The first commercial airplanes had rectangular windows. True, everything changed with the advent of jet aircraft, which replaced propeller aircraft.
For the first time, a jet plane was created in Great Britain in the middle of the 20th century. Since 1952, such aircraft are actively used. Also, the windows were still rectangular at that time. However, during the year of operation of the aircraft, three ships crashed. As it turned out, this was due to metal fatigue. And the reason for this was a strong tension around the windows.
In addition, it turned out that when using rectangular windows, several stress zones appear around them, where metal breaks due to strong external loads. This is due to the high speeds of jet aircraft.
Therefore, in the end it was decided to abandon the rectangular windows. In addition, the oval shape better withstands high loads during flight.
Source: Ferra
