Resultant relative wind definition.

• A. Rotational relative wind modified by induced flow
• B. Rotational relative wind added to forward speed
• C. Induced flow only
• D. Free stream wind

Answer: (A)

The wind a rotor blade element sees is a combination of the blade’s rotation and the air moving through the disk due to thrust (and forward speed). The tangential component from the blade’s spin is the rotational relative wind. The air moving axially through the disk, caused by thrust (induced flow) and any forward flight, modifies that axial component. The resulting relative wind is the vector sum of the rotational component and the axial component, i.e., the rotational relative wind modified by induced flow. This captures how rotation and induced downwash together determine the wind the blade element actually encounters.

So, the best description is that the resultant relative wind is rotational relative wind modified by induced flow. It’s not just free stream wind, not just induced flow alone, and not simply rotational wind added to forward speed without accounting for the induced flow’s effect.