Rajan Wilcox
The placement of fuel tanks in airliners is a crucial aspect of aircraft design, impacting weight distribution, aerodynamics, and safety. While the wings are the most common location for fuel tanks, some airliners also have fuel tanks in the fuselage or cargo hold. The 747-400 and MD-11 models are said to have fuel tanks in the horizontal stabilizer, which helps manage the centre of gravity on long-haul flights. Fuel tanks in the wings provide strength and stability during takeoff, while also reducing the structural load on the wings. However, wing-mounted fuel tanks come with a higher risk of catastrophic damage in the event of in-flight fuel ignition.
| Characteristics | Values |
|---|---|
| Location of fuel tanks in airliners | The most common location for fuel tanks in modern aircraft is in the wings. Fuel tanks can also be found in the fuselage, the belly of the plane, the rear of the plane, and the horizontal stabilizers. Some aircraft have the ability to load fuel tanks in the cargo hold. |
| Advantages of wing-mounted fuel tanks | Wing-mounted fuel tanks provide strength and stability to the aircraft during takeoff, increase the rigidity of the wings, and reduce the structural load on the fuselage. They also allow for gravity feeding of fuel to the engines and can help balance the weight of the aircraft during flight. |
| Disadvantages of wing-mounted fuel tanks | Wing-mounted fuel tanks can increase the risk of catastrophic damage in the event of in-flight fuel ignition. They can also lead to repeating stresses that shorten the aircraft's lifespan. |
| Other considerations | The placement of fuel tanks in aircraft is subject to safety regulations and is designed to minimize the risk of accidents. Fuel tanks can be classified as internal (integral, rigid removable, bladder) or external (conformal, drop). |
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What You'll Learn
Fuel tanks in the wings
Firstly, locating fuel tanks in the wings helps to maintain the structural integrity of the aircraft. By placing weight in the wings, the overall structural load is reduced. This is because, during flight, an aircraft rests on its wings, and weight distribution becomes critical. The bending moments caused by wing-bending and different gravitational forces between full and empty tanks can result in repeating stresses that shorten the aircraft's lifespan. Therefore, distributing weight along the wings can reduce these stresses.
Secondly, wing-mounted fuel tanks improve safety by locating the fuel away from the passenger compartment. This configuration also reduces fuel system complexity, particularly in high-wing single-engine aircraft. In multi-engine aircraft, wing fuel allows designers to direct fuel from each wing directly to its respective engine, simplifying the fuel delivery system.
Additionally, fuel tanks in the wings offer counter-stress and weight balance benefits. They can help counter the wing's lift and the fuselage's weight, reducing wing flutter. This configuration also allows for a lighter and thinner wing spar design, increasing the aircraft's overall strength.
Furthermore, fuel tanks in the wings provide more space for passengers and cargo. By partially or completely eliminating fuel storage in the fuselage, designers can increase the practical cargo capacity of the aircraft. This configuration also reduces the need for complex plumbing systems to balance fuel flow, as seen in the King Air series aircraft.
While fuel tanks in the wings offer several advantages, there are also some considerations. One risk associated with this design is the sloshing of fuel during flight, which can lead to lateral weight shift and potential instability. Additionally, in aircraft without automatic fuel management systems, manual selection of the fuel feed is necessary to prevent lateral imbalance and potential fuel starvation of the engine.
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Fuel tanks in the fuselage
While most aircraft store fuel in their wings, some aircraft also have tanks in the center fuselage, or center body, known as center tanks. These are used first during the course of a flight, before the fuel in the wings is drained. Center tanks are subject to usage restrictions depending on the type of aircraft and the stage of the flight. For example, the 737 has restrictions on when the center fuel pumps can be on, based on the amount of fuel in the tank and the stage of the flight.
The use of center tanks can be dangerous in the event of a crash landing. For instance, if the landing gear fails to extend and the plane is forced to make a belly landing, a fire could potentially break out in the center tank. However, some sources argue that if center fuel tanks were dangerous, aviation authorities would not allow them in commercial aircraft. Furthermore, the use of center tanks can improve safety by isolating passenger cabins from the initial effects of smoke and flames, permitting additional evacuation routes and time.
The use of fuselage tanks can also increase the complexity of the aircraft's fuel system. Fuselage tanks would require complex and heavy baffling to avoid CG changes as a result of pitch changes and acceleration. They would also impact the overall shape and size of the aircraft body, increasing the weight and drag of the aircraft.
The use of wing tanks, on the other hand, can improve the overall structural efficiency of an aircraft by counter-balancing the wing's lift and the fuselage's weight. This reduces aircraft fuel system complexity and improves passenger safety by locating fuel away from the passenger compartment. Wing tanks also centralize fuel around the center of gravity of the aircraft, reducing the impact of sloshing on pilot inputs and handling characteristics.
