What is a Cantilever?

Daniel Liden

A cantilever is a beam that is supported at only one end and carries a load at the other end. Cantilevers are often used in architecture, as they allow for overhanging structures that do not need to be supported from the outside. In many cases, partially-constructed buildings create cantilevers that allow builders to work without needing falsework. Airplane wings are also cantilevers, as they are usually only supported from the body of the plane.

Typically constructed on steel and concrete, cantilever bridges can hold heavy loads, such as constant automobile traffic.
Typically constructed on steel and concrete, cantilever bridges can hold heavy loads, such as constant automobile traffic.

Because only one end of the beam is supported, a cantilever is typically subjected to a great deal of stress. The top half of a cantilever experiences tensile stress, which elongates the fibers of the beam. The bottom half is subjected to compressive stress, which compresses the fibers. If it can't handle all of the stress, a cantilever may arc downward or even break. As such, engineers and architects work to design beams and balance loads in such a way that they will not suffer from such structural issues.

Most aircraft have cantilevered wings.
Most aircraft have cantilevered wings.

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Sometimes, cantilevers are used in the construction of bridges. Such a type of bridge is known as a cantilever bridge. A simple cantilever bridge is constructed of two cantilevers that meet in the middle of the area to be crossed. The cantilevers are typically constructed of structural steel or concrete and can hold significant loads, such as sustained vehicle traffic. These bridges are often easier to design than other bridges, as they support their own weight and require little or no falsework to keep them intact during construction.

The wings of most modern aircraft are cantilevers, as they are built into the body of the aircraft but are not supported on the end. Earlier aircraft were usually designed with two or more wings on each side that supported each other, like a truss on a bridge. This biplane configuration, however, caused unfavorable airflow and reduced the effectiveness of the aircraft. The use of a singe cantilever wing on each side of the plane tends to reduce the total weight of the plane and increase the maximum potential speed and efficiency.

Cantilevers have been utilized for many purposes in science and in engineering. They have been used for storage units, furniture, microelectrical structures, balconies, and many other things. A cantilever chair, for example, has no back legs. its front legs are supported by a flat surface of some kind on the bottom, and the seat of the chair is not supported in the back. Such chairs typically work because of the superior materials they are designed from.

A simple cantilever bridge is constructed of two cantilevers that meet in the middle of the area to be crossed.
A simple cantilever bridge is constructed of two cantilevers that meet in the middle of the area to be crossed.

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Discussion Comments

bythewell

@pleonasm - To be honest, cantilevers make me nervous, whether or not they are on a plane. Whenever I have to be on a balcony or whatever that's basically made up of a cantilever I try to make an excuse not to be there.

I know that mathematically I should be fine and that they calculate all that kind of loading bearing stuff when they build these shapes. But they just look like they are going to tip and that makes me nervous.

pleonasm

I had no idea that airplane wings are considered to be cantilevers. I guess it makes sense, since they do bear a lot of weight when they are in the air. It just looks as though they aren't because the weight is from the air itself and from the plane too, I suppose.

I always wondered why they changed the wing design from the two wings to a single wing on each side. I wonder if they will one day change it again and people will wonder how we ever used to fly the planes we do today.

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