What shape is NOT typically a recognized window shape in aircraft?

In the context of aircraft design, the recognized window shapes are typically functional and derived from considerations of aerodynamics, structural integrity, and safety. The bubble, square, and oval shapes are commonly utilized due to their ability to withstand pressure changes and reduce the risk of structural failure, particularly at high altitudes.

The square shape, although less common than oval or round shapes, is applied in certain aircraft for aesthetic or design purposes. Bubble windows, often found in some smaller aircraft, provide better visibility and are specifically designed to reduce drag.

On the other hand, the triangle shape is not a standard or recognized window shape in aircraft design. This is largely due to the structural challenges associated with sharp corners that can lead to stress concentrations, increasing the likelihood of cracks or failure under pressure. As a result, aircraft typically use rounded or more curved shapes, which help distribute stress more evenly across the structure, enhancing safety and durability in flight.