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Fuel tank switching schedules
Most general aviation aircraft store fuel in their wings, and in some cases, additional tanks may be present in the fuselage or centre of the aircraft. For low-wing aircraft, fuel must be pumped to the engine, while high-wing designs like the Cessna 120 utilise gravity to feed fuel from the wings.
The procedure for switching fuel tanks may vary, but typically involves the following steps: checking the fuel pressure gauge, turning on the electric fuel pump, checking the gauge again, switching tanks, and then turning off the pump. Pilots must exercise caution during this process, especially when flying at low altitudes, as switching tanks incorrectly or encountering issues like undetected water in a tank can lead to engine problems or failure.
Some aircraft have a "Both" setting that allows them to draw fuel from two tanks simultaneously, but many aircraft draw from tanks unequally. Setting a timer can help pilots remember when to switch tanks, and organisations like the AOPA Air Safety Institute recommend switching tanks on descent before reaching pattern altitude.
Ultimately, conservative fuel planning and adhering to recommended procedures minimise the odds of fuel-related incidents.
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Fuel tanks in the cargo hold
The 747-400 and the MD-11 are two examples of aircraft that have fuel tanks in the horizontal stabilizer, which is located at the rear of the plane. The 747-8 may also have these tanks, but this information could not be confirmed.
Some older aircraft designs, such as the Boeing 747 and the Concorde, use fuselage fuel tanks. The Concorde used forward and aft "Trim Tanks" to manage CG location as the center of pressure shifted forward and aft during supersonic flight. However, these designs are being phased out of passenger and cargo use due to increased engineering complexity and safety concerns.
Modern aircraft typically locate the fuel tanks in the wings due to wing structure, systems, and passenger safety. Placing the majority of the weight inside an airplane's wings is beneficial as it sets the heaviest weight inside the source of lift for the plane. This reduces stress on the wings and improves overall structural efficiency by counter-balancing the wing's lift and the fuselage's weight. Additionally, locating the fuel tanks in the wings isolates passengers from fire and fume hazards associated with jet and aviation fuel.
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Fuel tank safety
Fuel tanks are an essential component of aircraft, and their placement and design are carefully considered to ensure safety. While the most common location for fuel tanks in modern aircraft is the wings, there are several other locations, including the fuselage, cargo hold, and horizontal stabilizers.
Wing Fuel Tanks
Wing fuel tanks provide strength and stability to the aircraft during takeoff. The weight of the fuel helps to keep the aircraft level and balanced, reducing the structural load on the wings. Wing fuel tanks also allow for gravity feeding, reducing reliance on fuel pumps. Baffles within the tanks prevent fuel from sloshing during flight, and rigid partitions with small holes further enhance stability.
Fuselage and Cargo Hold Fuel Tanks
Some aircraft, such as certain models in the Airbus A320 family, have the ability to load fuel tanks in the cargo hold or fuselage. These additional tanks can increase the range of the aircraft. However, adding more tanks in the fuselage can increase stress on the wings during flight and reduce practical cargo capacity.
Horizontal Stabilizer Fuel Tanks
Fuel tanks in the horizontal stabilizers, such as those found in the 747-400 and MD-11 aircraft, serve a dual purpose. They provide ballast to manage the center of gravity on long-haul flights, improving stability, and they also act as fuel reservoirs.
Safety Considerations
To ensure safe fuel tank operations, several precautions must be taken. During maintenance, all fuel must be drained from the tanks, and fuel vapors must be excreted to prevent ignition. Respiratory tools must be used by technicians to protect their health. Additionally, fuel tanks must be constructed with fuel-resistant sealants to prevent leakage, and rigid removable tanks must be securely held in place with quilted strap arrangements to avoid shifting in flight.
In conclusion, while aircraft fuel tanks are not inherently dangerous, their placement and design are critical to ensuring the safety of the aircraft and its passengers. By following established safety procedures and utilizing appropriate tank configurations, the risks associated with fuel tanks can be effectively managed.
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Frequently asked questions
No, the most common place for fuel tanks is in the wings. However, some airliners have fuel tanks in the fuselage or cargo hold.
There are several reasons why aircraft designers have chosen to place the primary fuel tanks in the wings. The wings contain a lot of extra space, are easily accessible, and are responsible for creating lift for the aircraft. Placing the fuel in the wings also increases the strength and stability of the aircraft during takeoff.
Different gravitational forces and wing-bending between full and empty tanks result in repeating stresses that shorten the aircraft's lifespan. There is also a higher risk of catastrophic damage to the wings in the case of in-flight fuel ignition.
There are internal and external fuel tanks. Internal fuel tanks include integral tanks, rigid removable fuel tanks, and bladder tanks. External fuel tanks include conformal fuel tanks and drop tanks.
