Many of us love to take the window seat whenever we are travelling by air. Sometimes you may have wondered why aeroplane windows are all round and NOT usual rectangle or square.We know, you have concluded that thought process by thinking that the round windows are for aesthetic purpose as according to the aerodynamic shape, the round windows go well. But, the actual reason is something else and more serious.
The commercial air travel became popular in the middle of the 20th century. More and more people started travelling by air. All the airlines decided to fly at higher altitudes as that saves them a substantial amount of money. This is because, at higher altitude, the air density is lower. That brings down the drag or friction on the aircraft. This means the engine has to do a lesser amount of work. This saves money.
But, since air density is low at higher altitude, the cabin is needed to be pressurised so that the passengers can breathe normally. To make that feasible, the cabin was redesigned to a cylindrical shape in order to support the inside pressure of the cabin. Initially, the aeroplanes were fitted with square windows only but air drag repeatedly created stress and cracks on those windows.
It can be proved through simple physics calculation that circular or oval windows face less pressure around their corners than the square windows. Incidentally, there were three air crash incidents during 1950 because of the cracking of the square windows and subsequent disintegration of the fuselages.