Why do aircraft store fuel in the wings?
There are several reasons why many modern aircraft designers have elected to place the primary fuel tanks in the wings. An aircraft's wing contains a significant amount of extra space not used for storage, is easily accessible, and is 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 and leaves room for additional cargo capacity.
Storage, and the lift factor
When considering the aerodynamics of an aircraft, the wings are directly responsible for creating the lift, which supports the fuselage containing cargo and passengers 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 gross weight.
The Boeing 747 notably burns up to one gallon of fuel per second of flight and must carry enough accordingly. Even next-generation jets must maintain significant fuel to cover the actual trip alongside reserves for taxiing, diverting, contingencies, and other emergencies. Today's twin-engine aircraft, such as the Airbus A350, are able to carry over 37,000 gallons of fuel.
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 wings also contain controls for the ailerons and flaps, alongside various flight electronic and hydraulic equipment. Luggage and other cargo, however, are not typically stored in the wing due to height restrictions but are instead stored in the fuselage.
Strength, understanding the flex and flutter
The fuel tanks in the wings, especially when full, provide strength and stability to the aircraft during takeoff. The full tanks increase the rigidity of the wings and spread the total takeoff weight more evenly across the aircraft. As the aircraft speeds down the runway, the extra weight helps to keep the wingtips down and level to balance the disproportionally heavy fuselage.
Some aircraft's wings are designed to flex to improve aerodynamic stability. This development is most notable 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 aircraft with reduced drag and the ability to adapt more dynamically to turbulence.