Self-sealing fuel tank

In aviation, self-sealing fuel tank is a fuel tank technology in wide use since World War II that prevents fuel tanks primarily on aircraft from leaking fuel and igniting after being damaged by enemy fire.

Self-sealing tanks have two layers of rubber, one of vulcanized rubber and one of untreated rubber that can absorb oil and expand when wet. When a fuel tank is punctured, the fuel will spill on to the layers, causing the swelling of the untreated layer, thus sealing the puncture.

World War II

In the newer generations of pre-war and early-war aircraft, self-sealing tanks were tanks used to minimise the potential damage from leaking or burning fuel. A conventional fuel tank, when hit by enemy fire, would leak fuel rapidly. This would not only reduce the aircraft's effective range, but was also a significant fire hazard. Damaged fuel tanks can also rupture, destroying the airframe or critically affecting flight characteristics.

It was realised early on that it was not practical for weight reasons to add armour plate to the fuel tank hence a way of stopping fuel leaking from damaged tanks was necessary.

Early attempts at protecting fuel tanks consisted of metal tanks, covered inside or outside by a material that expanded after being pierced. Research revealed that the "exit" of the projectile, rather than the entry, was the problem, as it tumbled and created a large exit hole. Amongst the earliest versions of these types of tanks were those manufactured in the United Kingdom at Portsmouth airport by Fireproof Tanks Ltd [http://en.wikipedia.org/wiki/FPT_Industries] . These tanks were first installed in the Fairey Battle with other versions installed in Spitfires, the Hawker Hurricane and larger aircraft such as the Avro Lancaster.

Goodyear chemist James Merrill was awarded a patent [http://www.google.com/patents?id=qjpYAAAAEBAJ&printsec=abstract&zoom=4&dq=james+merrill+goodyear] in 1941 for refining and successfully testing his method for manufacturing self sealing tanks using a two-layer system of rubber compounds encased in a metal outer shell (or the wing of the aircraft). In 1942, he received a War Production Board citation from President Roosevelt and the Goodyear tanks were subsequently placed in service in Goodyear-produced Corsair fighters, as well as other aircraft. By 1942 Fireproof Tanks had developed the first flexible fuel bladders as range extender tanks for the MkIX Spitfire. These tanks were flexible containers, made of a laminated self-sealing material like vulcanized rubber and with as few seams as possible to minimise leak paths.

As early tests showed that the impact could overpressure a fuel tank, the self-sealing fuel cell is suspended, allowing it to absorb shocks without rupture. U.S. Navy fuel tanks during the war were able to withstand .50 caliber (12.7 mm) bullets and, on occasion, 20 mm cannon shells.

Not all fighters were fitted with the relatively new invention. Those that were regularly took more punishment than those without self-sealing fuel tanks. Victory ratios in the Pacific showed that the heavily protected American aircraft could take far more damage than the lightly armored Japanese designs without self-sealing fuel tanks (for instance, the Mitsubishi Zero).

Modern use

Most jet fighters have some type of self-sealing tanks. High altitudes require the tanks to be pressurized, making self-sealing difficult. Newer technologies have brought advances like inert foam-filled tanks to prevent detonation and self-healing designs. This foam is an open cell foam that effectively divides the gas space above the remaining fuel into thousands of small spaces none of which contain sufficient vapour to support combustion. This foam also serves to reduce fuel slop. Major manufacturers of this technology include Amfuel, Zodiac and Fireproof Tanks Ltd under their modern name FPT Industries.

In additions to fighter aircraft some military patrol vehicles and armoured limousines for VIP use also feature self sealing fuel tanks.

Self sealing fuel tanks using military technology are also required in some motorsport categories.

References

# Gustin, Emmanuel (1999). [http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-ar.html Fighter Armour] . Retrieved Aug. 4, 2005.
# "The Story of the Self-Sealing Tank". (Feb. 1946). "US Naval Institute Proceedings", pp.205.