6 transfer simultaneously and at about the same rate afterwards and therefore run empty at approximately the same time, which decelerates the forward CG shift.

I have not found any information in the RL manuals that would explain why cells 5 and 6 do not transfer while the internal wing tanks are feeding.

transfer.trk

Edited 13 hours ago by Stickler

[Zabuzard]

I see what you mean.

Worth noting that G affect the fuel distribution a lot since all tanks are connected in chain via gravity feed pipes. So for example tank 2 and 3, as well as tanks 4 and 5 are actually connected via one-directional gravity-feed pipes (despite not visually being shown in the EFB).

So depending on how you fly (positive or negative Gs etc), the fuel will distribute quite differently. Which means that for these tests its crucial to actually fly the mentioned profile and not just active-pause+afterburner+time acceleration.

Anyways, will try to figure out whats up there.

[Zabuzard]

(And btw, they definitely do feed. But I see that they feed much less while the wing tanks still have fuel to replenish tanks 3/4)