Drop tank

In aviation, a drop tank (external tank, wing tank, or belly tank) is used to describe auxiliary fuel tanks externally carried by aircraft. A drop tank is expendable and often jettisonable. External tanks are commonplace on modern military aircraft and occasionally found in civilian ones, although the latter are less likely to be discarded except in the event of emergency.

Drop tank
A 330 US gallons (1,200 L) Sargent Fletcher drop tank being moved across the flight deck of an aircraft carrier

Overview

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)
Drop tank storage aboard USS Harry S. Truman (CVN-75)

The primary disadvantage with drop tanks is that they impose a drag penalty on the aircraft carrying them. External fuel tanks will also increase the moment of inertia, thereby reducing roll rates for air maneuvres. Some of the drop tank's fuel is used to overcome the added drag and weight of the tank itself. 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; however, some versions can only be removed on the ground.

History

Истребитель Heinkel He-51B
Bulgarian Heinkel He-51B, with drop tank under fuselage
Messerschmitt Bf 109 drop tank Keski-Suomen ilmailumuseo
A standard 300 litre capacity drop tank of the German WW II Luftwaffe
Me110
A Bf 110 of 9./ZG 26 with the rarely used, fin-stabilized 900 litre drop tanks

The drop tank was 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. During World War II, the German Luftwaffe began using external fuel tanks with the introduction of a 300-liter (80 US gallon) 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 liter tank, available in at least four differing construction formats — including at least one impregnated paper material, single-use version — and varying only slightly in appearance, became the standard volume for most subsequent drop tanks in Luftwaffe service, with a rarely used 900 litre (238 U.S. gallon), 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 in order 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.

RabaulTainanZeros
A6M3 Model 22, flown by Japanese top ace Hiroyoshi Nishizawa over the Solomon Islands, 1943

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).[1] The Zero entered service in 1940.

Bomber theorists insisted formations of heavy bombers with elaborate defensive armaments would be self-defending, believing long-range escort fighters to be "a myth"[2] as they could be easily forced to drop the tanks by minor harassment at the beginning of the raid[2] being more concerned that long-range medium bombers might compete for resources and so compromise their goal of creating vast fleets of heavy bombers.[3] 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 such as the Lockheed P-38 Lightning.

Lockheed P-38G-1-LO Lightning LOC fsa.8d22579
A Lockheed P-38 Lightning with a drop tank

It was only with drop tanks supplying 450 US gallons (1,700 l; 370 imp gal) of extra fuel per fighter that P-38s could carry out Operation Vengeance, the downing of Admiral Isoroku Yamamoto's airplane. (For this mission, each fighter carried one drop tank of approximately 150 to 165 US gal (570 to 620 L), and a larger one of approximately 300 to 330 US gal (1,100 to 1,200 L).[4][5]

P-51-361
A P-51 Mustang with 75-gallon metal drop tanks

Even after such experience showed the necessity for drop tanks, inflexible thinkers such as 8th Air Force General Ira C. Eaker had to be transferred out of commanding positions (and replaced with Maj. Gen. Jimmy Doolittle) so that drop tanks and range extension plans could be widely implemented in 1944 for American escort fighters.[6]

External drop tanks turned the Republic P-47 Thunderbolt from a short-range interceptor aircraft into a long-range escort and air superiority fighter, enabling it to accompany bombers from 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 300-to-330-gallon drop tanks for its longest sorties. This teardrop-shaped tank design was 13 feet (4.0 m) long and 3 feet (0.91 m) in diameter at its widest point.[7]

Paper-based drop tanks

Jettison Petrol Tanks- the Production of Jettison Tanks For USE by the United States Army Air Force and Royal Air Force, Britain, 1944 D23460
110 US-gallon (416 litre) paper drop tanks, destined for USAAF and RAF use, being manufactured at a British factory (1944)
359th Fighter Group - External Fuel Tanks
Paper droptanks stockpiled for use by the 359th Fighter Group, 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 take off, jettisoned in the event of an aborted mission and only being required for the outbound portion of any 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 centre section created by wrapping layers of the impregnated paper around a cylinder, the end caps hand-laminated with petal-shaped pieces sometimes named 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 6 PSI 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.)[8]

