Types of Aircraft Fuel Tanks

Aircraft fuel tanks are sealed containers engineered to store and deliver fuel under controlled pressure and flow conditions throughout all phases of flight. These components play a foundational role in determining range, payload distribution, and overall system integration across different aircraft classes, making it useful for anyone involved in the industry to have a general understanding of them. In this blog, we will explore the main types of aircraft fuel tanks currently in use and examine how their configurations support both performance and structural design priorities.

What Design Factors Influence Aircraft Fuel Tank Configuration?

Selecting a fuel tank design involves balancing several interrelated factors, including structural load paths, internal airframe volume, and total fuel capacity requirements. Beyond these constraints, engineers should also evaluate how tank placement affects crash survivability and adherence to regulatory requirements for redundant fuel feed paths or compartmentalization. Additional considerations include ensuring compatibility with onboard fuel management systems and facilitating inspection, upkeep, or modular replacement over an aircraft’s service life.

How Are Integral Fuel Tanks Used in Modern Aircraft?

Integral fuel tanks are built directly into an aircraft’s wing or fuselage structure, using sealed portions of the airframe to contain fuel without relying on independent tank assemblies. These tanks are commonly used in large commercial aircraft and offer several key advantages:

• Optimized Internal Volume: Integral fuel tanks are generally able to utilize structural cavities, such as those within wings, that would otherwise go unused.
• Structural Integration: By residing within load-bearing elements, integral fuel tanks help support aircraft balance and contribute to overall rigidity.
• Weight Reduction: These fuel tanks are designed to eliminate the need for freestanding components, which can lower empty weight while increasing usable volume.

What Are the Characteristics of Bladder-Type Fuel Tanks?

Bladder-type fuel tanks are flexible, self-contained fuel cells that are installed within designated cavities in an airframe. The following design features help distinguish bladder-type tanks from common alternatives:

• Ease of Replacement: These tanks can typically be removed and replaced without the need to disassemble major internal structures or airframe load paths.
• Crash Resistance: The flexible walls of bladder-type tanks can absorb impact forces during hard landings or crashes, improving the likelihood of fuel containment and overall crash survivability.
• Contamination Isolation: Bladder-type tanks are designed to reduce the risk of debris or moisture entering the broader fuel system.

When Are Rigid Fuel Tanks Still Preferred?

Typically constructed from aluminum or composite materials, rigid fuel tanks are freestanding, enclosed containers mounted within designated sections of an airframe. These tanks remain in use across legacy platforms and refurbishment programs for several key reasons:

• Legacy Design Compatibility: Many older airframes were originally certified with rigid tank installations, making continued use the most direct path for maintaining type conformity.
• Streamlined Recertification Opportunities: Retaining rigid fuel tanks can simplify the regulatory approval process when operators perform structural updates or component upgrades on existing aircraft.
• Direct Inspection Access: The exposed, fixed-wall design of rigid tanks often allows for visual inspection and maintenance without the need for disassembling internal structural elements.

What Specialized Fuel Tank Designs Are Also in Use?

In addition to the primary fuel systems found on most aircraft, several specialized tank designs are used to support extended range, balance control, or mission-specific fuel needs. Some of these configurations include:

• Tip Tanks: These tanks are mounted on the outboard sections of aircraft wings to increase total fuel capacity and enhance lateral balance during flight.
• Drop Tanks: Designed for external mounting, drop tanks are commonly used on military aircraft to extend operational range and can be jettisoned when empty to reduce aerodynamic drag.
• Ferry Tanks: Ferry tanks can provide temporary internal or external fuel storage during repositioning flights, enabling extended range beyond normal operational limits.
• Ballast Tanks: In aircraft with specialized loading or performance requirements, ballast tanks are used to carry fuel or inert fluids to adjust the center of gravity.

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