Self-sealing fuel tank
Encyclopedia
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 multiple layers of rubber
and reinforcing fabric, one of vulcanized
rubber and one of untreated natural rubber that can absorb oil and expand when wet. When a fuel tank is punctured, the fuel will seep into the layers, causing the swelling of the untreated layer, thus sealing the puncture.
. A conventional fuel tank, when hit by enemy fire, could leak fuel rapidly; this would not only reduce the aircraft's effective range, but was also a significant fire hazard. Damaged fuel tanks could 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 aero fuel tanks, hence a way of stopping fuel leaking from damaged tanks was necessary.
Early attempts at protecting fuel tanks consisted of using 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 greater problem, as it often tumbled, thus creating a large exit hole. Among the earliest versions of these types of tanks were those manufactured in the United Kingdom at Portsmouth
airport by Fireproof Tanks Ltd
. These tanks were first installed in the Fairey Battle
with other versions installed in Supermarine Spitfire
s, Hawker Hurricane
s and larger aircraft such as the Avro Lancaster
. The Henderson Safety Tank company provided crash-proof self-sealing tanks for the Miles Master trainer.
The Germans were using layers of rubber laid over leather hide with a treated fibre inner surface for the self-sealing tanks on their Ju-88
bombers early in the war.
In the US, Goodyear
chemist James Merrill was awarded a patent
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 lining 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 impact could overpressurize 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; self-sealing tanks tended to be heavier with lower capacity than non-sealed tanks. Nonetheless, aircraft that were fitted with self-sealing tanks regularly successfully took more punishment than those without. Combat experience in the Pacific
showed that the heavily protected American aircraft could sustain far more damage than the lightly armored Japanese designs without self-sealing fuel tanks (for instance, the Mitsubishi Zero).
The same principles were applied to give self-sealing fuel lines in aircraft (MIL-PRF-7061C).
s and all US military rotary wing aircraft have some type of self-sealing tanks. Military rotary wing fuel tanks have the additional feature of being crashworthy
. 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. 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 slosh. Major manufacturers of this technology include Amfuel (Zodiac) (formerly Firestone
), Meggitt (formerly Goodyear
), GKN
USA and FPT Industries
. For military use, tanks are qualified to MIL-DTL-27422 (includes crashworthiness
requirements) or MIL-DTL-5578.
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.
Aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
, self-sealing fuel tank is a fuel tank
Fuel tank
A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
technology in wide use since World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
that prevents fuel tanks primarily on aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
from leaking fuel and igniting after being damaged by enemy fire.
Self-sealing tanks have multiple layers of rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
and reinforcing fabric, one of vulcanized
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...
rubber and one of untreated natural rubber that can absorb oil and expand when wet. When a fuel tank is punctured, the fuel will seep into the layers, causing the swelling of the untreated layer, thus sealing the puncture.
World War I
George J. Murdock applied for the patent "War Aeroplane Fuel Tanks" on February 7, 1917 but was temporarily blocked by an order of the Federal Trade Commission, signed by Secretary Leonidas L. Bracken on February 6, 1918, to keep any discussion or publication of the invention secret. This order was in conformity with the provisions of the Trading with the Enemy Act and of the Executive Order of October 12, 1917. Violation of the order entailed a fine of up to $10,000 or imprisonment of 10 years or both. The order was rescinded by the United States Patent Office on September 26, 1918. Murdock was eventually granted United States Patent 1,386,791 "Self-Puncture Sealing Covering for Fuel-Containers" on August 9, 1921. Military aircraft built by the Glenn L. Martin Company used this self-sealing fuel tank.World War II
In the newer generations of pre-war and early-war aircraft, self-sealing tanks were tanks used to minimize the potential damage from leaking or burning fuelFuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
. A conventional fuel tank, when hit by enemy fire, could leak fuel rapidly; this would not only reduce the aircraft's effective range, but was also a significant fire hazard. Damaged fuel tanks could also rupture, destroying the airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...
or critically affecting flight characteristics
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
.
It was realised early on that it was not practical for weight reasons to add armour plate to aero fuel tanks, hence a way of stopping fuel leaking from damaged tanks was necessary.
Early attempts at protecting fuel tanks consisted of using 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 greater problem, as it often tumbled, thus creating a large exit hole. Among the earliest versions of these types of tanks were those manufactured in the United Kingdom at Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...
airport by Fireproof Tanks Ltd
FPT Industries
FPT Industries was formed in 1939 as Fireproof Tanks Ltd in the boardroom of Airspeed Ltd at Portsmouth Airport in response to an Air Ministry requirement for the development and manufacture of self-sealing fuel tanks for the impending war with Germany.The intention of the board of directors was...
