What effect does flush riveting have on an airplane?

Flush riveting has the primary effect of reducing skin friction drag on an airplane. This technology involves setting the rivets so that their heads are flush with the surface of the airplane's skin. By creating a smooth surface, flush rivets minimize turbulence and drag that can occur at protruding fasteners.

When an aircraft is designed for aerodynamic efficiency, it's crucial to consider all aspects of surface smoothness. Anything that protrudes from the surface, like traditional rivets, can create vortices that increase drag. By using flush rivets, the overall aerodynamic profile of the aircraft is improved, leading to better fuel efficiency and performance.

In this context, while increasing weight is often a consideration in aircraft material and engineering decisions, flush riveting is designed to make structures as lightweight as possible. Similarly, it does not inherently increase drag; rather, it reduces it, which directly contradicts any option that suggests that it increases drag or enhances thrust, as thrust is not affected by the riveting technique itself.