Katerina Swanson
External fuel tanks, also known as drop tanks, are auxiliary fuel tanks that are externally attached to aircraft. They are commonly used on military aircraft and occasionally on civilian aircraft, although the latter are rarely discarded except in emergencies. The first drop tanks were designed to be released when empty or during combat or emergencies to reduce drag and increase manoeuvrability. The fuel in these tanks is typically consumed first, and only when it is depleted do aircraft switch to their internal fuel tanks. Drop tanks can be challenging to ignite, even when empty, and are often repurposed after being jettisoned.
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What You'll Learn
Drop tanks are not retrieved and reused
Drop tanks, also known as external tanks, wing tanks, or belly tanks, are auxiliary fuel tanks that are externally attached to aircraft. They are commonly used on military aircraft and occasionally on civilian aircraft. Drop tanks are designed to be discarded in specific situations, such as when they are empty, during combat, or in emergencies, to reduce drag, weight, and improve manoeuvrability.
While drop tanks are not typically retrieved and reused, their fate depends on where they land. For instance, drop tanks jettisoned in Vietnam have been repurposed into boats. Additionally, after World War II, war surplus drop tanks were used by hot rodders racing in California's dry lakes to set new land speed records. These surplus tanks were converted into vehicles known as "lakesters," which continue to compete at the Bonneville Salt Flats.
The decision to discard or retain drop tanks depends on various factors. Modern external tanks are often retained and returned to base with the aircraft, especially in non-emergency situations or when needed for specific flight operations. This is because drop tanks are not cheap and are complex structures comparable to the wings of an aircraft. They feature multiple cells, pumps, valves, pressurization systems, and other components that contribute to their high cost.
During World War II, the Allies commonly employed drop tanks to extend the range and patrol time of their fighters over continental Europe. The RAF extensively used external fuel tanks, with over 13,000 papier-mâché tanks deployed during the war, conserving a significant amount of metal. Despite their expendable nature, the lightweight and fragile paper tanks were not considered robust, and very few examples have survived.
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Drop tanks are expensive and complex
Drop tanks, or external fuel tanks, are commonly used on modern military aircraft and occasionally on civilian aircraft. These tanks are expendable and can be jettisoned in the event of an emergency. While drop tanks allow aircraft to carry additional fuel for long-range flights, they come with several disadvantages and complexities.
Firstly, drop tanks are expensive. They are not typically jettisoned unless absolutely necessary because of their high cost. The expense of drop tanks is further emphasised by the fact that they are only used when essential to the mission, as they impose a drag penalty on the aircraft. This drag increases with the square of the aircraft's speed, negatively impacting performance and requiring some of the fuel to be used to overcome it.
The use of drop tanks also reduces the aircraft's manoeuvrability and agility. The additional weight and moment of inertia from the external tanks decrease the roll rates for air manoeuvres. This reduction in agility can be detrimental, especially for fighter aircraft that rely on their manoeuvrability in combat.
Additionally, drop tanks occupy external hardpoints, reducing the aircraft's weapon-carrying capacity. This limitation can be significant, as it may require a trade-off between fuel range and weapons load. The use of drop tanks also increases the aircraft's radar signature, making it easier to detect and track.
Moreover, the design and construction of drop tanks can be complex. For example, during World War II, the British developed papier-mâché drop tanks, which were lightweight but fragile. Despite initial criticism, the American 8th Air Force successfully used over 15,000 of these paper tanks. Metal drop tanks were also utilised, with the most common being the 570-to-620-litre (150 to 165 US gal) model used by several American fighter aircraft.
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Drop tanks are used by military aircraft
Drop tanks, also known as external, wing, or belly tanks, are auxiliary fuel tanks that are externally attached to aircraft. They are commonly used on modern military aircraft and occasionally on civilian aircraft, although civilian aircraft rarely discard them except in emergencies. Drop tanks were first used on 5 March 1923 and became popular in the late 1930s, particularly during World War II. During the Spanish Civil War, drop tanks allowed fighter aircraft to carry additional fuel for long-range escort flights without needing a larger, heavier fuselage. They were also used by the Luftwaffe, the Messerschmitt Bf 109 fighter, and the Mitsubishi A5M, which began carrying an external underside drop tank in 1937.
The primary disadvantage of drop tanks is the drag penalty they impose on the aircraft, which reduces roll rates for air maneuvers. Additionally, drop tanks reduce the number of external hardpoints available for weapons and increase the aircraft's radar signature. Despite these drawbacks, drop tanks provide significant advantages in terms of extended range and patrol time. During World War II, the Allies used drop tanks to increase the range and patrol time of their fighters over continental Europe, such as during the transit of Supermarine Spitfires to Malta in 1942.
Drop tanks were also used as makeshift bombs during World War II and the Korean War, filled with napalm for close air support missions. This practice was later criticized for its potential for collateral damage and increased casualties.
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 occupy external hardpoints, but some versions can only be removed on the ground.
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Drop tanks are occasionally used by civilian aircraft
In aviation, a drop tank (also known as an external tank, wing tank, or belly tank) is an auxiliary fuel tank that is carried externally by an aircraft. Drop tanks are commonplace on modern military aircraft and are occasionally found on civilian aircraft.
The first drop tanks were designed to be discarded when empty or in the event of combat or emergency situations to reduce drag, weight, and increase manoeuvrability. Modern external tanks may be retained in combat and are only dropped in emergency situations. Drop tanks were first used on 5 March 1923 and were later used during the Spanish Civil War to allow fighter aircraft to carry additional fuel for long-range flights without requiring a larger, heavier fuselage.
The use of drop tanks on civilian aircraft is less common and they are rarely discarded except in emergency situations. The primary disadvantage of drop tanks is that they impose a drag penalty on the aircraft, reducing roll rates for air manoeuvres. Additionally, the use of drop tanks reduces the number of external hardpoints available for weapons and increases the aircraft's radar signature.
The cost of drop tanks is also a factor in their use, as they are not typically discarded unless necessary. In wartime, drop tanks are usually jettisoned when air combat is imminent or when returning to base, to reduce drag and improve aircraft performance.
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Drop tanks are rarely used by private jets
Drop tanks, also known as external, wing, or belly tanks, are auxiliary fuel tanks that are attached to the exterior of aircraft. They are commonly used by military aircraft and, occasionally, civilian aircraft. Drop tanks are typically jettisoned in emergency situations or when increased manoeuvrability is required.
Private jets rarely use drop tanks due to several factors. Firstly, the market for external tanks is limited as aircraft with sufficient internal fuel capacity already exist. For instance, jets like the Global Express, Gulfstreams, and Falcons can fly long distances without the need for external tanks. Additionally, private jet owners usually have a clear understanding of their travel requirements and select jets with the appropriate range. The need for extended range is infrequent and does not justify the extra weight and maintenance required for external tanks.
Another disadvantage of drop tanks is the drag penalty they impose on aircraft. This increased drag results in higher fuel consumption, making the operation more expensive. Drop tanks also reduce the manoeuvrability of the aircraft, which may not be desirable for private jets. Furthermore, the use of drop tanks reduces the available space for weapons and increases the aircraft's radar signature, which is typically not a concern for private jets.
In rare cases where private jets may require extended range, alternative options are available, such as mid-air refuelling services or chartering a larger jet for specific trips. These alternatives provide flexibility without the drawbacks associated with drop tanks.
While drop tanks can provide significant additional fuel capacity, their disadvantages, such as drag, weight, and reduced manoeuvrability, make them less appealing for private jets. Private jet owners and operators prioritize comfort, efficiency, and customization to suit their travel needs, and internal fuel tanks better meet these requirements.
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