Types of Aircraft Fuel Tanks

Posted on April 7, 2021 John Symond

Unsurprisingly, the fuel tank is a critical part of every aircraft. To accommodate the wide range of aircraft types, there are many different types of aircraft fuel tanks. The three most common are rigid removable fuel tanks, bladder fuel tanks, and integral fuel tanks. In this blog, we will discuss each of these three types and their unique characteristics.

Rigid Removable Fuel Tanks

Many aircraft, especially older models, use rigid removable fuel tanks. They are made from materials such as aluminum alloy or stainless steel, and riveted & seam welded to prevent leaks. Regardless of the fuel tank’s construction, they must be supported by the airframe and held in place by a padded strap arrangement to resist shifting during flight. They are most commonly placed in the wings, and some tanks are formed to be a part of the wing’s leading edge. As new materials are being tested and developed, fuel tanks are being made from materials other than aluminum and stainless steel. For example, newer tanks can be made from an isophthalic polyester resin composite. Fuel tanks of this material have seamless, lightweight constructions.

Removable tanks offer the benefit of being able to remove the tank if it needs repair or replacement. Repairs to fuel tanks must be done in accordance to manufacturer specifications, and it is especially important to follow all safety procedures during welding. For example, prior to welding, all fuel vapors must be removed from the tank to prevent explosion. This typically involves washing out the tank with water and detergent in addition to steam or water being run through the tank. Following repair, the tank must be pressure checked before being reinstalled.

Bladder Fuel Tanks

Fuel tanks made from reinforced flexible materials are known as bladder tanks. They have many of the same features of rigid tanks but do not require as large an opening in the aircraft to install. The tank can be rolled up and put into a small opening and then unfurled to its full size once inside. Bladder tanks must lie smooth and unwrinkled in the bay, as wrinkles can block fuel contaminants from settling into the fuel tank sump. Bladder fuel tanks are used on aircraft of all sizes. They are strong, have a long service life, and are seamless apart from the areas around installed features such as the tank vents, sump drain, filler spout, and so on.

Integral Fuel Tanks

In some aircraft, especially transport category and high performance aircraft, part of the structure of the wings or fuselage is sealed with a fuel resistant sealant to form a fuel tank. Integral fuel tanks provide the highest volume of space with the lowest weight. They are most commonly placed in the otherwise unused space inside the wings. When an aircraft maneuvers, integral tanks require baffling to prevent the fuel from sloshing in the wings. To do this, baffle check valves, which allow fuel to move to the low, inboard sections but prevent it from moving outboard, are used.

When entering the fuel tank to perform maintenance, all fuel must be emptied and safety protocols must be adhered to. Fuel vapors must be purged from the tank and respiratory equipment must be worn. Aircraft that use integral fuel tanks typically feature sophisticated fuel systems that include in-tank boost pumps. There are typically two or more pumps in each tank that provide fuel to the engine or engines under positive. These boost pumps are also used to transfer fuel to the other tanks, jettison fuel, and defuel the aircraft.

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