Why are airplane windows rounded?
Short answer
Airplane windows have rounded corners so that the forces caused by cabin pressure differences do not become concentrated at sharp corners. This reduces the risk of cracks starting in the fuselage structure around a window.
How it works
When a passenger aircraft flies high, the cabin is kept at a higher pressure than the outside air so that people can breathe more comfortably. During takeoff, climb, and descent, the aircraft experiences repeated changes in pressure.
Cutting an opening for a window changes how forces flow through the aircraft skin. A sharp corner, as in a square opening, can concentrate stress in one small area. A rounded corner lets the force flow more smoothly around the opening and reduces the local load.
A lesson from aviation history
In the 1950s, the de Havilland Comet 1 jet airliner had relatively square windows. Investigations and tests found high stress concentrations at the corners of the windows and frames, where repeated pressurization could lead to metal-fatigue cracks. Rounded window shapes then became a common feature of passenger aircraft.
Key point
- Passenger windows are usually rounded rectangles or oval shapes, not perfect circles, so they can provide a useful viewing area while avoiding sharp corners.
- Rounded corners smooth the flow of forces caused by the pressure difference and reduce stress concentration.
- Safety depends not only on window shape, but also on the window assembly, its mounting structure, the fuselage design, and inspection.