Explain me the fuel transfer function in the F-4

[FZG_Immel]

Ok, explain me how it works. whenever I take external fuel tanks, its seems random at which moment the fuel transfers from wing bags or center fueselage tank, to the internal one.. 

 

How do i optimize it so that i can have my internal fuel tanks topped up as often as possible, so in case I have to jettison my external tank, i have transferred as much fuel from them as possible. 

 

thanks.

 

 

[razo+r]

 You put the switch to center or outboard and then they will automatically transfer fuel as soon as the internal fuel is below a certain value. Once that happens, the external fuel is pumped into the internal until they are full. Then the transfer stops until the internal fuel reaches the value again and the process repeats until the external tanks are empty.

For more information, you should consult the manual.

How to optimize it? Just keep the switch in the outboard or center position until the externals are empty.

[Zabuzard]

It is actually quite complex because it is super dynamic and there is no way for you, as pilot, to "look into" it.

Essentially, the switches on your fuel panel can open and close the valves for the external tanks or the internal wing tanks, which connects them to the fuel circuit.

They are connected to cells 3 and 5 and will start transferring whenever those fall below a certain threshold.

It is not really possible for you to influence this or to see what fuel level those cells currently have. They gravity feed cells 4 and 6, which also depends on their fuel level and forces acting on the plane.
Those cells feed cells 1 and 2 via gravity and pumps, which also depends on their level and other factors.

So it is a highly dynamic system and you cannot really predict nor influence the transfer.

Details in the manual:
https://f4.manuals.heatblur.se/systems/engines_and_fuel_systems/fuel_system.html#transfer-sequence

In practice however, this system pretty much ensures that the non-fuselage tanks (internal wing or external tanks) are "emptied first" more or less by topping off the internal fuselage tanks every couple of seconds.

So there isnt really any reason to be concerned. If you connect your ext tanks the external fuel will be emptied first more or less and you can jettison it essentially as early as possible.

[FZG_Immel]

49 minutes ago, Zabuzard said:

It is actually quite complex because it is super dynamic and there is no way for you, as pilot, to "look into" it.

Essentially, the switches on your fuel panel can open and close the valves for the external tanks or the internal wing tanks, which connects them to the fuel circuit.

They are connected to cells 3 and 5 and will start transferring whenever those fall below a certain threshold.

It is not really possible for you to influence this or to see what fuel level those cells currently have. They gravity feed cells 4 and 6, which also depends on their fuel level and forces acting on the plane.
Those cells feed cells 1 and 2 via gravity and pumps, which also depends on their level and other factors.

So it is a highly dynamic system and you cannot really predict nor influence the transfer.

Details in the manual:
https://f4.manuals.heatblur.se/systems/engines_and_fuel_systems/fuel_system.html#transfer-sequence

In practice however, this system pretty much ensures that the non-fuselage tanks (internal wing or external tanks) are "emptied first" more or less by topping off the internal fuselage tanks every couple of seconds.

So there isnt really any reason to be concerned. If you connect your ext tanks the external fuel will be emptied first more or less and you can jettison it essentially as early as possible.

Thank you for confirming me the relative 'randomess' of the process. sometimes with my external wing tanks it starts trasfering into my internal below 900 on the counter, but some it stops before being full.. than later in the flight I am at 700, and it starts filling up again. So much so that I was never able to deduct the logic behind it etc.. Also often with the 3 external tanks it seems even more random. Anyway, glad to see I am not doing anything particulary wrong.  I'll just keep my external long

[Zabuzard]

Thank you for confirming me the relative 'randomess' of the process. sometimes with my external wing tanks it starts trasfering into my internal below 900 on the counter, but some it stops before being full.. than later in the flight I am at 700, and it starts filling up again. So much so that I was never able to deduct the logic behind it etc.. Also often with the 3 external tanks it seems even more random. Anyway, glad to see I am not doing anything particulary wrong.  I'll just keep my external long

The counter observation could be because the counter includes the internal wing tanks, which the external tanks cant feed into. So the internal fuselage tanks all being full (in particular the two cells the ext tanks can feed into) could happen at different counter values in case the internal wing tanks have been used throughout the flight.

The tape above the counter is a "safer" way to inspect what's happening in this situation, as that only includes the internal fuselage tanks (cells 1-6, reserve cell 7 excluded). Which are exactly the cells that the external tanks can influence. They transfer directly into cells 3 and 5, and indirectly into cells 4, 6, 2 and 1 :)

(On that note, the internal wing tanks transfer through the same pipes and mechanism as the ext tanks and are hence mutually exclusive)

[felixx75]

On 12/17/2024 at 8:41 PM, FZG_Immel said:

Ok, explain me how it works. whenever I take external fuel tanks, its seems random at which moment the fuel transfers from wing bags or center fueselage tank, to the internal one.. 

 

How do i optimize it so that i can have my internal fuel tanks topped up as often as possible, so in case I have to jettison my external tank, i have transferred as much fuel from them as possible. 

 

thanks.

 

 

https://youtu.be/2u2yLEM1iHM?si=sq834BySyfAaOrgA