Which factor is critical in manipulating the radar cross-section of an aircraft?

The shape of an aircraft is a critical factor in manipulating its radar cross-section. This is because radar cross-section (RCS) is primarily influenced by the geometry of the aircraft. The design and contours of the aircraft can either reflect radar waves away from the source or absorb them, thereby reducing the detectable signature. A well-designed shape can minimize the points at which radar waves can bounce back towards the radar receiver, effectively lowering the visibility of the aircraft on radar systems.

In contrast, while size is important as larger surfaces may present a larger target area to radar waves, it is the specific design and angles of those surfaces that dictate how radar waves interact with the aircraft. Weight, though important for flight performance, does not directly affect radar signature. Similarly, paint color may have an impact on visual detection, especially in certain environments, but it plays a negligible role in shaping the radar cross-section compared to the geometric design of the aircraft. Thus, the shape is paramount when discussing the manipulation of radar visibility.