Why are the windows in airplane passenger cabins oval?

When it comes to designing and constructing an aircraft, special considerations are undertaken. Since they serve to cover vast distances and fly high above the skies, there is no chance of any kind of failure. Therefore, essential components such as the engines, wings, and even relatively smaller components such as windows are carefully designed and thought out. 

To begin with, it should be mentioned that airplane windows were not always oval. Initially, they used to be rectangular, like the windows of your house. However, as technology advanced and airplanes flew higher to avoid turbulence, reduce drag, and improve fuel efficiency, specific changes were made to the shape of windows. Above all, since the airplanes were now flying at comparatively much higher altitudes, it was imperative that the cabins had to be pressurized. At such heights, the cabins must be properly pressurized to keep the passengers comfortable.

Furthermore, in order for a cabin to remain properly pressurized, it needs to be of a cylindrical shape. This, in turn, creates a difference in pressure between the inside air and outside air as the plane gets higher. During this, the body of the plane expands slightly due to pressure, which is passed onto the material. This is where the shape of the windows comes in. It is an important part of the equation without which a plane will not be possible to achieve high altitudes we hear of today. 

A plane that has a cylindrical shape easily allows the stress to flow but is interrupted with the introduction of windows. If the windows happen to be rectangular, the stress flow will be more significant. Moreover, it will build up even more pressure on sharp corners. This could ultimately crack the windows and cause serious damage to the plane’s body. However, if the windows are oval, the stress is balanced out.

Unfortunately, it took two airplane crashes in the past for the engineers to realize that, but it paved the way for much safer planes today. Although one might underestimate the shape of the windows, but when an airplane is already under extreme stress, it needs to prevent the additional build-up of stress. You might have also wondered about the ‘breather hole,’ existing in all airplane windows. Then again, it has to do with balancing the internal and external pressure. Basically, each window is made of three layers. The hole allows the air pressure between the outer and middle panes to equilibrate. As a result, the pressure is only applied to the outer pane, while the middle pane is kept reserved for emergencies. 

Moreover, Rounded holes in the thin fuselage are structurally more sound, and much less prone to stress fractures. Stress fractures in a pressurized cabin can lead to explosive decompression and outright structural failure.

The seriousness of the issue was highlighted when the first commercial jet, the De Havilland Comet of Britain, was plagued with three crashes shortly after its introduction in 1952. Much to their shock, thorough investigations revealed that the main culprit in all three crashes was likely metal fatigue. And more of the deterioration started at the corners of the Comet’s large, rectangular windows. Up to 70% of the aircraft’s ultimate stress under pressure was concentrated on the corners of the aircraft’s window. The comet was then redesigned with a stronger fuselage and round windows.

If round windows are best, why do Boeing and Airbus provide us with oval ones?

Here’s the explanation: Having round windows would necessarily mean more solid material in the gap between windows. By elongating the windows vertically, aircraft designers can provide more viewing area (more surface area devoted to windows) and also better accommodate passengers of differing heights.

Concluding, constant research and advancement in aviation technology have brought airplanes to the point where they have nearly become impossible to crash. In some cases, there might be some technical problems, but then the competency of highly trained pilots come into place. Today, many engineers are off the view that airplanes are much safer when they are at high altitudes. It gives the pilot more time to think and act in case of emergencies. However, there is always room for improvement. 

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