Conformal fuel tank

Conformal fuel tanks (CFTs) are additional fuel tanks fitted closely to the profile of an aircraft that extend the endurance of the aircraft.

Advantages

CFTs have a reduced aerodynamic penalty compared to external drop tanks, and do not significantly increase an aircraft's radar cross-section. Another advantage CFTs provide is that they do not occupy ordnance hardpoints like drop tanks, allowing the aircraft to carry its full payload.

Disadvantages

Conformal fuel tanks have the disadvantage that, unlike drop tanks, they cannot be discarded in flight, because they are plumbed into the aircraft and so can only be removed on the ground. As a result, they will impose a slight drag-penalty and minor weight gain on the aircraft even when the tanks are empty, without any benefit. They can also impose slight g-load limits, although not always an absolute issue: the CFTs on the F-15E allow the same maneuverability without g-limitations.

Examples

Conformal fuel tanks

F-15C Eagle/F-15E Strike Eagle/F-15EX Eagle II

F-15C entered service with CFT capability.^[1] Initially known as FAST packs (Fuel And Sensor Tactical),^[1] each unit carried an additional 750 US gallons (2,800 L) of fuel,^[2] while retaining hardpoints for four AIM-7F Sparrow missiles or bombs, some on the FAST packs.^[3] They were first tested on the F-15B in 1974. All U.S. F-15Es, and Strike Eagle export variants such as the Israeli and Singapore models, are fitted with CFTs under the wing^[4] outside the engine intake and require modification to fly without them.^[5] 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.^[1]

F-16C/D Block 50/52+, F-16E/F Block 60, F-16V Block 70/72 and F-16I Sufa

Export aircraft for Greece, Chile, Israel, Poland, Pakistan, Turkey, Singapore, Morocco, Egypt and the UAE are plumbed for carriage of two CFTs mounted atop the aircraft near the wing root. Together they hold 450 US gallons (1,700 L) or 3,050 pounds (1,380 kg) of fuel.^[6]^[7]

Dassault Rafale

Two 300-US-gallon (1,150 L) CFTs were first tested by Dassault in April 2001.^[8] A static aircraft equipped with CFTs was seen in social media posts prior to the 2025 Paris Air Show.^[9]

Mikoyan MiG-29SMT – MiG-29S (Product 9.13)- Mikoyan MiG-35

One 250-US-gallon (950 L) CFTs in a further enlarged spine.^[10]^[11]

Eurofighter Typhoon

Wind tunnel tested by BAE, two CFTs with 400 US gallons (1,500 L) of capacity each.^[12]^[13]

AIDC F-CK-1 Ching-kuo

The F-CK-1D prototype ("Brave Hawk") and the F-CK-1C single-seater prototype are equipped with the new CFTs. The prototype Indigenous Defence Fighter II “Goshawk” has over-wing CFTs.^[14]

Chengdu J-10

Wind tunnel tested by Chengdu.^[15]

WWII:
- Supermarine Spitfire in the belly.
- Messerschmitt Bf 109 in the belly.
- Messerschmitt Bf 110D-1 in the belly – nicknamed Dackelbauch (dachshund's belly).

Distended internal tanks

Distended internal tanks are fuel tanks that either create a bulge in the fuselage, or are mounted flush with the fuselage.

English Electric Lightning^[16] 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 300 US gallons (1,100 L). They were known as "bosom tanks" or "Sabrinas".^[17]^[18]
Gloster Meteor.^[19]
Shenyang J-6.
Nanchang Q-5 "Fantan" weapons bay fuel tank extends below the fuselage profile.^[20]