What does the term tip path plane refer to?

• A. The vertical plane through the rotor hub
• B. The plane traced by the rotor blade tips during rotation
• C. The plane of the aircraft's fuselage
• D. The horizontal plane at ground level

Answer: (B)

The tip path plane is the plane in which the rotor blade tips travel as the rotor turns. Imagine watching the tips as the blades spin; they trace out a path that lies in a single plane. In hover this plane is basically horizontal and aligns with the rotor disc, while in forward flight or with flapping the blade tips may tilt the path a bit, but the fundamental idea remains: it’s the plane that contains the actual motion of the blade tips. This concept helps explain how cyclic pitch and blade flapping affect the aerodynamic loads and blade speeds across the disk. The other planes mentioned don’t describe the movement of the blade tips: the vertical plane through the hub, the plane of the fuselage, or the horizontal ground plane are not the planes that define the tip motion.