Define rotational relative wind as applied to an airfoil.

Define rotational relative wind as applied to an airfoil.

• A. The flow of air parallel to and opposite the flight path of an airfoil
• B. The flow of air perpendicular to the flight path
• C. The flow of air along the trailing edge
• D. The flow of air around the wing surface

Answer: (A)

Rotational relative wind is the air flow seen by the airfoil as it moves through the air. It is the wind that is opposite to the airfoil’s velocity through the air, i.e., it acts in the direction opposite to the airfoil’s motion. In forward flight this relative wind is effectively parallel to the flight path, coming from ahead. That’s why the description about air moving parallel to and opposite the flight path best captures the idea. The other descriptions—flow perpendicular to the flight path, along the trailing edge, or around the wing surface—don’t describe the direction of air relative to the blade’s motion.

Rotational relative wind is the air flow seen by the airfoil as it moves through the air. It is the wind that is opposite to the airfoil’s velocity through the air, i.e., it acts in the direction opposite to the airfoil’s motion. In forward flight this relative wind is effectively parallel to the flight path, coming from ahead.

That’s why the description about air moving parallel to and opposite the flight path best captures the idea. The other descriptions—flow perpendicular to the flight path, along the trailing edge, or around the wing surface—don’t describe the direction of air relative to the blade’s motion.