There are a number of good reasons why modern aircraft manufacturers have elected to place the primary fuel tanks in the wings. An aircraft’s wings contain a significant amount of extra space not used for storage, they're easily accessible and are responsible for creating lift for the entire airframe. Placing the fuel in the wings also increases the strength and stability of the aircraft during takeoff - one of the critical phases of flight. It also leaves room for additional cargo capacity. Commercial airliners are built to carry as much payload as possible. The payload includes passengers, luggage, and cargo. If you took a cross-section of the plane, you would see that the bottom half is for carrying freight and the upper half for passengers. This leaves the virtually hollow wings as a perfect place to store the fuel.
When considering the aerodynamics of an airplane, the wings are directly responsible for creating lift, which supports the fuselage during flight. On some long-haul flights, the fuel contained in the aircraft at takeoff can account for as much as a third of the aircraft’s total gross weight. If this extra weight were to be stored entirely in the fuselage, it would reduce available cargo space and increase the strain and stress on the aircraft structure. Loading the fuel into the wings brings a significant portion of the weight directly to the source of lift, which reduces the pressure on the wings in flight and spreads the load more evenly across the airframe.
The full fuel tanks increase the rigidity of the wings and spread the total takeoff weight more evenly across the aircraft. As the plane speeds down the runway, the extra weight helps to keep the wingtips down and level to balance the disproportionally heavy fuselage. Some aircraft wings are designed to flex to improve aerodynamic stability. This development was more noticeable in jetliners such as the Boeing 787 Dreamliner, which incorporates composite technology to allow the wings to flex up to 25 feet. The result is a more streamlined airliner with reduced drag and the ability to adapt more dynamically to turbulence.
Baffles further subdivide the fuel tanks and allow the fuel to flow properly to the engines. These rigid partitions within the tanks are placed perpendicular to the wings and feature small holes to prevent the fuel from sloshing from side to side during flight maneuvers. Sloshing is defined as the movement of liquid contained within an enclosed area. As the motion changes the dynamics of the container, it affects the liquid inside, which sloshes across the walls of the container. The sloshing of fuel in aircraft fuel tanks is a common occurrence that can impact flight dynamics and the aircraft’s center of gravity during flight. While some sloshing is impossible to avoid, a reduction is extremely helpful in avoiding unwanted dynamics that can affect the stability of flight. Some aircraft also include systems to rebalance the tanks manually should one side become heavier than the other due to uneven fuel burn.
Aircraft fuel has not always been stored in the wings, and while it’s the most common location in today’s commercial jetliners, there are still some outliers. The Airbus A321LR, for instance, can hold up to three removable fuel tanks for long-range trips. The A321XLR features an integrated central fuel tank to increase its range. One additional benefit of storing fuel in the wings is the ability to gravity feed it. As the fuel tanks are above the engines in many aircraft, this helps in reducing reliance on a fuel pump. Aircraft that feature a center fuel tank in the belly of the plane usually empty it first to ensure that gravity feeding is available for as long as possible. Some wide-body aircraft include fuel tanks in the rear of the plane. The fuel in tanks set in the horizontal stabilizers doubles as ballast to manage the center of gravity on long-haul flights.
There may be some changes in fuel storage ahead, especially concerning the introduction of hydrogen aircraft. When it comes to Airbus” ZEROe concepts, the European aircraft manufacturer’s turbofan and turboprops are being conceptualized to have their liquid hydrogen storage and distribution units behind the rear pressure bulkhead. The innovative blended-wing-body (BWB) design features liquid hydrogen storage tanks stored underneath the wings. Airbus’ ambition is to bring to market the world’s first hydrogen-powered commercial aircraft by 2035. To get there, their ZEROe project is exploring a variety of configurations and technologies, as well as preparing the ecosystem that will produce and supply the hydrogen.
Weight is also a significant factor in the fuel consumption of an aircraft. The more wright an aircraft carries, the more fuel it needs to burn to generate the necessary lift and maintain altitude. This is because the heavier an aircraft is, the more power its engines need to keep it in the air. As a result, airlines and pilots carefully calculate the weight of the aircraft, including passengers, baggage, cargo and fuel to ensure that they are within proper limits. Correct calculations help to minimize fuel consumption and maximize efficiency. Proper balance also comes into play here as an overloaded or improperly balanced aircraft will require more power and greater fuel consumption to maintain flight.
Today’s commercial aircraft are complicated machines requiring extremely powerful engines powered by large quantities of fuel. And that fuel is heavy. Aviation fuel weighs about six pounds per gallon. To put this in context, a Boeing 747 flying from New York to Los Angeles would have onboard a minimum of more than 100,000 pounds of fuel. Placing the majority of this weight inside the aircraft’s wings is beneficial as it sets the heaviest weight inside the source of lift for the plane.
Until next time…safe travels.
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