Drop tank

{{anchor|Aeronautic}}

File:US Navy 100525-N-6003P-076 Aviation Ordnancemen 3rd Class Eric Johnson and Robert Latner complete a 364-day inspection of an F-A-18C Hornet in the hangar bay of the Nimitz-class aircraft carrier USS Harry S. Truman (CVN 75).jpg

The primary disadvantage with drop tanks is that they impose a drag penalty on the aircraft. External fuel tanks will also increase the moment of inertia, thereby reducing roll rates for air maneuvers. Some of the drop tank's fuel is used to overcome the added drag and weight of the tank. Drag in this sense varies with the square of the aircraft's speed. The use of drop tanks also reduces the number of external hardpoints available for weapons, reduces the weapon-carrying capacity and increases the aircraft's radar signature. Usually the fuel in the drop tanks is consumed first, and only when all the fuel in the drop tanks has been used, the fuel selector is switched to the airplane's internal tanks. Some modern combat aircraft use conformal fuel tanks (CFTs) instead of or in addition to conventional external fuel tanks. CFTs produce less drag and do not take up external hardpoints but some versions can only be removed on the ground.

File:Истребитель Heinkel He-51B.jpg

File:Messerschmitt Bf 109 drop tank Keski-Suomen ilmailumuseo.JPG

File:Me110.jpg with the rarely-used, fin-stabilized 900-liter drop tanks]]

According to Selfridge Field's history, drop tanks were first used on 5 March, 1923.[https://www.127wg.ang.af.mil/Media/Articles/Article-Display/Article/865880/selfridge-angb-home-of-the-drop-tank/ Selfridge ANGB: Home of the Drop Tank]

The drop tank was later used during the Spanish Civil War to allow fighter aircraft to carry additional fuel for long-range escort flights without requiring a dramatically larger, heavier, less maneuverable fuselage.

Mitsubishi A5M, designed by Jiro Horikoshi, began carrying an external underside drop tank to provide fuel for extended range in 1937 and during World War II, the Luftwaffe began using external fuel tanks with the introduction of a {{convert|300|L|adj=on}} light alloy model for the Ju 87R, a long-range version of the Stuka dive bomber, in early 1940. The Messerschmitt Bf 109 fighter also used this type of drop tank, starting with the Bf 109E-7 variant introduced in August 1940. Fitted also to the Focke-Wulf Fw 190, the 300-litre tank, available in at least four construction formats — including at least one impregnated paper material, single-use version — and varying only slightly in appearance, became the standard volume for most drop tanks in Luftwaffe service, with a rarely used {{convert|900|L|adj=on}}, fin-stabilized large capacity drop tank used with some marks of the Messerschmitt Bf 110 heavy fighter and other twin-engined Luftwaffe combat aircraft.

The first drop tanks were designed to be discarded when empty or in the event of combat or emergency to reduce drag, weight, and to increase maneuverability. Modern external tanks may be retained in combat, to be dropped in an emergency. The Allies commonly used them to allow fighters increased range and patrol time over continental Europe. The RAF used such external fuel tanks in 1942, during the transit of Supermarine Spitfires to Malta. The Imperial Japanese Navy design specification for what came to be the Japanese Mitsubishi A6M Zero fighter included endurance with drop tanks of two hours at full power, or six to eight hours at cruising speed. Drop tanks were commonly used with the Zero, even on combat air patrol (CAP).{{Cite book|title=The First Team: Pacific Naval Air Combat from Pearl Harbor to Midway|last=Lundstrom|first=John B.|publisher=Naval Institute Press}} The Zero entered service in 1940.

