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External Tanks Questions


JayRoo

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Sorry if this post is a bit “off the wall” with such hot topics like HARM and ATFLIR around. Im just the learning type and DCS is such a great study sim...

 

I will refer to them as ETs.

 

I was looking at the diagram of the fuel system and the picture i was using didnt show the connection to the ETs. Nor have i read any SOPs for the use of ETs on the ground/inflight...

 

Ground Ops:

Do the engines start on internal fuel? Are they supposed to? Is the fuel source controlled by AMAD automatically with weight on wheels with the ET switches in NORM? Is it SOP to takeoff using internal fuel? Is it automatically done with flaps half or thrust lever setting to a certain TLA? (which it is definitely monitoring bc it checks for flaps when you push the power up).

 

Air to Air refueling:

If you were to refuel in the air with external tanks attached (on wing and/or centerline), will the fuel backfill the tanks? Or are you limited to internal fuel once the exterior tanks run dry?

 

ORIDE:

What is the function of OveRIDE setting on the ET switch panel? (between fuel probe and fuel dump). Is it used to fill internal tanks from that source if the other is set to off? Basically why is it different from NORM?

 

Strategy for max endurance/target area loitering:

If A2A refueling does not backfill the external tanks, my guess would be to takeoff and fly initially on internal fuel only (ETs set to off). I dont know if there are any Zero Fuel Weight issues in the FA18? You then should hook up with the tanker to top off internal fuel and then set ET switches to NORM to begin using them once your aircraft is completely full....

 

Thank you guys for your time and consideration if you made it this far!!! :thumbup:

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External tanks are definitely refueled in AAR (infact they are refueled at the same time as internal, you can see this with the fuel page), and you can pretty much leave everything in auto/norm, the plane should handle everything. Dunno about engine start, though I assume it involves starting with internal fuel, and then pumping ET fuel to the internal tanks, just like how it works the rest of the time. ORIDE afaik is a setting that either forces them on or off, probably off (don’t take my word on that)

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Heres all the relevant data I could find from a quick scan through the NATOPS manual for the C/D.

 

"Fuel is carried internally in four interconnected fuselage tanks and two internal wing (wet) tanks. External fuel is carried in 315 or 330 gallon tanks which may be mounted on the centerline and/or inboard wing station pylons. A fuel quantity indicating system provides fuel quantity indications in pounds. All tanks may be refueled on the ground through a single pressure refueling point. Airborne, they can be refueled through the aerial refueling probe. The internal wing tanks, tank 1, and tank 4 are transfer tanks. Tanks 2 and 3 are engine feed tanks. The tanks are arranged so internal fuel gravity transfers (at a reduced rate) even if the transfer pumps fail. Regulated engine bleed air pressure transfers fuel from the external tanks and also provides a positive pressure on all internal fuel tanks.

 

External fuel is transferred by conditioned engine bleed air pressure. A single regulator supplies pressurization to all installed external tanks when weight is off the wheels, the air refueling probe is retracted, and either the HOOK handle or LDG GEAR handle is UP. Once the external tanks are pressurized, shut-off valves controlled by the external tank fuel control switches provide selection of fuel transfer from either the external wing tanks only, the external centerline tank only or all three external tanks at the same time. All external tanks can be pressurized any time either external tank fuel control switch is in ORIDE. On F/A-18C/D aircraft, selecting ORIDE also overrides any Signal Data Computer (SDC) stop transfer command. With the external tanks pressurized, fuel transfers when the FUEL LO caution is displayed (the air refueling probe must be retracted in F/A-18C/D aircraft), regardless of the position of the external tank fuel control switches.

 

External Tank Fuel Control Switches. Two EXT TANKS fuel control switches, labeled WING (for external wing tanks) and CTR (for centerline tank), are on the FUEL panel.

NORM With the external tank(s) pressurized, external fuel transfers to any internal tank that accepts it.

 

STOP With the external tank(s) pressurized, external fuel does not transfer until FUEL LO caution display is on.

 

ORIDE Pressurization of and fuel transfer from all installed external tanks is provided (HOOK handle must be up in F/A-18A/B aircraft). The other external tank fuel

control switch must be in STOP if fuel transfer from its tank(s) is not desired."

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I'll answer this bit first:

 

ORIDE:

What is the function of OveRIDE setting on the ET switch panel? (between fuel probe and fuel dump). Is it used to fill internal tanks from that source if the other is set to off? Basically why is it different from NORM?

 

External fuel is driven from the external tanks into the internal tanks by pressurised air, provided by the bleed air system - it isn't pumped like internal fuel. Normally (NORM switch setting) this air supply (and therefore external tank fuel transfer) is disabled with weight on wheels or with the A/A refueling probe extended (I think those are the scenarios). ORIDE re-enables fuel transfer in these scenarios.

 

Do the engines start on internal fuel? Are they supposed to? Is the fuel source controlled by AMAD automatically with weight on wheels with the ET switches in NORM? Is it SOP to takeoff using internal fuel? Is it automatically done with flaps half or thrust lever setting to a certain TLA? (which it is definitely monitoring bc it checks for flaps when you push the power up).

 

Engines start on internal fuel. As per above, (unless ORIDE) fuel doesn't transfer from external tanks with weight on wheels. Also, fuel cascades into internal tanks first (no direct link from external tanks to engines) anyway.

 

Schematic here:

 

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  • 10 months later...

Hay Guys,

 

 

with external tanks on, can I "force" my centerline (or wing) external tanks to feed first so I can jettison any or all of them, whenever they get empty?

 

 

Intention is to use external fuel first on the way to combat area, but then jettison empty tank before getting into dogfight.

 

 

 

Thanks

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.. can I "force" my centerline (or wing) external tanks to feed first so I can jettison any or all of them, whenever they get empty?

- have CNTR on STOP (right one)

- jettison select button on the ready LI and RI

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- have CNTR on STOP (right one)

- jettison select button on the ready LI and RI

- have "Select Jett" on the ready also, click twice to '- STORES'

After jettison you return CNTR to 'NORMAL'

 

3 tanks will empty all 3 at once if you do not stop center tank


Edited by majapahit

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If you mean how can you use external fuel first, that happens automatically.

 

If you mean selecting which external tanks feed first, use the EXT TANKS panel behind the throttle to stop the flow of fuel as you desire. (Note: ignore ORIDE; it's used in certain failure modes, none of which I suspect are modelled).

 

 

Thanks Squirell (and everyone), I wasn't specific enough. Yes, I had only centerline as external, and yes, I saw it afterwards it feeds first anyway. And the other answers spared me my next questions I guess... :thumbup::doh::smartass:

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Just to give you a bit of perspective on RW ops though, jettisoning fuel tanks is a very rare occurrence. So much so that all navy pilots I’ve ever spoken to have never seen it happen even during deployments where they saw action. ETs are actually hard to come by and there’s a finite number of them on the boat. That being said, these are guys who’ve been flying in highly permissive environments these last 2 decades and who’ve never been in a knife fight. All bets are off if they were to engage other combat aircraft and I imagine the first order of business would be to make your bird leaner

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