Some 13,000 papier-mâché tanks were made and used by the RAF, the vast majority used in the course of the war, conserving a considerable amount of metal. Very few examples survive due to their expendable nature and low intrinsic value at the time of their creation, and the fact that they are not inherently robust.[8] While probably a nuisance for those under the flight path when the empty tanks were released, as they were lightweight and comparatively fragile it is unlikely to cause anything but anxiety, the Germans authorities going so far as to distribute leaflets, explaining that drop tanks are not bombs.[8]

P-51 Mustang droptanks (7326241066)
110-gallon paper, and 75-gallon metal drop tanks displayed at the Luchtoorlogsmuseum, an aviation museum in the Netherlands (2012)

U.S. paper tanks were developed by Col. Bob Shafer and Col. Cass Hough, who spent many hours developing a 110-gallon (416 litre) 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". 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.

However it may explain why the most often-used fuel tanks for single-engined American fighters operating in Northern Europe were the 75-gallon (284 litre) 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 150-to-165-gallon model used by P-51s, P-47s and P-38s.[9]

Post-war use

The Matra JL-100 is a special hybrid drop tank and rocket pack; it combines a rocket launcher in front with 19 SNEB 68 mm (2.7 in) rockets and 250 litres (66 US 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.

Automotive use

Henry Ford Museum August 2012 29 (1951 Beatty belly tank lakester)
The 1951 Beatty belly tank lakester on display at the Henry Ford Museum in 2012.

After World War II, hot rodders raced the dry lakes of California to set new land speed records. War surplus drop tanks were plentiful and aerodynamically neutral, and it didn't take long to make one into a car, dubbed a lakester. According to GM historians,[10] Bill Burke of the So-Cal Speed Shop first attempted to convert a 168-gallon P-51 Mustang belly tank, before switching to the larger 305-gallon P-38 Lightning tank. Even now, lakesters compete at the Bonneville Salt Flats.

References

  1. ^ Lundstrom, John B. The First Team: Pacific Naval Air Combat from Pearl Harbor to Midway. Naval Institute Press.
  2. ^ a b Rosen, Stephen Peter (1994). Winning the next war: Innovation and the modern military (5th printing. ed.). Ithaca, N.Y: Cornell University Press. pp. 173–177. ISBN 0-8014-8196-1.
  3. ^ Kelsey, Benjamin S. (1982). The Dragon's Teeth?: The Creation of United States Air Power for World War II. Smithsonian Institution Press. ISBN 0-87474-574-8.
  4. ^ Air Power History. 50. Air Force Historical Foundation. 2003. pp. 33–34.
  5. ^ Polmar, Norman (2008). Aircraft Carriers: A History of Carrier Aviation and Its Influence on World Events, Volume II: 1946-2006. Potomac Books. p. 308. ISBN 1574886657.
  6. ^ Bodie, Warren M. (1991). The Lockheed P-38 Lightning. Widewing Publications. ISBN 0-9629359-5-6.
  7. ^ Wilkinson, Stephan (2005). Man And Machine: The Best of Stephan Wilkinson. Globe Pequot. p. 97. ISBN 1599216795.
  8. ^ a b c "Necessity is the Mother of Invention: Paper Drop Tanks of WWII". Warbird News. 13 August 2013. Retrieved 6 August 2016.
  9. ^ Christensen, Mark; Thacker, Tony (2005). So-Cal Speed Shop: The Fast Tale of the California Racers Who Made Hot Rod History. MotorBooks International. p. 66. ISBN 1610591852.
  10. ^ 2003 So-Cal Lakester
Aircraft dope

Aircraft dope is a plasticised lacquer that is applied to fabric-covered aircraft (both full-size and flying models). It tightens and stiffens fabric stretched over airframes, which renders them airtight and weatherproof.Typical doping agents include nitrocellulose, cellulose acetate and cellulose acetate butyrate. Liquid dopes are highly flammable; nitrocellulose, for instance, is also known as the explosive propellant "guncotton". Dopes often include colouring pigments to facilitate even application, and are available in a wide range of colors.Dope has been applied to various aircraft fabrics, including madapolam, but also more recently on polyester and other fabrics with similar fine weave and absorbent qualities.