American bomber theorists (the so-called Bomber Mafia) wanted to create vast fleets of heavy bombers. They insisted formations of heavy bombers with multiple machine-gun positions would be self-defending, and that long-range escort fighters would be unnecessary, or even impossible to design. They were also concerned that long-range medium bombers might compete for resources. For all these reasons, official policy in the United States held that drop tanks should not be developed or encouraged.{{cite book|last=Rosen|first=Stephen Peter|title=Winning the next war: Innovation and the modern military|year=1994|publisher=Cornell University Press|location=Ithaca, N.Y|isbn=0-8014-8196-1|pages=173–177|url=https://books.google.com/books?id=ncLRUf-q-XYC&pg=PA175|edition=5th printing.}}{{cite book|title=The Dragon's Teeth?: The Creation of United States Air Power for World War II|last=Kelsey|first=Benjamin S.|year=1982|publisher=Smithsonian Institution Press|isbn=0-87474-574-8|url=https://books.google.com/books?id=sq64AAAAIAAJ}} In the face of such entrenched attitudes in 1941 airmen such as Benjamin S. Kelsey and Oliver P. Echols worked quietly to get drop tank technology added to American fighters, beginning with the Lockheed P-38 Lightning. It was only with drop tanks supplying {{convert|450|gal|l|order=flip}} of extra fuel per fighter that P-38s could carry out Operation Vengeance, the downing of Admiral Isoroku Yamamoto's aircraft. (For this mission, each fighter carried one drop tank of approximately {{convert|150|to|165|gal|L|order=flip}}, and a larger one of approximately {{convert|300|to|330|gal|L|order=flip|disp=or}}).{{cite book|title=Air Power History|volume=L|publisher=Air Force Historical Foundation|year=2003|pages=33–34}}{{cite book|url=https://books.google.com/books?id=6z7quhWS-BoC&pg=PA308|pages=308|first=Norman|last=Polmar|title=Aircraft Carriers: A History of Carrier Aviation and Its Influence on World Events, Volume II: 1946-2006|publisher=Potomac Books|year=2008|isbn=978-1574886658}}

File:P-51-361.jpg with {{convert|75|USgal|L|adj=on}} metal drop tanks]]

8th Air Force General Ira C. Eaker experimented with British hardened paper drop tanks for the purpose of extending range for his Republic P-47 Thunderbolt fighters, so that they could fly with and defend the strategic bombers for extended periods. But the paper experiments did not satisfy American planners, and Eaker's inflexible bomber defense strategy was holding back the fighters, so he was replaced with Major General Jimmy Doolittle who gave escort fighters freedom to engage the enemy far ahead, and implemented metal drop tanks in 1944 for American fighters.{{cite book|title=The Lockheed P-38 Lightning|last=Bodie|first=Warren M.|year=1991|publisher=Widewing Publications|isbn=0-9629359-5-6|url=https://books.google.com/books?id=KzHpAAAACAAJ}} External drop tanks turned the Thunderbolt from a short-range interceptor aircraft into a long-range escort and air superiority fighter, enabling it to accompany bombers from the British Isles into Germany and made it possible for heavy bomber formations to undertake daylight raids under escort by North American P-51 Mustangs. The P-38 could also carry two {{convert|300|to|330|USgal|L|order=flip}} drop tanks for its longest sorties. This teardrop-shaped tank design was {{cvt|13|ft|m|order=flip}} long and {{cvt|3|ft|cm|order=flip|sigfig=1}} in diameter at its widest point.{{cite book|url=https://books.google.com/books?id=uFVqaS_QjW4C&pg=PA97|page=97|title=Man And Machine: The Best of Stephan Wilkinson|first=Stephan|last=Wilkinson|publisher=Globe Pequot|year=2005|isbn=1599216795}}

File:Jettison Petrol Tanks- the Production of Jettison Tanks For USE by the United States Army Air Force and Royal Air Force, Britain, 1944 D23460.jpg

File:359th_Fighter_Group_-_External_Fuel_Tanks.jpg, RAF East Wretham, 1944]]

Faced by wartime metal shortages and a need to extend the range of fighter craft, the British came up with drop tanks made of glue-impregnated kraft paper, which had excellent tolerance characteristics for extreme heat and cold necessary for operation on an aircraft as well as being waterproof.

Since the glue would slowly dissolve from the solvent effects of the fuel (sometimes developing leaks within a few hours of being loaded with fuel) these were strictly a single-use item, used in typically chilly Northern European conditions, filled immediately before takeoff, jettisoned in the event of an aborted mission and only being required for the outbound portion of a flight. Such papier-mâché tanks were assembled from three main components, the nose cone, tail cone and the body, each shaped over wooden forms, the center section created by wrapping layers of the impregnated paper around a cylinder, the end caps hand-laminated with petal-shaped pieces sometimes called gores.

Before final assembly wooden anti-slosh baffles were installed, pipes and fittings were attached and the interiors coated with fuel-resistant lacquer and the three pieces were bonded together in press. Once the tank had cured, it was pressure tested to {{cvt|6|psi|kPa|order=flip|lk=on}} and passing tanks were given two coats of cellulose dope followed by two coats of aluminium paint. (British paper drop tanks can be distinguished from outwardly similar metal tanks by colour, paper tanks were silver in appearance, while metal tanks were grey.){{cite web|url=http://www.warbirdsnews.com/warbird-articles/necessity-mother-invention-paper-drop-tanks-wwii.html|title=Necessity is the Mother of Invention: Paper Drop Tanks of WWII|publisher=Warbird News|date=13 August 2013|access-date=6 August 2016}} Some 13,000 papier-mâché tanks were made and used by the RAF, the vast majority during the war, conserving a considerable amount of metal. Very few examples survive due to their expendable nature, low intrinsic value and the fact that they are not inherently robust. While probably a nuisance for those under the flight path when the empty tanks were released, they were lightweight and comparatively fragile. Though they were likely to cause nothing but anxiety, the German authorities went so far as to distribute leaflets explaining that drop tanks were not bombs.

