Rotational wind on the rotor disk flows in which direction relative to the forward motion?

Rotational wind on the rotor disk flows in which direction relative to the forward motion?

• A. Same as forward motion
• B. Perpendicular to forward motion
• C. Opposite to forward motion
• D. Upward toward the hub

Answer: (C)

Rotational wind is the tangential component of the air flow through the rotor disc created by the blade rotation. As the rotor turns, it drags air around the disc in a circular direction. When you compare that swirl to the aircraft’s forward motion, the tangential flow on the disk is opposite in sense to the forward progression of the air entering the rotor (the swirl tends to push air around in the opposite direction to the forward travel). So the rotational wind on the rotor disk is directed opposite to the forward motion. In hover, there’s no forward speed, so you only have the tangential swirl. In forward flight, you still have that tangential, rotational component, but it combines with the forward axial wind. The key point is that the rotation of the rotor induces a swirl that, in relation to the forward motion, is opposite in direction.

Rotational wind is the tangential component of the air flow through the rotor disc created by the blade rotation. As the rotor turns, it drags air around the disc in a circular direction. When you compare that swirl to the aircraft’s forward motion, the tangential flow on the disk is opposite in sense to the forward progression of the air entering the rotor (the swirl tends to push air around in the opposite direction to the forward travel). So the rotational wind on the rotor disk is directed opposite to the forward motion.

In hover, there’s no forward speed, so you only have the tangential swirl. In forward flight, you still have that tangential, rotational component, but it combines with the forward axial wind. The key point is that the rotation of the rotor induces a swirl that, in relation to the forward motion, is opposite in direction.