As we hinted earlier, when aviation started taking off in the 1920s, 30s, and 40s, the windows were rectangular.
The reason was aesthetic; they looked better with that design. And functionality? There was no problem either, as the aircraft flew at a prudent height and there were no issues.
However, airport activity and the sector began to grow, and in response, companies made a decision: cut costs.
What did they need to do to cut costs? Well, fly at higher altitudes, since less air density means less drag on the plane, thus saving fuel.
For the infrastructure to withstand this change in altitude, good pressurization in the aircraft was necessary, which also meant modifying the interior design, even the shape of the aircraft. Thus, the aircraft became cylindrical, and the design of seats, windows, and the cabin were modified.
Additionally, turbulence is less noticeable in the upper atmosphere, making the flight much smoother for passengers and crew.
In the 1950s, three accidents marked a turning point in the decision to change the window design: The aircraft broke into pieces due to a cabin depressurization problem, as they had used square windows in their design.
This happened because, as the aircraft ascended, there was a significant difference between the pressure inside the cabin and outside, concentrating pressure on the window frames. Also, stress accumulated at those sharp corners.
Thus, in those aircraft with square windows, the force accumulated at those points and caused the windows to break, leading to the disintegration of the cabin.
Conversely, in oval windows, the stress distribution is more even, and the pressure flows smoothly around the edges, thus avoiding major problems.
How was this phenomenon discovered? It was thanks to the manufacturer De Havilland, who investigated the accidents and discovered that this pressure build-up occurred due to what is called “metal fatigue”.
At that time, materials science was not well known, but De Havilland managed to determine, after many tests with the aircraft’s fuselage, that it was the metal surrounding the corners of the windows that cracked as the aircraft ascended during flights.
If the accumulated pressure in the corners increased the likelihood of breakage, the metal used also did not help.
If you are observant, you will have noticed that, at the bottom of the airplane window, there is a small hole. But no, it’s not connected to the outside, but to the structure of the plane. That is, it is a closed hole but performs an essential function.
This small perforation helps to balance the pressure between the passenger cabin and the various layers of the window, thus maintaining uniformity between these layers. The main reason is that if there were different levels of force between the layers, they could crack and break.
Not only that, but these holes also prevent the window from fogging up due to temperature changes, and allow moisture to escape, thus also preventing some layers of the window from freezing under adverse weather conditions or at very high altitudes.
A recurring complaint among travelers is the lack of comfort due to the reduced space between seats, which has become increasingly limited. Moreover, the seats are often not aligned with the windows, making it difficult for passengers to fully enjoy the views of the aerial landscape.
This leads us to question why the seats are not always aligned with the windows. It’s important to note that this depends on the configuration chosen by each airline and is not directly the responsibility of the aircraft manufacturers.
Besides why airplane windows are round, another very common question is: Why aren’t the seats aligned with the windows?
We regret to inform you that the reason has little to do with the reason for the oval shape of the windows, but since we are discussing design, we will answer this million-dollar question.
It is the responsibility of the airline, as the manufacturer aligns the seats with the windows, but the company can choose to place more or fewer seats, add rows, remove them, and even put narrower seats.
Why? Mainly for economic reasons, to be able to transport more people and make each trip more profitable.
If you’ve been wondering why are airplane windows round, you now have your answer.
We remind you of the key points behind that decision: the distribution of force over the corners of the windows, and the difference in pressure between the outside and inside of the aircraft.
If you found this article helpful, don’t forget that on our aviation blog you can find explanations for other industry dilemmas, such as what the black box is, or what pilot stripes mean.
