When you get on a plane, you may have wondered why the windows of this means of transport have an oval shape. If you look closely, it’s not just the windows: it’s also the armrests, trays, screens and any interior furniture. has a circular shape. Although it may seem like something merely aesthetic, there is actually a scientific reasoning behind this choice. But before going into the technical details, let’s talk a little about the history of aviation and how two fatal accidents changed everything.
In their early days, airplanes had rectangular windows like the ones in any house. As taking to the skies became more popular in the 1950s, airlines began to fly at higher altitudes. This guaranteed them considerable economic savingssince the thin air generates less resistance and, therefore, consumes less fuel, as well as allows a more comfortable ride with less turbulence.
But in order for the planes to fly at such heights, manufacturers were also forced to make design changes. The cabin had to be pressurized so that the pilots could breathe without problems. And a pressurized cabin requires a cylindrical shape to function, which creates a pressure difference between the inside air and the outside air that increases as the plane rises. The flat body expands very slightly and therefore stress is applied to the material.
And this is where the shape of the windows come into play. In 1954 there were two fatal accidents that caused the death of 56 passengers and crew. The reason the fuselage disintegrated had to do with a design flaw, which is that they had kept the windows square. Due to its right angles, the cabin pressure was concentrated in its corners and was multiplied by three, more than in the rest of the fuselage. That caused the windows to end up exploding.
It must be taken into account that planes usually fly at an altitude of 10,000 meters or more and that level atmospheric pressure it is about a third of normal. As Real Engineering explains in this video, “When a material changes shape like this, stress is created in the material. Eventually, the stress can get so high that the material breaks.” This is exactly what happened in the aforementioned accidents.
However, in a circular plane, stress flows smoothly through the material, a flow that is interrupted by the introduction of a window. But if the window is oval, the stress levels are more evenly balanced. The same principle applies to the cargo and cabin doors. And that’s why we also see it in the windows of ships and spacecraft. Unfortunately, it took two plane crashes and several decades of research to realize the ills that square windows were causing.
Also, as Anthony Harcup, director of the Teague design firm, who has worked with Boeing for more than 75 years, comments in this Travel + Leisure article: “Sharp edges hurt elbows, knees, hips… .or any part of the body they come into contact with.Rounding of all parts of the plane is also done for the “deletalization”a design principle that ensures that when subjected to Murphy’s Law, a passenger cannot be injured on any part of the aircraft seat.”
And what is the breath hole?
It’s not just the shape of aircraft windows that has changed over the years, but also their material. The windows you see on airplanes aren’t actually glass, but acrylic, which is more durable than the former. Also, as you may have noticed, there are three layers in each window. In fact, the inside window facing passengers isn’t even part of the plane’s structure (it’s just a safety measure so the outside window doesn’t get scratched or touched). And the second layer exists as a reinforcement to keep the pressure on the end if the outer window was damaged.
If you have looked at the window, you will have also seen a small hole in this layer. Its role is essential since it serves as a valve to equalize the pressure between this inner window and the outer window. Between the inner and outer window there is a small air chamber and this hole automatically regulates the pressure between the two sheets. In addition, it allows to balance the humidity level, preventing the window from fogging up or freezing. Everything on an airplane is pure science.
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