Conformal fuel tank

A McDonnell Douglas F-15E Strike Eagle fitted with conformal fuel tanks under the wing roots.

Ground crew handling the CFT of an F-15E.

Conformal fuel tanks (CFTs) are additional fuel tanks fitted closely to the profile of an aircraft that 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, because they are plumbed into the aircraft and so 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 can also impose g-load limits and they add a slight, though negligible, weight gain to the aircraft, even when empty. While the weight gain and drag penalty are always present, g-load limitation is not always an absolute issue. The CFTs on the F-15E actually allow the same maneuverability without g-limitations.

Other advantages CFTs provide is that they can free up hardpoints that would normally be used to carry weapons or fuel tanks and that they do not significantly increase an aircraft's radar cross-section.

Examples

Conformal fuel tanks

• F-15C Eagle/F-15E Strike Eagle

F-15C entered service with CFT capability.^[1] Initially known as FAST packs (Fuel And Sensor Tactical),^[1] 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, some on the FAST packs.^[2] 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 CFTs under the wing^[3] outside the engine intake and require modification to fly without them.^[4] 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]

Israeli F-16I Sufa, based on the F-16D Block 50/52+, with 2 attached CFTs on top of the aircraft near the wing root and 2 wing-mounted drop tanks.

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

Export aircraft for Greece, Chile, Israel, Poland, Turkey, Singapore, Morocco, Egypt and the UAE are 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)

• Dassault Rafale

Two 1,150 litres (300 US gal) CFTs were first tested by Dassault in April 2001.^[5]

• Eurofighter Typhoon

Wind tunnel tested by BAE, two CFTs with 1,500 litres (400 US gal) capacity.^[6][7]

• 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.^[8]

• Advanced Super Hornet

Conformal fuel tanks are mounted above the wings to replace the drag of underwing tanks. Combined, they carry 3,500 lb of extra fuel, while adding extra lift and expanding combat radius by 260 nmi with a small transonic acceleration penalty.^[9]

• Chengdu J-10

Wind Tunnel tested by Chengdu.^[10]

• BAC Strikemaster

Conformal fuel tanks were installed on the wingtips.^[11]

• 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 create a bulge from the fuselage or are mounted flush with the fuselage.

• English Electric Lightning^[12] 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"^[13][14]
• Gloster Meteor^[15]
• Shenyang J-6
• Nanchang Q-5 "Fantan" weapons bay fuel tank extends below the fuselage profile ^[16]

References

Notes

• Green, William and Gordon Swanborough. The Complete Book of Fighters. New York: Barnes & Noble Inc., 1988. ISBN 0-7607-0904-1.
• Lambert, Mark, ed. Jane's All the World's Aircraft 1993–94. Alexandria, Virginia: Jane's Information Group Inc., 1993. ISBN 0-7106-1066-1.