Ameer Randolph
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft, extending its range and endurance. They are designed to be more aerodynamic and lightweight than traditional drop tanks, and they don't occupy ordnance hardpoints, allowing the aircraft to carry its full payload. CFTs have been used on several modern aircraft, including the F-15, F-16, and F/A-18 Super Hornet, as well as some World War II-era planes like the Supermarine Spitfire and Messerschmitt Bf-110. While CFTs offer increased range and manoeuvrability, they also come with challenges, such as the need for extensive flight testing and potential fatigue issues.
| Characteristics | Values |
|---|---|
| Definition | Additional fuel tanks fitted closely to the profile of an aircraft that extend the endurance of the aircraft |
| Advantages | Reduced aerodynamic and drag penalty compared to external drop tanks; do not occupy ordnance hardpoints, allowing the aircraft to carry its full payload; increase range and endurance |
| Disadvantages | Cannot be discarded in flight, unlike drop tanks; impose a slight drag-penalty and minor weight gain on the aircraft when empty; may impose slight g-load limits |
| Examples | F-16 (F-16I and Block 50/52/60 models), F-15E, F-18E (Superhornet), F-CK-1D prototype ("Brave Hawk"), F-CK-1C single-seater prototype, Messerschmitt Bf-110, Supermarine Spitfire, English Electric Lightning |
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What You'll Learn
- Conformal fuel tanks are additional fuel tanks that are fitted closely to the profile of an aircraft
- They are known as FAST packs (Fuel And Sensor Tactical), carrying extra fuel while retaining hardpoints for weapons
- They are more aerodynamic and lighter than external drop tanks, increasing the range and endurance of the aircraft
- They cannot be discarded in flight as they are plumbed into the aircraft, imposing a slight drag penalty when empty
- They are used by several aircraft, including the F-15, F-16, F-18, and the Super Hornet
Conformal fuel tanks are additional fuel tanks that are fitted closely to the profile of an aircraft
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft to extend its endurance. They are designed to reduce the aerodynamic penalty caused by external drop tanks, and they do not significantly increase the aircraft's radar cross-section. CFTs are plumbed into the aircraft and cannot be discarded in flight, which means that even when empty, they impose a slight drag penalty and minor weight gain. However, they do not occupy ordnance hardpoints, allowing the aircraft to carry its full payload.
CFTs were first tested on the F-15B in 1974 and have since been adopted by various aircraft models. All U.S. F-15Es and export variants such as the Israeli and Singaporean models are fitted with CFTs under the wing outside the engine intake. The F-16 (F-16I and Block 50/52/60 models) also features CFTs as standard, and the Silent Eagle model of the F-15E proposed by Boeing for South Korea includes them as well. Additionally, the F-18E (Superhornet) has recently demonstrated the use of CFTs.
The use of CFTs is not limited to modern aircraft. Some World War II Supermarine Spitfires used a "slipper tank," which could hold up to 90 gallons of fuel. The Messerschmitt Bf-110 used a conformal fuel tank under the forward fuselage, nicknamed "Dackelbauch" (Dachshund belly). The English Electric Lightning employed a 'conformal ventral store' that could accommodate either a fuel tank or a rocket engine.
While CFTs offer advantages in terms of reduced drag and increased payload capacity, they also present challenges. The process of bolting CFTs onto an aircraft can be expensive and time-consuming, requiring extensive flight testing. Additionally, CFTs may introduce fatigue issues, impacting the structural life of the aircraft. In the case of the Super Hornet, the addition of CFTs was expected to extend its flying life, but it encountered significant fatigue problems that incurred substantial costs for users.
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They are known as FAST packs (Fuel And Sensor Tactical), carrying extra fuel while retaining hardpoints for weapons
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft, extending its endurance. They are more aerodynamic and lighter than external drop tanks, reducing drag and increasing range.
CFTs were initially known as FAST packs (Fuel And Sensor Tactical). They were first tested on the F-15B in 1974 and each unit carried 750 US gallons (2,839.1 litres) of fuel. The FAST pack was originally intended to carry a navigational and targeting infrared sensor system, but the F-15 instead carried LANTIRN pods for ground-attack missions.
FAST packs allow aircraft to retain hardpoints for weapons while carrying extra fuel. For example, the F-15 could carry four AIM-7F Sparrow missiles or bombs, some on the FAST packs. This combination of fuel and weapons increases the offensive capability of the aircraft.
The use of FAST packs can, however, have some drawbacks. The added weight and drag of the fuel tanks can reduce acceleration, endurance, cruise speed, and increase fuel burn. Additionally, CFTs cannot be discarded in flight as they are plumbed into the aircraft, which means that they impose a slight weight penalty even when empty.
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They are more aerodynamic and lighter than external drop tanks, increasing the range and endurance of the aircraft
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft, extending its endurance. They are more aerodynamic and lighter than external drop tanks, increasing the range and endurance of the aircraft.
CFTs have a reduced aerodynamic penalty compared to external drop tanks, which are typically carried on the wings of an aircraft. By mounting CFTs above the wings, drag is reduced, resulting in increased range and endurance. The F-18E (Superhornet) and F-16 (F-16I and Block 50/52/60 models) are examples of aircraft that have recently demonstrated or adopted the use of CFTs, showcasing their potential benefits.
The reduced drag and increased lift provided by CFTs contribute to a significant expansion of the aircraft's combat radius. For instance, the combined use of CFTs can result in an additional 130 nmi (240 km) of range. This increased range can be crucial for military operations, as it allows aircraft to fly longer distances without refuelling and provides greater flexibility in mission planning.
