Aircraft fuel tanks

Self-sealing fuel tank of a Messerschmitt Me 262 on display at the Deutsches Museum, Munich

Aircraft fuel tanks are a major component of aircraft fuel systems. They can be classified into internal or external tanks and further classified by method of construction or intended use. Safety aspects of aircraft fuel tanks were examined during the investigation of the 1996 TWA Flight 800 in-flight explosion accident.

Internal tanks

Integral tanks

Integral tanks are areas inside the aircraft structure that have been sealed to allow fuel storage. An example of this type is the "wet wing" commonly used in larger aircraft. Since these tanks are part of the aircraft structure, they cannot be removed for service or inspection. Inspection panels must be provided to allow internal inspection, repair, and overall servicing of the tank. Most large transport aircraft use this system, storing fuel in the wings, fuselage, and empennage of the aircraft.^[1]

Rigid removable tanks

Rigid removable tanks are installed in a compartment designed to accommodate the tank. They are typically of metal, plastic or fibreglass construction, and may be removed for inspection, replacement, or repair.^[2] The aircraft does not rely on the tank for structural integrity. These tanks are commonly found in smaller general aviation aircraft, such as the Cessna 172. Combat aircraft and helicopters generally use self-sealing fuel tanks.^[1]

Bladder tanks

Bladder tanks, bag tanks or fuel cells, are reinforced rubberised bags installed in a section of aircraft structure designed to accommodate fuel. The bladder is rolled up and installed into the compartment through the fuel filler neck or access panel, and is secured by means of snap fasteners or cord and loops inside the compartment. Many high-performance light aircraft, helicopters and some smaller turboprop aircraft use bladder tanks.^[1]

Tip tanks

Many aircraft designs feature fixed tip tanks mounted at the end of each wing. The weight of the tanks and fuel counteract wing bending loads during manoeuvres and reduce fatigue on the spar structure.

External tanks

F-4E Phantom carrying two underwing pylon tanks and a centreline tank

Conformal fuel tank

Conformal fuel tanks (CFTs) or 'Fast Packs' are additional fuel tanks fitted closely to the profile of an aircraft which extend either the range or endurance of the aircraft, with a reduced aerodynamic penalty compared to external drop tanks.^[3]

Drop tank

Drop tanks, external tanks, wing tanks, pylon tanks or belly tanks are all terms used to describe auxiliary externally mounted fuel tanks. Drop tanks are generally expendable and often jettisonable. External tanks are commonplace on modern military aircraft and occasionally found in civilian ones, although the latter are less likely to be discarded except in the event of emergency.^[1]

Drop tanks were originally designed to be jettisoned when empty or in the event of combat or emergency in order to reduce drag and weight, increasing manoeuvrability and range. Modern external tanks may be retained in combat, to be dropped in an emergency and are often not designed for the stresses of supersonic flight.^[1]

Safety

Fuel tanks have been implicated in aviation disasters, being the cause of the accident or worsening it (fuel tank explosion).

The official explanation for the explosion and subsequent crash of TWA Flight 800 is that an explosive fuel/air mixture was created in one of the aircraft's fuel tanks. Faulty wiring then provided an ignition source within the tank, destroying the airliner.^[4] While the accuracy of the official findings is still questioned in this case, similar explosions have occurred in other aircraft. It is possible to reduce the chance of fuel tank explosions by a fuel tank inerting system or fire fighting foam in the tanks.^[5]

See also

• Aircraft fuel system
• Sargent Fletcher - Manufacturer of aircraft drop tanks

References

Notes

1. Whitford 2004, p. 153.
2. FAA 1988, p. 282.
3. Whitford 2004, p. 155.
4. NTSB p. 308.
5. Whitford 2004, p. 157.

Bibliography

• Federal Aviation Administration, Acceptable Methods, Techniques and Practices-Aircraft Inspection and Repair, AC43.13.1A, Change 3. U.S Department of Transportation, U.S. Government Printing Office, Washington D.C. 1988.
• Whitford, Ray. Fundamentals of Fighter Design. Marlborough, Wiltshire. The Crowood Press Ltd., 2004 ISBN 1 86126 664 2
• National Transportation Safety Board. Aircraft Accident Report: In-flight Breakup Over the Atlantic Ocean Trans World Airlines Flight 800