Most People Will Go Their Entire Lives Without Ever Knowing Why Airplane Windows Are Round

The fuselage is essentially a metal tube being inflated like a balloon—over and over again, flight after flight.

And nowhere is this stress more concentrated than around openings in the structure.

Like windows.

Stress Concentration: The Silent Killer
In engineering, there’s a concept called stress concentration. It refers to how force behaves when it encounters changes in shape or material.

When a structure is smooth and continuous, stress is distributed evenly. But when there’s a sharp corner, edge, or sudden change in geometry, stress tends to concentrate at that point.

Think of tearing a piece of paper.

If you try to tear it from a flat edge, it’s difficult. But if you make a small cut or nick, the paper tears easily from that spot. The cut concentrates the force.

The same principle applies to metal.