Aircraft fuel tanks

Aircraft fuel tanks are a major component of aircraft fuel systems. They can be classified into internal or external fuel tanks and can be further classified by method of construction or intended use. Safety aspects of aircraft fuel tanks were examined during the investigation of the 1996 TWA Flight 800 in-flight explosion accident.

Big Red (motorcycle)

Big Red was the machine with which American Don Vesco took the motorcycle land-speed record, 405.25 kilometres per hour (251.81 mph), on September 17, 1970 at the Bonneville Salt Flats in Utah.

At Bonneville Speed Week in 1969, Vesco took Big Red to a speed of 365 km/h (227 mph). The following year, with the five and a half meter long motorcycle built from an aircraft drop tank, he undertook several more attempts to break the 395.363-kilometre-per-hour (245.667 mph) record set by Robert Leppan in 1966. He succeeded in setting a new record of 405.25 km/h (251.81 mph). A month later, the record was broken again: Cal Rayborn reached an averaged 427.25 kilometres per hour (265.48 mph) in two runs in opposite directions.

The bike is now an exhibit of the Barber Vintage Motorsports Museum.

Cruciform tail

The cruciform tail is an aircraft empennage configuration which, when viewed from the aircraft's front or rear, looks much like a cross. The usual arrangement is to have the horizontal stabilizer intersect the vertical tail somewhere near the middle, and above the top of the fuselage. The design is often used to locate the horizontal stabilizer away from jet exhaust, propeller and wing wake, as well as to provide undisturbed airflow to the rudder.

DSK Airmotive Hawk

The DSK Airmotive DSK-1 Hawk was an unusual homebuilt aircraft designed in the United States in the early 1970s. While the design itself was utterly conventional - a single-seat low-wing cantilever monoplane with fixed tricycle undercarriage - its method of construction was not, since the DSK-1 Hawk used a surplus 200 US Gal military drop tank as its fuselage. Designer Richard Killingsworth sold over 250 sets of plans.

Lakester

A Lakester is a car with a streamlined body but with four exposed wheels. It is most often made out of a modified aircraft drop tank. The main attraction is the drop tank's excellent aerodynamics, due to it being streamlined for aircraft use. Building lakesters became popular after World War II when surplus drop tanks were available cheaply.

Leading edge

The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one.

As an example of the distinction, during a tailslide, from an aerodynamic point of view, the trailing edge becomes the leading edge and vice versa but from a structural point of view the leading edge remains unchanged.

Lockheed Star Clipper

Lockheed's Star Clipper was a proposed Earth-to-orbit space shuttle based on a large lifting body spacecraft and a wrap-around drop tank. Originally proposed during a USAF program in 1966, the basic Star Clipper concept lived on during the early years of the NASA Space Shuttle program, and as that project evolved, in a variety of new versions like the LS-200.

Although the Star Clipper design did not progress far in the Space Transportation System (STS) program, it had an enormous effect on the emerging Space Shuttle design. The detailed study of the cost advantages of the drop tank design demonstrated a dramatic reduction in development risk, and as a result, development costs. When funding for STS development was cut, the drop tank was taken up as a way to meet the developmental budgets, leading to the semi-reusable Space Shuttle design.

Longeron

In engineering, a longeron is a load-bearing component of a framework. The term is commonly used in connection with aircraft fuselages and automobile chassis. Longerons are used in conjunction with stringers to form structural frameworks.

Messerschmitt Bf 109 variants

Due to the Messerschmitt Bf 109's versatility and time in service with both the Luftwaffe and other foreign air forces, numerous variants were produced over the eight years of service with the Luftwaffe and even more were produced by its foreign users.

Mitsubishi A5M

The Mitsubishi A5M, formal Japanese Navy designation Mitsubishi Navy Type 96 Carrier-based Fighter (九六式艦上戦闘機), experimental Navy designation Mitsubishi Navy Experimental 9-Shi Carrier Fighter, company designation Mitsubishi Ka-14, was a Japanese carrier-based fighter aircraft. It was the world's first monoplane shipboard fighter to enter service and the direct predecessor of the famous Mitsubishi A6M "Zero". The Allied reporting name was Claude.

