How does the surface roughness of an aircraft affect aerodynamic drag?

Smoother surfaces reduce drag due to a phenomenon known as skin friction. In aerodynamics, drag is affected by how well the airflow adheres to the surface of the aircraft. A smooth surface allows the airflow to remain attached for a longer portion of the wing or fuselage, reducing the turbulence and energy loss due to friction. This results in lower skin friction drag, which is a significant component of total aerodynamic drag.

In contrast, rough surfaces can disturb the airflow, causing it to separate sooner, which leads to increased turbulence and higher drag levels. This is particularly important in aviation, where efficiency translates directly to fuel economy and operational cost-effectiveness.

While the other options present various concerns, they do not accurately capture the relationship between surface roughness and aerodynamic drag.