During rotation and flapping up, what direction is the arrow facing?

During rotation and flapping up, what direction is the arrow facing?

• A. Straight opposite
• B. Two arrows same direction
• C. Slightly downwards
• D. Slightly up

Answer: (C)

The key idea is how the blade’s motion combines with the airflow. At any instant the blade element experiences a velocity that is the vector sum of the rotor’s downwash (mostly downward) and the blade’s own vertical motion from flapping. When the blade flaps upward, that upward motion partially cancels the downward inflow, so the resultant relative wind seen by the blade tilts toward the lower part of the frame. In the diagram this means the velocity arrow points slightly downward, not straight or upward.

The key idea is how the blade’s motion combines with the airflow. At any instant the blade element experiences a velocity that is the vector sum of the rotor’s downwash (mostly downward) and the blade’s own vertical motion from flapping. When the blade flaps upward, that upward motion partially cancels the downward inflow, so the resultant relative wind seen by the blade tilts toward the lower part of the frame. In the diagram this means the velocity arrow points slightly downward, not straight or upward.