Airplane fuel is stored in specific tanks located in different parts of the aircraft. Most commercial aircraft store the majority of their fuel in the wings, the most common fuel storage area for these planes. Integral tanks - areas inside the aircraft structure sealed with a fuel-resistant two-part sealant - can be located anyplace on the aircraft, including the belly or rear.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
Where is the airplane fuel tank located?
In an airplane, fuel is stored across tanks in the belly, tail, or center fuselage. On most commercial jets the largest fuel volume is stored in the integral tanks built inside the wing structure, an arrangement that keeps the heavy fuel mass close to the centre of lift and the centre of gravity, refining balance and reducing structural weight. Wing tanks are used preferentially because they place fuel away from the passenger compartment, boosting safety by isolating people from fire or fumes. In many designs the innermost bays of the wing serve as inner tanks while the sections nearer the tips form outer tanks, and the leading edge or tip houses additional cells.
Some aircraft add a centre tank - called a centre fuselage tank or rear centre tank - located under the cabin floor between the wings. The Boeing 747 and the long-range Airbus A321XLR are examples that carry such a tank. A smaller trim or tail tank is sometimes installed in the empennage of long-haul models, allowing in-flight transfer of fuel to maintain the correct centre of gravity as fuel is consumed. Thus, while the wings hold the bulk of the fuel, the complete system includes tanks in the belly, tail, or center fuselage, all connected by pumps and pipelines that deliver fuel to the engines attached to the wings.
How is an airplane fuel tank designed?
An airplane fuel tank is first classified by method of construction. The three basic types are integral fuel tanks, rigid removable tanks, and bladder tanks. Integral tanks are unused spaces inside the wings or fuselage that are sealed with a fuel-resistant two-part sealant. They are also called wet wings and are the most efficient way to carry fuel because they save weight and are cheap to maintain. Rigid removable tanks are built separately from the aircraft, installed in the wings or fuselage, aided by the airframe, and typically made from aluminum alloy or stainless steel. They undergo pressure testing to guarantee they will not leak or collapse, and they allow easy repairs or replacements. Bladder tanks are reinforced rubberised bags installed in a section of the aircraft structure designed to accommodate fuel. They are non-rigid removable tanks made of reinforced flexible materials.
Each tank must be sealed to contain fuel and to prevent external contamination. Construction methods prevent leaks through riveting and seam welding, and parts are sulfuric-acid anodized to reduce susceptibility to corrosive attack. Newer tanks experiment with isophthalic polyester resin composite material for seamless and lightweight constructions.
Fuel tanks must be designed, located, and installed so as to retain fuel when subjected to upward acceleration of 3.0 G (29.42 m/s; 4.5 G (44.13 m/s) for an acrobatic category), forward acceleration of 9.0 G (88.26 m/s ), sideward acceleration of 1.5 G (14.71 m/s ), and downward acceleration of 6.0 G (58.84 m/s ). The integral fuel tank must be able to withstand pressure developed during maximum limit acceleration when fully filled with fuel and must withstand vibration, aerodynamic forces, heat, cold, inertial loads, and lightning strikes. The tank design must allow any hazardous quantity of water to drain from any part of the tank to its sump with the airplane in the normal ground attitude. Each tank must have a drainable sump with an effective capacity of 8 fluid ounces (0.24 liters) or 0.25 percent of the tank capacity when the tank is larger than 25 gallons (94.64 liters). Fuel tanks must have baffles to keep fuel from splashing into the wings during maneuvers and to prevent fuel sloshing. Baffle check valves let fuel flow to the low inboard sections but stop it from flowing outboard.
Fuel tanks must be vented from the top part of their volume to allow air to move freely in and out with changes in fuel level, air pressure, and temperature. The vent must discharge clear of the airplane unless expansion space equal to at least 2 percent of the fuel volume has been designed into the tank. Tanks also vent to each other so they have the same pressure, and a vent surge tank is located in each wing’s lower surface. Fuel tanks must be isolated from personnel compartments by a fume-proof, fuel-proof enclosure that is vented and drained to the exterior of the airplane.
Modern aircraft fuel tanks also act as a thermal sink dissipating engine-generated heat. Fuel tanks are made inert to reduce the risk of combustion and flammability. Designing and simulating an aircraft fuel tank inerting system model allows engineers to reduce the risk of explosions. Multiple tanks are usually interconnected by a manifold allowing for single point refueling from one location. From the refueling point, a pipework system is connected to all the tanks in the aircraft. Fuel tanks must have pumps that deliver fuel to the engines, and all wing tank pumps are fitted with pressure relief sequence valves which guarantee that. When all pumps are running, the center tank pumps deliver fuel preferentially. Each tank must have access panels for inspection and repairs, and technicians enter the tank via manholes after draining fuel.
