What is the name of the spiraling motion imparted to the slipstream by a fast-spinning propeller?

• A. Turbulent wake
• B. Mach cone
• C. Spiraling slipstream (corkscrew effect)
• D. Vortex ring state

Answer: (C)

Propeller blades don’t push air straight back only; they also spin the air around the axis of the propeller. This imparts angular momentum to the slipstream, so the air stream behind the propeller follows a helical, corkscrew-like path as the aircraft moves forward. That twisting, spiraling motion is precisely what the term spiraling slipstream (corkscrew effect) describes. It’s a specific outcome of the blade’s rotation combined with forward speed.

The other options describe different phenomena: a turbulent wake is a general disturbed flow behind objects, not the focused rotational motion behind a fast-spinning propeller; a Mach cone only forms at supersonic speeds and isn’t the usual condition for propellers; vortex ring state is a rotorcraft condition during certain descent or hover scenarios and doesn’t describe the propeller slipstream behind a simple propeller.