Whether a passenger aircraft is small or large, all seem to share the same style of windows, those of which are small and circular. While one could imagine the benefit of having large, square-shaped windows for increased viewing of one’s surroundings, there are very specific reasons for why this is neither feasible nor safe. In this blog, we will discuss why the design of aircraft windows is fairly unchangeable, and how the shape of windows is directly tied to the aerodynamics of the aircraft itself.
To keep passengers safe at extreme altitudes, the fuselage of the aircraft must always be sealed with a pressure-controlled environment in the cabin. While the outside atmosphere may exhibit a pressure rating of 5 psi, the passenger cabin will be kept at around 11 or 12 psi for comfort and safety. With a difference in pressure between the inside and outside of the fuselage, aircraft parts such as the windows will be faced with high amounts of stress that fluctuates across pressurization cycles. By using the standard, oval shape for windows, the pressure acting on such surfaces is evenly distributed, leading to slower deformation and aging. As a result, the oval window has become a standard that has been followed for over 70 years now.
While small, rounded aircraft windows are a staple of aircraft design in the modern era, this was not always the case. In the 1950s as passenger aircraft became pressurized, windows were often designed with a square shape reminiscent of the windows of a house or similar building. However, in 1954, two de Havilland Comets broke apart mid-flight, resulting in the death of passengers. After extensive research, it was determined that the cause of the accident was the square window design. As the aircraft reached high altitudes and had a significant pressure difference, around 70% of pressure-induced stress would be exerted on the edges of the window pane. This led to cracking over time, resulting in extremely hazardous situations. As a result, engineers sought new designs, eventually settling on the circular window design that all aircraft follow.
Despite rounded windows having the advantage of more equalized pressure, this is not the sole reason that modern aircraft windows are so reliable. If one were to look at a window assembly in an airliner, they would notice that there are three layers of acrylic pane that separate the interior from the outside atmosphere. The outermost pane is the thickest and strongest, while the closest pane to the cabin is a thin scratch-guard that prevents damage over time. The middle pane is also thick, and it contains a small hole that allows for pressure to equalize to a further degree for increased reliability. As windows are an essential component for passenger safety, it is crucial that they are well maintained, repaired, and replaced as necessary. If you find yourself in need of various aircraft windows and aircraft parts, let the experts at Emergent Aviation help you source everything you require.
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