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Fuel transfer sequence


Leviathan667

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Hi,

Per manual, page 25, there two fuel transfer sequence configurations. But there is no discussion on their respective merits. What are they?


 

Switch to LISSE (CLEAN)

Switch to BIDONS (EXT. TANKS)

1. Ext. tanks and wing tanks

1. Ext. tanks and wing tanks

2. Central front

2. ⅔ or laterals rear

3. ⅔ or laterals rear

3. Central front

4. Laterals front

4. Remaining ⅓ or laterals rear

5. Remaining ⅓ or laterals rear

5. Laterals front

6. Remaining at feeders

6. Remaining at feeders

7. Negative-g flight accumulator

7. Negative-g flight accumulator

 

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On 7/22/2022 at 4:44 PM, Leviathan667 said:

there two fuel transfer sequence configurations. But there is no discussion on their respective merits. What are they?

 

The sequences are for minimizing variations on the center of gravity, depending on if you have external fuel tanks or not. Use the sequence that corresponds with your aircraft current configuration.

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Clean the order is: 1; 2; 3; 4; 5.

With external tanks, the order is: 0; 1; 3; 2; 5; 4

0: external tanks

1: wings tanks (2 X 190L)

2: central front (585L)

3: top of the aft lateral tanks (2 X 374L)

4: forward lateral tanks (2 X 545L)

5: bottom of the aft lateral tanks (2 X 186L)

Then the end of the feeder tanks (2 X 290L)

 

@+

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Select the switch to Bidons if you have Ext Tanks, and leave it at Liss if no Ext tanks. 

This sets up the right sequence for current config.


Edited by Rhinozherous
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  • 4 weeks later...
On 7/26/2022 at 9:27 AM, gillouf1 said:

Clean the order is: 1; 2; 3; 4; 5.

With external tanks, the order is: 0; 1; 3; 2; 5; 4

0: external tanks

1: wings tanks (2 X 190L)

2: central front (585L)

3: top of the aft lateral tanks (2 X 374L)

4: forward lateral tanks (2 X 545L)

5: bottom of the aft lateral tanks (2 X 186L)

Then the end of the feeder tanks (2 X 290L)

Based on the manual, even the "LISSE" (Clean) position consumes external tanks first. (I can verify this, having flown numerous missions without switching.) The LISSE position also empties external tanks first. Since both positions empty the external tanks first, then the wing tanks, that means there's ZERO difference between the two switch positions until you've moved to fuselage tanks.

As such, I suspect that the "BIDONS" ("tanks") position is intended for (non-combat) use, when you will be retaining external tanks even after emptying them. Think about it. In a combat setting, as soon as that tank is empty, you're jettisoning it. (IRL, you might keep them for low-intensity and/or ground attack missions, but in-game there's no real reason not to ditch them.)

This is backed up by my own experience as well. One time on Enigma's CW server, I departed the airfield, and flew in full burner straight towards the fight/front line. I glanced down, saw my external tanks were empty, and hit selective jettison as I entered the combat zone. However, on an earlier sortie, I had taken wing missiles and a belly tank, but forgot to switch my jettison selector switch to wings, so instead of ditching my wing tanks, I had ditched my belly missile.  When I returned to base, I had burned through a decent chunk of my internal fuel. In landing configuration, as soon as I got to ~150kts, the nose would come up hard, requiring lots of trim and/or stick force to keep the nose down. Why? Because I didn't ditch the tanks, which shifted the CoG back, and made the aircraft tail-heavy.

Essentially, keep it in LISSE, unless you're carting around empty external tanks.

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All the switch does is alter the sequence of fuselage tank transfers to help with C of G control. It doesn't control external fuel transfer.

From the Flight manual:

"Two fuselage tank transfer sequences are possible. They enable variations of the aircraft center of gravity to be reduced according to the configuration (clean or with pylon tanks)"

The Sequence Clean : 1,2,3,4,5

The numbers 3,5 refer to two sections in one physical tank structure in the Aft Lateral tanks. So if you have the switch in "Lisse" you first consume Fuel from all externals, then the fuel in  in the internal wing tanks (1), then the Forward central tank (2), then 374l (3)from each Aft lateral tank (whose total vol is 560l), next you get the fuel from the Forward lateral tanks (4) and finally the last remaining 186l in the aft Lateral tank (5), and finally whats left in the Feeder tanks.

