The corkscrew or spiral rotation of the slipstream behind a propeller is most accurately described as:

• A. Spiraling slipstream (corkscrew effect)
• B. Wake turbulence
• C. Boundary layer separation
• D. Induced drag

Answer: (A)

The main idea is that a propeller’s blades not only push air backward but also twist it around the propeller axis. This imparts a tangential velocity to the air, causing the wake behind the prop to take a helical, corkscrew-like path. That spiraling slipstream is a specific kind of wake created by the rotation of the blades, hence the term spiraling slipstream (corkscrew effect). It’s not just generic wake turbulence, which refers to the broader, turbulent vortices shed by aircraft; it’s also not boundary layer separation (flow detaching from a surface) or induced drag (a drag component related to lift, not the airflow pattern behind the prop).