In addition to the internally and CFT stored amount of fuel, the F-15E can carry up to 3 external fuel tanks. These tanks are interchangeable (even with other F-15 models) and jettisonable. Theoretically CFT's are considered external fuel tanks too, since they are removeable, but they are discussed in another article. Two external tanks can be mounted on the inboard wing pylon on each wing, and a third one can be attached to the centerline pylon under the belly of the jet (see figure below).

External tanks can be fueled through their external filler points. Fuel from external tanks are transferred to the internal tanks by regulated engine bleed air pressure (this latter provides positive pressure on all internal tanks during flight).

In case of emergency, all internal, external and CFT fuel can be dumped overboard via the Fuel Dumping System. External fuel tanks are vented through vent outlets located on their individual pylons.

Fuel Transfer

The task of the fuel transfer system is to transfer fuel to and from internal and external tanks to prevent imbalances caused by different fuel quantities in different tanks.

External wing and centerline fuel transfer is accomplished by regulated engine bleed air pressure, provided that the landing gear handle is in UP position (i.e. the aircraft is in flight). External fuel is not transferred when the landing gear handle is DOWN, or when the aerial refueling door is open (unless FUEL LOW condition occurs).

There is no backup transferring method for external fuel. In case of a total electrical failure, external fuel is not transferred. External fuel normally transfers when internal fuel tanks starts to deplete (meaning that external tanks empty first). Normally external wing tank fuel transfers before centerline tank fuel. If engine consumption exceeds transfer capacity, then all internal and external tanks transfer simultaneously.

Pilot Controls

The aircraft's fuel management systems can be controlled by switches on the fuel panel, located forward on the pilot left side console (see figure below). The switches and their functions are discussed below.

The three fuel control switches (1, 2, 3) control transfer and refuel procedures of all external tank types: external wing tanks (WING), centerline tank (CTR) and conformal fuel tanks (CFT). They all have three positions: NORM, STOP TRANS, STOP REFUEL.

If a switch is placed in NORM position, then its corresponding tank provides normal transfer and refuel functions. In STOP TRANS position it stops fuel transfer from its corresponding tank, including automatic transfer from external tanks (note that if a FUEL LOW condition occurs, then fuel transfer restarts again, regardless of switch position). In STOP REFUEL position it prevents refilling of its corresponding tanks.

The fuel dump switch (4) is used to dump fuel. Its functions are discussed in details in article Fuel Dumping System.

The CFT emergency transfer switch (5) is used in emergency situations to transfer CFT fuel. Its functions are discussed in details in article Conformal Fuel Tanks.

The external transfer switch (6) is used to select the transfer sequence of external fuel (provided that both external drop tanks and CFT's are installed on the jet). The switch has two positions: WING/CTR and CONF TANK. The unselected tanks stop transferring fuel, unless the engine consumes more that the current transfer rate or the selected tanks become empty. If the transfer rate from external tanks to internal tanks is insufficient, then all external tanks start to transfer simultaneously, regardless of switch position.

If CFT's are installed and external drop tanks are not installed AND the switch is placed in WNG/CTR position, then cyclig CFT fuel transfer will occur. In this case the system lets the internal tank fuel level to decrease 3000 pound below their full level and then starts CFT fuel transfer. Once the internal tanks get full, CFT fuel transfer stops and the cycle starts all over again. This cyclic operation is true in an opposite case, when there are no CFT's but external drop tanks are installed (note, that this is an "almost never" chance with an F-15E).

If the aircraft is on the ground, external tanks are depressurized, hence cannot transfer fuel. However CFT's can transfer, so on the ground only CFT's transfer fuel, regardless of switch position.

The slipway switch (7) controls the aerial refueling receptacle door. Its functions are discussed in details in article Air Refueling System.

Sources

• F-15E Flight Manual (TO 1F-15E-1) C 15 August 1990, courtesy of eFlightManuals

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