Expert: Ray Wilkinson - 5/12/2007

Question
Hello Mr wilkinson
Please say me how much the I-shape beams are important in an airplane structure. or how much they helped the structure to be lighter?

Answer
Hi Omid

Beams in any structure are components that are loaded in bending. The taller the beam the stiffer it will be, as the aim is to get material as far from the middle as possible. Thus the material at the top and bottom of the beam (assuming the load is applied in a vertical direction) takes the highest load, and the material right in the middle takes almost nothing.

With any aircraft structure, the aim is to get the highest stress possible within the limits of the material, since this gives the lightest structure that is capable of carrying the load. So much of the material near the middle is removed, as it isn't adding much strength. Of course the material weighs the same wherever it is located, so removing the middle bit saves weight without significantly reducing strength or stiffness. The result is an I beam.

I hope this answers your question.

Regards

Ray