File:P-51 Mustang droptanks (7326241066).jpg

US paper tanks were developed by Col. Bob Shafer and Col. Cass Hough, who spent many hours developing a {{convert|110|usgal|l|order=flip|adj=on}} paper tank, then getting them into series production at Bowater-Lloyd's of London, only to be told by experts at Wright Field "paper tanks are absolutely unfeasible and will not do the job for which they are intended".{{cite magazine |last=Morgan |first=Len |date=January 1998 |title=Vectors |magazine=Flying |publisher=Hachette Filipacchi |page=93 |language=en}} Since by the time the experts made that pronouncement 8th Air Force fighters had already used more than 15,000 paper tanks without a failure, the criticism was not taken seriously. It may explain why the most often-used fuel tanks for single-engined American fighters operating in Northern Europe were the {{convert|75|usgal|l|order=flip|adj=on}} capacity all-metal tank (made from two halves of formed aluminium with a prominent horizontal seam running along the tank's midline). Another common metal drop tank was the {{convert|150|to|165|USgal|L|adj=on|order=flip}} model used by P-51s, P-47s and P-38s.{{cite book|url=https://books.google.com/books?id=pib4YDfV-joC&pg=PA66|page=66|title=So-Cal Speed Shop: The Fast Tale of the California Racers Who Made Hot Rod History|publisher=MotorBooks International|year=2005|first1=Mark|last1=Christensen|first2=Tony|last2=Thacker|isbn=1610591852}}

The Matra JL-100 is a special hybrid drop tank and rocket pack; it combines a rocket launcher in front with 19 SNEB {{convert|68|mm|abbr=on}} rockets and {{convert|250|L|gal}} of fuel behind into one single aerodynamically shaped pod for mounting on combat aircraft such as the Dassault Mirage IIIs and English Electric Lightnings. The Convair B-58 Hustler, the first operational bomber capable of Mach 2 flight, had no bomb bay: it carried a single nuclear weapon plus fuel in a combination bomb/fuel pod underneath the fuselage.

File:Henry Ford Museum August 2012 29 (1951 Beatty belly tank lakester).jpg in 2012]]

After World War II, hot rodders raced the dry lakes of California to set new land speed records. War surplus drop tanks (aka belly tanks) were plentiful, aerodynamically neutral and it did not take long to convert one into a car, dubbed a lakester.{{fact|date=January 2024}} According to GM historians, Bill Burke of the So-Cal Speed Shop first attempted to convert a {{convert|168|USgal|L|adj=on|order=flip}} P-51 Mustang belly tank, before switching to the larger {{convert|305|USgal|L|adj=on|order=flip}} P-38 Lightning tank. Even now, lakesters compete at the Bonneville Salt Flats.{{cite web | title=2003 So-Cal Lakester | website=Supercars.net | date=2016-04-22 | url=https://www.supercars.net/blog/2003-cal-lakester/ | access-date=2021-06-12}}

At least two aircraft have been built using re-purposed drop tanks. The Prue 160 glider from 1945 had its forward fuselage built from a Lockheed P-38 Lightning drop tank.{{cite magazine|last=Said |first=Bob |title=1983 Sailplane Directory|work= Soaring Magazine|page=54 |publisher=Soaring Society of America |date=November 1983}} The 2013 Malliga MAL 04 Speedbird used a McDonnell Douglas F-4 Phantom II drop tank as its fuselage.{{cite web |last=Haider-Krätschmer |first=Sonja | title=Für sein Hobby legte er sich mit der CIA an |url=http://www.kleinezeitung.at/steiermark/murtal/4063738/Fuer-sein-Hobby-legte-er-sich-mit-der-CIA-an |archive-url=https://web.archive.org/web/20180303185322/http://www.kleinezeitung.at:80/steiermark/murtal/4063738/Fuer-sein-Hobby-legte-er-sich-mit-der-CIA-an|website=www.all-aero.com |publisher=Kleine Zeitung |archive-date=3 March 2018 |access-date=21 April 2025 |date=29 June 2013|lang=DE}}

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{{Commons category-inline|Drop tanks}}

{{Aircraft fuel tanks}}

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Category:Aircraft fuel system components

Category:Fuel containers