The Squence "Bidons" : 1,3,2,5,4

Similar but as soon as the External tanks and internal wing tanks are empty you get 374l (3) from each Aft lateral tank. So the 585L in the Forward central tank (2) stays there a bit longer therfore affecting the C of G.

All of this Fuel transfer artistry is controlled by Differences in pressurization and  valves at different levels  in the Feeder tanks . The external tanks are pressurized to 850-890Mb, with the wing and fuselage tanks at 440-480mb with the feeder tanks at 90-130mb.

If you follow the sequence completely in game you will see that AERGES have done the fuel system in exquisite detail..

 

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5 hours ago, DJBiscuit1818 said:

Based on the manual, even the "LISSE" (Clean) position consumes external tanks first. (I can verify this, having flown numerous missions without switching.) The LISSE position also empties external tanks first. Since both positions empty the external tanks first, then the wing tanks, that means there's ZERO difference between the two switch positions until you've moved to fuselage tanks.

As such, I suspect that the "BIDONS" ("tanks") position is intended for (non-combat) use, when you will be retaining external tanks even after emptying them. Think about it. In a combat setting, as soon as that tank is empty, you're jettisoning it. (IRL, you might keep them for low-intensity and/or ground attack missions, but in-game there's no real reason not to ditch them.)

This is backed up by my own experience as well. One time on Enigma's CW server, I departed the airfield, and flew in full burner straight towards the fight/front line. I glanced down, saw my external tanks were empty, and hit selective jettison as I entered the combat zone. However, on an earlier sortie, I had taken wing missiles and a belly tank, but forgot to switch my jettison selector switch to wings, so instead of ditching my wing tanks, I had ditched my belly missile.  When I returned to base, I had burned through a decent chunk of my internal fuel. In landing configuration, as soon as I got to ~150kts, the nose would come up hard, requiring lots of trim and/or stick force to keep the nose down. Why? Because I didn't ditch the tanks, which shifted the CoG back, and made the aircraft tail-heavy.

Essentially, keep it in LISSE, unless you're carting around empty external tanks.

FYI No fighter pilot this side of the Korean War jettisoned droptanks when empty.  They were jettisoned when attacked or if you HAD to get somewhere very fast.  The F-15Cs in Desert Storm One did do this whenever they were running down MiGs, only because they were authorized.   The Navy calls them external tanks- bring them back or have a very good reason they are gone.

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  • 2 weeks later...
On 7/22/2022 at 11:44 PM, Leviathan667 said:

Hi,

Per manual, page 25, there two fuel transfer sequence configurations. But there is no discussion on their respective merits. What are they?


 

Switch to LISSE (CLEAN)

Switch to BIDONS (EXT. TANKS)

1. Ext. tanks and wing tanks

1. Ext. tanks and wing tanks

2. Central front

2. ⅔ or laterals rear

3. ⅔ or laterals rear

3. Central front

4. Laterals front

4. Remaining ⅓ or laterals rear

5. Remaining ⅓ or laterals rear

5. Laterals front

6. Remaining at feeders

6. Remaining at feeders

7. Negative-g flight accumulator

7. Negative-g flight accumulator

Normal sequence is 12345. Whenever you carry external fuel tanks select sequence 13254

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6 hours ago, Grimleo said:

Interestedly "Lisse" is translated as 'Smooth' and "Bidons" is translated as 'Canisters' by Google Translate.

"Lisse" refer to something without rugosity nor asperity, primarly to qualify a surface. "Bidon" refer to container for liquid, so the translation by Google is not really correct. Better translation for "bidon" is indeed actualy "tank" or "jerrycan", considering a "bidon" can contain any liquid.


Edited by sedenion
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On 9/7/2022 at 5:25 AM, Grimleo said:

Google Translate

Google Translate isn't exactly known for its accuracy. Use DeepL instead:

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