Conformal fuel tank
Conformal fuel tanks (CFTs) are additional fuel tanks fitted closely to the profile of an aircraft which extend either the range or "time on station" of the aircraft, with a reduced aerodynamic penalty compared to external drop tanks.
Conformal fuel tanks have the disadvantage that, unlike drop tanks, they cannot be discarded in flight. This is because conformal tanks are plumbed into the aircraft, and can only be removed on the ground. As a result they may impose a drag-penalty on the aircraft, even when the tanks are empty, without any benefit; they could impose g-load limits as well and; they also add a slight weight gain to the aircraft even when empty (though negligible -- they don't weigh all that much): While the weight gain is always present, drag and g-load penalty is not always an absolute issue. The CFT's on the F-15C actually reduce drag and allow higher speeds than otherwise.
Other advantages CFT's provide is that they can free-up hardpoints that would normally be used to carry weapons or fuel tanks; they also have the advantages of not significantly increasing an aircraft's radar cross-section
Conformal fuel tanks
- F-15C entered service with CFT capability. Initially known as FAST packs (Fuel And Sensor Tactical), each unit carried an additional 849 US gallons (3,213.8 L) of fuel, while retaining hardpoints for four AIM-7F Sparrow missiles or bombs.They were first tested on the F-15B in 1974. All U.S. F-15Es, and Strike Eagle export variants such as the IAF and Singapore models, are fitted with CFT's between the wing and fuselage and require modification to fly without them. The FAST pack was originally intended to carry a navigational and targeting infrared sensor system (thus "Fuel And Sensor"); however, the F-15 simply began carrying LANTIRN pods for ground-attack missions instead.
- Export aircraft for Greece, Israel, Poland, Turkey, Singapore, Morocco, Egypt and the UAE all plumbed for carriage of two CFTs mounted on top of the aircraft near the wing root. Each is capable of holding 450 US gallons (1,703.4 L)
- Wind tunnel tested by BAE, two CFTs with 1,500 litres (400 US gal) capacity.
- The F-CK-1D prototype ("Brave Hawk") and the F-CK-1C single-seater prototype are equipped with the new CFTs.
- Advanced Super Hornet Conformal fuel tanks are mounted above the wings to replace the drag of underwing tanks.
- Supermarine Spitfire in the belly.
- Messerschmitt Bf 109 in the belly.
- Messerschmitt Bf 110 D-1 in the belly.
Distended internal tanks
Fuel tanks which create a bulge from the fuselage or mounted flush with the fuselage.
- English Electric Lightning Conformal ventral store was used for a small or large belly fuel tank which bulges out from the underbody
- Gloster Javelin fitted with dual flush-mounted belly tanks with a capacity of 1,137 liters (300 US gallons). They were known as "bosom tanks" or "Sabrinas"
- Gloster Meteor
- Shenyang J-6
- Q-5 Fantan weapons bay fuel tank expands below the fuselage profile 
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- The Gloster Javelin
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