Spiraling slipstream refers to what effect?

• A. The slipstream of a propeller-driven airplane rotates around the airplane and strikes the left side of the vertical fin, causing the aircraft to yaw slightly
• B. It increases lift on the right wing
• C. The slipstream rotates around the airplane and strikes the right side of the vertical fin
• D. It reduces drag on the fuselage

Answer: (A)

Spiraling slipstream is the rotating air produced by the propeller, which doesn’t just move straight back but wraps around the fuselage in a corkscrew pattern. As this air streams past the airplane, it tends to impinge on one side of the vertical stabilizer, creating a yawing moment. In a typical tractor-propeller aircraft, that rotating flow strikes the left side of the vertical fin, causing the nose to yaw to the left. This effect is about a yaw, not an increase in lift on a wing or a reduction of drag on the fuselage, and it depends on the direction of the propeller’s rotation.