Mitsubishi A6M Zero

The Mitsubishi A6M "Zero" is a long-range fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945. The A6M was designated as the Mitsubishi Navy Type 0 carrier fighter (零式艦上戦闘機, rei-shiki-kanjō-sentōki), or the Mitsubishi A6M Rei-sen. The A6M was usually referred to by its pilots as the Reisen (零戦, zero fighter), "0" being the last digit of the imperial year 2600 (1940) when it entered service with the Imperial Navy. The official Allied reporting name was "Zeke", although the use of the name "Zero" (from Type 0) was used colloquially by the Allies as well.

The Zero is considered to have been the most capable carrier-based fighter in the world when it was introduced early in World War II, combining excellent maneuverability and very long range. The Imperial Japanese Navy Air Service (IJNAS) also frequently used it as a land-based fighter.

In early combat operations, the Zero gained a reputation as a dogfighter, achieving an outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled Allied pilots to engage the Zero on generally equal terms. By 1943, due to inherent design weaknesses, such as a lack of hydraulic ailerons and rudder rendering it extremely unmaneuverable at high speeds, and an inability to equip it with a more powerful aircraft engine, the Zero gradually became less effective against newer Allied fighters. By 1944, with opposing Allied fighters approaching its levels of maneuverability and consistently exceeding its firepower, armor, and speed, the A6M had largely become outdated as a fighter aircraft. However, as design delays and production difficulties hampered the introduction of newer Japanese aircraft models, the Zero continued to serve in a front-line role until the end of the war in the Pacific. During the final phases, it was also adapted for use in kamikaze operations. Japan produced more Zeros than any other model of combat aircraft during the war.

Pave Tack

The Ford Aerospace AN/AVQ-26 Pave Tack is an electro-optical targeting pod developed by the United States Air Force (USAF) for military attack aircraft. It uses a laser and a forward looking infrared to find and designate targets for laser-guided bombs and other precision-guided munitions. Pave Tack's images are routed to a cockpit display, usually for the weapon systems officer.

Pave Tack was developed in the late 1970s and entered service in 1982, and was initially used by the USAF McDonnell Douglas F-4 Phantom II and General Dynamics F-111F Aardvark strike aircraft. Its combat debut came in 1986 during Operation El Dorado Canyon's air raid against Libya by F-111F aircraft stationed at RAF Lakenheath, England. F-111s used it to great effect in the Gulf War of 1991, both against fixed targets and against tanks (the destruction of tanks with LGBs designated GBU-12, became known as "tank plinking").

Pave Tack is a large installation, with the pod alone weighing some 629 kg (1,385 lb) and measuring 4,220 mm (166 inches) in length. On the F-4, the size of the pod meant that it had to be carried on the centerline station in place of the standard drop tank, and it imposed a substantial aerodynamic drag penalty; crews referred to it as "Pave Drag," and it was generally unpopular. The F-111C and F-111F carried the Pave Tack pod on a rotating carriage in its internal bomb bay, retracting it when not in use to reduce drag and protect the sensors from damage.

About 150 AVQ-26 pods were built, substantially less than originally planned. The last USAF Pave Tacks were withdrawn with the retirement of the F-111 in 1996.

The Royal Australian Air Force (RAAF) purchased ten Pave Tack pods in 1980 for its F-111 fleet. All 24 F-111Cs were wired for the pod, although there were not enough pods for all to be simultaneously equipped. Following the retirement of the USAF's F-111F in 1996 the RAAF purchased surplus pods to equip each of its F-111Cs to carry its own.The Republic of Korea Air Force (RoKAF) ordered an initial batch of eight pods in 1984 for delivery in 1987. It may have subsequently obtained additional pods from USAF surplus. The RoKAF uses the pods on its F-4 Phantoms.

The age of the Pave Tack system has made for a maintenance and reliability headache, since many of its parts are obsolete and no longer available.

