Why in airplanes oval portholes?

Any angles, and in particular direct and sharp, as well as welds, holes and all other necessary features of the design, disturbing the continuity of the material, perform the role of voltage concentrators. That is, they become the weak place of construction, in which cracks will first be formed.

It is from the angles of a rectangular porthole. Cracks will begin to diverge

During cyclic loading (and each flight of the aircraft is just such a cycle) it is these voltage concentrators that are the main factors that reduce the strength of the entire design. Cracks will begin to diverge the corners of the rectangular porthole. And it can lead to a loss of the aircraft.

At the dawn of the passenger reactive aircraft construction, the British company de Havilland created a liner called "Comet", completely unique for the 1950s in its high-speed and technical specifications. But already in 1954, two "comets" collapsed right in the air, having carried out 56 people.

In connection with the tragedies, additional tests of the issued aircraft began, which showed that during cyclic pressure on the cabin, the fuselage is in the end burst, and cracks are formed in direct angles of portholes.

The concept of an aircraft, which will not have a single porthole, and instead of them on the outside of the fuselage will be installed cameras broadcasting the image by side of panoramic displays inside

Since then, the aircraft designers have abandoned attempts to create a plane with square portholes. Today, their form varies from round to oval. Also appear projects of passenger aircraft at all without portholes.