{{Short description|Aircraft component}} [[File:Me-262, selbstabdichtender Kraftstofftank.JPG|thumb|upright=1.14|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 fuel tanks and can be 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=== {{Main|Wet wing}} 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 to store fuel in the wings, fuselage and empennage of the aircraft.<ref name="Whitford153">Whitford 2004, p. 153.</ref>
===Rigid removable tanks=== {{Main|Self-sealing fuel tank}} Rigid removable tanks are installed in a compartment designed to accommodate the tank. They are typically made of metal, plastic or fibreglass construction, and may be removed for inspection, replacement, or repair.<ref>FAA 1988, p. 282.</ref> Rigid removable tanks are not relied on for the aircraft's 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.<ref name="Whitford153"/>
===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.<ref name="Whitford153"/>
===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.{{citation needed|date=December 2018}}
==External tanks== {{Main|Conformal fuel tank|Drop tank}} [[File:AIM-4 and AIM-7 on F-4E.jpg|thumb|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.<ref>Whitford 2004, p. 155.</ref>
===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.<ref name="Whitford153"/>
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.<ref name="Whitford153"/>
==Safety== {{See also|TWA Flight 800|Inerting system}}
Fuel tanks have been implicated in aviation disasters, being the cause of the accident or worsening it (fuel tank explosion).
The National Transportation Safety Board concluded that explosion and subsequent crash of TWA Flight 800 was the result of 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.<ref>{{cite report |date=August 23, 2000 |title=In-flight Breakup Over The Atlantic Ocean, Trans World Airlines Flight 800, Boeing 747-131, N93119, Near East Moriches, New York, July 17, 1996 |url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0003.pdf |url-status=live |publisher=National Transportation Safety Board |id=NTSB/AAR-00/03 |archive-url=https://web.archive.org/web/20160304065721/http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0003.pdf |archive-date=March 4, 2016 |access-date=20 June 2025}}</ref>{{rp|308}} 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.<ref>Whitford 2004, p. 157.</ref>
The Boeing 737, for example, has two systems that reduce the chance of a fuel tank ignition. One shuts off fuel pumps when fuel output pressure is low, to prevent them from heating (since they rely on the fuel itself for cooling). The other enriches the nitrogen levels in the air in the fuel tank, so there is insufficient oxygen there for burning.<ref name="Mentour" /> The aircraft engines are also capable of getting fuel via suction in the result of a failure in the backup pumps, though this produces less reliable thrust.<ref name="Mentour" />
==Placement== On passenger planes, fuel tanks are often integrated into the wings, and when there are also tanks inside the body of the aircraft, the wing tanks are used preferentially.<ref name="aviation.com">{{cite web |url=http://www.an-aviation.com/why-is-fuel-stored-in-the-wings-of-aircraft/ |title=Why is fuel stored in the wings of aircraft? |date=10 Aug 2017}}</ref><ref name="Mentour" /> The placement reduces the stress on the wings during takeoff and flight, by putting the heavy fuel directly inside the source of lift.<ref name="aviation.com" /> Putting tanks in the main wings rather than near the tail or nose also reduces the amount of weight that is off-center from the plane's center of gravity, and which changes as it flies<ref name="aviation.com" /> and which would make the aircraft less efficient by requiring increased use of elevators.<ref name="Mentour">{{cite web |url=https://www.youtube.com/watch?v=VpzUbYex4dg |title=Why do aircraft store fuel in the wings? |date= |author=Mentour Pilot}}</ref> Given their irregular shape and lack of windows, wings are often unusable for storage of cargo or seating of passengers. But their hollow structure makes in-wing fuel storage feasible and an efficient use of space; the presence of structural spars in "wet wing" tanks reduces sloshing.<ref name="Mentour" /> Placement of fuel tanks in the wings also moves them further from passengers and crew in the event of a leak or explosion.{{Citation needed|date=January 2021}}
==See also== *Aircraft fuel system *Sargent Fletcher - Manufacturer of aircraft drop tanks
==References== {{Commons category}} ;Notes {{reflist}} ;Bibliography {{refbegin}} *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. [https://www.ntsb.gov/doclib/reports/2000/AAR0003.pdf Aircraft Accident Report: In-flight Breakup Over the Atlantic Ocean Trans World Airlines Flight 800]. {{Webarchive|url=https://web.archive.org/web/20121007110704/https://www.ntsb.gov/doclib/reports/2000/AAR0003.pdf|date=2012-10-07}} {{refend}}
{{Aircraft fuel tanks}}
Category:Aircraft fuel system components Category:Fuel containers