Large aircraft wings are essentially 2 pieces, left and right wings. The fuselage has to attach to these wings to transfer all the loads between them, and to do that in the simplest way is to have an adapter structure that mates the 2 wings to the fuselage, permanently. This is the “wing box” or more accurately the “center wing box”. NOT to be confused with a “box spar”.
Not only does it mount the wings to the fuselage, it also usually mounts the main landing gear. As a result, the wing box is the strongest part of the plane. It carries ALL the flight loads, landing loads and mounts a lot of auxiliary equipment as well. It is usually first attached to the fuselage before each wing is attached.
On smaller aircraft, the wing box is split in two and each is part of the wing structure, and joined together as one whole wing, then the fuselage is dropped on and permanently attached.
Then there is the wing with multiple spars. They are built with the upper and lower skins attached, but before the leading and trailing edges are attached. That spar structure is also known as a wing box. Again, not to be confused with a “box spar”.
There are several variations. On large planes, some smaller ones as well, the center wing box forms the center fuselage section where the whole fuselage is made from 3 or 5 barrel sections. Then all the pieces, first the fuselage is joined up, then the wings are attached.
The image below is the B737 center section, with the center fuselage being integral with the center wing box.
Most planes have multiple large sections that go together in sequence as sub-assemblies then final assembly, but all centred around the wing box/center section..
The wingbox is an important part of nearly all fixed-wing airplanes. It forms the structural center of an airplane’s wings while simultaneously allowing for the use of other wing parts like flaps and wingtips. It’s known as the “wingbox” because it’s shaped like a box. The box runs through the wings and into the fuselage. Here are five facts about wingboxes that may surprise you.
1) One of the Strongest Parts of an Airplane
The wingbox is one of the strongest parts of an airplane. It serves as the mounting surface for the wings. Therefore, the wingbox must be able to withstand the load of the wings. Designing a structurally sound airplane requires the use of a strong wingbox.
2) Typically Made of Carbon Fiber
In the past, most wingboxes were made of stainless steel, but you can now find these essential aerospace parts made of carbon fiber. Most wingboxes, in fact, are now made of carbon fiber. Carbon fiber is prized for its strength-to-weight ratio. Stainless steel is strong as well, but it weighs more than its carbon fiber counterpart. With its high strength-to-weight ratio, carbon fiber has become the preferred choice of material for wingboxes.
3) Attaches to Landing Gear
You might be surprised to learn that landing gear is oftentimes attached to the wingbox. The wings, of course, attach to the sides of the wingbox. But landing gear may attach to the underside of the wingbox as well. The wingbox is installed in the rear section of the fuselage, making it an ideal mount point for landing gear.
4) Not the Same as Box Spars
Wingboxes aren’t the same as box spars. Box spars are box-shaped skeletal frames for wings. All airplanes have spars. Box spars live up to their namesake by consisting of a box-shaped frame. Wingboxes, in comparison, are box-shaped structural units to which the wing, as well as landing gear, attach. Aside from featuring a similar shape, wingboxes and box spars are completely different.
5) Available as a Single Piece
Airbus recently developed a single-piece wingbox made of carbon fiber. The European aerospace manufacturing company unveiled it in 2017. With only a single piece, Airbus says the new carbon-fiber wingbox will cost 20% less to manufacture.
Wingboxes are important. They form the structural center of an airplane’s wings, and they are used to mount the wings and landing gear.
Author – Joel Berson & monroeaerospace.com
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