|Conformal Fuel Tanks|
|Written by Sabc|
Conformal fuel tanks are the best way to increase the aircraft's onboard fuel capacity at a price of only a slight increase of aircraft drag. F-15E CFT's have no effect on the aircraft's maneuverability and G-limitations at all.
Conformal fuel tanks in the F-15E are attached to the sides of the jet directly besides the air intakes on the outboard side of each engine intake (see figure below). They can be removed, but are almost always present on an F-15E.
Each CFT is fitted with 2x3 weapon racks (note that all current F-15E CFT's are of type IV, earlier type CFT's are without weapon racks). The lower three pylons were moulded into a single, straight runner which contains 3 BRU-47/A racks. The upper three pylons feature BRU-46/A racks. The maximum payload for the upper pylons is 1100 pounds, the forward and aft lower pylons have a combined maximum load of 2200 pounds, while the middle lower pylon can hold up to 3300 pounds of weapon load.
If the F-15E is configured for an air-to-air role, the BRU-46/A racks can slide back to their stowage compartments in the lower elongated pylon and two LAU-106 missile launchers can be revealed (they are between the three bomb racks). Upon configuring the jet for an air-to-gorund role, the missile launchers can be moved into their own stowage area and the bomb racks could then be used. For more info on weapon pylons see corresponding articles in section Weapon Stores.
Fuel from CFT's are transferred to the internal tanks by electronically operated fuel transfer pumps. Each CFT is pressurized by a self-contained ram air pressurization and vent system. Intake scoops of this system are located towards the back of each CFT.
All tanks can be refuelled from a single point either from the ground or from the air. On the ground a single pressure fueling connection is used, while in the air an air refueling receptacle is used. In case of emergency, all internal, external and CFT fuel can be dumped overboard from an outlet located at the right wingtip (see photo section).
CFT's use the same survivability measures as internal tanks (see article on Internal Fuel System). For increased survivability all CFT compartments incorporate explosion suppression foam slabs.
Each CFT is equipped with a self-contained air pressurization and vent system, which provides regulated ram air pressure to prevent fuel boiloff at higher altitudes with lower external air pressure. Ram air is acquired from a flush inlet on the side of the CFT and it is used to pressurize all three compartments. This system also provides pressure relief of the CFT through the overboard vents during climb and aerial refueling, and vacuum relief during ground operation.
There is a refuel lockout valve located at the front end of each CFT. If the valve is in LOCKOUT position then CFT refuel is prohibited. CFT refuel is allowed only if the valve is in NORMAL position.
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. The system should keep fuel imbalances between left and right sides below 200 pounds in case of internal wing tanks and below 1000 pounds in case of CFT's. If the aircrew experiences any imbalance greater than these and lasting for more than 5 minutes, then it's a malfunction and should be reported.
Fuel holding area of each CFT is divided into 3 compartments: forward, center and aft compartments. Each CFT contains two fuel transfer pumps, one in the center compartment and one in the aft compartment. The center pump transfers fuel from the forward and center compartments, while the aft pump transfers fuel from the aft compartment.
The center and aft compartments are isolated from each other by a floating type valve, which remains closed until the aft compartment is nearly empty or the aft transfer pump fails. In normal operation when the aft fuel level drops very low, the interconnect valve opens.
There is a fuel ejector pump in the forward compartment which transfers fuel from forward to center compartment.
All CFT transfer pumps operate continuously when electrical power is on, the engine master switch is on and the aerial refueling door is closed. Fuel transfers within the CFT are programmed to maintain aircraft center of gravity within limits.
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). Their functions are discussed in details in article External Fuel 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. It has 3 positions: NORM (normal), L (left) and R (right). The switch should be in NORM position during all normal operation. L and R positions come into play when the aircraft in running of emergency generator power. In this case setting the switch to L or R disables all pitot heating and activates the center compartmen trasfer pump in the selected CFT (left or right). Note that pitot heating deactivates in the coreesponding switch position even if CFT's are not installed.
The external transfer switch (6) is used to schedule external fuel transfer. Its functions are discussed in details in article External Fuel Tanks.
The slipway switch (7) controls the aerial refueling receptacle door. Its functions are discussed in details in article Air Refueling System.
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|Last Updated on Monday, 30 May 2011|
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