Another advantage of CFTs is that they do not occupy ordnance hardpoints, which are desired for munitions. This allows the aircraft to carry its full payload of weapons and utilise the hardpoints more efficiently. The primary reason for adopting CFTs on certain aircraft, such as the F-15E, is to increase their range while still retaining the ability to carry a substantial payload.
However, it is important to consider the trade-offs associated with CFTs. Unlike drop tanks, CFTs cannot be discarded in flight since they are plumbed into the aircraft. As a result, they impose a slight drag penalty and minor weight gain even when empty, without providing any fuel-related benefits. Additionally, CFTs may introduce slight g-load limitations, although this is not always a significant issue, as evidenced by the F-15E retaining its manoeuvrability without g-limitations.
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They cannot be discarded in flight as they are plumbed into the aircraft, imposing a slight drag penalty when empty
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft, extending its endurance. They are designed to be more aerodynamic and lightweight than external drop tanks, reducing drag and increasing range. CFTs do not occupy ordnance hardpoints, allowing the aircraft to carry its full payload.
However, one significant disadvantage of CFTs is that they cannot be discarded in flight. Unlike drop tanks, CFTs are plumbed into the aircraft, becoming a permanent part of its structure. This fixed installation means that CFTs cannot be easily removed or discarded during flight. As a result, when the conformal fuel tanks are empty, they impose a slight drag penalty and a minor weight gain on the aircraft. The aircraft continues to experience increased aerodynamic drag and weight even without the benefit of the additional fuel.
The inability to discard CFTs during flight can have several implications. Firstly, it affects the aircraft's performance, especially during manoeuvres that require high agility and speed. The extra weight and drag can impact the aircraft's acceleration, turning capabilities, and overall handling characteristics. Secondly, the permanent nature of CFTs may require modifications to the aircraft's design or flight control software to accommodate the changes in structural loads, acceleration, and manoeuvrability. This can lead to expensive and time-consuming flight test programs to ensure the aircraft's safety and performance.
While the drag penalty and weight gain associated with empty CFTs are considered slight, they can still influence the overall efficiency and performance of the aircraft. In some cases, the benefits of increased fuel capacity and endurance may outweigh the slight penalties incurred when the tanks are empty. Additionally, some aircraft, like the F-15E, have demonstrated that CFTs can provide the same manoeuvrability without g-limitations.
Despite the slight drag penalty when empty, CFTs offer advantages over external drop tanks. Their streamlined design reduces aerodynamic drag, improving the aircraft's overall performance and efficiency during flight. CFTs also do not occupy ordnance hardpoints, allowing the aircraft to carry its full weapon payload without compromising fuel capacity. This flexibility enhances the aircraft's operational capabilities and mission versatility.
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They are used by several aircraft, including the F-15, F-16, F-18, and the Super Hornet
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft to extend its endurance. They are designed to reduce the aerodynamic penalty compared to external drop tanks and do not significantly increase the aircraft's radar cross-section. CFTs also do not occupy ordnance hardpoints, allowing the aircraft to carry its full payload.
CFTs are used by several aircraft, including the F-15, F-16, F-18, and the Super Hornet. The F-15B was the first aircraft to test CFTs in 1974. All U.S. F-15Es, and Strike Eagle export variants such as the Israeli and Singapore models, are fitted with CFTs under the wing outside the engine intake. The F-16 (F-16I and Block 50/52/60 models) also have CFTs as standard, mounted on top of the wing/fuselage area. The F-18 Super Hornet has also demonstrated the use of CFTs, with the next-generation model featuring larger engines, internal stores, and other improvements.
The use of CFTs on these aircraft provides several advantages, including increased fuel capacity, extended range, and improved endurance. However, CFTs also have some disadvantages, such as imposing slight drag and weight penalties, even when the tanks are empty. Additionally, CFTs cannot be discarded in flight like drop tanks and can only be removed on the ground, which may impact the aircraft's maneuverability and performance.
The adoption of CFTs on the F-15, F-16, F-18, and Super Hornet showcases the importance of extended range and endurance for modern aircraft. By utilising CFTs, these aircraft can undertake longer missions, carry additional payloads, and enhance their operational capabilities. While there are some trade-offs in terms of drag and weight, the benefits of CFTs have led to their integration on multiple aircraft platforms to meet the demands of contemporary aerial operations.
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Frequently asked questions
Conformal fuel tanks (CFTs) are additional fuel tanks that are fitted closely to the profile of an aircraft to extend its endurance.
Conformal fuel tanks are somewhat common. They have been used for quite a while in several different designs. Some aircraft that have them include the F-16, F-15E, F-18E, F-CK-1D prototype, and F-CK-1C single-seater prototype.
CFTs have a reduced aerodynamic penalty compared to external drop tanks and do not occupy ordnance hardpoints, allowing the aircraft to carry its full payload. They also do not significantly increase an aircraft's radar cross-section.
Unlike drop tanks, CFTs cannot be discarded in flight as they are plumbed into the aircraft. Therefore, they impose a slight drag penalty and minor weight gain even when empty. They can also impose slight g-load limits. Additionally, the process of bolting CFTs onto an aircraft can be expensive and time-consuming, requiring extensive testing.
Yes, some World War II Supermarine Spitfires used what was called a "slipper tank," which could hold up to 90 gallons of fuel. The Messerschmitt Bf-110 used a conformal fuel tank under the forward fuselage, nicknamed "Dackelbauch" (Dachshund belly).