. These tanks were first installed in the Fairey Battle
Fairey Battle
The Fairey Battle was a British single-engine light bomber built by the Fairey Aviation Company in the late 1930s for the Royal Air Force. The Battle was powered by the same Rolls-Royce Merlin piston engine that gave contemporary British fighters high performance; however, the Battle was weighed...
with other versions installed in Supermarine Spitfire
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...
s, Hawker Hurricane
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...
s and larger aircraft such as the Avro Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...
. The Henderson Safety Tank company provided crash-proof self-sealing tanks for the Miles Master trainer.
The Germans were using layers of rubber laid over leather hide with a treated fibre inner surface for the self-sealing tanks on their Ju-88
Junkers Ju 88
The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...
bombers early in the war.
In the US, Goodyear
Goodyear Tire and Rubber Company
The Goodyear Tire & Rubber Company was founded in 1898 by Frank Seiberling. Goodyear manufactures tires for automobiles, commercial trucks, light trucks, SUVs, race cars, airplanes, farm equipment and heavy earth-mover machinery....
chemist James Merrill was awarded a patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
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 lining 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
F4U Corsair
The Vought F4U Corsair was a carrier-capable fighter aircraft that saw service primarily in World War II and the Korean War. Demand for the aircraft soon overwhelmed Vought's manufacturing capability, resulting in production by Goodyear and Brewster: Goodyear-built Corsairs were designated FG and...
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 impact could overpressurize 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
Autocannon
An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun . Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a...
shells.
Not all fighters were fitted with the relatively new invention; self-sealing tanks tended to be heavier with lower capacity than non-sealed tanks. Nonetheless, aircraft that were fitted with self-sealing tanks regularly successfully took more punishment than those without. Combat experience in the Pacific
Pacific Theater of Operations
The Pacific Theater of Operations was the World War II area of military activity in the Pacific Ocean and the countries bordering it, a geographic scope that reflected the operational and administrative command structures of the American forces during that period...
showed that the heavily protected American aircraft could sustain far more damage than the lightly armored Japanese designs without self-sealing fuel tanks (for instance, the Mitsubishi Zero).
The same principles were applied to give self-sealing fuel lines in aircraft (MIL-PRF-7061C).
Modern use
Most jet fighterFighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
s and all US military rotary wing aircraft have some type of self-sealing tanks. Military rotary wing fuel tanks have the additional feature of being crashworthy
Crashworthiness
Crashworthiness is the ability of a structure to protect its occupants during an impact. This is commonly tested when investigating the safety of aircraft and vehicles. Depending on the nature of the impact and the vehicle involved, different criteria are used to determine the crashworthiness of...
. High altitudes require the tanks to be pressurized, making self-sealing difficult. Newer technologies have brought advances like inert foam-filled
Ballistic foam
Ballistic foam is a foam that sets hard. It is widely used in the manufacture and repair of aircraft to form a light but strong filler for aircraft wings. The foam is used to surround aircraft fuel tanks to reduce the chance of fires caused by the penetration of incendiary projectiles....
tanks to prevent detonation. 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 slosh. Major manufacturers of this technology include Amfuel (Zodiac) (formerly Firestone
Firestone Tire and Rubber Company
The Firestone Tire and Rubber Company is an American tire company founded by Harvey Firestone in 1900 to supply pneumatic tires for wagons, buggies, and other forms of wheeled transportation common in the era. Firestone soon saw the huge potential for marketing tires for automobiles. The company...
), Meggitt (formerly Goodyear
Goodyear Tire and Rubber Company
The Goodyear Tire & Rubber Company was founded in 1898 by Frank Seiberling. Goodyear manufactures tires for automobiles, commercial trucks, light trucks, SUVs, race cars, airplanes, farm equipment and heavy earth-mover machinery....
), GKN
GKN
GKN plc is a multinational automotive and aerospace components company headquartered in Redditch, United Kingdom. The company was formerly known as Guest, Keen and Nettlefolds and can trace its origins back to 1759 and the birth of the Industrial Revolution.GKN is listed on the London Stock...
USA and FPT Industries
FPT Industries
FPT Industries was formed in 1939 as Fireproof Tanks Ltd in the boardroom of Airspeed Ltd at Portsmouth Airport in response to an Air Ministry requirement for the development and manufacture of self-sealing fuel tanks for the impending war with Germany.The intention of the board of directors was...
. For military use, tanks are qualified to MIL-DTL-27422 (includes crashworthiness
Crashworthiness
Crashworthiness is the ability of a structure to protect its occupants during an impact. This is commonly tested when investigating the safety of aircraft and vehicles. Depending on the nature of the impact and the vehicle involved, different criteria are used to determine the crashworthiness of...
requirements) or MIL-DTL-5578.
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
Motorsport
Motorsport or motorsports is the group of sports which primarily involve the use of motorized vehicles, whether for racing or non-racing competition...
categories.