Republic P-47 Thunderbolt

The Republic P-47 Thunderbolt was a World War II era fighter aircraft produced by the United States from 1941 through 1945. Its primary armament was eight .50-caliber machine guns and in the fighter-bomber ground-attack role it could carry five-inch rockets or a bomb load of 2,500 pounds (1,103 kg). When fully loaded, the P-47 weighed up to eight tons, making it one of the heaviest fighters of the war. The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp engine, which was also used by two U.S. Navy/U.S. Marine Corps fighters, the Grumman F6F Hellcat and the Vought F4U Corsair. The Thunderbolt was effective as a short-to medium-range escort fighter in high-altitude air-to-air combat and ground attack in both the European and Pacific theaters.

The P-47 was one of the main United States Army Air Forces (USAAF) fighters of World War II, and also served with other Allied air forces, including those of France, the United Kingdom, and the Soviet Union. Mexican and Brazilian squadrons fighting alongside the USAAF also flew the P-47.

The armored cockpit was relatively roomy and comfortable and the bubble canopy introduced on the P-47D offered good visibility. A present-day U.S. ground-attack aircraft, the Fairchild Republic A-10 Thunderbolt II, takes its name from the P-47.

Self-sealing fuel tank

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

Typical self-sealing tanks have multiple layers of rubber and reinforcing fabric, one of vulcanized rubber, and one of untreated natural rubber, which can absorb fuel, swell, and expand when it comes into contact with the fuel. When a fuel tank is punctured, the fuel seeps into the layers, causing the untreated layer to swell and thus seal the puncture.

A similar concept is also employed for making self-sealing run-flat tires.

Trailing edge

The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential flight control surfaces are attached here to control the direction of the departing air flow, and exert a controlling force on the aircraft. Such control surfaces include ailerons on the wings for roll control, elevators on the tailplane controlling pitch, and the rudder on the fin controlling yaw. Elevators and ailerons may be combined as elevons on tailless aircraft.

The shape of the trailing edge is of prime importance in the aerodynamic function of any aerodynamic surface. George Batchelor has written about:

“ ... the remarkable controlling influence exerted by the sharp trailing edge of an aerofoil on the circulation.”Other sharp-edged surfaces that are attached to the trailing edges of wings or control surfaces include:

On control surfaces:trim tabs

servo tabs

anti-servo tabsOther surfaces:flapsOther equipment that may be attached to the trailing edges of wings include:

anti-shock bodies

static dischargers

Wet wing

A wet wing is an aerospace engineering technique where an aircraft's wing structure is sealed and used as a fuel tank. Wet wings are also called integral fuel tanks.Wet wings are common among most civilian designs, from large transport aircraft, such as airliners, to small general aviation aircraft. Because the tanks are an integral part of the structure, they cannot be removed, and require access panels for routine maintenance and visual inspections.A disadvantage of the wet wing is that every rivet, bolt, nut plate, hose and tube that penetrates the wing must be sealed to prevent fuel from leaking or seeping around these hardware components. This sealant must allow for expansion and contraction due to rapid temperature changes (such as when cold fuel is pumped into a warm wing tank) and must retain its sealing properties when submerged in fuel and when left dry for long periods of time. Working with this sealant can be difficult and replacing old sealant inside a small wing tank can be harder if the old sealant needs to be removed as well before new sealant can be applied.Notable accidents in which the wet wing design and its drawbacks were causative include Chalk's Ocean Airways Flight 101 and the 1961 Goldsboro B-52 crash.

Wing root

The wing root is the part of the wing on a fixed-wing aircraft or winged-spaceship that is closest to the fuselage. On a simple monoplane configuration, this is usually easy to identify. On parasol wing or multiple boom aircraft, the wing may not have a clear root area.Wing roots usually bear the highest bending forces in flight and during landing, and they often have fairings (often named "wing fillets") to reduce interference drag between the wing and the fuselage.The opposite end of a wing from the wing root is the wing tip.

Yaw damper

A yaw damper is a device used on many aircraft (usually jets and turboprops) to damp (reduce) the rolling and yawing oscillations known as the Dutch roll mode. It consists of yaw-rate sensors and a processor that provides a signal to an actuator connected to the rudder. The use of a yaw damper helps provide a better ride for passengers by preventing the uncomfortable yawing and rolling oscillation. On some aircraft it is mandatory for the yaw damper to be operational at all times during flight above a specified altitude.

Internal tanks
External tanks
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